Heat transfer coefficient V flow rate in heat exchangers
Heat transfer coefficient V flow rate in heat exchangers
(OP)
I am trying to determine why the cooling circuit for our air compressors is not sufficient, and if there is a way of optimising it.
We have a fin fan cooler, cooling the cooling water circuit.
I wish to model the heat transfer in the system at different cooling water flow rates. I suspect the cooling water flow is higher than design rates (and therefore there's higher heat transfer than is designed for). I wish to determine how the system will behave if I vary the low rates through the coolers.
Is there a way of obtaining a reasonable correlation between heat transfer coefficient and flow rate?
Thanks,
NF.
We have a fin fan cooler, cooling the cooling water circuit.
I wish to model the heat transfer in the system at different cooling water flow rates. I suspect the cooling water flow is higher than design rates (and therefore there's higher heat transfer than is designed for). I wish to determine how the system will behave if I vary the low rates through the coolers.
Is there a way of obtaining a reasonable correlation between heat transfer coefficient and flow rate?
Thanks,
NF.





RE: Heat transfer coefficient V flow rate in heat exchangers
Patricia Lougheed
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RE: Heat transfer coefficient V flow rate in heat exchangers
NeilForster: since this is apparently a heat exchanger effectiveness issue, I suggest to read J.P. Holman's Heat Transfer, McGraw-Hill. The IV Ed. has example 10-7 similar to the subject you are bringing up.
RE: Heat transfer coefficient V flow rate in heat exchangers
That said, you will need an accurate flow measurement and inlet and outlet temps at each location.
If you are not getting enough cooling it raises some questions.
Did you ever get enough cooling?
Has the compressor duty changed?
How clean is the outside of you finfan? Ever pressure wash the fins?
My guess, you fins are fouled and your flow rate is low from pump wear.
= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.
http://www.trenttube.com/Trent/tech_form.htm
RE: Heat transfer coefficient V flow rate in heat exchangers
Rule of thumb is a little hard since a HX is like selling rubber bands by the meter:
Vary any parameter and you get a new situation - that can be countered etc.
Usually the "heat resistance" will be much large on one side than the other - thus changing the "other" flow rate will not change UA much - but it may change LMTD and thus change the duty this way.
Best regards
Morten
RE: Heat transfer coefficient V flow rate in heat exchangers
AndreChE
RE: Heat transfer coefficient V flow rate in heat exchangers
For example, if you increase the mass flow rate, the tube side coefficient increases by (G1/G2)^0.6 for turbulent flow. On the shell side, the correlation is (G1/G2)^0.8