Hybrid Car – More Fun with Less Gas

Using finned tubing to dissipate heat

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Posted by Morris Dovey on February 28, 2009, 2:00 pm

I'm getting ready to build the solar powered fluidyne similar to the one
shown in the drawing at the bottom of


My objective is to dissipate as much of that heat to the open
environment (say 70F, although it could range from 32F to 130F) as
rapidly as practically possible.

I've found a manufacturer of brazed fintube that'll withstand the
expected operating pressures and well more than the expected 725F input
temperature, but I need to supply tubing diameter, fin height, and fin
spacing - and I haven't a clue what to ask for.

It would be really great, just this once, to get things right on the
first try. :-p

I've Googled, and found no shortage of links - but haven't found
anything that even approached being clear guidance.

Can anyone advise or provide a link to anything definitive?

Morris Dovey
DeSoto Solar
DeSoto, Iowa USA

Posted by azuredu on February 28, 2009, 8:59 pm

Custom design convective heat exchange efficiency should be computed:
heat flux, flow speed, Reynolds number, Prandtl number, Nusselt
number, etc.

The biggest problem with your design is that horizontal fins are
highly inefficient. Air will stagnate between the fins, and no heat
exchange will occur. Try to modify the design into vertical fins. In a
way that your supplier can manufacture. Then I can give you a quick
(approximative) formula. The formula won't work with horizontal fins.

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