question on compressors performance
question on compressors performance
(OP)
hi all,
here is a basic question that has been a source of confusion ,,let me start discusion for those interested ( and know correct answers) by these two qustions ,,
i always thought that for a constant speed compressor :
1- for any change in suction properties like pressure ,mw ,T SUCTION VOLUME FLOW WILL REMAIN CONSTANT,but power will change propotional to mass flow? is this correct ?
2- in case of throtting suction or discharge volume flow will change(decrease ) cause head will change (increased) as compressor will back up on its curve ? is this correct ?
thnx in advance
here is a basic question that has been a source of confusion ,,let me start discusion for those interested ( and know correct answers) by these two qustions ,,
i always thought that for a constant speed compressor :
1- for any change in suction properties like pressure ,mw ,T SUCTION VOLUME FLOW WILL REMAIN CONSTANT,but power will change propotional to mass flow? is this correct ?
2- in case of throtting suction or discharge volume flow will change(decrease ) cause head will change (increased) as compressor will back up on its curve ? is this correct ?
thnx in advance





RE: question on compressors performance
Volume and mass flow will both change when changing the inlet properties of a compressor or fan. If it is a positive displacement compressor, the volume will remain constant although the mass will change due to varying pressure/fluid density.
I'm flying by the seat of my pants here, but I can't see why power wouldn't still vary by the cube root of the mass flow (as opposed to the volume flow) change. If I double my mass flow, I think power will go up eight-fold, as mass flow and volume flow are linearly related by density. That's my story and I'm sticking with it.... for now.... but don't take this to the bank. If I get a chance I'll think some more about this and repost. -CB
RE: question on compressors performance
small correction here ...
to be exact , power will change ,propotional to the product change of new head and new mass flow , the cube route relation is known fan laws but when changing impeller diameter or speed which are both fixed in my problem ..
i have gone through many literatures on the subject , all were contradicting ,
one opinion is that the for dynamic machines , keep dicusion to dynamic machines, the diameter and speed are only factors fixing volume flow.any change in suction property will reflect on mass flow but not volume flow!!
another opinion , see norman lieberman's "A WORKING GUIDE TO PROCESS EQUIPMENT " PAGE 367-368 " ..THE REDUCED SUCTION PRESSURE INCREASES THE SUCTION VOLUME (ACFM) OF GAS FLOWING TO THE COMPRESSOR ..." ,the example in norman book is a constant speed single stage compressor ...
any machinery or process guru's help is most welcomed !