4 replies to this topic

[ryoma]

Dear all,

 

I would like to size a compressor for two different gas, so different molecular weight 28 g/mol and 44 g/mol. from what i read the polytropic head will be smaller for the gas with higher molecular weight and so the shaft power will be smaller aswell. Howewer there is something i'm confused with.

 

1. If temperature and pressure of the inlet are fixed, the rotational speed aswell, i read in the book "Forsthoffer's Best Practice Handbook for Rotating Machinery" that if the molecular weight is changed, then the pressure ratio is changed aswell. I guess it's for the same power shaft delivered right ? if i supply more power i can reach the same pressure ratio. 

 

2. If temperature and pressure of the inlet are fixed, the rotational speed aswell, what is the evolution of the volumetric flow rate and mass flow rate if the moleculat weight change ? i read in some articles people use the corrected mass flow rate from the continuity equation, so if the molecular weight increase the mass flow rate increase. But does the volumetric flow rate increase too ? 

 

thank you for your help.

[breizh]

Hi,

Consider this resource to support your query.

Breizh 

[Bobby Strain]

This query sounds as if it comes from a student. If so, you should not pose as a professional. Then you will get more help.

 

Bobby

[ryoma]

Thank you Breizh for the document it was really helpful ! Still got a question ! In the document it's mentioned thé molecular weight affect the pressure ratio, so we have a louer volumetric flow. However if we use the continuity law, if the molecular weight increase, the mass Flow rate decrease (and volumetric Flo). Is there like a compétition between the correcte flow rate and the pressure ratio decrease ? Thank you for your help !

[breizh]

Hi,

another resource to support your investigation. Centrifugal Compressor Performance Calculator (elliott-turbo.com)

 

Good luck

Breizh