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Temperature, Heat, & Combustion. EGR 1301: Introduction to Engineering. Models. “A system of postulates, data, and inferences presented as a mathematical description of an entity or state of affairs” Quantitative approximation of reality Mathematical equations Computer simulations - PowerPoint PPT Presentation
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EGR 1301
Temperature, Heat,& Combustion
EGR 1301: Introduction to Engineering
EGR 1301
Models
• “A system of postulates, data, and inferences presented as a mathematical description of an entity or state of affairs”
• Quantitative approximation of reality Mathematical equations Computer simulations Physical scale models
• Why do we use them? Reality is too complex!!!
Source: Merriam-Webster .com, 2010
EGR 1301
Energy Conversion Tables
Source: Foundations of Engineering, Holtzapple & Reece, 2003
“For those who want some proof that physicists are human, the proof is in the idiocy of all the different units which they use for measuring energy.” Richard Feynman
EGR 1301
Utility of Energy for Analysis
• Incandescent bulb Resistance heating
in filament Light• When filament
reaches sufficiently high temperature Light is radiated
60 Watts of electricity• 800 lumens of light• ~10 cals of heat
• Fluorescent bulb Stream of electrons
collide with Hg electronsLight• Generates very little
heat
23 Watts of electricity• 800 lumens of light• ~1 cal of heat
Source: http://www.fullspectrumsolutions.com/26w_powercompact_65_prd1.htm
EGR 1301
Temperature – What Is It?
• NOT the same as HEAT• A quantitative measure of “hotness”• More accurately described on an atomic
scale Measures vibrational kinetic energy
EGR 1301
Temperature vs. Heat
• Temperature A measure of the intensity of internal energy
in a system (gas, liquid, or solid)• Heat
A measure of the total quantity of thermal energy flow into or out of a system
EGR 1301
Temperature vs. Heat
• Example: A cup of water at 60°C has much less energy
than a hot water heater full of water at 60°C.
BUT, the intensity of heat is the same.
EGR 1301
Heat Capacity
• Energy required to raise temperature of matter by one degree (at constant pressure or constant volume)
Q = energy in calories m = mass in grams ΔT = temperature change in degrees (C or K)
TmQC
EGR 1301
Constant Pressure Heat Capacities
Source: Foundations of Engineering, Holtzapple & Reece, 2003
EGR 1301
Converting Work into Heat:Joule’s Experiment
Source: Foundations of Engineering, Holtzapple & Reece, 2003
TCmQ
xFW maF
QU
outinoutinoutinpk MMQQWWUEE
QW
EGR 1301
Heat CapacityExample Problem
• In Joule’s experiment, Beaker contains 5 kg of water Mass spinning the stirrer is 90 kg
(g=9.81m/s2) The water increases in temperature by 0.1°C How far did the mass travel?
TCmQ xFW
maF QW
EGR 1301
Heat Capacity
calCkggkg
CgcalQ 5001.0
11000500.1
Jsmkg
calJ
smkg
calmaQ
FWx
1
1
1184.4
81.990
500 2
2
2
mx 4.2
TCmQ xFW maF QW
EGR 1301
States of Matter
Source: Foundations of Engineering, Holtzapple & Reece, 2003
EGR 1301
Phase Diagram
Source: Foundations of Engineering, Holtzapple & Reece, 2003
EGR 1301
Phase Change
• Constant temperature process of transition between phases Melting / Solidification Boiling (vaporization) / Condensation
EGR 1301
Phase (or State) Change Energy
• Where m = mass (kg) ΔHvap = latent heat of vaporization (kJ/kg) ΔHfus = latent heat of fusion (kJ/kg)
vapvap HmQ fusfus HmQ
EGR 1301
Phase-Change EnergySource: Foundations of Engineering, Holtzapple & Reece, 2003
EGR 1301
Combustion
• Similar to phase change
• Where Qcomb = energy released (MJ) m = mass (kg) ΔHcomb = specific heat of combustion (MJ/kg)
• Table 22.4
combcomb HmQ
EGR 1301
Example 1:Phase-Change Energy
• When water changes from solid to liquid, it must absorb 333.56 kJ/kg from the surroundings What is the energy absorbed to melt ice in
units of cal/g?
Jcal
kJJ
gkg
kgkJ
12390.01000
1000156.333
gcal7.79
EGR 1301
Example 2a:1st Law of Thermodynamics
• If you have 100 g of water at 22°C and add 20 g of ice at 0°C, what will be the temperature of the 100 g of water once all the ice has melted to form 20 g of water at 0°C?
CTgm
22100
1
1
CTgm
020
2
2
:Given
EGR 1301
Example 2a:1st Law of Thermodynamics
CTgm
22100
1
1
CTgm
020
2
2
:Given :Eqns
HmHfusion
TCmQ
gcalg 7.7920 Tg
Cgcal
10000.1
CT 94.15 CCT
b 06.694.1522
1
EGR 1301
Example 2b:1st Law of Thermodynamics
• What will be the final temperature when the system temperature is uniform (i.e., water from melted ice has warmed and surrounding water has further cooled so that all water is at one temperature)?
CTgmCTgm
b
020
06.6100
2
2
1
1
)06.6(10000.1 CTgCgcal
f
:Given
)0(2000.1 CTgCgcal
f
CTf
05.5
EGR 1301
Example 3:Latent Heat
• If the latent heat of vaporization for water is 2,256.7 kJ/kg, what is the latent heat for water in cal/g?
Jcal
kgkJ
12390.07.2256
gcal4.539
EGR 1301
Example 4a:1st Law of Thermodynamics
• If by sweat and evaporation, you lose 0.031 slugs of water during exercising, how many calories of energy in the form of heat is removed from your body? Weight (mg) of 1 lb is associated with mass of 0.031
slugs Note on p.688 the conversion from slugs to grams
gcal
sluggslug 4.53914594031.0
cal244032
EGR 1301
Example 4b:1st Law of Thermodynamics
• If your body mass is 68,100 g (i.e., 150 lbs), how much would your body temperature rise if you did not sweat and evaporate the sweat in order to cool yourself? Assume the heat capacity for your body is that for
water, because your body is ~ 75% water.
TCmQ TgCg
calcal
)68100(1244032
FCFCT
45.65958.3
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