I got an email from a person doing a school project who wanted to use soda pop cans to make a water heating collector. Pop cans are used a lot for making air heating collectors, but I did not know of any water heating designs using the cans. This is the result of an hour in the shop trying to work out one.
The idea was to make use of recycled the aluminum both for the recycling and for low cost.
The finned pipes that are being made in the picture are for use in a collector like this...
Start by smashing down the pop cans flat:
Using some scrap plywood, make the tool shown. Its just two pieces of
5/8 inch plywood screwed to a plywood base so that a 5/8 inch wide groove is
formed between the two pieces.
Then place the alum can over the groove and use a 5/8 inch steel rod to make the groove in the pop can.
You can line up a bunch of flattened pop cans and do them all at once. The sledge hammer held as shown and dropped down vertically on the rod is an easy way to make the groove.
The next picture show one way to attach the pop cans to the tube -- maybe not the best way.
Place the copper tube in the groove and press it down. The tube does not have to be copper -- it might be CPVC or PEX.
Place a strip of plywood over the tubes and can. The plywood does not have to be as thick as shown -- quarter inch would be fine.
Flip the whole thing over.
Staple the cans to the plywood strip. Squeeze the cans onto the tube as tightly as possible when you are stapling. Good thermal contact between the can and tube is important.
The finished pop can fin tube.
There are probably a lot of opportunities for improving this -- let me know if you come up with any ideas.
The can metal is approximately 0.003 inch thick, so 0.006 inch for the crushed can. Fin width is about 4 inches.
The fin efficiency for a single glazed collector works out to: 90%, which is not bad.
Remember that that the fin efficiency calculator assumes a perfect thermal connection between the fin and tube, and only accounts for the heat loss out the surface of the fins.
Gary November 6, 2011