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I would like to make an ice cream machine for home use. That is a mixing bowl which can be stored in the freezer over night and then keeps cold long enough to freeze the ingredients while mixing them.

At first I thought I would just wrap a mixing bowl in commercial cooling packs, but apparently, in the hard shell cooling packs, they often simply use water. Now I would like to come up with a more fancy design.

My idea would be to get a long copper pipe and bend it around my cooling bowl. After bending, it would be like a long spiral around the bowl. At one end, I would plug it shut, then it's filled with water and with a bit of air left, the other end is plugged.

Would the pressure from freezing water be enough to unbend the copper? Do you have ideas on fastening the copper spiral?

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If you really want to use the copper pipe, insert a thin strip of closed-cell foam into the length of the pipe. The ice expansion will crush it rather than the pipe, and unlike leaving an air gap, it will remain positioned along the entire interior.

But this might actually be an instance of "the X Y Problem".


One possible alternative (I'm sure there are better) is to use a larger bowl that fits under your metal mixing bowl. Put the water into the larger bowl, insert the metal bowl, and using a weight across the rim of the outer bowl, force the inner bowl to remain sunken almost to the rim while the liquid is being frozen.

If you start with too much liquid, when it freezes it will simply spill out through the gap between the two bowls. Next time use less. When you have the correct amount, you can permanently keep it in a large and tough plastic bag and avoid all the mess.


The other problem is the use of water.

You are going to chill the water in a freezer that provides some unknown temperature. Experiment with different concentrations of salt until you find the strongest concentration that will freeze solid in your freezer. This will ensure that as the ice melts, the liquid will be as cold as possible.

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The best ice cream is made with the outside bucket temperature below 0 oC. See this link https://www.icecreamnation.org/science-of-ice-cream/. The common approach is the tried and true method to use ice and rock salt in the outer bucket.

When you want to make a bucket-in-a-bucket, use a liquid with a freezing point below 0 oC. You could use tips from the links below to make your own liquid ice pack.

https://www.spine-health.com/blog/how-make-your-own-gel-ice-pack-or-moist-heat-pack

https://www.themakeyourownzone.com/5-ways-to-make-homemade-ice-packs/

Otherwise, to your direct questions ...

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Water, on freezing can easily split copper pipe - have had to repair several.

The air-gap idea, while good, may not work in all situations... If the water freezes in the middle of the copper pipe then the blocked end can then split.

So you should consider a solution that will not freeze until it gets down to -20 degrees C or so... A temperature chosen on the grounds that is what most household freezers get to.

If you have liquid nitrogen about for your cooling, then you will need a different fluid...

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  • $\begingroup$ Hm, I guess I could salt the water. But as far as I understood, the coolant is supposed to freeze. The enthalpy of changing aggregate state is what makes it effective. $\endgroup$ – lhk Jun 11 at 7:07
  • $\begingroup$ You are right about the enthalpy but there might be a solution. You could add some antifreeze to the water so that it does not freeze at -20°C. And to compensate for the missing aggregate change you could add a reservoir with a couple of liters. And from there on you could also add a pump into the system. But salt water would be the easiest way to do it. And keep in mind that you need to transfer the heat from the bowl to whatever you are using for cooling. $\endgroup$ – Daniel H. Jun 11 at 7:58
  • $\begingroup$ I have used Coolflow DTX in cooling circuits and it works well. I am not sure a coiled copper pipe will give you the best heat transfer though. $\endgroup$ – am304 Jun 11 at 13:27

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