5 e Thermo Glossary

8/13/2019 5 e Thermo Glossary

http://slidepdf.com/reader/full/5-e-thermo-glossary 1/55



Glossaryto accompany

Thermodynamics: An Engineering Approach, 5th edition

by Yunus A. Çengel and Michael A. Boles

Adiabatic saturation process is the process in which a steady stream of unsaturated air

of un'nown specific humidity is passed through a long insulated channel that contains a pool of water. As the air flows over the water! some water will evaporate and mi$ with

the airstream. #he moisture content of air will increase during this process! and itstemperature will decrease! since part of the latent heat of vapori"ation of the water thatevaporates will come from the air. 3f the channel is long enough! the airstream will e$it as

saturated air (/00 percent relative humidity) at the e$it temperature.

Adiabatic saturation temperature is the e$it temperature that air attains in the adiabaticsaturation process.

Afterburner is a section added between the turbine and the no""le of an aircraft turbineengine where additional fuel is in4ected into the o$ygenrich combustion gases leaving

the turbine. As a result of this added energy! the e$haust gases leave at a higher velocity!

providing e$tra thrust for short ta'eoffs or combat conditions.

Air conditioners are refrigerators whose refrigerated space is a room or a building

instead of the food compartment.

Air–fuel ratio AF is a fre5uently used 5uantity in the analysis of combustion processes

to 5uantify the amounts of fuel and air. 3t is usually e$pressed on a mass basis and is

defined as the ratio of the mass of air to the mass of fuel for a combustion process.

Air-source heat pumps use the cold outside air as the heat source in winter.

Air-standard assumptions reduce the analysis of gas power cycles to a manageablelevel by utili"ing the following appro$imations6

1. #he wor'ing fluid is air! which continuously circulates in a closed loop and always behaves as an ideal gas.

2. All the processes that ma'e up the cycle are internally reversible.

3. #he combustion process is replaced by a heataddition process from an e$ternal

source.

4. #he e$haust process is replaced by a heat re4ection process that restores the

wor'ing fluid to its initial state.

Air-standard cycle is a cycle for which the airstandard assumptions are applicable.

Amagat’s la of additive volumes states that the volume of a gas mi$ture is e5ual to thesum of the volumes each gas would occupy if it e$isted alone at the mi$ture temperature

and pressure.

Annual fuel utili!ation efficiency AF"# is the efficiency of space heating systems of

residential and commercial buildings which accounts for the combustion efficiency as

-






well as other losses such as heat losses to unheated areas and startup and cooldown

losses.

Apparent gas constant of a mi$ture is the universal gas constant divided by the apparentmolar mass of the mi$ture.

Apparent molar mass of a mi$ture can be e$pressed as the sum of the products of the

mole fraction and molar mass of each component in the mi$ture.

Atmospheric air is the air in the atmosphere! which normally contains some water vapor

(or moisture).

Autoignition is the premature ignition of the fuel that produces an audible noise! which

is called engine 'noc'.

Average gas constant (see apparent gas constant)

Average molar mass (see apparent molar mass)

Average velocity is the average value of the normal velocity across an entire flow cross

section and if the velocity were the average velocity all through the cross section! the

mass flow rate would be identical to that obtained by integrating the actual velocity profile.

$ac% pressure is the pressure applied at the no""le discharge region.

$ac% or% ratio is the ratio of the compressor wor' to the turbine wor' in gasturbine

power plants.

$ar is the unit of pressure e5ual to /07 pascal.

$arometer is a device that measures the atmospheric pressure& thus! the atmospheric pressure is often referred to as the barometric pressure.

$eattie-$ridgeman e'uation of state is one of the best 'nown and is a reasonablyaccurate e5uation of state. 3t is given by

where the constants for various substances are found in #able -8.

$enedict-(ebb-)ubin e'uation of state is one of the more recent and very accurate

e5uations of state. 3t is given by

,






where the constants for various substances are given in #able -8.

$ernoulli e'uation is the result of the energy analysis for the reversible! steadyflow of

an incompressible li5uid through a device that involves no wor' interactions (such as a

no""le or a pipe section). 9or frictionless flow! it states that the sum of the pressure!velocity! and potential energy heads is constant. 3t is also a form of the conservation of

momentum principle for steadyflow control volumes.

$inary vapor cycle is a vapor cycle in which the condenser of the hightemperature

cycle (also called the topping cycle) serves as the boiler of the lowtemperature cycle

(also called the bottoming cycle). #hat is! the heat output of the hightemperature cycle is

used as the heat input to the lowtemperature one.

$lac%body is an ideali"ed surface that emits radiation at the ma$imum rate given by the

2tefanBolt"mann law.

$lac%body radiation is amount of radiation emitted by a blac'body.

$oiler is basically a large heat e$changer where the heat originating from combustion

gases! nuclear reactors! or other sources is transferred to the water essentially at constant

pressure.

$oiling is the phase change process that occurs at the solidli5uid interface when a li5uidis brought into contact with a surface maintained at a temperature sufficiently above thesaturation temperature of the li5uid.

$olt!mann relation is the e$pression of the entropy as a function of thermodynamic

probability.

$olt!mann’s constant! ' has the value of /.,:0; × /0-, <=%.

$ore is the diameter of a piston.

$ottom dead center $*+ is the position of the piston when it forms the largest volumein the cylinder.

$ottoming cycle is a power cycle operating at lower average temperatures that receives

heat from a power cycle operating at higher average temperatures.

$oundary is the real or imaginary surface that separates the system from its

surroundings. #he boundary of a system can be fixed or movable.

8






$oundary or% ( Pd > wor') is the wor' associated with the e$pansion or compressionof a gas in a pistoncylinder device. Boundary wor' is the area under the process curve

on a ?> diagram e5ual! in magnitude! to the wor' done during a 5uasie5uilibriume$pansion or compression process of a closed system.

$ourdon tube, named after the 9rench inventor @ugene Bourdon! is a type of commonly

used mechanical pressure measurement device which consists of a hollow metal tube bent

li'e a hoo' whose end is closed and connected to a dial indicator needle.

$o ave (see detached obli5ue shoc')

$rayton cycle was first proposed by George Brayton around /:0. 3t is used for gas

turbines! which operate on an open cycle! where both the compression and e$pansion

processes ta'e place in rotating machinery. #he open gasturbine cycle can be modeled asa closed cycle by utili"ing the airstandard assumptions. #he combustion process is

replaced by a constantpressure heataddition process from an e$ternal source! and the

e$haust process is replaced by a constantpressure heatre4ection process to the ambientair. #he ideal Brayton cycle is made up of four internally reversible processes6

/- 3sentropic compression (in a compressor)!

-, 1onstant pressure heat addition!

,8 3sentropic e$pansion (in a turbine)!8/ 1onstant pressure heat re4ection.

$rayton cycle ith regeneration is the Brayton cycle modified with a regenerator (a

counterflow heat e$changer) to allow the transfer of heat to the high pressure airleaving the compressor from the hightemperature e$haust gas leaving the

turbine.

$ritish thermal unit $" is the energy unit in the @nglish system! representing the

energy needed to raise the temperature of / lbm of water at ;:°9 by /°9.

+aloric is heat treated as a fluidli'e substance! according to the caloric theory! that is a

massless! colorless! odorless! and tasteless substance that can be poured from one body

into another.

+alorie (cal) is the amount of energy in the metric system needed to raise thetemperature of / g of water at /7 °1 by /°1.

+arnot cycle was first proposed in /:-8 by 9rench engineer 2adi 1arnot. 3t is composed

of four reversible processestwo isothermal and two adiabatic! and can be e$ecuted

either in a closed or a steadyflow system.

7






+arnot efficiency is the highest efficiency a heat engine can have when operating

between the two thermal energy reservoirs at temperatures T C and T +

ηth! rev D / T C = T +.

+arnot heat engine is the theoretical heat engine that operates on the 1arnot cycle.

+arnot heat pump is a heat pump that operates on the reversed 1arnot cycle. Ehen

operating between the two thermal energy reservoirs at temperatures T C and T +! the

1arnot heat pump can have a coefficient of performance of 1?+?! rev D /= (/ T C = T +) DT + =( T + T C).

+arnot principles are two conclusions that pertain to the thermal efficiency of reversibleand irreversible (i.e.! actual) heat engines and are e$pressed as follows6

1. #he efficiency of an irreversible heat engine is always less than the efficiency of a

reversible one operating between the same two reservoirs.2. #he efficiencies of all reversible heat engines operating between the same two

reservoirs are the same.

+arnot refrigerator is a refrigerator that operates on the reversed 1arnot cycle. Ehen

operating between the two thermal energy reservoirs at temperatures T C and T + the

1arnot refrigerator can have a coefficient of performance of 1?&! rev D /= (T + = T C /) D

T C =( T + T C).

+ascade refrigeration cycles perform the refrigeration process in stages! that is! to have

two or more refrigeration cycles that operate in series.

+elsius scale (formerly called the centigrade scale; in /F8: it was renamed after the

2wedish astronomer A. 1elsius! /0//88! who devised it) is the temperature scale usedin the 23 system. n the 1elsius scale! the ice and steam points are assigned the values of

0 and /00 °1! respectively.

+hemical energy is the internal energy associated with the atomic bonds in a molecule.

+hemical e'uilibrium is established in a system when its chemical composition does not

change with time.

+hemical e'uilibrium reactions are chemical reactions in which the reactants aredepleted at e$actly the same rate as they are replenished from the products by the reverse

reaction. At e5uilibrium the reaction proceeds in both directions at the same rate.

+hemical potential is the change in the Gibbs function of the mi$ture in a specified

phase when a unit amount of a given component of the mi$ture in the same phase isadded as pressure and temperature and the amounts of all other components are held

constant. #he chemical potential of a component of an ideal gas mi$ture depends on the

;






mole fraction of the components as well as the mi$ture temperature and pressure! and is

independent of the identity of the other constituent gases.

+hemically correct amount of air is the stoichiometric or theoretical air! or /00 percenttheoretical air.

+ho%ed flo occurs in a no""le when the mass flow reaches a ma$imum value for the

minimum flow area. #his happens when the flow properties are those re5uired to

increase the fluid velocity to the velocity of sound at the minimum flow area location.

+ho%ed )ayleigh flo occurs in a duct when a fluid can no longer be accelerated by

heating above sonic velocity to supersonic velocities.

+lapeyron e'uation, named after the 9rench engineer and physicist @. 1lapeyron

(/FF/:;8)! relates the enthalpy change associated with a phase change (such as theenthalpy of vapori"ation hfg) from 'nowledge of P ! v! and T data alone.

+lapeyron–+lausius e'uation is used to determine the variation of saturation pressurewith temperature.

+lassical thermodynamics is the macroscopic approach to the study of thermodynamics

that does not re5uire 'nowledge of the behavior of individual particles.

+lausius ine'uality, first stated by the German physicist &. <. @. 1lausius (/:--/:::)!

is e$pressed as the cyclic integral of δQ/T is always less than or e5ual to "ero. #his

ine5uality is valid for all cycles! reversible or irreversible.

+lausius statement of the second la is e$pressed as follows6 3t is impossible toconstruct a device that operates in a cycle and produces no effect other than the transfer

of heat from a lowertemperature body to a highertemperature body.

+learance volume is the minimum volume formed in the cylinder when the piston is attop dead center.

+losed feedater heater is a feedwater heater in which heat is transferred from thee$tracted steam to the feedwater without any mi$ing ta'ing place. #he two streams are

typically not at the same pressures! since they do not mi$. 3n an ideal closed feedwaterheater the feedwater is heated to the e$it temperature of the e$tracted steam! whichideally leaves the heater as a saturated li5uid at the e$traction pressure. 3n actual power

plants the feedwater leaves the heater below the e$it temperature of the e$tracted steam

because a temperature difference of at least a few degrees is re5uired for any effectiveheat transfer to ta'e place.






+losed system consists of a fi$ed amount of mass (control mass)! and no mass can cross

its boundary. But energy! in the form of heat or wor'! can cross the boundary.

+losed system eergy (nonflow e$ergy) is the reversible wor' that could be done by aclosed system undergoing a reversible process to e5uilibrium with its surroundings. 9or a

mass m the e$ergy is D (! ! 0) P 0(" " 0) T 0(# # 0) m -" =- mg$ . n a unit

mass basis! the e$ergy of a closed system is e$pressed as φ D (% %0) P 0(v v0) T 0( s

s0) -" =- g$ where %0! v0! and s0 are the properties of the system evaluated at the dead

state. *ote that the e$ergy of a system is "ero at the dead state since % & %0! v & v0! and s& s0 at that state. #he e$ergy change of a closed system during a process is simply the

difference between the final and initial e$ergies of the system.

+oefficient of performance +/0 is the measure of performance of refrigerators and

heat pumps. 3t is e$pressed in terms of the desired result for each device (heat absorbed

from the refrigerated space for the refrigerator or heat added to the hot space by the heat pump) divided by the input! the energy e$pended to accomplish the energy transfer(usually wor' input).

+ogeneration is the production of more than one useful form of energy (such as processheat and electric power) from the same energy source.

+old-air-standard assumption combines the airstandard assumptions with theassumption that the air has constant specific heats whose values are determined at room

temperature (-7H1! or H9).

+ombined cycle (see combined gasvapor cycle)

+ombined efficiency (see overall efficiency)

+ombined gas–vapor cycle! or 4ust the combined cycle! is the gasturbine (Brayton)

cycle topping a steamturbine (&an'ine) cycle! which has a higher thermal efficiency

than either of the cycles e$ecuted individually.

+ombustion is a chemical reaction during which a fuel is o$idi"ed and a large 5uantity

of energy is released.

+ombustion air is dry air which can be appro$imated as -/ percent o$ygen and F percent nitrogen by mole numbers. #herefore! each mole of o$ygen entering a

combustion chamber will be accompanied by 0.F=0.-/ D ,.; mol of nitrogen. #o supplyone mole of o$ygen to a combustion process! 8.; mol of combustion air are re5uired.

:






+ombustion efficiency is defined as the ratio of the amount of heat released during combustion

to the heating value of the fuel burned.

+omplete combustion is a combustion process in which all the carbon in the fuel burnsto 1-! all the hydrogen burns to +-! and all the sulfur (if any) burns to 2-. #hatis! all the combustible components of a fuel are burned to completion during a

complete combustion process.

+omponent pressure is the pressure a component in a gas mi$ture would have if ite$isted alone at the volume and temperature of the mi$ture.

+omponent volume is the volume a component in a gas mi$ture would occupy if ite$isted alone at the temperature and pressure of the mi$ture.

+ompressed li'uid has a pressure greater than the saturation pressure corresponding tothe temperature.

+ompressed li'uid region is all compressed li5uid states located in the region to the leftof the saturated li5uid line and below the critical temperature line. 3n the absence of

compressed li5uid data! a general appro$imation is to treat compressed li5uid as saturated

li5uid at the given temperature.

+ompressibility factor ' is a correction factor to account for deviation from idealgas

behavior at a given temperature and pressure. ' D Pv/(T)

+ompressing flo is a flow that produces an obli5ue shoc'.

+ompression-ignition + engines are reciprocating engines in which the combustionof the airfuel mi$ture is selfignited as a result of compressing the mi$ture above its

selfignition temperature.

+ompression ratio r of an engine is the ratio of the ma$imum volume formed in thecylinder to the minimum (clearance) volume. *otice that the compression ratio is a

vol%me ratio and should not be confused with the pressure ratio.

+ompressor is a device that increases the pressure of a gas to very high pressures

(typical pressure ratios are greater than ,).

+ondenser is a heat e$changer in which the wor'ing fluid condenses as it re4ects heat to

the surroundings. 9or e$ample! in the condenser of a steam power plant steam leaving

the turbine as a vapor condenses to the saturated li5uid state as the result of heat transferto a cooling medium such as the atmosphere or water from a la'e or river.

F






+onduction is the transfer of energy from the more energetic particles of a substance to

the ad4acent less energetic ones as a result of interaction between particles.

+onservation of energy principle states that during an interaction! energy can changefrom one form to another but the total amount of energy remains constant. #hat is! energycannot be created or destroyed (see first law of thermodynamics).

+onservation of mass principle is e$pressed as net mass transfer to or from a control

volume during a time interval is e5ual to the net change (increase or decrease) in the totalmass within the control volume during the time interval.

+onservation of mass principle for combustion (or the mass balance) is the principleused to balance chemical reaction e5uations. 3t can be stated as the total mass of each

element is conserved during a chemical reaction. #he total mass of each element on the

righthand side of the reaction e5uation (the products) must be e5ual to the total mass ofthat element on the lefthand side (the reactants) even though the elements e$ist in

different chemical compounds in the reactants and products. @ven though the mass must

be conserved! the total number of moles is not necessarily conserved during a chemicalreaction.

+onstant-volume gas thermometer measures the temperature on the idealgas

temperature scale using a rigid vessel filled with a gas! usually hydrogen or helium! atlow pressure. #he temperature of a gas of fi$ed volume varies linearly with pressure at

sufficiently low pressures.

+ontinuity e'uation is the conservation of mass e5uation as it is often referred to influid mechanics.

+ontinuum is a view of mass as continuous! homogeneous matter with no holes. Matter

is made up of atoms that are widely spaced in the gas phase. Yet it is very convenient to

disregard the atomic nature of a substance. #he continuum ideali"ation allows us to treat

properties as point functions! and to assume the properties to vary continually in spacewith no 4ump discontinuities. #his ideali"ation is valid as long as the si"e of the system

we deal with is large relative to the space between the molecules. #his is the case in

practically all problems! e$cept some speciali"ed ones.

+ontrol mass (see closed system)

+ontrol surface is the boundary of a control volume , and it can be real or imaginary.

+ontrol volume (also see open system) is any arbitrary region in space through whichmass and energy can pass across the boundary. Most control volumes have fi$ed

boundaries and thus do not involve any moving boundaries. A control volume may also

involve heat and wor' interactions 4ust as a closed system! in addition to mass interaction.

/0






+onvected energy (see flow wor')

+onvection is the mode of energy transfer between a solid surface and the ad4acent fluidthat is in motion! and it involves the combined effects of conduction and fluid motion.

+onvection heat transfer coefficient is the e$perimentally determined parameter that is

the ratio of the rate of convection heat transfer and the product of the heat transfer area

and surface to bul' fluid temperature.

+onverging–diverging no!!le! also called Caval no""le after 1arl G. B. de Caval! is a

duct in which the flow area first decreases and then increases in the direction of the flowand is used to accelerate gases to supersonic speeds.

+ooling capacity is the rate of heat removal from the refrigerated space by arefrigeration system.

+ooling pond is a large la'e open to the atmosphere into which warm water containingwaste heat is pumped. +eat transfer from the pond surface to the atmosphere is very

slow thus! the cooling pond re5uires much more surface area than that of a spray pond to

achieve the same cooling.

+riterion for chemical e'uilibrium is the e5uation set e5ual to "ero that involves the

stoichiometric coefficients and the molar Gibbs functions of the reactants and the

products in the e5uilibrium reaction.

+ritical point is defined as the point at which the saturated li5uid and saturated vapor

states are identical.

+ritical pressure P cr is the pressure of a substance at the critical point.

+ritical properties are the properties of a fluid at a location where the Mach number isunity.

+ritical ratios are the ratios of the stagnation to static properties when the Mach numberis unity.

+ritical temperature T cr is the temperature of a substance at the critical point.

+ritical volume vcr is the volume of a substance at the critical point.

+utoff ratio r c is the ratio of the cylinder volumes after and before the combustion

process in the Iiesel cycle.

//






+ycle is a process! or series of processes! that allows a system to undergo state changes

and returns the system to the initial state at the end of the process. #hat is! for a cycle theinitial and final states are identical.

+yclic relation of partial derivatives shows that the derivatives of a function of twovariables are related in a cyclic manner by

/ $ x y

x y $

y $ x

∂ ∂ ∂= − ∂ ∂ ∂

*aily calorie needs depends on the nutrition levels of people and will vary greatly withage! gender! the state of health! the activity level! the body weight! and the composition of

the body as well as other factors.

*alton’s la of additive pressures states that the pressure of a gas mi$ture is e5ual tothe sum of the pressures each gas would e$ert if it e$isted alone at the mi$ture

temperature and volume.

*ead state is the state a system is said to be in when it is in thermodynamic e5uilibrium

with its environment.

*ecrease of eergy principle states the e$ergy of an isolated system during a process

always decreases or! in the limiting case of a reversible process! remains constant. 3n

other words! e$ergy never increases! and it is destroyed during an actual process. 9or anisolated system! the decrease in e$ergy e5uals e$ergy destroyed.

*eficiency of air results when the amounts of air are less than the stoichiometric amount.

*eflection angle (see turning angle)

*ehumidifying is the process of removing moisture from atmospheric air.

*ensity is defined as mass per unit volume.

*erivative of a function f*x+ with respect to x represents the rate of change of f with x.

#he derivative is e5uivalent to steepness of a curve at a point as measured by the slope of

a line tangent to the curve at that point.

0 0

( ) ( )lim lim x x

d f f f x x f x

dx x x∆ → ∆ →

∆ + ∆ −= =∆ ∆

*erived dimensions (see secondary dimensions)

*etached obli'ue shoc% or a bo ave is an obli5ue shoc' that has become curved and

detached from the nose of a wedge.

/-






*e-point temperature is defined as the temperature at which condensation beginswhen the air is cooled at constant pressure.

*iesel cycle is the ideal cycle for compressignition reciprocating engines! and was first proposed by &udolf Iiesel in the /:F0s. Jsing the airstandard assumptions! the cycle

consists of four internally reversible processes6

/- 3sentropic compression!

-, 1onstant pressure heat addition!,8 3sentropic e$pansion!

8/ 1onstant volume heat re4ection.

*iffuser is a device that increases the pressure of a fluid by decreasing the fluid velocity.

*imensionally homogeneous means that every term in an e5uation must have the sameunit. #o ma'e sure that all terms in an engineering e5uation have the same units is the

simplest error chec' one can perform.

*imensions are any physical characteri"ations of a 5uantity.

*irect-contact feedater heater ( see open feedwater heater)

*isplacement volume is the volume displaced by the piston as it moves between top

dead center and bottom dead center.

*odecane! 1/-+-;! is a common li5uid fuel that appro$imates diesel fuel.

*ome is the saturation states located beneath the 4oined saturated li5uid line andsaturated vapor line.

*ry air is air that contains no water vapor.

*ry-bulb temperature is the ordinary temperature of atmospheric air.

*ual cycle is the ideal cycle which models the combustion process in both gasoline anddiesel engines as a combination of two heattransfer processes! one at constant

volume and the other at constant pressure.

*ynamic temperature is the 'inetic energy per unit mass divided by the constant

pressure specific heat and corresponds to the temperature rise during the stagnation

process.

#fficiency is defined as the ratio of desired result for an event to the input re5uired to

accomplish the event. @fficiency is one of the most fre5uently used terms in

/,






thermodynamics! and it indicates how well an energy conversion or transfer process is

accomplished.

#fficiency of a coo%ing appliance is defined as the ratio of the useful energy transferredto the food to the energy consumed by the appliance.

#fficiency of a ater heater is defined as the ratio of the energy delivered to the house

by hot water to the energy supplied to the water heater.

#fficiency of resistance heaters is /00 percent as they convert all the electrical energy

they consume into heat.

#lectrical polari!ation or% is the product of the generali"ed force ta'en as the electric

field strength and the generali"ed displacement ta'en as the polari"ation of the medium

(the sum of the electric dipole rotation moments of the molecules).

#lectrical poer is the rate of electrical wor' done as electrons in a wire move under the

effect of electromotive forces! doing wor'. 3t is the product of the potential differencemeasured in volts and the current flow measured in amperes.

#lectrical or% is wor' done on a system as electrons in a wire move under the effect ofelectromotive forces while crossing the system boundary.

#missivity is a surface property that is a measure of how closely a surface appro$imatesa blac'body for which the emissivity e5ual to one.

#nergy $alance is the net change (increase or decrease) in the total energy of the system

during a process is e5ual to the difference between the total energy entering and the totalenergy leaving the system during that process.

#nergy efficiency rating ##) is the performance of refrigerators and air conditioners!and is the amount of heat removed from the cooled space in BtuKs for / Eh (watthour)

of electricity consumed.

#nergy transport by mass is the product of the mass of the flowing fluid and its total

energy. #he rate of energy transport by mass is the product of the mass flow rate and the

total energy of the flow.

#nglish system, which is also 'nown as the !nited #tates %stomary #ystem (J212)!

has the respective units the poundmass (lbm)! foot (ft)! and second (s). #he pound

symbol lb is actually the abbreviation of libra, which was the ancient &oman unit ofweight.

/8






#nthalpy - (from the Gree' word enthalpien! which means to heat) is a property and is

defined as the sum of the internal energy ! and the P" product.

#nthalpy change of an ideal gas is given as ? ?! av - /( ) ( )h T dT T T ∆ = ≅ −∫ .

#nthalpy departure is the difference between the enthalpy of a real gas and the enthalpy

of the gas at an ideal gas state and it represents the variation of the enthalpy of a gas with

pressure at a fi$ed temperature.

#nthalpy departure factor is the nondimensionali"ed form of the enthalpy departure.

#nthalpy of a chemical component at a specified state is the sum of the enthalpy of formation of

the component at -7°1! / atm! and the sensible enthalpy of the component relative to -7°1! / atm!

which is the difference between the sensible enthalpy at the specified state ad the sensible

enthalpy at the standard reference state of -7

°1 and / atm. #his definition enables us to use

enthalpy values from tables regardless of the reference state used in their construction.

#nthalpy of combustion h1 is the enthalpy of reaction during a steadyflow combustion process when / 'mol (or / 'g) of fuel is burned completely at a specified temperature and

pressure and represents the amount of heat released.

#nthalpy of formation is the enthalpy of a substance at a specified state due to itschemical composition. #he enthalpy of formation of all stable elements (such as -! *-!

+-! and 1) has a value of "ero at the standard reference state of -7°1 and / atm.

#nthalpy of reaction h& is defined as the difference between the enthalpy of the productsat a specified state and the enthalpy of the reactants at the same state for a complete

reaction.

#nthalpy of vapori!ation (or latent heat of vapori"ation) is the 5uantity hfg listed in the

saturation tables.

#ntropy (from a classical thermodynamics point of view) is a property designated # and

is defined as d# &(δ Q/T )int rev.

#ntropy (from a statistical thermodynamics point of view) can be viewed as a measure

of molecular disorder! or molecular randomness. #he entropy of a system is related to thetotal number of possible microscopic states of that system! called thermodynamic

probability p! by the Bolt"mann relation, e$pressed as # & . ln p where . is theBolt"mann constant.

#ntropy balance for any system (including reacting systems) undergoing any processcan be e$pressed as net entropy transfer entropy by heat and mass plus entropy

generation e5uals the change in entropy.

/7






#ntropy balance relation for a control volume states that the rate of entropy changewithin the control volume during a process is e5ual to the sum of the rate of entropy

transfer through the control volume boundary by heat transfer! the net rate of entropytransfer into the control volume by mass flow! and the rate of entropy generation withinthe boundaries of the control volume as a result of irreversibilities.

#ntropy balance relation in general is stated as the entropy change of a system during a

process is e5ual to the net entropy transfer through the system boundary and the entropygenerated within the system as a result of irreversibilities.

#ntropy change of a closed system is due to the entropy transfer accompanying heattransfer and the entropy generation within the system boundaries and is greater than or

e5ual to the integral over the process of δL=#.

#ntropy departure is the difference between the entropy of a real gas at a given P and T

and the entropy of the gas at an ideal gas state at the same P and T .

#ntropy departure factor is the nondimensionali"ed form of the entropy departure.

#ntropy generation # gen is entropy generated or created during an irreversible process! is

due entirely to the presence of irreversibilities! and is a measure of the magnitudes of theirreversibilities present during that process. @ntropy generation is always a positive

5uantity or "ero. 3ts value depends on the process! and thus it is not a property.

#ntropy transfer is the transfer of entropy across a boundary by heat or mass.

#nvironment refers to the region beyond the immediate surroundings whose propertiesare not affected by the process at any point.

#'uation of state is any e5uation that relates the pressure! temperature! and specific

volume of a substance. ?roperty relations that involve other properties of a substance ate5uilibrium states are also referred to as e5uations of state.

#'uilibrium implies a state of balance. 3n an e5uilibrium state there are no unbalanced potentials (or driving forces) within the system. A system in e5uilibrium e$periences no

changes when it is isolated from its surroundings.

#'uilibrium constant for an e5uilibrium reaction is the ratio of the product of the

product componentKs partial pressure raised to their stoichiometric coefficients and the

product of the reactant componentKs partial pressure raised to their stoichiometriccoefficients. #he e5uilibrium constant of an idealgas mi$ture at a specified temperature

can be determined from 'nowledge of the standardstate Gibbs function change at the

same temperature. #he number of e5uilibrium constant relations needed to determine the

/;






e5uilibrium composition of a reacting mi$ture is e5ual to the number of chemical species

minus the number of elements present in e5uilibrium)

#'uivalence ratio is the ratio of the actual fuelair ratio to the stoichiometric fuelairratio.

#ricsson cycle is made up of four totally reversible processes6

/- T D constant e$pansion (heat addition from the e$ternal source)!

-, ? D constant regeneration (internal heat transfer from the wor'ing fluid to theregenerator)!

,8 # D constant compression (heat re4ection to the e$ternal sin')!

8/ ? D constant regeneration (internal heat transfer from the regenerator bac' to thewor'ing fluid).

#vaporation is the phase change from li5uid to vapor and occurs at the li5uidvaporinterface when the vapor pressure is less than the saturation pressure of the li5uid at a

given temperature.

#vaporative coolers! also 'nown as swamp coolers! use evaporative cooling based on

the principle that as water evaporates! the latent heat of vapori"ation is absorbed from the

water body and the surrounding air. As a result! both the water and the air are cooled

during the process. @vaporative coolers are commonly used in dry climates and provideeffective cooling.

#vaporator is a heat e$changer in which the wor'ing fluid evaporates as it receives heat

from the surroundings.

#act differentials are the differential changes for point functions (i.e.! they depend onthe state only! and not on how a system reaches that state)! and they are designated by the

symbol d) ?roperties are an e$ample of point functions that have e$act differentials.

#cess air is the amount of air in e$cess of the stoichiometric amount.

#ergy availability or available energy is property used to determine the useful wor'

potential of a given amount of energy at some specified state. 3t is important to reali"ethat e$ergy does not represent the amount of wor' that a wor'producing device will

actually deliver upon installation. &ather! it represents the upper limit on the amount of

wor' a device can deliver without violating any thermodynamic laws.

#ergy balance can be stated as the e$ergy change of a system during a process is e5ual

to the difference between the net e$ergy transfer through the system boundary and thee$ergy destroyed within the system boundaries as a result of irreversibilities (or entropy

generation).

/






#ergy balance for a control volume is stated as the rate of e$ergy change within the

control volume during a process is e5ual to the rate of net e$ergy transfer through thecontrol volume boundary by heat! wor'! and mass flow minus the rate of e$ergy

destruction within the boundaries of the control volume as a result of irreversibilities.

#ergy destroyed is proportional to the entropy generated and is e$pressed as destroyed D

T 0 # gen ≥ 0. 3rreversibilities such as friction! mi$ing! chemical reactions! heat transfer

through a finite temperature difference! unrestrained e$pansion! non5uasie5uilibrium

compression! or e$pansion always generate entropy! and anything that generates entropyalways destroys e$ergy.

#ergy of the %inetic energy (wor' potential) of a system is e5ual to the 'inetic energyitself regardless of the temperature and pressure of the environment.

#ergy of the potential energy (wor' potential) of a system is e5ual to the potentialenergy itself regardless of the temperature and pressure of the environment.

#ergy transfer by heat heat is the e$ergy as the result of heat transfer Q at a location atabsolute temperature T in the amount of heat D (/T 0 /T )Q.

#ergy transfer by mass results from mass in the amount of m entering or leaving a

system and carries e$ergy in the amount of mψ ! where ψ D (h h0) T 0( s s0) -" =-

g $ ! accompanies it. #herefore! the e$ergy of a system increases by mψ when mass in the

amount of m enters! and decreases by the same amount when the same amount of mass atthe same state leaves the system.

#ergy transfer by or% is the useful wor' potential e$pressed as wor' D 0 0 surr for

closed systems e$periencing boundary wor' where 0 surr D P 0(v- v/) and P 0 isatmospheric pressure! and " / and " - are the initial and final volumes of the system! and

wor' D 0 for other forms of wor'.

#haust valve is the e$it through which the combustion products are e$pelled from the

cylinder.

#othermic reaction is a reaction during which chemical energy is released in the form

of heat.

#panding flo are those flows where supersonic flow is turned in the oppositedirection however! the flow does not turn suddenly! as through a shoc'! but gradually

each successive Mach wave turns the flow by an infinitesimal amount.

#pansion fan is a continuous e$panding region of supersonic flow composed of an

infinite number of Mach waves called ?randtlMeyer e$pansion waves.

/:






#tensive properties are those whose values depend on the si"eor e$tentof the

system. Mass m! volume " ! and total energy E are some e$amples of e$tensive properties.@$tensive properties of a nonreacting idealor realgas mi$ture are obtained by 4ust

adding the contributions of each component of the mi$ture.

#ternal combustion engines are engines in which the fuel is burned outside the system

boundary.

#ternally reversible process has no irreversibilities to occur outside the system boundaries during the process. +eat transfer between a reservoir and a system is an

e$ternally reversible process if the surface of contact between the system and the

reservoir is at the temperature of the reservoir.

Fahrenheit scale (named after the German instrument ma'er

G. 9ahrenheit! /;:;/,;) is the temperature scale in the @nglish system. n the9ahrenheit scale! the ice and steam points are assigned ,- and -/- °9.

Fan is a device that increases the pressure of a gas slightly (typical pressure ratios areless than ,) and is mainly used to mobili"e a gas.

Fan-et engine (see turbofan engine)

Fanno line is the locus of all states for frictionless adiabatic flow in a constantarea duct

plotted on an hs diagram. #hese states have the same value of stagnation enthalpy and

mass flu$ (mass flow per unit area).

Feedater heater is the device where the feedwater is heated by regeneration. #his

techni5ue is used to raise the temperature of the li5uid leaving the pump (called thefeedwater) before it enters the boiler. A practical regeneration process in steam power

plants is accomplished by e$tracting! or Nbleeding!O steam from the turbine at various

points. #his steam! which could have produced more wor' by e$panding further in the

turbine! is used to heat the feedwater instead.

First la (see first law of thermodynamics)

First la of thermodynamics is simply a statement of the conservation of energy

principle! and it asserts that total energy is a thermodynamic property. <ouleKse$periments indicate the following6 9or all adiabatic processes between two specifiedstates of a closed system! the net wor' done is the same regardless of the nature of the

closed system and the details of the process. 3t may be e$pressed as follows6 @nergy can

be neither created nor destroyed it can only change forms. #he net change (increase ordecrease) in the total energy of the system during a process is e5ual to the difference

between the total energy entering and the total energy leaving the system during that

process. #he energy balance can be written e$plicitly as

/F






E in E out D(Qin Qout ) (0 in 0 out ) ( E mass! in E mass! out ) D ∆ E system

First la of thermodynamics for a closed system using the classical thermodynamicssign convention is

Qnet! in 0 net! out D ∆ E system or Q 0 &∆ E

where Q & Qnet! in D Qin Qout is the net heat input and 0 & 0 net! out D 0 out 0 in is the net

wor' output. btaining a negative 5uantity for Q or 0 simply means that the assumed

direction for that 5uantity is wrong and should be reversed.

Flo energy (see flow wor').

Flo eergy results from mass entering or leaving a system and carries e$ergy per unit

mass in the amount ψ D (h h0) T 0( s s0) -" =- g $ with it. #herefore! the e$ergy of a

system increases by ψ when mass enters! and decreases by the same amount when massat the same state leaves the system.

Flo or% (flow energy) is wor' re5uired to push mass into or out of control volumes.n a unit mass basis this energy is e5uivalent to the product of the pressure and specific

volume of the mass Pv.

Forced convection (convected energy) is convection heat transfer when the fluid is

forced to flow in a tube or over a surface by e$ternal means such as a fan! pump! or the

wind.

Forced-draft cooling toer, or induceddraft cooling tower! is a wet cooling tower inwhich the air is drawn through the tower by fans.

Formal sign convention (classical thermodynamics sign convention) for heat and wor'

interactions is as follows6 heat transfer to a system and wor' done by a system are

positive heat transfer from a system and wor' done on a system are negative.

Four-stro%e internal combustion engines are engines in which the piston e$ecutes four

complete stro'es (two mechanical cycles) within the cylinder! and the cran'shaftcompletes two revolutions for each thermodynamic cycle.

Fourier’s la of heat conduction states that rate of heat conduction in a direction is proportional to the temperature gradient in that direction.

Free convection (natural convection) is convection heat transfer when the fluid motion is

caused by buoyancy forces induced by density differences due to the variation oftemperature in the fluid.

-0






Friction is a familiar form of irreversibility associated with bodies in motion which

results from the force that opposes the motion developed at the interface of the two bodies in contact when the two bodies are forced to move relative to each other.

Frosting , which occurs in humid climates when the temperature falls below - to 7H1! isthe ma4or problem with airsource systems. #he frost accumulation on the evaporator

coils is highly undesirable since it seriously disrupts heat transfer. #he coils can be

defrosted! however! by reversing the heat pump cycle (running it as an air conditioner).

#his results in a reduction in the efficiency of the system.

Fuel is any material that can be burned to release energy.

Fuel–air ratio is the reciprocal of airfuel ratio.

Fuel cells operate on the principle of electrolytic cells in which the chemical energy ofthe fuel is directly converted to electric energy! and electrons are e$changed through

conductor wires connected to a load. 9uel cells are not heat engines! and thus their

efficiencies are not limited by the 1arnot efficiency. #hey convert chemical energy toelectric energy essentially in an isothermal manner.

Fundamental dimensions (see primary dimensions)

5age pressure is the difference between the absolute pressure and the local atmospheric

pressure.

5as constant ( is different for each gas and is determined from ( & (u= 1)

5as phase of a substance has molecules that are far apart from each other! and amolecular order is none$istent. Gas molecules move about at random! continually

colliding with each other and the walls of the container they are in.

5as poer cycles are cycles where the wor'ing fluid remains a gas throughout the entirecycle. 2par'ignition automobile engines! diesel engines! and conventional gas turbines

are familiar e$amples of devices that operate on gas cycles.

5as refrigeration cycle is based on the reversed Brayton cycle where the compressor

e$it gases are cooled and then e$panded in a turbine to further reduce the temperature of

the wor'ing fluid. #he lowertemperature fluid is used to produce the refrigerationeffect.

5enerali!ed compressibility chart shows that by curvefitting all the data! gases seemto obey the principle of corresponding states reasonably well.

-/






5enerali!ed enthalpy departure chart is a plot of the enthalpy departure factor as a

function of reduced pressure and reduced temperature. 3t is used to determine thedeviation of the enthalpy of a gas at a given P and T from the enthalpy of an ideal gas at

the same T)

5enerali!ed entropy departure chart is a plot of the entropy departure factor as a

function of reduced pressure and reduced temperature. 3t is used to determine the

deviation of the entropy of a gas at a given P and T from the entropy of an ideal gas at the

same P and T)

5enerator efficiency is defined as the ratio of the electrical power output to the

mechanical power input to a generator.

5eothermal heat pumps (also called groundsource heat pumps) use the ground as the

heat source.

5ibbs–*alton la! an e$tension of IaltonKs law of additive pressures! states that under

the idealgas appro$imation! the properties of a gas in a mi$ture are not influenced by the presence of other gases! and each gas component in the mi$ture behaves as if it e$ists

alone at the mi$ture temperature and mi$ture volume.

5ibbs function is defined as the enthalpy minus the product of the temperature andentropy (G = H - TS).

5ibbs phase rule provides the number of independent variables associated with a

multicomponent! multiphase system.

5ravimetric analysis is one way to describe the composition of a mi$ture that is

accomplished by specifying the mass of each component.

5ravitational acceleration g is F.:0 m=s- at sea level and varies by less than / percent

up to ,0!000 m. #herefore! g can be assumed to be constant at F.:/ m=s-.

5reenhouse effect is the heating effect causing the increase in temperature of the earthKs

atmosphere as the result of solar radiation entering the earthKs atmosphere during the day!

but heat radiated by the earth at night is bloc'ed by gases such as carbon dio$ide and

trace amounts of methane! nitrogen o$ides and other gases.

5obal climate change (see global warming).

5lobal arming (global climate change) is the undesirable conse5uence of the

greenhouse effect.

6eat (see heat transfer).

--






6eat-driven systems are refrigeration systems whose energy input is based on heat

transfer from an e$ternal source. Absorption refrigeration systems are often classified asheatdriven systems)

6eat engines are devices designed for the purpose of converting other forms of energy(usually in the form of heat) to wor'. +eat engines differ considerably from one another!

but all can be characteri"ed by the following6

1. #hey receive heat from a hightemperature source (solar energy! oil furnace!

nuclear reactor! etc.).

2. #hey convert part of this heat to wor' (usually in the form of a rotating shaft).

3. #hey re4ect the remaining waste heat to a lowtemperature sin' (the atmosphere!

rivers! etc.).

4. #hey operate on a cycle.

6eat echangers are devices where two moving fluid streams e$change heat withoutmi$ing. +eat e$changers are widely used in various industries! and they come in various

designs. #he simplest form of a heat e$changer is a doubletube (also called tubeand

shell) heat e$changer composed of two concentric pipes of different diameters. ne fluidflows in the inner pipe! and the other in the annular space between the two pipes. +eat is

transferred from the hot fluid to the cold one through the wall separating them.

2ometimes the inner tube ma'es a couple of turns inside the shell to increase the heat

transfer area! and thus the rate of heat transfer.

6eat pump is a cyclic device which operates on the refrigeration cycle and discharges

energy to a heated space to maintain the heated space at a high temperature. 3t is a cyclic

device which causes the transfer of heat from a lowtemperature region to a hightemperature region.

6eat pump coefficient of performance is the efficiency of a heat pump! denoted by

1?+?! and e$pressed as desired output divided by re5uired input or 1? +? 7 Q+ / Enet! in.

6eat rate is the e$pression of the conversion efficiency of power plants in the Jnited2tates and is the amount of heat supplied! in BtuKs! to generate / 'Eh of electricity. #he

smaller the heat rate! the greater the efficiency.

6eat reservoir is a thermal energy reservoir since it can supply or absorb energy in the

form of heat.

6eat sin% is a heat reservoir that absorbs energy in the form of heat.

6eat source is a heat reservoir that supplies energy in the form of heat.

6eat transfer (heat) is defined as the form of energy that is transferred between two

systems (or a system and its surroundings) by virtue of a temperature difference. 3t is the

-,






area under the process curve on a T# diagram during an internally reversible process

however! this area has no meaning for irreversible processes.

6eating value of a fuel is defined as the amount of heat released when a fuel is burnedcompletely in a steadyflow process and the products are returned to the state of thereactants. 3n other words! the heating value of a fuel is e5ual to the absolute value of the

enthalpy of combustion of the fuel.

6elmholt! function a is defined as a & % 2 Ts)

6enry’s constant is the product of the total pressure of the gas mi$ture and the mole

fraction of a specie in the li5uid phase.

6enry’s la states that the mole fraction of a wea'ly soluble gas in the li5uid is e5ual to

the partial pressure of the gas outside the li5uid divided by +enryKs constant.

6igher 6eating value 668 of fuel is the amount of heat released when a specified

amount of fuel (usually a unit of mass) at room temperature is completely burned and thecombustion products are cooled to the room temperature when the water formed during

the combustion process is completely condensed and leaves as a li5uid.

6umidity ratio (see absolute humidity)

6umidifying is the process of adding moisture to atmospheric air.

6ydrocarbon fuels are the most familiar fuels and consist primarily of hydrogen andcarbon. #hey are denoted by the general formula 1n+m. +ydrocarbon fuels e$ist in all

phases! some e$amples being coal! gasoline! and natural gas.

6ypersonic flo occurs when a flow has a Mach number 1 33 /.

deal cycle is an actual cycle stripped of all the internal irreversibilities and comple$ities.#he ideal cycle resembles the actual cycle closely but is made up totally of internally

reversible processes.

deal gas is a gas that obeys the idealgas e5uation of state.

deal-gas e'uation of state (or idealgas relation) predicts the PvT behavior of a gas5uite accurately within some properly selected region where Pv & (T .

deal gas specific heat relation is p D v (.

deal gas temperature scale is a temperature scale that turns out to be identical to the

%elvin scale. #he temperatures on this scale are measured using a constant-volume gas

-8






thermometer, which is basically a rigid vessel filled with a gas! usually hydrogen or

helium! at low pressure. #he temperature of a gas is proportional to its pressure atconstant volume.

deal miture or ideal solution is a mi$ture where the effect of dissimilar molecules in ami$ture on each other is negligible and the chemical potential of a component in such a

mi$ture is simply ta'en to be the Gibbs function of the pure component.

deal vapor-compression refrigeration cycle completely vapori"es the refrigerant before it is compressed and e$pands the refrigerant with a throttling device! such as an

e$pansion valve or capillary tube. #he vaporcompression refrigeration cycle is the most

widely used cycle for refrigerators! airconditioning systems! and heat pumps. 3t consistsof four processes6

/- 3sentropic compression in a compressor!

-, 1onstantpressure heat re4ection in a condenser!,8 #hrottling in an e$pansion device!

8/ 1onstantpressure heat absorption in an evaporator.

gnition temperature is the minimum temperature to which a fuel must be brought to

start the combustion.

mmediate surroundings refer to the portion of the surroundings that is affected by the process.

ncomplete combustion is a combustion process in which the combustion products

contain any unburned fuel or components such as 1! +-! 1! or +.

ncompressible substances! such as li5uids and solids! have densities (or specificvolumes) that have negligible variation with pressure.

ncrease of entropy principle (see second law of thermodynamics)

ndependent properties e$ist when one property can be varied while another property is

held constant.

nert gas is a gaseous component in a chemical reaction that does not react chemically

with the other components. #he presence of inert gases affects the e5uilibrium

composition (although it does not affect the e5uilibrium constant).

neact differentials are the differential amount of change for path functions and are

designated by the symbol δ. #herefore! since heat and wor' are path functions! a

differential amount of heat or wor' is represented by δQ or δ0 ! respectively! instead of

dQ or d0 .

-7






nta%e valve is an inlet through which the air or airfuel mi$ture is drawn into the

cylinder.

ntensive properties are those that are independent of the si"e of a system! such astemperature! pressure! and density. 3ntensive properties of a nonreacting idealor realgasmi$ture are obtained by dividing the e$tensive properties by the mass or the mole number

of the mi$ture in the gas mi$ture. #he internal energy! enthalpy! and entropy of a gas

mi$ture per unit mass or per unit mole of the mi$ture can be determined by summing the

products of the mass fractions and the specific property or summing the products of themole fractions and the molar specific property. #hat is! the intensive properties of a gas

mi$ture are determined by either a mass weighted or a mole weighted average of the

properties.

ntercooling is a techni5ue used to reduce the compression wor' for the gas turbine

cycle. #he compression process is completed in stages while cooling the wor'ing fluid between stages. 2ince the steadyflow compression wor' is proportional to the specific

volume of the flow! the specific volume of the wor'ing fluid should be as low as possible

during a compression process.

nternal combustion engines are engines where the energy is provided by burning a fuel

within the system boundaries.

nternal energy ! of a system is the sum of all the microscopic forms of energy.

nternal energy change of an ideal gas is given as v v! av - /( ) ( )% T dT T T ∆ = ≅ −∫ .

nternally reversible process has no irreversibilities that occur within the boundaries of

the system during the process. Iuring an internally reversible process! a system proceeds

through a series of e5uilibrium states! and when the process is reversed! the system passes

through e$actly the same e5uilibrium states while returning to its initial state.

nversion line is the line that passes through the points of "ero slope of constantenthalpy

lines or "ero <oule#homson coefficient on the TP diagram. #he slopes of the h &

constant lines are negative ( µ <# P 0) at states to the right of the inversion line and positive

( µ <# Q 0) to the left of the inversion line.

nversion temperature is the temperature at a point where a constantenthalpy lineintersects the inversion line.

rreversible processes are processes which , once having ta'en place in a system! cannotspontaneously reverse themselves and restore the system to its initial state.

rreversibilities are the factors that cause a process to be irreversible. #hey include

friction! unrestrained e$pansion! mi$ing of two gases! heat transfer across a finite

-;






temperature difference! electric resistance! inelastic deformation of solids! and chemical

reactions.

rreversibility 4 is any difference between the reversible wor' 0 rev and the useful wor'0 u due to the irreversibilities present during the process. 3rreversibility can be viewed asthe wasted wor' potential or the lost opportunity to do wor'.

sentropic efficiency of a compressor is defined as the ratio of the wor' input re5uired

to raise the pressure of a gas to a specified value in an isentropic manner to the actualwor' input.

sentropic efficiency of a no!!le is defined as the ratio of the actual 'inetic energy of thefluid at the no""le e$it to the 'inetic energy value at the e$it of an isentropic no""le for

the same inlet state and e$it pressure)

sentropic efficiency of a turbine is defined as the ratio of the actual wor' output of the

turbine to the wor' output that would be achieved if the process between the inlet state

and the e$it pressure were isentropic.

sentropic process is an internally reversible and adiabatic process. 3n such a process

the entropy remains constant.

sentropic stagnation state is the stagnation state when the stagnation process is

reversible as well as adiabatic (i.e.! isentropic). #he entropy of a fluid remains constant

during an isentropic stagnation process.

so- prefi$ is often used to designate a process for which a particular property remains

constant.

sobaric process is a process during which the pressure P remains constant.

sochoric process (isometric process) is a process during which the specific volume vremains constant.

solated system is a closed system in which energy is not allowed to cross the boundary.

sometric process (see isochoric process).

sothermal compressibility relates how volume changes when pressure changes as

temperature is held constant.

sothermal efficiency of a compressor is defined as the ratio of the wor' input to a

compressor for the reversible isothermal case and the wor' input to a compressor for the

actual case.

-










<ach angle is the shoc' angle for Mach waves and is a uni5ue function of the Machnumber.

<ach number! named after the Austrian physicist @rnst Mach (/:,:/F/;)! is the ratioof the actual velocity of the fluid (or an ob4ect in still air) to the speed of sound in the

same fluid at the same state.

<ach ave is the wea'est possible obli5ue shoc' at a Mach number.

<acroscopic forms of energy are those a system possesses as a whole with respect to

some outside reference frame! such as 'inetic and potential energies.

<agnetic or% is the product of the generali"ed force as the magnetic field strength

and the generali"ed displacement as the total magnetic dipole moment.

<anometer is a device based on the principle that an elevation change of ∆ $ of a fluid

corresponds to a pressure change of ∆?= ρg! which suggests that a fluid column can be

used to measure pressure differences. #he manometer is commonly used to measuresmall and moderate pressure differences.

<ass fraction is the ratio of the mass of one component in a mi$ture to the total mass of

the mi$ture.

<ass flo rate is the amount of mass flowing through a cross section per unit time.

<ass of a system is e5ual to the product of its molar mass 1 and the mole number *.

<aimum inversion temperature is the temperature at the intersection of the P& 0 line

(ordinate) on the T P diagram and the upper part of the inversion line.

<aell relations are e5uations that relate the partial derivatives of properties P ! v! T !and s of a simple compressible system to each other.

<ayer relation! named in honor of the German physician and physicist <. &. Mayer(/:/8/::! shows how the difference between the constantpressure specific heat and

constantvolume specific heat is related to the specific volume! temperature! isothermalcompressibility! and volume e$pansivity.

<ean effective pressure <#0 is a fictitious pressure that! if it acted on the piston during

the entire power stro'e! would produce the same amount of net wor' as that produced

during the actual cycle. #he mean effective pressure can be used as a parameter tocompare the performances of reciprocating engines of e5ual si"e. #he engine with a

larger value of M@? will deliver more net wor' per cycle and thus will perform better.

,0






<echanical efficiency of a device or process is the ratio of the mechanical energy outputto the mechanical energy input.

<echanical energy is the form of energy that can be converted to mechanical wor'completely and directly by an ideal mechanical device such as an ideal turbine.

<echanical e'uilibrium is related to pressure! and a system is in mechanical

e5uilibrium if there is no change in pressure at any point of the system with time.

<echanical or% is wor' associated a force acting in the direction of motion that causes

the movement of the boundary of a system or the movement of the entire system as awhole

<echanisms of entropy transfer # in and # out are heat transfer and mass flow. @ntropytransfer is recogni"ed at the system boundary as it crosses the boundary! and it represents

the entropy gained or lost by a system during a process. #he only form of entropy

interaction associated with a fi$ed mass or closed system is heat transfer! and thus theentropy transfer for an adiabatic closed system is "ero.

<egapascal <0a is the unit of pressure e5ual to /0; pascal.

<elting line separates the solid and li5uid regions on the phase diagram.

<etabolism is the thousands of chemical reactions that occur every second in the cells of

a body during which some molecules are bro'en down and energy is released and somenew molecules are formed. #his high level of chemical activity in the cells maintains the

human body at a temperature of ,H1 while performing the necessary bodily tas's.

<ethane, 1+8! is the appro$imation to gaseous hydrocarbon fuel natural gas that is a

mi$ture of methane and smaller amounts of other gases.

<ethyl alcohol, 1+,+! is a common li5uid hydrocarbon fuel that is also called

methanol and is used in some gasoline blends.

<etric = (from e #yst6me 4nternational d7 !nit8s)! which is also 'nown as the

4nternational #ystem! is based on si$ fundamental dimensions. #heir units! adopted in

/F78 at the #enth General 1onference of Eeights and Measures! are6 meter (m) forlength! .ilogram ('g) for mass! second (s) for time! ampere (A) for electric current!

degree 9elvin (%) for temperature! candela (cd) for luminous intensity (amount of light)!

and mole (mol) for the amount of matter.

,/






<icroscopic forms of energy are those related to the molecular structure of a system and

the degree of the molecular activity! and they are independent of outside referenceframes.

<iing chamber is the section of a control volume where the mi$ing process ta'es placefor two or more streams of fluids. #he mi$ing chamber does not have to be a distinct

Nchamber.KK Mi$ing chambers are sometimes classified as directcontact heat e$changers.

<olar analysis is one way to describe the composition of a mi$ture that is accomplished by specifying the number of moles of each component.

<olar mass 1 can simply be defined as the mass of one mole (also called a grammol e!abbreviated gmol) of a s%bstance in grams! or the mass of one .mol (also called a

.ilogrammol e! abbreviated 'gmol) in .ilograms. 3n @nglish units! it is the mass of /

lbmol in lbm. *otice that the molar mass of a substance has the same numerical value in both unit systems because of the way it is defined.

<ole fraction is the ratio of the number of moles of one component in a mi$ture to thetotal moles of the mi$ture. *ote that for an idealgas mi$ture! the mole fraction! the

pressure fraction! and the volume fraction of a component are identical.

<ollier diagram, after the German scientist &. Mollier (/:;,/F,7)! is the plot of property data on the hs diagram. #he Mollier diagram is useful when solving isentropic!

steady flow process problems dealing with no""les! turbines! and compressors.

<otor efficiency is defined as the ratio of the mechanical energy output of a motor to theelectrical energy input.

<oving boundary or% (see boundary wor')

<ultistage compression refrigeration system is a cascade refrigeration system where

the fluid used throughout the cascade refrigeration system is the same! and the heate$changer between the stages is replaced by a device that has better heattransfer

characteristics! a mi$ing chamber (called a flash chamber).

<ultistage compression ith intercooling re5uires the compression process in a

compressor to be carried out in stages and to cool the gas in between each stage such that

the wor' re5uired to compress a gas between two specified pressures can be decreased.

<ultistage epansion ith reheating re5uires the e$pansion process in a turbine be

carried out in stages and reheating the gas between the stages such that the wor' output ofa turbine operating between two pressure levels can be increased.

>atural convection (see free convection)

,-






>atural-draft cooling toer uses the naturally occurring density gradients between theinside airwater vapor mi$ture and the outside air which create an airflow from the

bottom to the top of a wet cooling tower.

>atural gas is produced from gas wells or oil wells rich in natural gas. 3t is composed

mainly of methane! but it also contains small amounts of ethane! propane! hydrogen!

helium! carbon dio$ide! nitrogen! hydrogen sulfate! and water vapor. 3t is stored either in

the gas phase at pressures of /70 to -70 atm as 1*G (compressed natural gas) or in the

li5uid phase at /;-°1 as C*G (li5uefied natural gas).

>eton >! in 23! is the force unit defined as the force re5uired to accelerate a mass of /'g at a rate of / m=s-.

>eton’s la of cooling defines the heat transfer by convection as the product of theconvection heat transfer coefficient! heat transfer area! and the difference between the

heat transfer surface temperature and the fluid bul' temperature away from the surface.

>onflo system eergy (see closed system e$ergy)

>onreacting gas miture is a mi$ture of gases not undergoing a chemical reaction and

can be treated as a pure substance since it is usually a homogeneous mi$ture of differentgases.

>ormal components are components that are perpendicular to the 5uantity in 5uestion.

>ormal shoc% ave is a shoc' wave resulting in an abrupt change over a very thin

section normal to the direction of flow.

>o!!le is a device that increases the velocity of a fluid at the e$pense of decreasing

pressure.

>uclear energy is the tremendous amount of energy associated with the strong bonds

within the nucleus of the atom itself.

/bli'ue shoc% is a complicated shoc' pattern consisting of inclined shoc' waves in

which some portions of an obli5ue shoc' are curved! while other portions are straight.

/ctane, 1:+/:! is a common li5uid fuel that appro$imates gasoline.

/ctane rating of a fuel is a measure of the engine 'noc' resistance of a fuel.

,,






/pen (or direct-contact) feedater heater is basically a mi$ing chamber! where the

steam e$tracted from the turbine mi$es with the feedwater e$iting the pump. 3deally! themi$ture leaves the heater as a saturated li5uid at the heater pressure.

/pen system is any arbitrary region in space through which mass and energy can passacross the boundary.

/rsat gas analy!er is a commonly used device to analy"e the composition of

combustion gases. #he amounts of carbon dio$ide! carbon mono$ide! and o$ygen aremeasured on a percent by volume and are based on a dry analysis.

/smotic pressure is the pressure difference across a semipermeable membrane thatseparates fresh water from the saline water under e5uilibrium conditions.

/smotic rise is the vertical distance saline water would rise when separated from thefresh water by a membrane that is permeable to water molecules alone at e5uilibrium.

/tto cycle is the ideal cycle for spar'ignition reciprocating engines. 3t is named after *i'olaus A. tto! who built a successful fourstro'e engine in /:; in Germany using the

cycle proposed by 9renchman Beau de &ochas in /:;-. #he ideal tto cycle! which

closely resembles the actual operating conditions! utili"es the airstandard assumptions.

3t consists of four internally reversible processes6/- 3sentropic compression!

-, 1onstant volume heat addition!

,8 3sentropic e$pansion!

8/ 1onstant volume heat re4ection.

/verall efficiency (combined efficiency) for a power plant is defined as the ratio of thenet electrical power output to the rate of fuel energy input and is e$pressed as the product

of the combustion efficiency! thermal efficiency and generator efficiency.

0ac%age icing is the practice of using ice in product pac'ages to remove heat and 'eepthe products cool during transit by ta'ing advantage of the large latent heat of fusion of

water commonly! but its use is limited to products that are not harmed by contact with ice

and the moisture provided by the ice.

0artial derivativeis the change in a function that depends on two (or more) variables!

such as $ & $ *x, y)! when allowing one variable to change while holding the othersconstant and observing the change in the function as another variable is held constant.

#he variation of $*x, y+ with x when y is held constant is called the partial derivative of $

with respect to $.

0 0

( ! ) ( ! )lim lim x x

y y

$ $ $ x x y $ x y

x x x∆ → ∆ →

∂ ∆ + ∆ − = = ∂ ∆ ∆

,8






0artial pressure of a component in a gas mi$ture is defined by IaltonKs law as the

product of the mole fraction and the mi$ture pressure. #he partial pressure is identical tothe component pressure for ideal gas mi$tures.

0artial volume of a component in a gas mi$ture is the product of the mole fraction andthe mi$ture volume. #he partial volume is identical to the component volume for ideal

gas mi$tures.

0ascal (?a) is the unit of pressure defined as newtons per s5uare meter (*=m- ).

0ascal’s la allows us to N4umpO from one fluid column to the ne$t in manometers

without worrying about pressure change as long as we donKt 4ump over a different fluid!and the fluid is at rest.

0ascal’s principle! after Blaise ?ascal (/;-,/;;-)! states that the conse5uence of the pressure in a fluid remaining constant in the hori"ontal direction is that the pressure

applied to a confined fluid increases the pressure throughout by the same amount.

0ath functions are functions whose magnitudes depend on the path followed during a

process as well as the end states.

0ath of a process is the series of states through which a system passes duringa process.

0eltier effect is the cooling effect that occurs when a small current passes through the

4unction of two dissimilar wires. #his effect forms the basis for thermoelectricrefrigeration and is named in honor of <ean 1harles Athanase ?eltier! who discovered this

phenomenon in /:,8.

0ercent deficiency of air is the deficiency of air e$pressed as a percent of stoichiometric

air. 9or e$ample! F0 percent theoretical air is e5uivalent to /0 percent deficiency of air.

0ercent ecess air or percent theoretical air is the amount of e$cess air usually

e$pressed in terms of the stoichiometric air. 9or e$ample! 70 percent e$cess air is

e5uivalent to /70 percent theoretical air.

0erpetual-motion machine is any device that violates either the first or second law of

thermodynamics.

0erpetual-motion machine of the first %ind 0<<1 is a device that violates the first

law of thermodynamics (by creating energy).

0erpetual-motion machine of the second %ind 0<<2 is a device that violates the

second law of thermodynamics.

,7






0hase diagram is the PT diagram of a pure substance and shows all three phasesseparated from each other by the sublimation line! vapori"ation line! and melting line.

0hase e'uilibrium is the condition that the two phases of a pure substance are ine5uilibrium when each phase has the same value of specific Gibbs function. Also! at the

triple point (the state at which all three phases coe$ist in e5uilibrium)! the specific Gibbs

function of each one of the three phases is e5ual.

0hase e'uilibrium for li'uid ater that is open to the atmosphere can be e$pressed as

follows6 #he vapor pressure of the water in the air must be e5ual to the saturation

pressure of water at the water temperature.

0ie!oelectric effect is the emergence of an electric potential in a crystalline substance

when sub4ected to mechanical pressure, and this phenomenon forms the basis for thewidely used straingage pressure transducers.

0ie!oelectric transducers, also called solidstate pressure transducers! wor' on the principle that an electric potential is generated in a crystalline substance when it is

sub4ected to mechanical pressure. #his phenomenon! first discovered by brothers ?ierre

and <ac5ues 1urie in /::0! is called the pie"oelectric (or presselectric) effect.

?ie"oelectric pressure transducers have a much faster fre5uency response compared tothe diaphragm units and are very suitable for highpressure applications! but they are

generally not as sensitive as the diaphragmtype transducers.

0olytropic process is a process in which pressure and volume are often related by P" n& 1! where n and are constants! during e$pansion and compression processes of

real gases.

0otential energy ?@ is the energy that a system possesses as a result of its elevation in a

gravitational field and is e$pressed as ?@ D mg".

0ound-force lbf ! in the @nglish system! is the force unit defined as the force re5uired to

accelerate a mass of ,-./8 lbm (/ slug) at a rate of / ft=s-.

0oer is the wor' done per unit time is called and has the unit '<=s! or 'E.

0randtl–<eyer epansion aves are the Mach waves that compose a continuouse$panding region called an e$pansion fan.

0randtl–<eyer function is the angle through which flow must e$pand! starting with the

function value of "ero at Ma D /! in order to reach a supersonic Mach number! Ma > /.

0ressure is defined as the force e$erted by a fluid per unit area.

,;






0ressure fraction of a gas component in a gas mi$ture is the ratio of the component pressure to the mi$ture pressure. *ote that for an idealgas mi$ture! the mole fraction! the


0ressure ratio is the ratio of final to initial pressures during a compression process.

0ressure transducers are made of semiconductor materials such as silicon and convert

the pressure effect to an electrical effect such as a change in voltage! resistance! orcapacitance. ?ressure transducers are smaller and faster! and they are more sensitive!

reliable! and precise than their mechanical counterparts.

0rimary or fundamental dimensions, such as mass m! length C! time t! and temperature

T ! are the basis for the derivation of secondary dimensions.

0rinciple of corresponding states is the fact that compressibility factor ' for all gases is

appro$imately the same at the same reduced pressure and temperature.

0roblem-solving techni'ue is a stepbystep approach to problem solving discussed in

1hapter /.

0rocess is any change that a system undergoes from one e5uilibrium state to another. #odescribe a process completely! one should specify the initial and final states of the

process! as well as the path it follows! and the interactions with the surroundings.

0rocess heat is re5uired energy input in the form of heat for many industrial processes.#he process heat is often obtained as heat transfer from highpressure! hightemperature

steam. 2ome industries that rely heavily on process heat are chemical! pulp and paper! oil production and refining! steel ma'ing! food processing! and te$tile industries.

0roducts are the components that e$ist after the reaction in a combustion process.

0roperty is any characteristic of a system. 2ome familiar properties are pressure ?!

temperature #! volume >! and mass m. #he list can be e$tended to include less familiar

ones such as viscosity! thermal conductivity! modulus of elasticity! thermal e$pansioncoefficient! electric resistivity! and even velocity and elevation.

0ropet engine is a turbo4et engine in which the shaft wor' is used to drive the propeller.

0ropulsive efficiency of an aircraft turbo4et engine is the ratio of the power produced to

propel the aircraft and the thermal energy of the fuel released during the combustion process.

,






0ropulsive poer is the power developed from the thrust of the aircraft gas turbines and

is the propulsive force (thrust) times the distance this force acts on the aircraft per unittime! that is! the thrust times the aircraft velocity.

0seudo-reduced specific volume v& is used with the generali"ed compressibility chart todetermine the third property when P and v! or T and v! are given instead of P and #.

0sychrometric chart presents the properties of atmospheric air at a specified pressure

and two independent intensive properties. #he psychrometric chart is a plot of absolutehumidity versus drybulb temperature and shows lines of constant relative humidity! wet

bulb temperature! specific volume! and enthalpy for the atmospheric air.

0ump is a steady flow device used to increase the pressure of a li5uid while compressors

increase the pressure of gases.

0ump efficiency is defined as the ratio of the mechanical energy increase of the fluid as

it flows through the pump to the mechanical energy input to the pump.

0ure substance is a substance that has a fi$ed chemical composition throughout.

P-v-T surface is a threedimensional surface in space which represents the PvT

behavior of a substance. All states along the path of a 5uasie5uilibrium process lie onthe PvT surface since such a process must pass through e5uilibrium states. #he single

phase regions appear as curved surfaces on the PvT surface! and the twophase regions

as surfaces perpendicular to the PT plane.

?uality x is the ratio of the mass of vapor to the total mass of a saturated mi$ture. #he

5uality lies in the range 0 / x≤ ≤ .

?uality of energy is a measure of how much of the energy can be converted to wor'.More of energy at high temperatures can be converted to wor'. #herefore! the higher the

temperature! the higher the 5uality of the energy.

?uasi-e'uilibrium process (see 5uasistatic process).

?uasi-static, or 'uasi-e'uilibrium, process is a process which proceeds in such a

manner that the system remains infinitesimally close to an e5uilibrium state at all times.A 5uasie5uilibrium process can be viewed as a sufficiently slow process that allows the

system to ad4ust itself internally so that properties in one part of the system do not change

any faster than those at other parts.

)adiation is the transfer of energy due to the emission of electromagnetic waves (or

photons).

,:






)amet engine is a properly shaped duct with no compressor or turbine! and is

sometimes used for highspeed propulsion of missiles and aircraft. #he pressure rise inthe engine is provided by the ram effect of the incoming highspeed air being rammed

against a barrier. #herefore! a ram4et engine needs to be brought to a sufficiently highspeed by an e$ternal source before it can be fired.

)an%ine is the temperature unit for the &an'ine scale in the @nglish system.

)an%ine cycle is the ideal cycle for vapor power plants. #he ideal &an'ine cycle doesnot involve any internal irreversibilities and consists of the following four processes6

/- 3sentropic compression in a pump!

-, 1onstant pressure heat addition in a boiler!,8 3sentropic e$pansion in a turbine!

8/ 1onstant pressure heat re4ection in a condenser.

)an%ine scale, named after Eilliam &an'ine (/:-0/:-)! is the thermodynamic

temperature scale in the @nglish system. #he temperature unit on this scale is the ran'ine,

which is designated by &.

)aoult’s la applies to a gasli5uid mi$ture when a gas is highly soluble in a li5uid

(such as ammonia in water) and relates the mole fractions of the species of a twophase

mi$ture in the li5uid and gas phases in an appro$imate manner.

)arefied gas flo theory applies to a substance in which the mean free path of its

molecules is large compared to the characteristic length of the systems such that the

impact of individual molecules should be considered! and the substance cannot bemodeled as a continuum.

)ate form is the form of a 5uantity e$pressed per unit time.

)ate of heat transfer is the amount of heat transferred per unit time.

)ayleigh flo is the steady onedimensional flow of an ideal gas with constant specific

heats through a constantarea duct with heat transfer! but with negligible friction.

)ayleigh line is the locus of all states for frictionless flow in a constantarea duct with

heat transfer plotted on an hs diagram and results from combining the conservation of

mass and momentum e5uations into a single e5uation.

)eactants are the components that e$ist before the reaction in a combustion process.

)eciprocity relation shows that the inverse of a partial derivative is e5ual to its

reciprocal.

,F






( )/

= y y

x

$ $ x

⎛ ⎞SD⎜ ⎟

S S S⎝ ⎠

)educed pressure P & is the ratio of the pressure to the critical pressure.

)educed temperature T & is the ratio of the temperature to the critical temperature.

)eference state is chosen to assign a value of "ero for a convenient property or

properties at that state.

)efrigerant is the wor'ing fluid used in the refrigeration cycle.

)efrigerator is a cyclic device which causes the transfer of heat from a lowtemperature

region to a hightemperature region. #he ob4ective of a refrigerator is to maintain therefrigerated space at a low temperature by removing heat from it.

)efrigerator coefficient of performance is the efficiency of a refrigerator! denoted by

1?& ! and e$pressed as desired output divided by re5uired input or 1?& 7 QC / Enet! in.

)egeneration is the process of transferring energy with in a cycle from a wor'ing fluidin a high temperature in part of the cycle to a lower temperature part of the cycle to

reduce the amount of e$ternal heat transfer re5uired to drive the cycle.

)egenerator (see feedwater heater)

)egenerator effectiveness is the e$tent to which a regenerator approaches an idealregenerator and is defined as the ratio of the heat transfer to the compressor e$it gas to

the ma$imum possible heat transfer to the compressor e$it gas.

)eheat )an%ine cycle is a modification of the &an'ine cycle in which the steam ise$panded in the turbine in two stages and reheated in between. &eheating is a practical

solution to the e$cessive moisture problem in the lowerpressure stages of turbines! and it

is used fre5uently in modern steam power plants.

)eheating is a techni5ue used to increase the e$pansion wor' for the gas turbine cycle.

#he e$pansion process is completed in stages while reheating the wor'ing fluid betweenstages. 2ince the steadyflow compression wor' is proportional to the specific volume of

the flow! the specific volume of the wor'ing fluid should be as large as possible during a

e$pansion process.

)elative density (see specific gravity)

80






)elative humidity is the ratio of the amount of moisture (water) in atmospheric air at a

given temperature to the ma$imum amount the air can hold at the same temperature. #herelative humidity can be e$pressed as the ratio of the vapor pressure to the saturation

pressure of water at that temperature.

)elative pressure P r is defined as the 5uantity e$p*s/(+ and is a dimensionless 5uantity

that is a function of temperature only since sH depends on temperature alone. &elative

pressure is used to relate the ratio of final to initial pressure in isentropic processes of

ideal gases where variable specific heats are re5uired.

)elative specific volume vr is defined as the 5uantity T = P r and is a function of

temperature only. P r is the relative pressure. &elative specific volume is used to relate theratio of final to initial volume in isentropic processes of ideal gases where variable

specific heats are re5uired.

)eversed +arnot cycle is a reversible cycle in which all four processes that comprise the

1arnot cycle are reversed during operation. &eversing the cycle will also reverse the

directions of any heat and wor' interactions. #he result is a cycle that operates in thecountercloc'wise direction. #he reversed 1arnot cycle is the 1arnot refrigeration cycle.

)eversible adiabatic compression is the process in which a wor'ing fluid is compressed

(decreases in volume) reversibly and adiabatically.

)eversible adiabatic epansion is the process in which a wor'ing fluid e$pands

(increases in volume) reversibly and adiabatically.

)eversible isothermal compression is the process in which the temperature is held

constant while a wor'ing fluid is compressed (decreases in volume) reversibly.

)eversible isothermal epansion is the process in which the temperature is held

constant while a wor'ing fluid e$pands (increases in volume) reversibly.

)eversible process is defined as a process that can be reversed without leaving any trace

on the surroundings. &eversible processes are ideali"ed processes! and they can be

approached but never reached in reality.

)eversible steady-flo or% is defined as the negative of the integral of the specific

volumepressure product. #he larger the specific volume the larger the reversible wor' produced or consumed by the steadyflow device. #herefore! every effort should be

made to 'eep the specific volume of a fluid as small as possible during a compression

process to minimi"e the wor' input and as large as possible during an e$pansion processto ma$imi"e the wor' output.

8/






)eversible or% 0 rev is defined as the ma$imum amount of useful wor' that can be

produced (or the minimum wor' that needs to be supplied) as a system undergoes a process between the specified initial and final states. &eversible wor' is determined from

the e$ergy balance relations by setting the e$ergy destroyed e5ual to "ero. #he wor' 0 inthat case becomes the reversible wor'.

)oc%et is a device where a solid or li5uid fuel and an o$idi"er react in the combustion

chamber. #he highpressure combustion gases are then e$panded in a no""le. #he gases

leave the roc'et at very high velocities! producing the thrust to propel the roc'et.

=aturated air is air which can hold no more moisture at its state. Any moisture

introduced into saturated air will condense.

=aturated li'uid is a li5uid that is about to vapori"e.

=aturated li'uid line is the saturated li5uid states connected by a line that meets the

saturated vapor line at the critical point! forming a dome.

=aturated li'uid–vapor miture (wet region) is a mi$ture of the li5uid and vapor

phases that coe$ist in e5uilibrium.

=aturated li'uid–vapor miture region is all the states that involve both the li5uid andvapor phases in e5uilibrium and are located under the dome.

=aturated vapor is a vapor that is about to condense.

=aturated vapor line is the saturated vapor states connected by a line that meets the

saturated li5uid line at the critical point! forming a dome.

=aturation pressure P sat is called the pressure at which a pure substance changes phase

at a given temperature.

=aturation temperature T sat is the temperature at which a pure substance changes phase

at a given pressure.

=cramet engine is essentially a ram4et in which air flows through at supersonic speeds

(speeds above the speed of sound).

=econdary dimensions, or derived dimensions! such as velocity! energy @! and volume

" ! are e$pressed in terms of the primary dimensions.

=econdary units are e$pressed in terms of the primary units.

8-






=econd la distinction beteen heat transfer and or% states that an energy

interaction that is accompanied by entropy transfer is heat transfer! and an energyinteraction that is not accompanied by entropy transfer is wor'.

=econd-la efficiency 33 is the ratio of the actual thermal efficiency to the ma$imum

possible (reversible) thermal efficiency under the same conditions. #he secondlaw

efficiency of various steadyflow devices can be determined from its general definition!

η33 D (e$ergy recovered)=(e$ergy supplied). #he second law efficiency measures how

well the performance of actual processes appro$imates the performance of thecorresponding reversible processes. #his enables us to compare the performance of

different devices that are designed to do the same tas' on the basis of their efficiencies.

#he better the design! the lower the irreversibilities and the higher the secondlaw

efficiency.

=econd la of thermodynamics (increase of entropy principle) is e$pressed as theentropy of an isolated system during a process always increases or! in the limiting case ofa reversible process! remains constant. 3n other words! the entropy of an isolated system

never decreases. 3t also asserts that energy has 5uality as well as 5uantity! and actual

processes occur in the direction of decreasing 5uality of energy.

=eebec% effect results when two wires made from different metals are 4oined at both ends

(4unctions)! form a closed circuit! and one of the ends is heated. As a result of the applied

heat a current flows continuously in the circuit. #he 2eebec' effect is named in honor of#homas 2eebec'! who made its discovery in /:-/.

=ensible energy is the portion of the internal energy of a system associated with the'inetic energies of the molecules.

=haft or% is energy transmitted by a rotating shaft and is the related to the tor5ue

applied to the shaft and the number of revolutions of the shaft per unit time.

=hoc% angle (wave angle) is the angle at which straight obli5ue shoc's are deflectedrelative to the oncoming flow as the flow comes upon a body.

=hoc% ave is an abrupt change over a very thin section of flow in which the flow

transitions from supersonic to subsonic flow. #his abrupt change in the flow causes a

sudden drop in velocity to subsonic levels and a sudden increase in pressure. 9lowthrough the shoc' is highly irreversible and! thus! it cannot be appro$imated as

isentropic.

=imple compressible system is a system in which there is the absence of electrical!

magnetic! gravitational! motion! and surface tension effects. #hese effects are due toe$ternal force fields and are negligible for most engineering problems.

8,






=imple cooling is the process of lowering the temperature of atmospheric air when no

moisture is removed.

=imple heating is the process of raising the temperature of atmospheric air when nomoisture is added.

=imultaneous reactions are chemical reactions that involve two or more reactions

occurring at the same time.

=ling psychrometer is a device with both a drybulb thermometer and a wetbulb

temperature mounted on the frame of the device so that when it is swung through the air

both the wetand drybulb temperatures can be read simultaneously.

=olid phase has molecules arranged in a threedimensional pattern (lattice) that is

repeated throughout. Because of the small distances between molecules in a solid! theattractive forces of molecules on each other are large and 'eep the molecules at fi$ed

positions.

=olubility represents the ma$imum amount of solid that can be dissolved in a li5uid at a

specified temperature.

=onic flo occurs when a flow has a Mach number 1 &/.

=onic speed (see speed of sound)

=par%-ignition = engines are reciprocating engines in which the combustion of theairfuel mi$ture is initiated by a spar' plug.

=pecific gravity, or relative density, is defined as the ratio of the density of a substance

to the density of some standard substance at a specified temperature (usually water at

8°1! for which the density is /000 'g=m,).

=pecific heat is defined as the energy re5uired to raise the temperature of a unit mass of a

substance by one degree. 3n general! this energy will depend on how the process is

e$ecuted.

=pecific heat at constant pressure p is the energy re5uired to raise the temperature ofthe unit mass of a substance by one degree as the pressure is maintained constant. p is ameasure of the variation of enthalpy of a substance with temperature. p can be defined

as the change in the enthalpy of a substance per unit change in temperature at constant

pressure.

=pecific heat at constant volume v is the energy re5uired to raise the temperature of

the unit mass of a substance by one degree as the volume is maintained constant. v is

88






related to the changes in internal energy. 3t would be more proper to define v as the

change in the internal energy of a substance per unit change in temperature at constantvolume.

=pecific heat ratio ' is defined as the ratio p= v.

=pecific heats for solids and li'uids! or incompressible substances! are e5ual.

=pecific humidity (see absolute humidity)

=pecific properties are e$tensive properties per unit mass. 2ome e$amples of specific

properties are specific volume (v&"/ m) and specific total energy (e& E/ m).

=pecific volume is the reciprocal of density and is defined as the volume per unit mass.

=pecific eight is the weight of a unit volume of a substance and is determined from

the product of the local acceleration of gravity and the substance density.

=peed of sound (sonic speed) is the speed at which an infinitesimally small pressure

wave travels through a medium.

=pray pond is a pond where warm water is sprayed into the air and is cooled by the airas it falls into the pond. 2pray ponds re5uire -7 to 70 times the area of a cooling tower

because water loss due to air drift is high.

=pring or% is the wor' done to change the length of a spring.

=table form of an element is the chemically stable form of that element at -7°1 and /

atm. *itrogen! for e$ample! e$ists in diatomic form (*- ) at -7°1 and / atm. #herefore!

the stable form of nitrogen at the standard reference state is diatomic nitrogen *- ! not

monatomic nitrogen *.

=tagnation enthalpy (total enthalpy) is the sum of the enthalpy and 'inetic energy of the

flow and represents the total energy of a flowing fluid stream per unit mass. 3t represents

the enthalpy of a fluid when it is brought to rest adiabatically with no wor'. #he

stagnation enthalpy e5uals the static enthalpy when the 'inetic energy of the fluid is

negligible.

=tagnation pressure is the pressure a fluid attains when brought to rest isentropically.9or ideal gases with constant specific heats! the stagnation pressure is related to the static

pressure of the fluid through the isentropic process e5uation relating pressure and

temperature.

87






=tagnation properties are the properties of a fluid at the stagnation state. #hese

properties are called stagnation temperature! stagnation pressure! stagnation density! etc.#he stagnation state and the stagnation properties are indicated by the subscript 0.

=tagnation temperature (total temperature) is the temperature an ideal gas will attainwhen it is brought to rest adiabatically.

=tandard reference state for the properties of chemical components is chosen as -7°1

(°9) and / atm. ?roperty values at the standard reference state are indicated by a

superscript (°) (such as h°and %°).

=tandard-state 5ibbs function change is the difference between the sum products of

the stoichiometric coefficients and the Gibbs function of a component at / atm pressureand temperature # for the products and reactants in the stoichiometric reaction.

=tate is the condition of a system not undergoing any change gives a set of properties thatcompletely describes the condition of that system. At this point! all the properties can be

measured or calculated throughout the entire system.

=tate postulate specifies the number of properties re5uired to fi$ the state of a system@

#he state of a simple compressible system is completely specified by two independent!

intensive properties.

=tatic enthalpy is the ordinary enthalpy of the flow measured at the fluid state.

=tationary systems are closed systems whose velocity and elevation of the center ofgravity remain constant during a process.

=tatistical thermodynamics! an approach to thermodynamics more elaborate thanclassical thermodynamics! is based on the average behavior of large groups of individual

particles.

=teady implies no change with time. #he opposite of steady is unsteady! or transient.

=teady-flo conservation of mass states that the total rate of mass entering a control

volume is e5ual to the total rate of mass leaving it.

=teady-flo devices operate for long periods of time under the same conditions.

=teady-flo process is a process during which a fluid flows through a control volume

steadily. #hat is! the fluid properties can change from point to point within the control

volume! but at any point! they remain constant during the entire process. Iuring asteadyflow process! no intensive or e$tensive properties within the control volume

change with time.

8;






=team generator is the combination of a boiler and a heat e$changer section (thesuperheater)! where steam is superheated.

=team poer plant is an e$ternalcombustion engine in which steam (water) is thewor'ing fluid. #hat is! combustion ta'es place outside the engine! and the thermal energy

released during this process is transferred to the steam as heat. A turbine in the power

plant converts some of the energy of the steam into rotating shaft wor'.

=tefan-$olt!mann la gives the ma$imum rate of radiation that can be emitted from a

surface as product of the 2tefanBolt"mann constant! surface area! and the fourth power

of the surface absolute temperature.

=tirling cycle is made up of four totally reversible processes6

/- T constant e$pansion (heat addition from the e$ternal source)!-, v constant regeneration (internal heat transfer from the wor'ing fluid to the

regenerator)!

,8 T constant compression (heat re4ection to the e$ternal sin')!8/ v constant regeneration (internal heat transfer from the regenerator bac' to the

wor'ing fluid).

=toichiometric air is the minimum amount of air! also called theoretical air! needed forthe complete combustion of a fuel. Ehen a fuel is completely burned with theoretical air!

no uncombined o$ygen will be present in the product gases.

=toichiometric coefficients are the mole numbers in the stoichiometric (theoretical)reaction.

=toichiometric combustion (theoretical combustion) is the ideal combustion process

during which a fuel is burned completely with theoretical air.

=toichiometric theoretical reaction is the balanced reaction e5uation for a chemicale5uilibrium reaction.

=tream eergy see flo eergy

=tro%e is the distance between the top dead center and the bottom dead center and is the

largest distance that the piston can travel in one direction within a cylinder.

=trong obli'ue shoc%s are straight obli5ue shoc's that have the larger possible values of

the shoc' angles for deflection angles less than the ma$imum deflection angle.

=ubcooled li'uid has a temperature less than the saturation temperature corresponding to

the pressure.

8






=ublimation is the process of passing from the solid phase directly into the vapor phase.

=ublimation line separates the solid and vapor regions on the phase diagram.

=ubsonic flo occurs when a flow has a Mach number 1 < /.

=uperheated vapor is a vapor that is not about to condense (not a saturated vapor). A

superheated vapor has a temperature greater than the saturation temperature for the pressure.

=uperheated vapor region is all the superheated states located to the right of thesaturated vapor line and above the critical temperature line.

=upersaturated steam is steam that e$ists in the wet region without containing anyli5uid. #his phenomenon would e$ist due to the supersaturation process.

=upersaturation is the phenomenon owing to steam flowing through a no""le with thehigh velocities and e$iting the no""le in the saturated region. 2ince the residence time of

the steam in the no""le is small! and there may not be sufficient time for the necessary

heat transfer and the formation of li5uid droplets! the condensation of the steam may be

delayed for a little while.

=upersonic flo occurs when a flow has a Mach number 1 3 /.

=urface tension is the force per unit length used to overcome the microscopic forces between molecules at the li5uidair interfaces.

=urrounding is the mass or region outside the thermodynamic system.

=urroundings are everything outside the system boundaries.

=urroundings or% is the wor' done by or against the surroundings during a process.

=amp coolers (see evaporative coolers)

Tds

relationsrelate the Tds product to other thermodynamic properties. #he first Gibbs

relation is Tds & d% = Pdv) #he second Gibbs relation is Tds & dh 2 vdP .

heoretical air (see stoichiometric air)

heoretical combustion (see stoichiometric combustion)

8:






herm is defined as an amount of energy produced by the combustion of natural gas and

is e5ual to -F., 'Eh.

hermal conductivity is defined as a measure of the ability of a material to conductheat.

hermal efficiency th is the ratio of the net wor' produced by a heat engine to the total

heat input! th D 0 net=Qin.

hermal efficiency of a heat engine is the fraction of the thermal energy supplied to a

heat engine that is converted to wor'.

hermal efficiency of a poer plant is defined as the ratio of the shaft wor' output ofthe turbine to the heat input to the wor'ing fluid.

hermal energy is the sensible and latent forms of internal energy.

hermal energy reservoir, or 4ust a reservoir is a hypothetical body with a relatively

large thermal energy capacity (mass specific heat) that can supply or absorb finiteamounts of heat without undergoing any change in temperature.

hermal e'uilibrium means that the temperature is the same throughout the entire

system.

hermodynamic e'uilibrium is a condition of a system in which all the relevant types

of e5uilibrium are satisfied.

hermodynamic system, or simply a system, is defined as a 5uantity of matter or a

region in space chosen for study.

hermodynamic temperature scale is a temperature scale that is independent of the

properties of the substances that are used to measure temperature. #his temperature scaleis called the %elvin scale, and the temperatures on this scale are called absolute

temperatures. n the %elvin scale! the temperature ratios depend on the ratios of heat

transfer between a reversible heat engine and the reservoirs and are independent of the

physical properties of any substance.

hermodynamics can be defined as the science of energy. @nergy can be viewed as the

ability to cause changes. #he name thermodynamics stems from the Gree' words therme(heat) and dynamis (power)! which is most descriptive of the early efforts to convert heat

into power. #oday the same name is broadly interpreted to include all aspects of energy

and energy transformations! including power production! refrigeration! and relationshipsamong the properties of matter.

8F






hermoelectric circuit is a circuit that incorporates both thermal and electrical effects.

hermoelectric generator uses the 2eebec' effect as the basis for thermoelectric power

generation.

hermoelectric refrigerator is a refrigerator using electric energy to directly produce

cooling without involving any refrigerants and moving parts.

hermo-mechanical eergy is the e$ergy associated with the conversion of thermalenergy to mechanical energy and disregards any mi$ing and chemical reactions.

hird la of thermodynamics states that the entropy of a pure crystalline substance atabsolute "ero temperature is "ero.

hroat is the smallest flow area of a convergingdiverging no""le.

hrottling valves are any 'ind of flowrestricting devices that cause a significant

pressure drop in a flowing fluid. 2ome familiar e$amples are ordinary ad4ustable valves!capillary tubes! and porous plugs. Jnli'e turbines! they produce a pressure drop without

involving any wor'. #he pressure drop in the fluid is often accompanied by a large drop

in temperature! and for that reason throttling devices are commonly used in refrigeration

and airconditioning applications. #he magnitude of the temperature drop (or! sometimes!the temperature rise) during a throttling process is governed by a property called the

<oule#homson coefficient! which is discussed in 1hapter /-.

hrust is the unbalanced force developed in a turbo4et engine that is caused by thedifference in the momentum of the lowvelocity air entering the engine and the high

velocity e$haust gases leaving the engine! and it is determined from *ewtonKs secondlaw.

on of refrigeration is the capacity of a refrigeration system e5uivalent to the energy

that can free"e / ton (-000 lbm) of li5uid water at 0°1 (,-°9) into ice at 0°1 in -8 h.

ne ton of refrigeration is e5uivalent to -// '<=min or -00 Btu=min (/-!000 Btu=h). #he

cooling load of a typical -00m- (-/7,ft-) residence is in the ,ton (/0'E) range.

op dead center *+ is the position of the piston when it forms the smallest volume in

the cylinder.

opping cycle is a power cycle operating at high average temperatures that re4ects heat

to a power cycle operating at lower average temperatures.

otal differential of a dependent variable in terms of its partial derivatives with respect

to the independent variables is e$pressed as! for $ & $ *x, y)!

70






y x

$ $ d$ dx dy

x y

∂ ∂ = + ∂ ∂

otal energy E of a system is the sum of the numerous forms of energy such as thermal!

mechanical! 'inetic! potential! electric! magnetic! chemical! and nuclear! and their

constituents. #he total energy of a system on a unit mass basis is denoted by e and isdefined as E/m.

otal energy of a floing fluid is the sum of the enthalpy! 'inetic! and potential energiesof the flowing fluid.

otal enthalpy (see stagnation enthalpy)

otal temperature (see stagnation temperature)

otally reversible process, or simply reversible process, involves no irreversibilitieswithin the system or its surroundings. A totally reversible process involves no heat

transfer through a finite temperature difference! no non5uasie5uilibrium changes! and

no friction or other dissipative effects.

ransport energy (see flow wor').

ransonic flo occurs when a flow has a Mach number 1 ≅ /.

rap is a device that allows condensed steam to be routed to another heater or to the

condenser. A trap allows the li5uid to be throttled to a lowerpressure region but traps thevapor. #he enthalpy of steam remains constant during this throttling process.

riple line is the locus of the conditions where all three phases of a pure substancecoe$ist in e5uilibrium. #he states on the triple line of a substance have the same pressure

and temperature but different specific volumes.

riple point of water is the state at which all three phases of water coe$ist in

e5uilibrium.

urbine is a device that produces shaft wor' due to a decrease of enthalpy! 'inetic! and potential energies of a flowing fluid.

urbine efficiency is defined as the ratio of the mechanical energy output of the turbineto the mechanical energy decrease of the fluid flow through the turbine.

urbine firing temperature see turbine inlet temperature)

7/






urbine inlet temperature (turbine firing temperature) is the temperature of the

wor'ing fluid at the turbine inlet. 3ncreasing the turbine inlet temperature has been the primary approach ta'en to improve gasturbine efficiency. #hese increases have been

made possible by the development of new materials and the innovative coolingtechni5ues for the critical components such as coating the turbine blades with ceramiclayers and cooling the blades with the discharge air from the compressor or in4ected

steam.

urbofan or fan-et engine is the most widely used engine in aircraft propulsion. 3nthis engine a large fan driven by the turbine forces a considerable amount of air through a

duct (cowl) surrounding the engine. #he fan e$haust leaves the duct at a higher velocity!

enhancing the total thrust of the engine significantly. A turbofan engine is based on the principle that for the same power! a large volume of slowermoving air will produce more

thrust than a small volume of fastmoving air. #he first commercial turbofan engine was

successfully tested in /F77.

urboprop engine uses propellers powered by the aircraft turbine to produce the aircraft

propulsive power.

urning angle (deflection angle) is the angle at which straight obli5ue shoc's are

deflected as flow comes upon a body! li'e that produced when a uniform supersonic flow

impinges on a slender! twodimensional wedge.

o-stro%e engines e$ecute the entire cycle in 4ust two stro'es6 the power stro'e and the

compression stro'e.

"niform implies no change with location over a specified region.

"niform-flo process involves the following ideali"ation6 #he fluid flow at any inlet or

e$it is uniform and steady! and thus the fluid properties do not change with time or

position over the cross section of an inlet or e$it. 3f they do change with time! the fluid

properties are averaged and treated as constants for the entire process.

"nits are the arbitrary magnitudes assigned to the dimensions.

"nity conversion ratios are ratios of units that are based on the definitions of the units in

5uestion that are identically e5ual to /! are unitless! and can be inserted into any

calculation to properly convert units.

"niversal gas constant (u is the same for all substances and its value is :.,/8 '<='molR%

and /.F:; Btu=lbmolR&.

7-






"nrestrained epansion of a gas is the process of the free e$pansion of gas!

unrestrained by a moving boundary such as the rapid e$pansion of air from a balloon thathas 4ust been burst.

"nsteady-flo! or transientflow! processes are processes that involve changes within acontrol volume with time.

"seful pumping poer is the rate of increase in the mechanical energy of a fluid as it

flows through a pump.

"seful or% 0 u is the difference between the actual wor' 0 and the surroundings wor'

0 surr .

"seful or% potential is the ma$imum possible wor' that a system will deliver as it

undergoes a reversible process from the specified initial state to the state of itsenvironment! that is! the dead state.

"tili!ation factor is a measure of the energy transferred to the steam in the boiler of asteam power plant that is utili"ed as either process heat or electric power. #hus the

utili"ation factor is defined for a cogeneration plant as the ratio of the sum of the net

wor' output and the process heat to the total heat input.

8acuum cooling is a way to cool a substance by reducing the pressure of the sealed

cooling chamber to the saturation pressure at the desired low temperature and evaporating

some water from the products to be cooled. #he heat of vapori"ation during evaporation is

absorbed from the products! which lowers the product temperature.

8acuum free!ing is the application of vacuum cooling when the pressure (actually! thevapor pressure) in the vacuum chamber is dropped below 0.; '?a! the saturation pressure

of water at 0H1.

8acuum pressure is the pressure below atmospheric pressure and is measured by avacuum gage that indicates the difference between the atmospheric pressure and the

absolute pressure.

van der (aals e'uation of state is one of the earliest attempts to correct the ideal gas

e5uation for real gas behavior. 3t is given by

( )( ) P a

vv b ( T + − =

-

where the constants a and b are functions of the critical constants of the gas.

van’t 6off e'uation is the e$pression of the variation of the chemical e5uilibrium

constant with temperature in terms of the enthalpy of reaction at temperature #.

7,






8apor implies a gas that is not far from a state of condensation.

8apor-compression refrigeration cycle is the most fre5uently used refrigeration cycleand involves four main components6 a compressor! a condenser! an e$pansion valve! andan evaporator.

8apor pressure is usually considered to be the partial pressure of water vapor in

atmospheric air.

8apori!ation line separates the li5uid and vapor regions on the phase diagram.

8enturi no!!le is a duct in which the flow area first decreases and then increases in the

direction of the flow and is used strictly for incompressible flow.

8irial e'uations of state is an e5uation of state of a substance e$pressed in a series form

as

P & (T/v = a*T+/v> = b*T+/v? = c*T+/v@ = d*T+/v5 =where the coefficients a(T )! b(T )! c(T )! and so on! are functions of temperature alone

and are called virial coefficient s.

8olume epansivity (also called the coefficient of volumetric e$pansion) relates howvolume changes when temperature changes when pressure is held constant.

8olume flo rate is the volume of the fluid flowing through a cross section per unit of

time.

8olume fraction of a gas component in a gas mi$ture is the ratio of the componentvolume to the mi$ture volume. *ote that for an idealgas mi$ture! the mole fraction! the


(aste heat is energy that must be dissipated to the atmosphere from a process such asthe heat transferred from condensing steam in the condenser of a steam power plant.

(asted or% potential represents irreversibility as the energy that could have beenconverted to wor' but was not and is the lost opportunity to do wor'.

(ater heater efficiency is defined as the ratio of the energy delivered to a house by hotwater to the energy supplied to the water heater.

(ave angle (see shoc' angle)

(ea% obli'ue shoc%s are straight obli5ue shoc's that have the smaller of the possible

values of the shoc' angles for deflection angles less than the ma$imum deflection angle.

78






(eight is the gravitational force applied to a body! and its magnitude is determined from *ewtonKs second law.

(et-bulb temperature is temperature measured by using a thermometer whose bulb iscovered with a cotton wic' saturated with water and blowing air over the wic'.

(et cooling toer is essentially a semienclosed evaporative cooler.

(et region (see saturated li5uidvapor mi$ture region)

(ilson line is the locus of points where condensation will ta'e place regardless of theinitial temperature and pressure as steam flows through a highvelocity no""le. #he

Eilson line is often appro$imated by the 8 percent moisture line on the hs diagram for

steam. #herefore! steam flowing through a highvelocity no""le is assumed to begincondensation when the 8 percent moisture line is crossed.

(or% is the energy transfer associated with a force acting through a distance.

(or% transfer is the energy in the form of wor' that is transferred across a system

boundary.

(or%ing fluid is the fluid to and from which heat and wor' is transferred while

undergoing a cycle in heat engines and other cyclic devices.

eroth la of thermodynamics states that if two bodies are in thermal e5uilibrium witha third body! they are also in thermal e5uilibrium with each other. By replacing the third

body with a thermometer! the "eroth law can be restated as two bodies are in thermale5uilibrium if both have the same temperature reading even if they are not in contact.

Documents

5 e Thermo Glossary