My friend and I are currently working on a cloud chamber cooled by the compressor of a deep-freezer. We have built an isolated box that contains the cold pipes of the compressor. The pipes cool down to a whopping -40C. On the top of our box lies an aluminium plate, and on top of that a well isolated chamber. With the aluminium plate 5 or 6 cm away from the compressor pipes, the plate just gets -15C. Connecting the tubes and the plate with a folded fin heatsink gives us -20C. Moving the plate down onto the tubes results in a much better -35C, however this is not a very favorable option as this makes the plate harder to look at. Unfortunately, bending the pipes is not an option either.
We think the air in the box is simply not thermally conductive enough. The heatsink was not doing a very good job either, presumably because the fins where too thin and were in contact with a lot of air.
Our question is: What would be the best way to transport the "coolness" of the pipes towards the plate. Would it be better to fill the box with some sort of liquid that would transport heat more efficient then air?
We are using a computer fan to circulate the air in the box. The fan is pointed upward, so the airflow flows via the pipes onto the plate.