Tube in Tube heat exchanger example problem?
Tube in Tube heat exchanger example problem?
(OP)
I havent done calculations for heat transfer in a long time. The heat exchanger we have is a single tube inside another single tube... the inner is sludge with a Cv of .909 BTU/lb*F the outer is 50/50 water/glycol mix with Cv of .832 BTU/lb*F. I've been told we need 1.77MMBTU to keep the temperature up in the sludge tank. I have to figure out the flow rate of each material so I can size the 2 pumps.... does anyone know of a good example of a similar calculation may be that I can look at? or just help me solve this one? I have the old Q=mCv(T1-T2) but I think that mass flowrate will be good for the 2 amounts it would take if you combined the fluids to transfer heat... thanks for any help





RE: Tube in Tube heat exchanger example problem?
RE: Tube in Tube heat exchanger example problem?
RE: Tube in Tube heat exchanger example problem?
RE: Tube in Tube heat exchanger example problem?
The heat transferred (Q) is equal so what you should have is
ṁscp(s)(T2(s) - T1(s)) = ṁgcp(g)(T1(g) - T2(g))
where the "s" subscript is sludge and the "g" is glycol. Since you said the fluids are flowing in opposite directions, the temperatures should be reversed (I believe.) Someone will correct me if I'm wrong.
Patricia Lougheed
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RE: Tube in Tube heat exchanger example problem?
RE: Tube in Tube heat exchanger example problem?
I'm not sure how you managed to balance the units, but you shouldn't have been able to.
TTFN
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RE: Tube in Tube heat exchanger example problem?
RE: Tube in Tube heat exchanger example problem?
TTFN
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RE: Tube in Tube heat exchanger example problem?
If the external tube is not thermally insulated it may lose some heat to the surroudings depending on the outside atmospheric conditions.
RE: Tube in Tube heat exchanger example problem?
RE: Tube in Tube heat exchanger example problem?
I'd add some % to the heat duty on account of loses. What do you think ?
RE: Tube in Tube heat exchanger example problem?
In any case, what you get out of the specific heat equation is a total mass. You need to have the flow rate, which then determines how long it takes to heat up the sludge
1.77MMBTU/C.p*deltaT = 1.77MMBTU/(0.909BTU/lb-°F * 35°F) = 55634 lb
So, if you have a flow rate of 1 lb/min (which implies the whole process taking 55634 min, i.e., ~1000hr, which is silly, but the equation scales)
(1 lb/min)*(0.909BTU/lb-°F * 35°F) = 559 W of net heat transfer required, so all you need to determine is how fast you want this to happen, and how much you're willing to pay for maintaining the required flow rates and size of exchanger.
TTFN
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RE: Tube in Tube heat exchanger example problem?