Nick, have you ever done a test, or do you know of tests, which found a
heat conductance value for copper tubing?


I have a copy of one test that used a 0.36 inch dia coil of copper
tubing arranged in a vertical helix inside of a 10 inch diameter
cylindrical tank. The coiled tube is about 128 inches long, and the
coil diameter was 8 inches (about 5 turns in the coil).

The water in the cylinder was maintained at a set temperature with an
immersion heater. Cooler water was pumped through the coiled copper
tube. The fluid in the cylindrical tank was not mixed in any way
except natural convection. The U value for the heat exchanger was
calculated using the measured input and output temperatures, and the
mass flows.

The U they got varies with flow rate, but its about 125 BTU/ft^2-hr-F
with a flow rate around 0.7gpm.

Where U is as in the eqn: U = Q/(A (Tb - Tm))
where Tb is bath temp, and Tm is mean temp in tube
A is surf area of tube

I have a pdf file on it, and can email it to you if you like.

This value seems to agree pretty well with the values given he
http://cheresources.com/uexchangers.shtml

Gary