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Homework Help: Thermodynamics (jet engine)

  1. Oct 15, 2008 #1
    1. The problem statement, all variables and given/known data
    http://img183.imageshack.us/img183/3628/jetlf0.jpg [Broken]

    http://img393.imageshack.us/img393/1759/jet2iu4.jpg [Broken]

    2. Relevant equations

    3. The attempt at a solution

    H = U + pV is the enthalpy, and hence the enthalpy per unit mass is h = U/m + pV/m which I have simplified to 7/2 RT/M

    I am then able to derive the expression in part b).

    Part c) though I'm very confused about, and then moving onto d) I'm pretty lost. I realise that in part say, to get change in T = 2Mq/7R, I can either set vf = vi = 0, or just simply vf = vi works too (where vf is final velocity and vi initial velocity). If someone could just point me in the right direction, that'd be awesome.

    For part d) dQ = 0 as its adiabatically compressed. Work done on the gas is p dV, and so dU = dQ + dW = pdV. p isn't constant, so I tried to rewrite as dU = nR dT (going for the long shots here hoping it will take me somewhere). Seeing as I seem to be going completely along the wrong lines, I'm not going to carry on..

    Any help is appreciated, thanks.
    Last edited by a moderator: May 3, 2017
  2. jcsd
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