evaluating compressors

[rgrokkam]

I wish to evaluate the performance of a compressor(reciprocating & centrifugal). Can I compare the adiabatic head / polytropic head with design values. If I have enough cushion on this, can I say that the compressor can handle more volume of gases?
Should I look at any other parameters?

 

[BigInch]

For the recip, suction capacity and rod load. For the centrifugal, stonewall and surge limits.

http://virtualpipeline.spaces.msn.com

 

[dcasto]

And always the driver capacity. on reciprocating compressors there isn't a head capacity like a centrifugal, its a mechanical head capacity limit.

On reciprocating, valve loss and gas flow patterns in the valve chambers is the largest variable componet of effiency, so don't over look that aspect too.

And finally, system constraints of piping loses, aftercooler capacities, and controls, pressure ratings.....

 

[BigInch]

...interstage and discharge temps. Be careful you don't melt a corrosion coating downstream.

http://virtualpipeline.spaces.msn.com

 

[rgrokkam]

Big Inch,
How can I calculate the suction volume?
For a recip compressor,
The actual adiabatic head= calculated adiabatic head/adiabatic efficiency.
Adiabatic efficiency= (T2-T1)/(T2actual-T1)
where T2 is the discharge temperature,
T1 is the suction temperature,
T2actual is the actual discharge tempereature.
But when I calculated adiabatic efficiency it comes to 1.7.
Am I going wrong in my steps?

Also, if the design adiabatic head is greater than actual adiabatic head can I say that the compressor can handle more gases?

 

[BigInch]

The volume of gas that can enter the cylinder at suction pressure and temperature.

After the piston completes its compression stroke, there is some gas that remains in the cylinder trapped in the head clearance and pocket clearance spaces above the piston at high pressure and discharge temperature. When the piston completes its expansion stroke, that trapped gas is expanded and then contained within the cylinder at a pressure a bit lower than suction pressure (and maybe at around the discharge temperature). When the suction gas tries to enter, it finds there is already some gas there and consequently can't fill the entire swept volume. The capacity is thereby reduced below actual swept volume.

http://virtualpipeline.spaces.msn.com

 

[dcasto]

Your calculations are wrong. You need to have ethalphy at the conditions of temperature and pressures.

 

[rgrokkam]

Dcasto,
"Your calculations are wrong. You need to have ethalphy at the conditions of temperature and pressures." (quote"

Can you explain? what is the right approach?

Many thanks

 

[dcasto]

Sustitute enthalphy (H) in your equation (H2 - H1) / (H2 actual- H1)

H2 = the H at constant s (entropy) therefore S at point 1 equals s at point 2.