# QOD- 8/15



## EdinNO (Aug 15, 2006)

A fluid in a tank is kept at 95?F by an internal tube running through it carrying hot oil. The oil inlet temperature is 200?F and the outlet temp is150?F. At what temperature should the film coefficient be evaluated for the fluid in the tank?


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## TouchDown (Aug 16, 2006)

Don't have my MERM again, but don't you average the oil temp - assume the tube is same temp as average oil... Then average the Tinfinity (solution) with the tube temp to get film temp? I get 135 deg. F


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## EdinNO (Aug 16, 2006)

Bingo. These were relatively easy ones- for you anyway!

Midpoint tube surface temperature is (assumed the same as the oil temp):

Ts = ? (200 + 150) = 175?F

Tinfinity = 95?F (given)

By Eqn. 35.11 in MERM, h should be evaluated at (1/2)(Ts + Tinfinity). The film temperature is

Th = (1/2) (175?F + 95?F) = 135?F

What do you do with the film tmep now? That would be the next question? 

Ed


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