Compressor Equation

  1. 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. jcsd
  3. FredGarvin

    FredGarvin 5,084
    Science Advisor

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

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

    You can see the same equation here:
    Last edited: Apr 7, 2007
  4. The site seems to be down at the moment but there are online calculators for recips and centrifs at

    To to process tools section.
  5. 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
  6. FredGarvin

    FredGarvin 5,084
    Science Advisor

    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.
  7. 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
  8. Hi, somebody knows this formula???

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

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



    PD: Sorry if I make a mistake in the english, I speak spanish.
  9. [tex]\dot{m}[/tex] is the mass flow rate, & is equal to [tex]\rho[/tex][tex]\dot{V}[/tex]

    ie. work required also depends upon the inlet density.
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