Centrifugal Compressors-Polytropic VS Adiabatic 1

[patrickraj]

Dear Members,

In Centrifugal Compressors we calculate Polytropic efficiency only -Why not adiabatic efficiency ?
Where we calculate and use adiabatic efficiency?

Thanks in advance.

 

[TD2K]

You can either either method, it's your choice. The polytropic efficiency is perhaps the most common but either is valid. The GPSA Engineering data book goes through both methods and has an estimate for converting polytropic efficiency to adiabatic efficiencies.

 

[majhi]

Dear Patric
For centrifugal compressors machine, polytropic efficiency is more accurate than adiabatic efficiency as poly effy doesnot change with change in press ratio.

Adiabatic waas used in before early 80s.

Majhi

 

[MortenA]

The following is quoted from Campbells "Gas confitioning and processing vol 2": "Traditionally compressor vendors have used polytropic rather than isentropic effeciency when quoting compresor performance. This is because polytropic efficiency is essentially independant of compression ratio and gas composition"

 

[tgmcg]

If you're gonna be doing a lot of compressor calcs, learn to use and convert between polytropic and isentropic efficiency. Most compressor vendors typically provide polytropic efficiency. Solar tends to use isentropic efficiency. Just be sure when you're comparing compressor performance between vendors that you do so on an apples to apples basis. I do a lot of compressor work and isentropic versus polytropic, insofar as the user is concerned, has never been a matter for concern. There's no right and wrong when it comes to efficiency.

Just be sure not to use isentropic efficiency when calculating power using polytropic head, and visa versa.

Regards,

Tom McGuinness