Compressor Head

[BE1980]

Hi there,

I have a question regarding compressor head. Is it accurate to state that Head is defined as the amount of energy it takes to compress a mass of gas from a certain suction pressure to a certain discharge pressure?

I know that, for a fixed discharge pressure and compressor speed, if the suction pressure increases, the head will reduce and the mass flowrate through the compressor will increase. Why does this actually happen? Is it because there is less work required of the compressor i.e. less energy required to compress a mass of gas due to the higher suction pressure, and therefore, more energy is being converted to kinetic energy, hence a larger flowrate is noticed?

Any help would be appreciated

Thank you

 

[25362]

Liberman and Lieberman have written a book titled A Working Guide to Process Equipment McGraw-Hill, explaining, in Chapter 28, the ins and outs of centrifugal compressors, in general, and polytropic heads and pressure effects, in particular. Would you care to have a look ?

 

[brainstorming]

The higher the suction pressure the less volumetric flow rate (ideal gas law PV=nRT), and hence the less work required to push less flow rate.

Regards

 

[25362]

I once had the chance to see a family of curves, probably published by Cooper Bessemer, showing the changes in BHP as function of the pressure ratio for reciprocating units at constant % clearances for a gas with a Cp/Cv=1.3.

The noticeable point was that for a p.r. increase from 2.6 to 3.0 and a clearance of 5%, there was almost no change, or even a small drop, in BHP for constant discharge pressure, while it showed a BHP increase of about 15% for a constant suction pressure situation.