Stirling engine-based can cooler

The unusually hot weather, combined with my unrefrigerated collection of Mountain Dew and lack of room for a minifridge in my room, drove me to invent something to remedy this unfortunate situation. Here’s what I came up with.

It uses, rather than a conventional evaporation-based cooling system like in an air conditioner or refrigerator, a decompression-based cooling system called a Stirling engine. You may have heard of Stirling engines being used to generate rotary motion or electricity from heat; well, it also works the other way–you can cool things off with one if you apply rotary motion.

(A Peltier cooler is also awesome, especially since it doesn’t have moving parts, but it’s ridiculously inefficient, so I barely considered it.)

This model has two cooling cylinders, one at the top and one at the bottom of the can–an improvement over most single-can coolers I’ve seen which usually have a single cooling unit at the bottom of the can (which is much less efficient than one at the top of the can, which permits convection to cool the drink faster). (The single-can coolers I’m talking about were all Peltier coolers; I couldn’t find any Stirling-engine based can coolers. I’m not sure why.)

And finally, no I haven’t built it yet, but I’m in the process of gathering parts for a foundry and hope to cast the parts for it out of aluminum and bronze/brass. We’ll see how well that works out. :slight_smile:

So, here’s what I’m looking for. Comments and criticism of the design (especially aesthetics) and also presentation tips–making the render/materials look better. Thanks!


this might be really cool if it works.

But, did you do any calculations? I think i remember from physics class (like 10 years ago) that the amount cooled is proportional to the volume of gas. I think that it might turn out very efficient but not very practical as you would decrease the temperature by 2-3 degrees with such small volume.

That is a good point. I will get out my slide rule and run through the calculations this evening. :slight_smile:

OK. Calculations will be forthcoming once I finish them–I would have worked them out this afternoon in class, but I accidentally left my sheaf of papers on the table at home. :-/

In the meantime I realized that I had neglected to take the regenerator into account in my design, so I reworked it a little. (And, I upgraded the pop can.) :wink:

I have everything rigged up to animate properly with TrackTo and Copy Location–maybe not the best/most versatile way to do it, but it works. I will post the animation when it’s done rendering.


Not a critique of the render, but of the technique:

You will lose a lot of efficiency through absorption throught the walls of your cooler. Best method would be to place a small insulated piston in the base of an insulated container, place the can IN the container, and allow air to leak in through a small hole in the top of the container. This will expand, blasting the top of the can with freezing air, as warmer air is removed from the bottom. By keeping the space between the can and the wall of the cooler narrow, you force the cool air to flow across the surface, rising to the temperature you finally want the can at by the time is reaches the bottom. All energy removed will be from the can, rather than most of it being from the environment. By measuring the temperature of the air leaving, you would know when the can was suitably cool.

Obviously, you could recycle the air back to the top if you wanted to save the energy of expelling air at below room temperature. Likewise you could run it through a compression cycle on the way back to the top, to expel more heat from it.


@ travellingmatt IMHO the most efficient way to build something like this was:
Make the can the displacer piston and insulate the “hot” side completely. Knit picking alert :slight_smile:

Well, after all considering that the air in your room already is unbearably hot, why would you want to suck more electrical energy into there to drive a “cooling” device … we all know it finally ends up in heating the room.

looks neat, but what are you using as you heat source to run your engine

-edit- didn’t read properly you want to cool things down so you just need to mechanically drive the engine -

awesome piece of engineering

sorry double post

I guess he would use his muscles to propel it (or a windup mechanism?)
Point is, entropy always works against you :wink:

But then the can’s contents will be all shaken up as it cycles back and forth. That will make it inconvenient (to say the least) to open it. =)

Secondly, I realize the device would convert some of the electricity to heat (and, incidentally, all that heat it’s taking out of the can is going to be re-radiated into the room as well). But I can live with that, I think. The important thing is to get the pop cooled down. :wink:

But notice that compressing the air will also increase the temperature, resulting in a net loss of zero (or, taking friction into account, a net gain of heat). The Stirling cycle avoids that problem by compressing the air in one cylinder (the “hot” cylinder) and expanding it in the other cylinder (the “cold” cylinder). The two cylinders are connected by a regenerator which cools down hot (compressed) air flowing into the expansion cylinder and warms up cold (expanded) air flowing back into the compression cylinder. The hot cylinder would have heat fins/a heat sink to radiate the excess heat out into the room, allowing it to keep the cold cylinder cold. Basically it’s acting like a heat pump.

Your point about insulation, though, is an excellent point. I don’t have any insulation shown in the current model, though it would definitely need to be implemented in the final design.

Here’s the animated render. Anybody know what’s causing the flicker on the gold reflection?

A windup mechanism would be sweet–or a gravity-based mechanism like a grandfather clock. HA! That’s intriguing. I’ll have to pursue that further. :smiley:

Use Edge-Split modifier.

Actually 2.5 should give any added cylinder edge split, there is no reason not to have it on.

Thanks Adam, that seems to have fixed the problem. I haven’t upgraded to 2.5 yet… I suppose I’ll have to sooner or later. :slight_smile:

On another note–I’m having trouble translating the equations I found for a Stirling engine into equations for a Stirling heat pump.

If anyone knows enough about the theory behind it to come up with a formula (or can point me in the direction of such a formula) I’d appreciate it. Barring that, my only recourse will be to build it and experiment to find out its effectiveness…

OK, got the flickery thing fixed–thanks Adam!

Obviously if you were going to recycle the air on the way back to the top, you would have to put it through a radiator of sorts to lose it’s ecxess heat back to the room.

What would be cool would be to use the C02 in the can to drive the engine!

Of course, if it took too long to cool down, it would be flat…


great idea. thnx, i didnt know the existence of the stirling engine, had a fine time researching on the net. maybe i’ll make one for the fun of it…

and this project its like one of these mad scientists grand ideas, like building a nuclear plant to make hot water for tea :RocknRoll:

That sounds like vapor-compression refrigeration. That’s certainly far more common–it’s used in most air conditioners, refrigerators, etc.–but generally, if I’m not mistaken, you can’t use air, you have to use Freon or some similar refrigerant.

Plus you don’t usually get the steampunk-esque feel of the moving pistons. Though I suppose the compressor could be exposed. And you could use a copper radiator…

That’s a whole new redesign I’m going to have to do. Are you happy now? :stuck_out_tongue:

This Stirling engine design is theoretically adaptable to heat up the drink too, instead of cooling it. Just sayin’. :wink: