polytropic efficiency of centrifugal compressors

[abeigzad]

Hello,

I am simulating centrifugal compressors in Aspenplus(ASME polytropic). As for the polytropic efficiency there is a default number however in a rules of thumb text book, I have found a graph that illustrates polytropic efficiencies of centrifugal compressors as a function of suction volume acfm.
Question 1: Is this graph a function of inlet pressure? or is it valid for any inlet pressure?
Question 2: why is the polytropic efficiency of a compressor a funciton of the inlet volumetric flow is this a thermodynamic limit in nature?
Your expert advice would be much appreciated.
Thank you
AB

 

[zdas04]

I didn't see a graph attached to your post. What did you mean by "this graph"? I lost the thread of your post.

David

 

[abeigzad]

Hello zdas04 thanks for your response.
X axis of the graph is suction volumetric flowrate (acfm),
Y axis is poly tropic efficiency.
As the volumetric flow increases the efficiency increases for centrifugal compressors
Efficiency increases from the 60's and goes up to 78%, for volumetric flows from 1000 increasing to 200000acfm.
I wish I had the graph with me so I could attach it, hope it is descriptive enough.
Thank you