19 Due 4/10

1. Consider the steam powerplant
   
   where $P_1$ = 20 MPa, $T_1$ = 700$\POW9,{\circ}$C, $P_2$ = 20 kPa, and $T_3$ = 40$\POW9,{\circ}$C. Make typical approximations for each component as needed.
   • Explain why phase 1 must be superheated. Find phases 2, 3, and 4 in separate $Ts$ diagrams. In the diagrams, list no more than is needed to construct the phase, but do list the values of the curves/points used.
   • Find the specific works out of the turbine and into the pump.
   • Find the thermal efficiency of the cycle.
   • Considering the average temperatures in the boiler and condenser, does the efficiency you get seem reasonable, too high, too low?

2. R-134a at 1MPa and 30$\POW9,{\circ}$C passes through an adiabatic expansion valve in which the pressure decreases to standard atmospheric pressure. Construct the initial phase in the $Ts$ diagram. Then construct the final phase in a separate $Ts$ diagram, find the final quality if defined, and then the entropy generated.

3. Steam at 15 kPa and a quality of 90% enters a constant pressure condenser at a rate of 3 kg/s and exits it as saturated liquid. The heat is transferred to cooling water with an average temperature of 17$\POW9,{\circ}$C. What is the entropy generated?

4. Air at 1000 kPa and 500 K enters an isobaric heat exchanger at a rate of 0.2 kg/s and exits at 300 K, having been cooled down by the ambient air at 300 K. Find the total rate of entropy generation. Use constant specific heats from table A-2(a), not table A-17.