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

1. Feb 11, 2013

### qablos

1. The problem statement, all variables and given/known data
An ideal simple gas turbine has a compression ratio of 5. What is its

2. Relevant equations
c=r(γ-1/γ)
η=1-(1/c)

3. 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.

2. Feb 11, 2013

### rock.freak667

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

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

3. Feb 11, 2013

### qablos

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

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.

4. Feb 11, 2013

### rock.freak667

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

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.

5. Feb 11, 2013

### SteamKing

Staff Emeritus
Re: An ideal simple gas turbine has a compression ratio of 5. What is

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

6. Feb 12, 2013

### qablos

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

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?

7. Feb 12, 2013

### SteamKing

Staff Emeritus
Re: An ideal simple gas turbine has a compression ratio of 5. What is

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

8. Feb 12, 2013

### qablos

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

I've done it now thanks!

But how do I calculate the heat rejected? :/

9. Feb 12, 2013

### SteamKing

Staff Emeritus
Re: An ideal simple gas turbine has a compression ratio of 5. What is

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.