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Homework Help: Thermodynamics HW Help!

  1. Apr 25, 2009 #1
    You are to design a small, directional control rocket to operate in space by proividing as many as 100 bursts of 5 seconds each with a mass flowrate of 0.5 lbm/s at a velocity of 400ft/s. Storage tanks that will contain up to 3000psia are available, and the tanks will be located in an environment whose temperature is 40 degrees F. Your design criterion is to minimize the volume of the storage tank. Should you use a compressed air or r134a system?

    Assuming the large energy balance, at the initial state the apparent energies should be (m1u1 - ([(mass flow)(delta t)](h2 + (1/2)(V2)^2 and at the final should be (m2u2) so:

    m1u1 - ([(mass flow)(delta t)](h2 + (1/2)(V2)^2) = m2u2

    I am having trouble figuring out how to start the actual calculations... assuming my energy balance is correct. Can you assume initial temperatures and pressures of 40F and 3000psia? They seem too far from normal to begin with.

    Also, there's obviously 250lbm of mass leaving the system, so we can assume (delta)m is 250lbm, but we can't assume m1 = 250lbm and m2 = 0lbm, can we?

    Thanks for any help you can give, and please ask if you have any questions!
  2. jcsd
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