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Thermodynamics - Diffusers

  1. Oct 25, 2015 #1
    1. The problem statement, all variables and given/known data
    Air enters a diffuser:
    The ambient temp at the inlet is 300K.
    The temp leaving the diffuser is 350K
    The flow speed of air at the inlet is 400m/s

    Assumptions:
    Potential energy = 0
    Kinetic energy at the diffuser exit is = 0
    Air is an ideal gas

    Q1: assuming air to be an ideal gas with variable spec heats, calculate the flow speed (m/s) for the outlet

    2. Relevant equations
    Ein=Eout
    m*(h1+ (V12/2)=m*(h2+ (V22/2)

    V2=[(V12+2(h1-h2)]0.5



    3. The attempt at a solution
    I looked up the enthapies for the given temps on the 'ideal-gas properties table'
    and got:
    h1=300.19
    h2=350.49

    then I sub into this formula:
    V2=[(V12+2(h1-h2)]0.5

    0=(350.49-300.19)kj/kg+((V22-(400m/s)2)/2)* (1kj/kg/1000m2/s2)
    V2=243.721

    but apparently the answer is 237m/s...
     
    Last edited: Oct 25, 2015
  2. jcsd
  3. Oct 30, 2015 #2
    Thanks for the post! This is an automated courtesy bump. Sorry you aren't generating responses at the moment. Do you have any further information, come to any new conclusions or is it possible to reword the post?
     
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