An ideal simple gas turbine has a compression ratio of 5. What is its

[qablos]

Homework Statement

An ideal simple gas turbine has a compression ratio of 5. What is its

Homework Equations

c=r^(γ-1/γ)
η=1-(1/c)

The Attempt at a Solution

I'm stuck, I think I need to use the above equations and possibly more. I just don't know how to find a value for the ratio of specific heats,γ.

 

[rock.freak667]

Do you have any other information about the compressor apart from its pressure ratio?

 

[qablos]

Do you have any other information about the compressor apart from its pressure ratio?

Yeah:
"The turbine
produces 6 MW (gross) and the compressor requires 2 MW to drive it."
It's just put after the question, so I assumed I need to use the compression ratio which is 5.

 

[rock.freak667]

Given the pressure ratio alone, I don't think you can find the ratio of the specific heat capacities.

I am assuming that is what you were asked to find.

 

[SteamKing]

Can you post the entire text of the problem? It looks like something is missing after
"What is its ..."

 

[qablos]

Can you post the entire text of the problem? It looks like something is missing after
"What is its ..."

An ideal simple gas turbine has a compression ratio of 5. What is its efficiency? If the turbine
produces 6 MW (gross) and the compressor requires 2 MW to drive it, what is the work ratio and how much heat is
rejected?

 

[SteamKing]

The ratio of specific heats is that for air, which is 1.4

 

[qablos]

The ratio of specific heats is that for air, which is 1.4

I've done it now thanks!

But how do I calculate the heat rejected? :/

 

[SteamKing]

I assume that the efficiency for the turbine was not 1.0. You know how much work output was obtained from the turbine. The efficiency of the turbine relates the output to the total heat input.