# Homework Help: Thermodynamics - Energy help

1. Jan 28, 2014

### Jay9313

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 = $\frac{ρv∏D2}{4}$ * ($\frac{P}{ρ}$ + $\frac{202}{2}$ + 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. Jan 31, 2014

### njoysci

it won't make any difference on gage or absolute

Last edited: Jan 31, 2014