Explanation Draw the T − s diagram for the turbine process as in Figure (1). Write the expression for the thermal efficiency of the Carnot cycle ( η th ) . η th = 1 − T L T H (I) Here, temperature at higher end is T H , and temperature at the lower end is T L . Write the expression for the temperature and pressure relation for the process 1-2 . P 2 P 1 = ( T 2 T 1 ) k / ( k − 1 ) (II) Here, pressure at state 1 is P 1 , pressure at state 2 is P 2 , temperature at state 1 is T 1 and temperature at state 2 is T 2 . Write the expression for the volume and pressure relation for process 1-2. ν 1 ν 2 = ( P 2 P 1 ) 1 / k (III) Here, volume at state 1 , ν 1 and volume at state 2 is ν 2 . Conclusion: Substitute 60 ° F for T L , and 50% for T H in Equation (I). 60% = 1 − 60 ° F T H 60 ( 1 100 ) = 1 − ( 60 + 460 ) R T H T H = 1300 R Thus, the minimum temperature of the heat source is 1300 R

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Chapter 9.12, Problem 158RP

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Chapter 9.12, Problem 157RP

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