Thermodynamics Steam Turbine Internal Efficiency Question

[frock]

1. Steam into a steam turbine at 7 MPa and 500 deg C. The turbine has an internal efficiency of 90 %. The steam exhausts at 20 kPa.

1) What is the exhaust enthalpy?
2) What is turbine work?
3) What is the quality of the exhaust steam?

This is a question I got on a 2nd class boilers branch thermodynamics exam, can anyone tell me what is the equation for internal efficiency of a steam turbine?

Homework Equations

The Attempt at a Solution

 

[SteamKing]

Check out the following article:

[PLAIN]http://en.wikipedia.org/wiki/Steam_turbine[/PLAIN]

Scroll down until you reach the section titled "Isentropic Turbine Efficiency"

 

[frock]

I don't see any link steamking...?

 

[mpreds]

Hi Frock,
The equation I suspect you are looking for is as follows:

efficiency (turbine) = Actual turbine work / isentropic turbine work

 

[SteamKing]

I apologize for the missing link. Here it is:

http://en.wikipedia.org8/wiki/Steam_turbine

 

[frock]

Thanks for all the replies guys. It was so simple, I am embarrassed. I have never heard Isentropic Efficiency referred to as Turbine Internal Efficiency and that threw me. If I didn't go into panic mode in the exam and had thought about it as Isentropic then I would have seen that the info they had given pointed to Isentropic. Once again thanks for the help.