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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.

Images: Top of the box with the aluminium plate Top of the box without the aluminium plate, you can see the pipes

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  • $\begingroup$ What's your budget for modifications? $\endgroup$
    – morristtu
    Jan 8 '17 at 14:50
  • $\begingroup$ @morristtu, unfortunately as low as possible. Its just for a school project.. Olin Lathrop, excuse me, I am not a native speaker. $\endgroup$ Jan 8 '17 at 15:53
  • $\begingroup$ Have you tried circulating the air in the bottom chamber? I'd like to know if putting a computer fan down there would work. Also, what kind of alcohol are you using in the upper section? $\endgroup$
    – morristtu
    Jan 8 '17 at 16:40
  • $\begingroup$ @morristtu, good comment! I forgot to mention that we are circulating the air inside the chamber using a 12mm fan. The fan is pointed upward, so the airflow flows from the pipes onto the plate. It made a diffrence of 3-5 degrees Celcius. In the upper section we are currently using 98% pure ethanol, we have also used 99% pure isopropanol. $\endgroup$ Jan 8 '17 at 16:53
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    $\begingroup$ @OlinLathrop - A polite and friendly reminder that StackExchange is an international community. Not all of our community members have English as their first language, and not all of community members were afforded the same level of education in grammar as you were. For the same or less amount of effort, you could have edited out the incorrect grammar instead. $\endgroup$
    – user16
    Jan 8 '17 at 18:08
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The goal is to remove heat energy from the aluminum plate to reach a temperature of at least $-15\unicode{xb0}$F = $-26.1\unicode{x2103}$ by increasing heat transfer between the plate and the refrigeration tubing.

One option is to try to increase convection. This would increase the "h" value in the heat transfer equation below. $$Q = h*A_S*\Delta T$$ $Q$ is the Heat Transferred. $h$ is the heat transfer coefficient. $A_S$ is the surface area. $\Delta T$ is the temperature difference.

Adding liquid might work, but would be heavy and messy.

I would suggest trying to increase conduction between the plate and the tubes. The distance between the plate and the tubes is too much for using heat transfer compound. An inexpensive option could be to lightly crumple up aluminum foil and put it under the plate in such a way where it contacts both the plate and tubing.

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  • $\begingroup$ What particular liquid would be suitable for transferring heat at -40C? $\endgroup$ Jan 8 '17 at 19:47
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    $\begingroup$ @SebasSmits Ethylene glycol solution 60% by volume has a freezing point of -52.8 C. 50% solution freezes at -36.8 C. $\endgroup$
    – morristtu
    Jan 8 '17 at 19:50

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