Superheated steam enters a steady-state, adiabatic throttling valve at T = 200°C and P = 1 bar. The pressure of the fluid leaving the valve is P = 0.5 bar. It has been suggested that perhaps it would make more sense to replace the valve with a turbine—the desired pressure drop will still occur, but some work would be obtained from the turbine.

A. Determine the physical state of the fluid leaving the valve.

B. Determine the rate at which entropy is generated in the valve, per kilogram of entering steam.

C. Determine the maximum work that could be produced by a turbine, per kilogram of entering steam, if the steam entering the turbine was identical to the steam entering the valve, and the pressure leaving the turbine was P=0.5 bar.

D. Compare the physical state of the fluid leaving the “idealized” turbine described in part C to the physical state of the fluid leaving the valve as described in part A. Are they identical? Can you rationalize why they are or are not identical?

E. Compare your answers to this problem to your answers to Problem 4-30.  How is the outcome for steam different from the outcome of a similar process involving liquid water?