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Thread: First law of thermodynamics! Simple yet complex question

  1. #1
    Associate Engineer
    Join Date
    Mar 2012

    First law of thermodynamics! Simple yet complex question

    Hi all I am really struggling with my worked example at my placement. Please help! My answers are awfully wrong.

    A pump compressing hydrogen from a low pressure to a high pressure tank where the tanks pressure is constant and H2 is an ideal gas.
    Hydrogen: (H2: MW = 2, Cv = 10 kJ/kgK)
    Low pressure tank: (P = 4 bar, T = 30oC)
    High pressure tank: (P = 100 bar).

    1) Apply the first law of thermodynamics eliminating terms not needed
    2) Find the compressor outlet temp when the compression goes along an adiabatic and polytrophic process

  2. #2
    Principle Engineer
    Join Date
    Mar 2011
    dQ=CvdT+PdV energy equation statement of 1st Law
    PdV+VdP=nRdT-= gas law
    Next prove

    Now from these you should be able to get
    PV^k= constant when dQ=0

    I gave you more than I should have to get you started
    Now you do the rest of your homework..

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