Should compressor Np be adjusted for RPMs to compare to design?

[ham5999]

I have calculated a polytropic efficiency for a centrifugal compressor at the set of conditions when the survey was conducted. I also have the design curve showing the predicted efficiency vs icfm.

Latest survey:
RPM = 8610
icfm = 14600
Np = 75.6

From Design Curve:
RPM = 8800
icfm = 14600
Np = 79.3

Does this mean that the efficiency is 3.6% below design or do I need to adjust to the design RPM? And if so, how do I do that?

I've used Fan Laws to adjust polytropic head for RPM but I can't find any info on the efficiency.

Thanks!

 

[ham5999]

Hi folks, just wondering if perhaps I need to move this to a different forum (i.e. gas compression engineering)? Or perhaps my question needs rephrased or more info supplied?

I have several surveys of this compressor at different RPMs and I'm just trying to understand if I can compare the efficiencies directly or if I need to compensate for the speed of the compressor.

Thank you!