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Unformatted text preview: 12-14 The validity of the last Maxwell relation for refrigerant-134a at a specified state is to be verified. Analysis We do not have exact analytical property relations for refrigerant-134a, and thus we need to replace the differential quantities in the last Maxwell relation with the corresponding finite quantities. Using property values from the tables about the specified state, s ? v =- P T T P
? s v - P T =80C T P =1200 kPa s1400 kPa - s1000 kPa (1400 - 1000) kPa ? v 100C - v 60C - (100 - 60 ) C T =80C P =1200kPa (1.0056 - 1.0458)kJ/kg K ? (0.022442 - 0.018404)m 3 /kg - (1400 - 1000)kPa (100 - 60)C - 1.005 10 - 4 m 3 /kg K -1.0095 10 - 4 m 3 /kg K since kJ kPam, and K C for temperature differences. Thus the last Maxwell relation is satisfied. 12-17 Using the Maxwell relations, a relation for (s/P)T for a gas whose equation of state is P(v-b) = RT is to be obtained. Analysis This equation of state can be expressed as v = R v = T P P From the fourth Maxwell relation, R s v = - =- P T T P P 12-19 Using the Maxwell relations and the ideal-gas equation of state, a relation for (s/v)T for an ideal gas is to be obtained. Analysis The ideal gas equation of state can be expressed as P = R P = T v v From the third Maxwell relation, R s P = = v T T v v RT . Then, v RT + b . Then, P ...
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This note was uploaded on 04/08/2008 for the course MECH 216 taught by Professor Beninati during the Spring '08 term at Bucknell.
- Spring '08