Your boss calls you into his office and hands you some literature from the Tuthill Corporation on steam turbines. He wants to purchase a “reconditioned” Coppus steam turbine for electrical generation needs. After some discussion, you tell him that there is 8 MPa steam (at 600 C) that is available for the turbine inlet, however it must exhaust at 100 kPa as a saturated vapor. He mentions to you that the turbine should produce 3100 kW of power. As you leave, he asks you to provide him with the following information (right after lunch!):

Question

(a) What is the mass flow rate required through the turbine?
(b) What is the efficiency of the turbine if operated in this manner?

Please answer his questions AND state all assumptions (with justification...why and/or how).

Answer 1

(a) Assume adiabatic turbine because the heat transfer surface area of the turbine is most likely relatively small. Also assume no potential and kinetic energy changes as they are negligible compared to enthalpy changes. Apply the simplified energy balance to the adiabatic turbine:



Where H ?_in=3642.4 kJ/kg from Appendix A-3 for 8 MPa (80 bar) steam @ 600 C

And H ?_out=2674.9kJ/kg from Appendix A-1 for 100 kPa saturated vapor


Apply entropy balance for a reversible turbine to find the maximum work obtained from this turbine keeping the inlet the same:





Plug into reversible turbine energy balance:



Calculate efficiency of original turbine: