How Is Actual Power Calculated in a Turbine with Given Isentropic Efficiency?

[dzj633]

Homework Statement

Steam at a pressure of 4 MPa and 400 C and flow rate of 10 kg/s is expanded in a turbine to a pressure of 10 kPa. If the isentropic efficiency of the turbine is 0.85 then the actual power produced by the turbine is?

Homework Equations

:[/B]
η_t= (m(h1-h2))/(m(h1-h2s)) = (W act) / (W max)
s2s=s1
s2s=sf +x(sfg) <~~ To get quality
h2=hf +x(hfg)

The Attempt at a Solution

I started by looking up enthalpies and entropies at state one and two. Since s2s = s1, i used sf and sfg of P2 to find the quality and used that quality to find h2. I substituted all known values into the isentropic efficiency equation and i found h2s. After that, i plugged in all known values back into the Isentropic Eff eqn to solve for Wact and its incorrect. Did i miss a step or did them incorrectly?

 

[Chestermiller]

Homework Statement

Steam at a pressure of 4 MPa and 400 C and flow rate of 10 kg/s is expanded in a turbine to a pressure of 10 kPa. If the isentropic efficiency of the turbine is 0.85 then the actual power produced by the turbine is?

Homework Equations

:[/B]
η_t= (m(h1-h2))/(m(h1-h2s)) = (W act) / (W max)
s2s=s1
s2s=sf +x(sfg) <~~ To get quality
h2=hf +x(hfg)

The Attempt at a Solution

I started by looking up enthalpies and entropies at state one and two. Since s2s = s1, i used sf and sfg of P2 to find the quality and used that quality to find h2. I substituted all known values into the isentropic efficiency equation and i found h2s. After that, i plugged in all known values back into the Isentropic Eff eqn to solve for Wact and its incorrect. Did i miss a step or did them incorrectly?

Please show the details of your calculations so I can check your numbers.

 

[dzj633]

Please show the details of your calculations so I can check your numbers.

I figured out what I did wrong, I used: h2=h1-nt(h1-h2s) to solve for h2 and my number was correct.