# Temperature Rise due to Increase in Pressure (Liquid)

## Main Question or Discussion Point

I need help finding the temperature rise of a liquid (specifically diesel) due to a pressure increase. The system contains a pump at 500 hp and runs at 524 gpm. The inlet temperature is 75 F and the pressure is 150 psi. The exit pressure is about 1155 psi. I have the specific gravity as 0.841. I've reduced my formula to -W=m(h1-h2) where W is the work of a pump, m is the mass flow rate, and h1 and h2 are the enthalpies. I've calculated the mass flow rate to be 3688 lb/min and the work as 21,204 Btu/min. Now, I'm stuck because I can't find the enthalpy for h1 to solve for h2. When I have h2, I was going to use that and the exit pressure to find the final temperature.

So, am I doing this correctly? And if so, how can I determine h1? I can't find any enthalpy/pressure/temperature tables for diesel.

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SteamKing
Staff Emeritus
Homework Helper
The specific heat of No. 2 Diesel is about 0.43 BTU/lb-F:

http://www.methanol.org/energy/resources/alternative-fuel/alt-fuel-properties.aspx [Broken]

This should allow you to calculate a temperature rise due to the fuel absorbing the pump work.

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OH! So, if the pump is working at maybe 70% efficiency, it's safe to assume that 30% of the horsepower isn't moving the fluid and is converted into heat? Then, I'd just take that number and find the temperature rise?

Thanks a lot by the way!

SteamKing
Staff Emeritus
Homework Helper
Pretty much.

Strictly speaking the fluid temperature will rise with pressure increase, even if no irreversible work is applied. But that increase is very small.

Well, I think I have an appropriate number. Thank you both so much!

Chestermiller
Mentor
OH! So, if the pump is working at maybe 70% efficiency, it's safe to assume that 30% of the horsepower isn't moving the fluid and is converted into heat? Then, I'd just take that number and find the temperature rise?

Thanks a lot by the way!
No. If the pump is working at 70% efficiency, then 70% of the supplied electrical power translates into enthalpy change. Since diesel fuel is nearly incompressible,

h2-h1=Cp(T2-T1)+V(P2-P1),

where V is the specific volume of the diesel fuel (the reciprocal of the density).

Chet

Oh, I see! Thanks a lot! Using your formula and a different method, I was able to come out with similar answers! I normally use tables so that formula helped me immensely!