Peltier-based water-chilling experiment

[Cathar]

Hi All,

This is the first stage of a longer term project I've got going. I picked up 2 x 172W 40x40mm peltiers today and setup a peltier-based water-chiller using my first Hydra prototype block (no - not the production prototype - just the first concept prototype I had made some months back).

Basically I've just conducted a non-heat-loaded experiment where I have an Eheim 1048 pump in a bucket, which pumps water to the Hydra block on the cold side of the pelt, and then back into the bucket again. The hot side ofthe peltier is cooled with a spare water-block I had kicking about which I just plugged into my main computer water-cooling loop so it would be cooled by the computer's main radiator.

The peltier was driven off the 12V rail from the PSU. Now this isn't exactly best for the peltier as it's rated for 24V. This is half-voltage, so as I raise the voltage I'm hoping that there's a good deal more cooling power to be had from the peltier (figure I'm at 80W now - hoping for 120W max).

Okay, so I got the system fired up with 4l of water in the bucket. The rate at which the water temperature was dropping is indicating that the peltier is removing heat at the rate of about 80W from the water. Not bad for a prototype block on the cold-side and for the hot side of the peltier not really being cooled that well, and the peltier at half power.

I got the water to ice solid in about 90 minutes, which if you think is crappy, then ask yourself how long does it take your freezer to get a room-temperature 2l bottle of coke to turn to ice?

I know you want to see them, so here's some piccies.

The Setup:









...and after the icing of the reservoir:



The water remains fluid until about -2.2C until the water ices up in the block. This causes the pump to stop, and then the currents stop in the reservoir, and over about 3-5 seconds the whole reservoir turns to ice and the temperature jumps up to -0.1C when the phase-change takes place. Very interesting to watch it happen.

This is just stage one of the experiment.

The end goal here is to power the peltiers properly (~18V) and hook them up in series with 4 blocks to provide around 3x the cooling power of this single peltier test. All up I'm aiming for 220-240W of cooling power to apply to the CPU and GPU water-blocks (which in total push out about 100W - being real watts - not "radiate" watts). Given that the 80W of cooling power of this test was able to bring the coolant down to -2.2C before it froze over, I'm hoping that with an alcohol/water mix and the surplus 120W of cooling power (220-100) of the final setup will allow me to achieve -10C (or maybe lower) coolant temperatures once I get the proper Hydra blocks onto the job.

[JimS]

Some chiller blocks I made:







You're setup should work, but you won't really know until you put a heat load on it.

[JimS]

Blocks installed in computer:





Using 250W(total of 3 pelts) of pelt pumping power, I am able to sustain water temps of 5-10C and CPU temps(Athlon 2.25ghz) of 10-15C. These chillers do work if setup correctly.

Link to another well done chiller project.

[RoboTech]

Hey Cathar,

Cool...

I'll be following your progress with interest. Should be fun!

[Since87]

Originally posted by Cathar

The peltier was driven off the 12V rail from the PSU. Now this isn't exactly best for the peltier as it's rated for 24W, so essentially the peltier is running at half capacity.

No, no, NO.

A TEC running at half Vmax is running at substantially more than half capacity and is running vastly more efficiently than one powered at Vmax. (In terms of cooling vs Watts dissipated in the TEC.)

Read this document.

I'm jumping on you Cathar, because I know you can understand this document, and when you do, you'll be effective at conveying the relevance of it. (Although your experiment has already helped to demonstrate this.)

I'm very seriously considering a chiller based on four 172 Watt TEC's running at 6V each, and before you say that's too expensive, consider the cost of the powersupply and kilowatt hours involved.

[JimS]

I've used 3 pelts which are rated at 90W at 8.9V, running them at 5V off a good computer PSU and gotten excellent results. Since87 makes some excellent points.

[Cathar]

Maybe I poorly phrased myself and that's what you're jumping on.

I'm well aware of peltier efficiency with respect to voltage. I really should have said "half-voltage", not "half-capacity". Before jumping on me, if you read through my post again, you'll notice that I said I'd be aiming to 120W of heat moving power per element, rather than 80W. I never thought for a moment that if I doubled the voltage/power than I'd achieve double the heat-moving potential.

Thanks for jumping on me Since87 and picking up on it, but in this instance you were merely jumping on my phrasing, rather than my understanding.

JimS/Robotech, yes, only just now have I started to poke around and have seen both of your experiments. Very good. Very inspirational. Gives me something to aim at!

The micro-fin blocks I'm getting made up are going to be some pretty finely engineered (read fine = small, rather than fine = good) blocks. Fine enough to make the smallest micro-fin heatsinks you've seen look "clunky" in comparison.

I already talked about getting a long one made up like JimS's with the machinists. What I'm aiming for here is for a more efficient heat exchange on both sides of the peltier to see if I can get those coolant temps well into the freezing range. My goal is with a White Water CPU block to get to below 0C full-load CPU temps. It may not be possible, but I'm going to try for it.

[RoboTech]

And I'll bet you get there too...

Another good article YOU might find interesting - The Effect of Heatsink Design on TEC Performance

[Cathar]

Originally posted by RoboTech
And I'll bet you get there too...

Another good article YOU might find interesting - The Effect of Heatsink Design on TEC Performance

Excellent link Robotech. This is exactly the sort of thing I wanted to see. Many, many thanks.

My only problem now is figuring out the C/W of the blocks. :shrug:

I can take some good educated guesses. I figure that the radiator itself may be the dominating factor on the hot side though.

[JimS]

Sounds like you are motivated and also know what you are doing. Keep us posted and good luck.

[Since87]

Originally posted by Cathar
Maybe I poorly phrased myself and that's what you're jumping on.

I'm well aware of peltier efficiency with respect to voltage. I really should have said "half-voltage", not "half-capacity". Before jumping on me, if you read through my post again, you'll notice that I said I'd be aiming to 120W of heat moving power per element, rather than 80W. I never thought for a moment that if I doubled the voltage/power than I'd achieve double the heat-moving potential.

Glad you know what you are talking about. And you know that doubling the voltage is roughly equivalent to quadrupling the power consumption?

I've spent a lot of time fighting the myth that TEC's are most efficient at 75% to 80% of Vmax.

It's true that if you have the typical CPU/Coldplate/TEC/WB stack, and a good radiator and fan, 75% to 80% will get you the best cooling. It's hard to imagine any sense of the word in which this is 'efficient' though.

When you start talking water chillers, multiple high Qmax TEC's at low voltage is definitely the way to go. (At least for those of us who pay our own electric bills.)

I like your plan. Very similar to what I'm also (very slowly) working on.

Most effective way to get the heat off the die - White Water.

Once the heat is in the water, it can be applied to a large surface area where multiple TEC's can be used relatively efficiently.