Question

Consider a steam power plant which operates on the simple ideal Rankine cycle (shown in the next page), where the boiler pressure is 3 MPa and the condenser saturation temperature is 50°C. The temperature at the exit of the boiler is 500°C. Water leaves the condenser as a saturated liquid. The mass flow rate through each component is 15 kg/s. Calculate:

1. The power output of the steam power plant

2. The thermal efficiency of the steam power plant

Now, the isentropic turbine is replaced by an actual turbine (as shown in the next page), whose isentropic efficiency is T = 80%. Calculate:

1. The new power output of the steam power plant

2. The new thermal efficiency of the steam power plant

3. The rate of entropy generation in the turbine Comment on the change in power output and thermal efficiency between the first case and the second case

Comment on the change in power output and thermal efficiency between the first case and the second case.

1-2 Isentropic compression in a pump 2-3 Constant pressure heat addition in a boiler 3-4 Isentropic expansion in a turbine 4-1 Constant pressure heat rejection in a condenser Wurb.out Wpump.in Turbine Condenser Yout Wturb,out in pumpin FIGURE 10-2 The simple ideal Rankine cycle. The modified Rankine cycle (with an actual turbine) 4a 4s 4a

Answer 1