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2300_les12

2300_les12 - IV First Law of Thermodynamics D Applications...

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1 lesson 12 IV. First Law of Thermodynamics D. Applications to steady flow devices 1. Heat exchangers - example: Clinker cooler for cement kiln Cooler Clinker 1400 C, 151 ton/h Secondary air 20 C, 157,000 lbm/h Secondary air 520 C, 157,000 lbm/h Clinker ? C, 151 ton/h lesson 12 IV. First Law of Thermodynamics a. Assumptions i. changes in kinetic and potential energy are negligible ii. steady state iii. constant mass flow rates iv. negligible heat loss to surroundings v. negligible nonflow work vi. Evaluate heat capacities at average temperatures b. Energy balance over clinker cooler = out e e in i i h m h m 0 ± ± ( ) ( ) cin cout c c aout ain a a T T C m T T C m = ± ± + + + + + = out e 2 e in i 2 i gz 2 h m gz 2 h m W Q 0 V V ± ± ± ±
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2 lesson 12 IV. First Law of Thermodynamics c. Analysis () cin aout ain c c a a cout T T T C m C m T + = ± ± Solving for T cout gives C 1160 C 1400 ) C 520 C 20 ( ) kgK / J 1120 ( h / lb 000 , 302 ) kgK / J 1040 ( h / lb 000 , 157 T cout = + = Comment : since the heat capacities were evaluated at the average temperatures and the final temperature of the clinker was not known,
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2300_les12 - IV First Law of Thermodynamics D Applications...

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