Quote:
Originally Posted by Squidward
More flow = better heat transfer. The rest becomes a proportional arrow analysis of heat transfer coefficients and Tins/Touts.
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Were you a nuke? Seems like I remember a couple on here.
I think if you'll recall your formulas ... more flow = more heat transfer (all things remaining constant), not better transfer. Transfer coefficients are based on materials used, medium of transfer and type of flow (laminar or turbulent). But yes total heat transfer in the sink would include Delta T and flow rate.
So, if an increase of flow changes a turbulent flow in to laminar, you could have a lower transfer coefficient. And if T-in is so low that the Delta T between heat source and heat sink are too small transfer efficiency can suffer depending on materials used etc. Not to mention possible aeration of the coolant which does bad things to heat transfer coefficients.
T-in and T-out are used to calculate total heat loss through the heat sink when combined with flow rate and btu/lb-ma of the transfer medium. Actual transfer coefficient calculation for the whole sink would have to take into consideration surface area of the heat sink, flow type, material coefficients, corrosion layers etc.
From a practical standpoint, yeah, ((t-in)-(t-out)) x flow rate(lb-ma) x btu/lb-ma would give you the total heat loss through the exchanger. But only in a perfect system. If flow rate alters flow type, or causes aeration, etc. it's not always a straight line relationship. And material thermo-conductivity changes based on temperature. Also radiation heat loses increase with temperature.
Every system has an ideal flow rate and Delta-T that it is designed to operate within. If flow rate was the only consideration .... all any system would need to be a better system would be bigger and bigger pumps. Usually the heat sink has to be matched with the heat source. Remove a thermostat and it's possible the temps could go down. It's also possible the heat sink would be incapable of lowering the temps beyond the designed limit ... such as 180 degrees, and also possible a flow rate which the system was not designed to handle could reduce the efficiency of the entire system. Also possible the radiator would be incapable of using the extra flow.
I would say it all depends on the particular system in question. Might cool some vehicles down, might make others run hotter.
Don't make me get out my Heat Transfer and Fluid Flow notes .... I still have them you know
Class of 7801 (Instructor at M.A.R.F. 79-82, Kesselring Site, NY)