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# 2300_les19 - VI Entropy H The Tds Relations and Changes in...

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1 lesson 19 VI. Entropy H. The Tds Relations and Changes in Entropy 4. Example 1 2 av T T ln mC S = Two pieces of copper, A and B, with masses 1 and 3 kg, and initial temperatures 0 and 200 C are brought together and allowed to equilibrate while insulated from the surroundings. Determine (a) the entropy change of A and B and (b) the entropy generation (S gen ) for the process, in kJ/K. Entropy change given by (7-28): lesson 19 VI. Entropy 4. Example [] ) each for C use if C 151 ( C 150 T 0 ) 200 T ( 3 ) 0 T ( 1 0 ) T T ( mC ) T T ( mC 0 W Q U av 2 2 2 B 1 2 av A 1 2 av = = + = + = = () K kJ 171 . 0 273 423 ln kg kJ 390 . 0 1 S A = = K kJ 134 . 0 473 423 ln kg kJ 400 . 0 3 S B = = Final temperature, T 2 , is obtained from energy balance. Entropy changes for A and B are

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2 lesson 19 VI. Entropy 4. Example () 2 1 gen sys Q SS S T δ −= + gen 2 1 A B sys kJ S S S S S 0.171 ( 0.134) 0.037 K ∆∆ =− = + = + = Entropy generation from overall entropy balance on composite system (7-9) There is no heat transfer ( Q = 0 ) so Because S gen > 0 , the process is irreversible. lesson 19 VI. Entropy 5. Isentropic processes with ideal gases a. approximate treatment assuming constant specific heats i. first isentropic relation ( applies to open and closed systems ), recall 22 v,av 11 Tv sc l n R l n =+ ( ideal gas , 7-33) Reversible and adiabatic
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2300_les19 - VI Entropy H The Tds Relations and Changes in...

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