# Heat transfer internal flow through circular tube.

## Main Question or Discussion Point

I have an enclosure in which the electrical components put off 10,500BTU/hr. At the top of the enclosure the internal hot air is in contact with circular aluminum tubes. Ambient outside air at 70 degrees F is blown through the center of the tubes at 500cfm. Internal hot air and outside ambient air are seperated by the aluminum tube wall. It is a air to air heat exchanger of sorts. I need to determine if with 33 aluminum tubes I can remove the 10,500BTU/hr. How do I approch this problem, any online examples I can follow? Can I simplify and just look at what 1 tube is able to remove and then multipy to determine the systems capabilities?

Related General Engineering News on Phys.org
The short answer is probably "yes," but only if you don't care what the temperature is inside the enclosure.

A more useful answer will require a better description of the problem. At a minimum, you'll need the maximum allowable temperature inside the enclosure, and dimensions & wall thickness of the tubes. You may also need a description of how the electrical components and the tubes themselves affect circulation inside the enclosure and, depending on wall thickness, the type of aluminum.

You may be able to get an estimate using a smaller enclosure, heat rate of 10500/33 BTU/hr, and 500/33 cfm.

Check out http://www.martindalecenter.com/Calculators3A_1_Sub.html . They have a number of heat transfer calculators that might help.

Good luck -- it's not a simple problem!

Is the internal hot air forced or natural convection? Normally you can calculate any heat exchanger problem with UATln. The area would be the inside or outside area of one tube times the amount of tubes. The choice of inside or outside surface area depends on how you calculate the heat transfer coëfficient U. You will need to find h-values for your particular problem which would be the hard part I think. But any good heat transfer handbook has examples like yours I think.