# Compressor Equation

1. Apr 7, 2007

### spiraltooth

Please give me the equation with a link if possible for determining power for a compressor. I know volume x pressure differential / efficiency but I think the gas being compressed also is a factor. Thank you.

2. Apr 7, 2007

### FredGarvin

From my old thermo notes, a non-isentropic compressor has a power of:

$$\dot{W} = \frac{\dot{m}C_pT_1}{\eta_c} \left[\left(\frac{P_2}{P_1}\right)^{(\frac{\gamma-1}{\gamma})}-1\right]$$

You can see the same equation here:
http://www.grc.nasa.gov/WWW/K-12/airplane/compth.html

Last edited: Apr 7, 2007
3. Apr 9, 2007

### quark

The site seems to be down at the moment but there are online calculators for recips and centrifs at www.processassociates.com

To to process tools section.

4. Apr 11, 2007

### spiraltooth

Fred, from your equation a vacuum pump that has a 1bar/.01bar pressure ratio needs more power than a compressor that has a ratio of 10bar/1bar? Is m the molecular weight or the volume?

Last edited: Apr 12, 2007
5. Apr 12, 2007

### FredGarvin

m is mass flow rate.

I'll have to look around a bit, but a vacuum pump most likely will not be applicable here. I'm not sure, I don't deal with them.

6. Nov 1, 2007

### powerpsy

Hello, I'm working on a model of a fan and I have the characteristic curves Flow/impelled power and flow/total pressure.

I also have the relation of adiabatic compression you have written but it concerns the Head (in meters) and not the mass flowrate. Therefore, my question is : how do you get the outlet pressure of a fan knowing the characteristic curves and the formula with the head ?

More clearly that possible to convert the Head (m) into a differential pressure (Pout-Pin) or even the outlet Pressure of the fan (Pout) ?

Thank you for any idea.

Last edited: Nov 1, 2007
7. Aug 12, 2009

### fmiranda

Hi, somebody knows this formula???

HP= Q * 63 * Ln(Pd/Ps)

Is a rare formula that are been used in a pipeline gas.

Thanks.

Felipe

PD: Sorry if I make a mistake in the english, I speak spanish.

8. Aug 13, 2009

### ank_gl

$$\dot{m}$$ is the mass flow rate, & is equal to $$\rho$$$$\dot{V}$$

ie. work required also depends upon the inlet density.