polytropic efficiency vs isentropic efficiency?

[jason.bourne]

been reading in many books that polytropic efficiency is always recommended over isentropic efficiency.

what are the advantages of using polytropic efficiency?

what makes it different from isentropic efficiency?

it is also told that polytropic efficiency is independent of pressure ratio? how is this possible?

[Topher925]

I always thought that polytropic efficiency was isentropic efficiency but at a incremental stage of a quasi-static process.

[jason.bourne]

yes you are right.

but when these efficiencies are calculated for the turbine or compressor machines which are multi staged, then they differ a lot.