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Homework Help: Calculating mass of air displaced in compressor.

  1. Oct 20, 2013 #1
    1. The problem statement, all variables and given/known data
    So, this question is to do with an experiment which investigates the operations of a pneumatic pump. You're asked to find the mass of air displaced in each 30 second period using the atmospheric pressure, temperature and theoretical displacement of the compressor. Also, you are told to use 2 of following equations: PV = mRT and P1V1n = P2V2n.

    2. Relevant equations
    Given in question.

    3. The attempt at a solution
    Well, the theoretical displacement is given as 106 l/min. Thus for a 30 second cycle, V = 53 l. Does it not make sense just to use PV = mRT for this? How is P1V1n = P2V2n relevant? Thanks.
  2. jcsd
  3. Oct 20, 2013 #2

    rude man

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    << Does it not make sense just to use PV = mRT for this? >>

    Don't know why not.

    Use dm/dt = (p/RT) dv/dt. R is specific to air of course, not the universal gas constant.

    If n = 1, p^n v^n = RT denotes an isothermal process. If n = cp/cv it's an adiabatic process.
    You don't know if it's either one so that's another reason I don't see any point in this equation here.
  4. Oct 20, 2013 #3
    I guess, once I carry out the experiment I can see my values for n and then judge whether it's an isothermal or adiabatic process. Does that sound reasonable?
    <<If n = 1, p^n v^n = RT>>
    Why is it p^n v^n = RT and not p^n v^n = mRT? Also, why is P raised to the power of n? Think I've lost track of you.
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