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# Heat exchanger

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Member Posts: 43
Just playing in the shop. Does anyone has a formula that would give me a close idea of BTU transfer, if we have all the variables such as, surface area of material ,type of material, delta T, gpm, etc. Thanks

• Member
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Try this

You might find something on this site.

http://www.flatplate.com/edrsrc.htm

Noel
• Member Posts: 549
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Here's The One I Use

Q = UA(LMTD)

Q = BTU/hr

U = heat transfer coefficient

A = surface area in square feet

LMTD = log of the mean temperature difference

The heat transfer coefficient varies with the type of HX. It's kind of where art meets science. Shell & tubes will run 100 to 300, while plates, and shell & coil will be in the 650 - 1000 range, depending.

The LMTD is a pain to calculate long hand, but I've got a nomograph, or a little spreadsheet, and can easily do it for you if you give me the inlet and outlet temperatures for both the hot and cold sides of the HX.

Material type really doesn't make a huge difference for most applications. There are other factors that can come into play, like baffles in a shell & tube design, pressure drop across both sides of the HX, nozzle sizes, etc.
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