POLYTROPIC COMPRESSION
POLYTROPIC COMPRESSION
(OP)
We know: PV^^n= constant and n (polytropic coefficient) is also constant.
We know in centrifugal compressor n could be higher than 1 (isotherm ) and lower than gamma Cp/Cv (isentropic).
My question is what is the difference between for example n=1.2 and n=1.3?
For a centrifugal compressor n=1.2 is better or n=1.3? which parameters define or specify n?
We know in centrifugal compressor n could be higher than 1 (isotherm ) and lower than gamma Cp/Cv (isentropic).
My question is what is the difference between for example n=1.2 and n=1.3?
For a centrifugal compressor n=1.2 is better or n=1.3? which parameters define or specify n?
RE: POLYTROPIC COMPRESSION
- go ahead and conduct the head calcs using 1.2 & 1.3 to determine the difference using same inlet/outlet conditions. you may be surprised at the results.
"For a centrifugal compressor n=1.2 is better or n=1.3? which parameters define or specify n? "
- the compressor does not care which is better. as far as what parameters, inlet/outlet conditions and gas composition.
RE: POLYTROPIC COMPRESSION
Good advices from pmover. Consider to study the document attached .
Good luck
Pierre
RE: POLYTROPIC COMPRESSION
Another document to support your work.
Pierre
RE: POLYTROPIC COMPRESSION
RE: POLYTROPIC COMPRESSION
read through the first document provided by pierreick and pay attention to page 6.
pierreick,
i long lost my copy of that document, so thank you. the second, i still have - obtained +20 years ago. fyi, both documents are valuable for personnel to use/learn from.
RE: POLYTROPIC COMPRESSION
I read these two document but I haven't found my question.
Imagine I want to buy a centrifugal compressor. Is it important to fix polytropic coefficient n for manufacturer? For example imagine I want to buy a compressor with n equal 1.1 . Do manufacturer build any centrifugal compressor with my fixed poly tropic coefficient? Do I have any restriction to specify or identify n?
RE: POLYTROPIC COMPRESSION
not really. it is more important to state the inlet/outlet conditions, gas composition, volumetric or mass flow, and other essential operating parameters. best to utilize the API-617 datasheet which can be purchased online. the GPSa databook is another resource.
"Do manufacturer build any centrifugal compressor with my fixed poly tropic coefficient? Do I have any restriction to specify or identify n?"
n is not necessary a requirement, but an option. you can specify n, but the mfg will take the gas composition, determine n, and size the compressor based on the operating parameters/criteria you provide.
contact a centrifugal mfg and discuss the matter with them. they will be glad to work with & discuss the matter with you.
RE: POLYTROPIC COMPRESSION
RE: POLYTROPIC COMPRESSION
One more observation about Perry's Theory of Compression, the graphic presentation has an additional curve for k > Cp/Cv with no further elaboration. You may want to do more research on that aspect of the graphic presentation.
RE: POLYTROPIC COMPRESSION
You may use this calculator and data sheet to support your work .
My advice with 40 years + experience as an engineer , don't over specified , let manufacturer do their job .
http://yrsp.elliott-turbo.com/public/comp_perf/ind...
another good reference is GPSA (Gas Processors Suppliers Association) (chapter 13)
Good luck
Pierre