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Compressor Equation

  1. Apr 7, 2007 #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. Apr 7, 2007 #2


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    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. Apr 9, 2007 #3
    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.
  5. Apr 11, 2007 #4
    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. Apr 12, 2007 #5


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    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. Nov 1, 2007 #6
    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. Aug 12, 2009 #7
    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. Aug 13, 2009 #8
    [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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