1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: 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
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted