Off Topic Hobbies > Cooking

Ice cream maker using peltier devices?

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Well, my sweetie (yes, we are married) and I like to fool around with food.. not that way.. but recently we've started making keto-friendly ice cream, (using coconut milk, mostly, and other things..
we currently are using a machine that only makes 1 pint at a time, which isnt that much. Since I have the electronics interest, a short time ago I bought a single peltier device, was amazed that it worked as well as it did while heatsinked and how it worked, so convinced I bought five more, hoping to get something built by June of this year.. Basically now I want to take these six and use them to make ice cream. I was wondering if anybody else here had done that. Here it is the middle of the winter now. (its been a very mild one) But in Australia, this must be summer.. Frankly, I know the principle of operation and have some ideas of how I might go about this but I can see its difficult to get it right. My wife is actually the engineer, though. Twice.
The instant cold of the Peltier devices and the cold on one side hot on the other aspect of the thermoelectric device is very cool.  I think that given an adequate current, it should be possible. But perhaps not so easy.
I am figuring 20 amps will do it. I have a converted PC supply. And two bench supplies. What I would love to do is make a "tight" convenient ice cream freezer.. that doesn't take up a lot of space. How should I approach this?
It gets very humid here in the summer so I know care is going to have to be put into isolating the cold area from the ultra moist summer air. Although since its distiilled water being condensed out of the air and a fairly low voltage, I dont think it will be that problematic. Maybe just making a cooled slab will do? I can get nice granite slabs really cheap.  Ive never used one. I have no idea how that works out. Would have to break my diet to try out the commercialized version of it.

Hmm, I would do first some back of the envelope calculations with the specific heat of water, well ice cream mix, the efficiency of the device, etc. to get the power required to make it feasible.

Lets run the numbers.  The latent heat of fusion of the water content is likely to dominate.   Coconut milk can be up to 20% fat and Ice Cream up to near 40% sugar, so lets assume there's only 50% water in the mix that needs freezing.  Lets assume you'll be doing a liter at a time, and the target cycle time is half an hour,
The heat of fusion of water is 333 Joules/g, so you need to pump 166.5 KJ of heat out just to freeze the water, + a bit more for the other ingredients and to chill it to a low enough holding temperature.  The approx 15% coconut lipids will push the total over 180 KJ.  You've got 1800 seconds to do so so you need to pump heat at a rate of 100W, at a fairly high temperature differential, maybe 40 deg C on a hot day,  with that high a differential + the need to run the heatsink hotter to be able to reject heat to ambient, the COP could fall below 20%. :(  That's not a freezer, that's a small room heater, literally tiled all over its exterior with Peltier modules to get enough heat out!

Peltiers Do Not Work.

Well, they do, but COP is just so horrible given any temperature differential that you basically have thermal runaway beyond sensible operating conditions.

If you just need cold temperature, i.e., cool a small amount of air or a few drops of water, but no need to do any serious work (i.e., energy), they do work, because with little power, efficiency does not matter.

If you need to actually transfer energy, then you can't get the temperature differential, because the COP drops as a linear function and reaches zero at maybe 50degC differential.

Huge amount of losses and inability to generate temperature differential is a bad combination; you need to spend some serious effort cooling the hot side, trying to keep that as close as ambient as possible.

This is a shame, Peltiers as simple solid state devices would be nice for DIYing cooling solutions.

They are good for calibration jigs of sensors, ICs, etc. For more cooling energy (i.e., freezing significant amounts of water), you can't avoid playing with real refrigeration systems, which requires quite a set of tools (pipe, brazing tools, flaring tools, vacuum pumps, and of course refrigerants, but you can use propane/butane). That's quite a rabbit hole.

Best would be to find a way to modify/utilize existing freezers.

You make a good point but the fact that I have a bunch of DC power supplies that could be used and six peltier devices that (last summer) I got to "do something with the technology" I'm determined to do something to help us stay cool this summer, with them. Its remarkable how much better a Peltier device works given adequate heat sinking and separation of the sides, isnt it? That really is the key, I can see, to getting your money's worth out of them.

Okay, I have to disclose here that I am hoping to be able to duplicate a keto version of ice cream on a slab which is extremely good. Years ago there used to be an ice cream store in San Francisco that made amazing "cheesecake" ice cream on a slab. It was in the Fillmore district. And it was amazing. Unfortunately I forget their name. They used a large marble slab to prepare their creations on. And fresh cheesecake. No it was not Cold Stone Creamery, but the concept was similar, however the ingredients were all freshly made. I think getting a flat piece of stone cool enough doesnt sound so super difficult, Ive seen it done using Peltier devices and heat sinks.

The magic of it is that even milk (regular milk) makes a delicious dessert - when mixed with hot muffins, cheesecake, etc. And its very fast to make.

Its sort of like this


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