Question

A steam turbine at steady state is operated at part load by throttling the steam to a lower pressure before it enters the turbine. Before throttling, the pressure and temperature are, respectively, 2 MPa and 300°C. After throttling, the pressure is 1 MPa. At the turbine exit, the steam is at 8 KPa and a quality of 85%. Heat transfer with the surroundings and all kinetic and potential energy effects can be ignored. Determine (a) the temperature at the turbine inlet, in °C, and (b) the power developed by the turbine, in kJ/kg of steam flowing.

Answer 1

a) 440° C

b) 808.354 kJ/kg

Step-by-step explanation:

Properties of 2.0 MPa and 300° C

`h_1` = 3024.2 kJ/kg

`s_1` = 6.7684 kJ/kg.K

Properties at 1 MPa and
`h_1 = h_2` = 3024.2 kJ/kg

Using properties at 1MPa and
`h_2` from steam Table

`T_2` = 440° C

At the turbine exit

the steam is at 8 KPa which is equivalent ⇒ 0.08 bar

Properties at 0.08 bar

`h_(fg)` = 173.84 kJ/kg

`h_(fg3)` = 2402.36 kJ/kg

`x_3=` 85% = 0.85

`h_3}= h_(f_3)} + x * h_(fg_3)`

= (173.84+(0.85*2402.36)

= 2215.846 kJ/kg

P = (3024.2 - 2215.846) kJ/kg

P = 808.354 kJ/kg