3 replies to this topic

[rmarzo]

Dear mates,

 

Two question in regards to affinity laws, dimensionless numbers and behaviour prediction in centrifugal compressors:

 

- Why can we consider as acceptable the affinity fan laws to evaluate the centrifugal compressor behaviour? As far as I know, this just could be applied when the compressibility factor is negligible and that happens with low Mach numbers (I am not very sure about this either,)

 

- How would the most accuarate way be to evaluate how the diff.head changes with the variation of the speed considering also the compressibility factor? Analysing the dimensionless numbers for centrifugal compressor, there isn't any that shows both head and speed... 

 

Thanks in advance.

 

Regards,

Rubén.

 

 

 

[demank]

Dear Marzo,

I am agree with your first statement, that

the fan laws ONLY apply to single stages or multi-stages with very low compression ratios or very low Mach No.

 

[rmarzo]

Following my inverstigation in regards to this amazing topic, I found this post ( http://www.cheresour...l-compressor/ )

 

According to the compressors maps, sometimes the manufacturers provide the compressor behaviour with two different molecular weights, and it reflects that working with heavy gas, the curve (Head-Flow rate at inlet conditions)  is above the curves with lower MW. 

 

My goal is knowing how the compressor map change if suddenly the MW changes, how I can edit the compressor map in accordance,where the operation point shifts in such conditions. The post I copied above is so helpful but I still have some doubts..

 

 

Thanks in advance.

 

Regards,

Rubén Marzo.

Edited by rmarzo, 14 June 2014 - 11:10 AM.

[rmarzo]

More in regards to this topic:

 

http://turbolab.tamu...28/Vol28017.pdf

 

On the page 12, the author describes how the compressor map changes if suddenly the MW changes. However, it is not clear how the operation points are defined in such curves. My understanding is that if the MW increase, the looses in the system will increase also, and the system curve is more sharply. Its interaction with the new compressor curve cause a higher Hp and Q.

 

Please advise.

 

Thanks.