I have used the two efficiency formulae to solve the following problem, but I get a different answer from each:

If I use the 1 - (1/PR^1.4-1/1) I get approx. 40%

If I use Work_nett/Heat_in I get approx. 27%

I can't figure why there is a discrepancy, is it do with the isentropic efficiencies of the compressor and turbine?

Many thanks

Hi, In this kind of situations, I always trust net work/heat input relation.

Yes, it has to do with isentropic efficiencies of turbine and compressor.

The 1-1/(rp^(n-1)/n) formula works only in ideal situations.

The irreversible/non-isentropic compressor needs more work input than ideal compressor and irreversible/non-isentropic turbine produces less work than ideal isentropic turbine.