An adiabatic turbine operates with a throttle governor as shown in the figure. S

Question

An adiabatic turbine operates with a throttle governor as shown in the figure. Steam approaches the throttle governor with a mass flow rate of 2.0 kg/sec at a pressure of 10 MPa and a temperature of 500C. The steam leaves the turbine with a pressure of 1.0 MPa. If the isentropic turbine efficiency is 80% and the power output is 700

kW, what is the pressure leaving the throttle governor?

An adiabatic turbine operates with a throttle governor as shown in the figure. Steam approaches the throttle governor with a mass flow rate of 2.0 kg/sec at a pressure of 10 MPa and a temperature of 500½C. The steam leaves the turbine with a pressure of 1.0 MPa. If the isentropic turbine efficiency is 80% and the power output is 700

Explanation / Answer

At P1 = 10 MPa and T1 = 500 C, from steam table:

h1 = 3375.058 KJ/Kg

Now h1= h2 = 3375.058 KJ/Kg, as process 1-2 is isenthalpic

Now, W actual = 700 KW

W ideal = Wactual/

   = 700/ 0.8 = 875 KW

under ideal condition of adiabatic and reversible condition, turbine gives an output of 875 KW
m_rate x (h2 - h3) = W ideal

2 x (3375.058 - h3) = 875

h3 = 2937.558 KJ/Kg

Now, At P3 = 1 MPa and h3 = 2937.558 KJ/Kg, from steam table:

s3 = 6.9157 KJ/Kg.K

Now, s2 = s3 = 6.9157 KJ/Kg.k (isentropic condition )

At h2 = 3375.058 KJ/Kg and s2 = 6.9157 KJ/Kg.K, from steam table:

P2 = 30 bar = 3 MPa

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