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Thermodynamics - Energy help

  1. Jan 28, 2014 #1
    ρ1. The problem statement, all variables and given/known data
    Oil with a density of 850 kg/m^3 is flowing at a velocity of 20 m/s at the atmospheric pressure in a horizontal tube elevated at 20m above the sea level. Please determine the diameter of the tube if the rate of mechanical energy for oil is 60000 J/s


    2. Relevant equations



    3. The attempt at a solution
    dE/dt = [itex]\frac{ρv∏D2}{4}[/itex] * ([itex]\frac{P}{ρ}[/itex] + [itex]\frac{202}{2}[/itex] + 9.81 * 20) = 60,000

    Now, my question is, P/ρ. I was told that it is at atmospheric pressure, but the pressure I use for that equation, is it absolute or gage?


    EDIT: It's not coming out properly, I just need to know if the P in P/ρ is gage or absolute or should it matter? I did it both ways and got a diameter difference of about 20mm
     
  2. jcsd
  3. Jan 31, 2014 #2
    it won't make any difference on gage or absolute
     
    Last edited: Jan 31, 2014
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