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Converging nozzle temperature difference - Steady flow energy equation

  1. Sep 20, 2012 #1
    I come from a civil engineering background and I'm about to start a masters in nuclear energy. I have no experience in thermodynamics and I've been doing a bit of revision before the course commences to get me up to speed. I've been working my way through 15 revision questions and I only have a couple left now. I posted a question on this forum yesterday but I'm stuck again with a different type of question on flow processes. This is meant to be one of the easiest questions in my revision booklet but so far the answer has eluded me.

    1. The problem statement, all variables and given/known data

    A converging nozzle is used to accelerate a flow of air from 50m/s at the inlet to 150m/s at the exit. The air temperature is 25°C at the inlet. Assuming heat transfer to the air is negligible, use the steady flow energy equation to calculate the temperature at the exit.

    2. Relevant equations

    Steady flow energy equation:

    h1+0.5V12+gZ1=h2+0.5V22+gZ2


    3. The attempt at a solution

    I've revised control volume analysis and steady flow processes but I'm not getting anywhere with this. I assume it will be a very simple calculation as all the other 'easy' revision questions have taken me about a minute or two.

    The correct answer is 15.1°C
     
  2. jcsd
  3. Sep 20, 2012 #2
    Is there no one who can help me? I've been looking at this similar question I found on the forums and I can't get 184°C by using the SFEE. I think I must be making a mistake with the units or something really stupid.

    https://www.physicsforums.com/showthread.php?t=249494

    Could somebody please just plug the numbers in and show me how he got 184°C? I would imagine it will take less than a minute and it would be a massive help to me.

    Thanks
     
  4. Sep 20, 2012 #3
    Use the energy equation you have above. The enthalpy is Cp*T. Ensure you get the units correct on the V^2/(2g) term.
    15.1 C is indeed correct.
     
  5. Sep 21, 2012 #4
    Thank you very much Lawrence. I was getting my units for Cp messed up but I've now managed to get 15.1°C.
     
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