Temperature Rise due to Increase in Pressure (Liquid)

[Skez]

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.

 

[SteamKing]

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

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

 

[Skez]

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]

Pretty much.

 

[Massow]

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

 

[Skez]

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

 

[Chestermiller]

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

 

[Skez]

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!