Redo Problem 4.9 using Aspen Plus.

Problem 4.9

a. A steam turbine in a small electric power plant is designed to accept 4500 kg/hr of steam at 60 bar and 500^◦C and exhaust the steam at 10 bar. Assuming that the turbine is adiabatic and has been well designed (so that Ṡ_gen = 0), compute the exit temperature of the steam and the power generated by the turbine.

b. The efficiency of a turbine is defined to be the ratio of the work actually obtained from the turbine to the work that would be obtained if the turbine operated isentropically between the same inlet and exit pressures. If the turbine in part (a) is adiabatic but only 80 percent efficient, what would be the exit temperature of the steam? At what rate would entropy be generated within the turbine? 

c. In off-peak hours the power output of the turbine in part (a) (100 percent efficient) is decreased by adjusting a throttling valve that reduces the turbine inlet steam pressure to 30 bar (see diagram) while keeping the flow rate constant. Compute T₁, the

Steam temperature to the turbine, T₂, the steam temperature at the turbine exit, and the power output of the turbine.

Transcribed Image Text:

Steam 60 bar 500°C 30 bar T₁ = ? Turbine W 10 bar T₂ = ?