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Divergent nozzle problem (find velocity)

  1. Oct 14, 2004 #1
    Determine change in velocity across ideal divergent nozzle with inlet enthalpy of 1,204 Btu/lbm and exit enthalpy of 1,203.91 Btu/lbm

    I know that delta v^2=(.09btu/lb)*(2)*(32.2lbm*ft/lbf sec^2)(778ftlbf/btu)

    so: deltav^2=4509.29ft^2/sec^2

    taking the sqrt deltav=67.15ft/sec

    My problem is this: I need to convert the above problem to SI units

    So far: (.21kj/kg)*(2)*(9.81m/sec^2)=4.1202

    Any help would be appreciated!

    Ken
     
  2. jcsd
  3. Oct 14, 2004 #2

    pervect

    User Avatar
    Staff Emeritus
    Science Advisor

    Well, for starters, you want

    h1-h2 = .5*(v2^2 - v1^2)

    http://members.aol.com/ricnakk/th_nozz.html

    Unfortunately for you, (v2^2-v1^2) is not equal to (v2-v1)^2. So I don't see how you can work the problem without more information, enough to determine v1.

    As far as converting units, I like google calculator, for example

    http://www.google.com/search?hl=en&lr=&q=btu+%2F+pound&btnG=Search
    http://www.google.com/search?hl=en&q=btu+in+joules&btnG=Google+Search

    (you can click on 'more about calculator to get some more help).

    The documentation isn't the best, but Google thinks of a pound as a mass, and a pound force as a force.

    The default output of the calculator is the value of the input in SI units, BTW.
     
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