8 replies to this topic

[SickPuppy0]

Hello, can someone please advise me whether the typical fan / affinity laws for centrifugal compressors are valid for varying suction conditions.

 

For context, the manufacturer has provided the performance curve with X = Inlet Volumetric Flow, Y = Polytropic Head, Z = Shaft Speed at compressor suction pressure of 10,000 kPa. Is this curve still valid for compressor suction pressure of 5,000 kPa and can I apply fan laws to evaluate compressor performance at the lower suction pressure.

 

Obviously inlet volumetric flowrate will change due to the change in gas density, however, I'm not sure whether the performance curve is still valid given the manufacturer has only supplied 1 set of curves at 10,000 kPa suction.

 

If the performance curve is not valid at 5,000 kPa suction, can I use HYSYS to extrapolate and generate a new performance curve for me from the original.

 

Thanks in advance

Edited by SickPuppy0, 25 January 2023 - 05:00 AM.

[breizh]

Hi,

You may find some interest in the document attached,

Edit: Let you read the comments related to change in Rotation speed and applicability of the Fan affinity laws. 

 

Fan Affinity Laws (engineeringtoolbox.com)

Breizh 

[SickPuppy0]

Thank you for sharing Breizh. In the paper attached it's stated "For a given inlet volume flow at a given rotational speed, the head output is constant". It's this statement I desire clarification on. If the head is the same for suction pressure of 10,000 kPa and 5,000 kPa for a given inlet volume flow and given rotational speed, then my problem is solved. However, I would have thought the dynamics of the compressor impeller would change. Thanks in advance

[latexman]

For context, the manufacturer has provided the performance curve with X = Inlet Volumetric Flow, Y = Polytropic Head, Z = Shaft Speed at compressor suction pressure of 10,000 kPa. Is this curve still valid for compressor suction pressure of 5,000 kPa and can I apply fan laws to evaluate compressor performance at the lower suction pressure.

 

Have you asked the manufacturer to provide a performance curve at 5,000 kPa suction pressure?  They should do it for you.

[PaoloPemi]

the solution proposed by Latexman is probably the most simple,

in general it depends from degree of accuracy you wish to obtain : for a simple and relatively accurate prediction you may consider similitude method which, for centrifugal compressors, is based on affinity law but corrected with a similtude parameter,  there are many papers available on the web...
for natural gas mixtures I prefer polytropic efficiency as similitude parameter  which I calculate with GERG 2008 in Prode Properties, a few macros in Excel allow to solve these problems,
probably you can do the same with your simulator...

[SickPuppy0]

Thank you all for the feedback, I will discuss with the manufacturer

[compressor-ctrend]

the solution proposed by Latexman is probably the most simple,

in general it depends from degree of accuracy you wish to obtain : for a simple and relatively accurate prediction you may consider similitude method which, for centrifugal compressors, is based on affinity law but corrected with a similtude parameter,  there are many papers available on the web...
for natural gas mixtures I prefer polytropic efficiency as similitude parameter  which I calculate with GERG 2008 in Prode Properties, a few macros in Excel allow to solve these problems,
probably you can do the same with your simulator...

Hello Paolo,

 

Can you please share some links or technical papers on correction with polytropic efficiency as similitude parameters and more generally on corrected/improved affinity laws for centrifugal compressors, if any as I am interested.

 

Thank you

[breizh]

Hi,

You may want to take a look at those documents.

Breizh

Attached Files

•  Centrifugal compressor polytropic perf..pdf   10.3MB   13 downloads
•  Polytropic calculation for centrifugal compressor.pdf   1.74MB   8 downloads

[PaoloPemi]

hi compressor_ctrend,

the general idea is to apply some correction to improve the accuracy of estimates,  you may search for

 

centrifugal compressors similarity scaling laws polytropic

 

or similar patterns...