seems like it would conduct heat further into your mass and more quickly. it will also restrict the flow through your flue, though. and you'll have to deal with the expansion and contraction of the copper, so it may not remain in contact with your thermal mass. might also crack the mass and allow gas to escape. probably worth experimenting with at the very least.
umm fins work but you ned to do them right. one trick i was sent was copper wire wrapping the pipe and the ends sticking out into the cob. seems to work good but its to soon to tell. Paul the foil idea probably wont work the way you outlined. but i look forward to hearing about it. I one time, would like pipe that has had fins welded on the outside length wise and use it on a bench.
one day when i have time to play with that.
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Ernie and Erica
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One important point: don't allow aluminum and copper to touch, except temporaritly. The aluminum won't last if they get wet; the two will form a galvanic couple, and the aluminum will lose the tug-of-war.
The copper will help tremendously, if the theory is correct.
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