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Home made cold stone ice cream

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I was daydreaming about 3D ice printers, and it occurred to me that I might be able to make Cold Stone style ice cream if I put a big chunk of metal in the freezer.

My first thought was to use steel, but aluminum turns out to have almost twice the specific heat of steel and about 4 times the thermal conductivity.  So for a given weight it can absorb more heat, and do it faster.

I had an 11 pound hunk of 4"x4"x12" aluminum left over from the rotary mill, so I cleaned it up and put it in the freezer for a few hours.


The tape was to help me more accurately measure the temperature with an infrared temperature gun, but I think a contact thermometer would be better.


I used a 1:1 mixture of cream and sweetened condensed milk with some fresh strawberries.


But even after lots of waiting and pushing it around on the plate, it never quite froze.


Later it occurred to me to work out the heat of fusion of the ice cream and see how that compares to the heat required to take the plate from my freezer's ~0F to 32F.  Wolfram Alpha tells me that "specific heat of aluminum * 11 pounds * 15 K difference" takes 67,700J, whereas 100g of water (~5.5 moles) needs to lose about 30kJ to freeze.  So that says my big chunk of aluminum should be able to absorb 2x as much energy as I need to freeze a small serving of ice cream, but that's assuming it starts at 0F and doesn't count any other losses (like ingredients that need to be cooled down to 32F, and absorbing ambient heat from my kitchen).

So I'll give it another go with the plate freezing overnight, but I suspect I'd need to start out colder than 0F to really make it work.  

And that makes me think this guy's clever solution of dry ice (-109F) cooling a griddle through an interface of liquid alcohol is probably a better solution.

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