GATE Thermodynamics Book

8/10/2019 GATE Thermodynamics Book

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THERMODYNAMICS

for

Mechanical Engineering

By

www the gate academy com
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Syllabus Thermodynamics

.

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Syllabus for Thermodynamics

Zeroth, First and Second laws of thermodynamics; thermodynamic system and processes;Carnot cycle. irreversibility and availability; behaviour of ideal and real gases, properties of puresubstances, calculation of work and heat in ideal processes; analysis of thermodynamic cyclesrelated to energy conversion.

Power Engineering: Steam Tables, Rankine, Brayton cycles with regeneration and reheat. I.C.Engines: air-standard Otto, Diesel cycles. Refrigeration and air-conditioning: Vapourrefrigeration cycle, heat pumps, gas refrigeration, Reverse Brayton cycle; moist air:

psychrometric chart, basic psychrometric processes.

Analysis of GATE Papers

(Thermodynamics)

Year Percentage of marks Overall Percentage

2013 10.00

13.22

2012 12.00

2011 19.00

2010 12.00

2009 12.00

2008 16.00

2007 10.67

2006 11.33

2005 16.00


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Contents Thermodynamics

THE GATE ACADEMY PVT.LTD. H.O.: #74, Keshava Krupa (third Floor), 30 th Cross, 10 th Main, Jayanagar 4 th Block, Bangalore-11080 65700750 i f @ h d C i h d W b h d

C O N T E N T S

Chapter Page No.1. Basic Thermodynamics 1 42

Thermodynamics Systems 1 2 Thermodynamics processes 3 6 Zeroth Law of Thermodynamics 6 7 Work and Heat Transfer 7 10 First Law of Thermodynamics 10 15 Second Law of Thermodynamics 15 17 Solved Examples 17 28

Assignment - 1 29 33 Assignment - 2 33 34 Answer Keys 35 Explanations 35 42

2. Properties of Gases and Pure Substances 43 71 Properties of Pure substances 43 47 Properties of Gases 47 50 Solved Examples 50 60 Assignment - 1 61 63 Assignment - 2 64 Answer Keys 65 Explanations 65 71

3. Entropy Availability and Irreversibility 72 106 Entropy 72 79 Availability and Irreversibility 79 83 Solved Examples 84 95 Assignment - 1 96 98 Assignment - 2 98 99 Answer Keys 100 Explanations 100 106

4. Thermodynamics Cycles and Property Relations 107 129 Thermodynamic Cycles 107 110 Thermodynamic relations 110 113 Joule Thomson Coeffficient 113 114 Solved Examples 115 121 Assignment - 1 122 123 Assignment - 2 123 124 Answer Keys 125 Explanations 125 129

5. Power Engineering 130 179 Vapour Power Cycles 130 137 Steam Turbines 137 139


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Contents Thermodynamics

THE GATE ACADEMY PVT.LTD. H.O.: #74, Keshava Krupa (third Floor), 30 th Cross, 10 th Main, Jayanagar 4 th Block, Bangalore-11080 65700750 i f @ h d C i h d W b h d

Impulse Turbines 139 140 Important Formulae 141 Solved Examples 142 158 Assignment - 1 159 163 Assignment - 2 163 165 Answer Keys 166 Explanations 166 179

6. Internal Combustion Engines 180 220 Introduction 180 Basic of I.C Engine 180 185 Air Standard Cycles 185 190 Solved Examples 191 207 Assignment - 1 208 211 Assignment - 2 211 212 Answer Keys 213 Explanations 213 220

7. Refrigeration 221 272 Refrigeration 221 224 COP of Vapor compression cycle 224 228 Solved Examples 229 - 248 Assignment - 1 249 254 Assignment - 2 254 256 Answer Keys 257 Explanations 257 272

8. Psynchrometrics 273 305 Psychrometry 273 275 Applications of Psychrometry 275 285 Solved Examples 286 292 Assignment - 1 293 295 Assignment - 2 295 296 Answer Keys 297 Explanations 297 -305

Module Test 306 334 Test Questions 306 317 Answer Keys 318 - Explanations 318 334

Appendix 335 354

Reference Books 355


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Chapter 1 Thermodynamics

THE GATE ACADEMY PVT.LTD. H.O.: #74, KeshavaKrupa (third Floor), 30 th Cross, 10 th Main, Jayanagar 4 th Block, Bangalore-11080 65700750 i f @ h d C i h d W b h d P 1

CHAPTER 1

Basic Thermodynamics

Thermodynamic Systems

A system is defined as a quantity of matter or a region in space chosen for study. The mass orregion outside the system is called the surroundings. The real or imaginary surface thatseparates the system from its surroundings is called the boundary. The boundary of a systemcan be fixed or movable.

Systems may be considered to be closed or open, depending on whether a fixed mass or a fixedvolume in space is chosen for study. A closed system (also known as a control mass or justsystem when the context makes it clear) consists of a fixed amount of mass and no mass cancross its boundary. That is, no mass can enter or leave a closed system, as shown in Fig. 1. Butenergy, in the form of heat or work, can cross the boundary and the volume of a closed systemdoes not have to be fixed. If, as a special case, even energy is not allowed to cross the boundary,that system is called an isolated system.

Figure 1 Mass cannot cross the boundaries of closed, but energy can.

An open system or a control volume as it is often called, is a properly selected region in space. Itusually encloses a device that involves mass flow such as a compressor, turbine or nozzle. Flowthrough these devices is best studied by selecting the region within the device as the controlvolume as shown in Fig 2. Both mass and energy can cross the boundary of a control volume.

A large number of engineering problems involve mass flow in and out of a system and therefore,are modelled as control volumes. In general, any arbitrary region in space can be selected as acontrol volume. The boundaries of a control volume are called a control surface and they can bereal or imaginary.


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Figure 2 An open system a control volume) with one inlet and one exit

Any characteristic of a system is called a property. Some familiar properties are pressure P,temperature T, volume V and mass m. The list can be extended to include less familiar ones suchas viscosity, thermal conductivity, modulus of elasticity, thermal expansion coefficient, electricresistivity and even velocity and elevation.

Properties are considered to be either intensive or extensive. Intensive properties are those that

are independent of the mass of a system, such as temperature, pressure and density. Extensiveproperties are those whose values depend on the size or extent of the system. Total mass,total volume and total momentum are some examples of extensive properties. An easy way todetermine whether a property is intensive or extensive is to divide the system into two equalparts with an imaginary partition, as shown in Fig. 3. Each part will have the same value ofintensive properties as the original system, but half the value of the extensive properties.

Figure 3 Criterion to differentiate intensive and extensive properties


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Thermodynamic Processes

Any change that a system undergoes from one equilibrium state to another is called a processand the series of states through which a system passes during a process is called the path of theprocess (Fig.4). To describe a process completely one should specify the initial and final states ofthe process, as well as the path it follows, and the interactions with the surroundings. When aprocess proceeds in such a manner that the system remains infinitesimally close to anequilibrium state at all times, it is called a quasi-static or quasi-equilibrium, process. A quasi-equilibrium process can be viewed as a sufficiently slow process that allows the system to adjustitself internally so that properties in one part of the system do not change any faster than thoseat other parts. It should be pointed out that a quasi-equilibrium process is an idealized processand is not a true representation of an actual process. These processes are analyzed using processdiagrams. Process diagrams plotted by employing thermodynamic properties as coordinates arevery useful in visualizing the processes. Some common properties that are used as coordinatesare temperature T, pressure P and volume V (or specific volume v).

Figure 4 A process between states 1 and 2 and the process path

Some of the general thermodynamic processes are explained as under with the help of processdiagrams.

Quasi static process: The departure of the state of the system from the thermodynamicequilibrium is infinitely small.

The quasi static process is an infinite slow process.

P

V

All are inthermodynamicequilibrium

1

2


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Representation of thermodynamic processes on P V diagram

Thermodynamic Process Index of expansion n)Constant volume (V = C) Constant pressure (P = C ) 0Isothermal (T = C) 1Polytrophic (P V c 1< n < 1.25Reversible adiabatic (P V C r (= 1.4 )

Zeroth Law of Thermodynamics

Based on our physiological sensations, we express the level of temperature qualitatively withwords like freezing cold, warm, hot and red-hot. However, we cannot assign numerical values totemperatures based on our sensations alone. Fortunately, several properties of materials changewith temperature in a repeatable and predictable way and this forms the basis for accuratetemperature measurement.

When a body is brought into contact with another body that is at a different temperature, heat istransferred from the body at higher temperature to the one at lower temperature until bothbodies attain the same temperature. At that point, the heat transfer stops and the two bodies aresaid to have reached thermal equilibrium. The equality of temperature is the only requirementfor thermal equilibrium.

P

PV= CPV= CT C

P C

V

.

P

PV n=C

T = C

P = C

V = C PVn = C

PV n = C

T=C

P = C

PV n=CV=C


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Documents

GATE Thermodynamics Book