Liquid metal 'hot loop'

EdZ

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I was browsing the various low melting point metals, and found a rather interesting fusible alloy called Cerrolow 136. It's melting point is only 57°C so the hot side of a peltier would easily be able to melt it, it's a lot less aggressive than Field's Metal or Wood's Metal (i.e. it shouldn't eat your blocks and radiator from the inside), and is Cadmium-free (the similar Cerrolow 117 melts at 10°C lower, but contains Cadmium).
The idea is to use a double-loop system: The 'cold' side is filled with Ethylene glycol, and runs sub-ambient (or below zero), and consists of a pump, the blocks for the CPU and GPU, and a compact heat exchanger attached the the peltier's cold side. The 'hot' loop would be filled with Cerrolow, and would just be a pump and a fanless radiator.
doubleloop.png

The main problem is that Cerrolow is eutetic, so it shrinks when cooling before expanding again. This means that as it cools in the loop, liquid will flow in around the cooled and contracted 'core', then as it cools further it will expand again and cause problems. The only solution I can think of is to keep the loop permanently hot, or use some sort of expanding concertina tubing to handle the expansion (and a really beefily sealed heat exchanger and radiator). I'd have to contact HiTech to find out what degree of initial shrinkage it exhibits (the expansion is to the same density as it's liquid state). If it also shrinks prior to melting again, the problem would probably be minimal.
The other problems would be pumping (could use a MHD pump, but I'm wary running a current through something that connects to the internals of a computer, even if it does form a closed circuit), preventing refreezing, startup (the hot loop may have to be pre-heated if heat in the cold loop builds up too fast. May not be a problem), and heat exchange between the hot and cold loops. My best guess is to use either a high-powered peltier (maybe even 1kW, but probably closer to 500W) and sandwich it between two standard heatsinks, or to use a physically larger peltier (or several peltiers) and fab a custom pair of blocks.
The idea behind using purely convective radiator cooling is that the larger temperature differential will make it relatively efficient, and to prevent accidental cooling back below the melting point. Plus it'd be quiet.

This is purely theoretical for the moment. Cerrolow is likely to be a little expensive (it's commercial use is to allow gunsmiths to take accurate barrel impressions, hence it's eutectic properties), through less so than some of the more exotic non-conductive oils. The only prices I've found peg it at between $20 and $200 per pound. The system might also be rather inefficient due to the peltier requirement. Running it straight to the blocks would mean a period where it would not be sinking heat before it melted causing a nasty temperature spike, and it could never cool anything below it's melting point. On the other hand, the 'hot' loop at least would be highly efficient, both due to the metal's excellent specific heat capacity. Though to get the most out of it would require a very powerful peltier, which might counter any efficiency increase. Less a viable cooling option, and more a "because it's cool" option. Imagine looking into an external reservoir and seeing quicksilver flowing inside.
Does anyone have any ideas on the solidifying problem, or if it even is a problem? I'm not quite sure that once the pump stops it'll cool and solidify as one, or if the residual heat (and thus cooling effect from the radiator) will cause a potentially damaging 'wave' of solidification to run down both arms of the loop to the heat exchange block. Any other obviously unfeasible components that I've overlooked?
 

dr papadakalis

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hm...

while it sounds really cool i have high doubts as to if it will work.

i would mainly be afraid of it solidifying in the pump and upon initial startup ruining it... 57c is MUCH higher than room temp, so unless you kept it on 100% of the time you'd have to find a way to preheat the hot loop before you started it. then there's also the cost factor.... no way in hell would i pay 200 per pound of something that MIGHT work. if you can get it for 20 a pound, i'd say go for it on a 478 rig or somehting just to see if it works... then if it does put it on a rig that costs money.
 

EdZ

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The idea would be to start the peltier, use the excess heat to melt the hot loop (might take a while if it's cooled significantly), then start the pumps for both sides. Would have an annoying long startup time, and you'd need a microprocessor to co-ordinate it all. Or a bank of ready lights. Or both, for the blinkenlichts effect.
 

Uberbob102000

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I'll be willing to bet your going to have to use something with a lower melting point. That's just too much warmer than room temp to work usefully.
 

AVT

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The main problem with all that is that the side with ethylene glycol runs at below-zero, which can cause condensation and a whole lot of other possible risks. You need to be very careful with it.

The other problem is that powering a peltier that's going to be powerful enough to cool all that could potentially be problematic.
 

OniExpress

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Condensation is the general problem with near- and sub-zero cooling and one of the main perks of immersion cooling. Of course, you could house the motherboard in a sealed container with a water-nil atmosphere. Flush it and use helium, for instance.

This concept gives me a lot of interesting ideas, but I don't know that it would work effectively here. The melting point is so high that the only truely effective use that I can think of is to use it as an additional stage before another cooling system, but even then you'd be stuck at keeping the peltier at about 60*C.
 

Nenu

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The Peltier would need to be run at quite a lot higher temp than 57C as that is the solidifying point and the very lowest temp the metal can be throughout the loop.
(really it needs to be a fair bit warmer than that at minimum to keep the flow rate up)
The metal liquid will need cooling and for the cooler to be any good, you need to remove a LOT of heat.
This will easily solidify the metal at the cooling fins if the starting temperature isnt high enough.

You will likely need a peltier that is made using high melting point solder (to keep it held together under high heat).
 

Sysjack

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I would do some research into this cooler. I don't know any more about it than what is on their website, but it looks interesting. Take your basic tower style air cooler, put liquid metal in the heat pipes, connect the ends of the heat pipes to form a loop over the top of the heat sink, and put an electromagnetic pump there. No idea what materials they are using for the liquid metal coolant or the heat pipes. The electromagnetic pumping is rather ingenious though.
 

Nenu

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I would do some research into this cooler. I don't know any more about it than what is on their website, but it looks interesting. Take your basic tower style air cooler, put liquid metal in the heat pipes, connect the ends of the heat pipes to form a loop over the top of the heat sink, and put an electromagnetic pump there. No idea what materials they are using for the liquid metal coolant or the heat pipes. The electromagnetic pumping is rather ingenious though.

Good find, although the price is extreme.
http://www.hexus.net/content/item.php?item=16332
They were quoting £235 last November !

although it appears to no longer be in production.
http://xtreview.com/addcomment-id-7657-view-Danamics-ceases-the-sales-of-LM10.html
Not sure if thats true as the there is no mention on Danamics website.
 

Sysjack

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I was more suggesting trying to find out something about the materials they are using in that cooler to make the OP's homemade solution more feasible.
 

serpretetsky

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what are the advantages to using Cerrolow 136 vs water? (heat conductivity? specific heat capacity?)

I can't find any numbers.
 

best [486]

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The main problem is that Cerrolow is eutetic, so it shrinks when cooling before expanding again. This means that as it cools in the loop, liquid will flow in around the cooled and contracted 'core', then as it cools further it will expand again and cause problems.

It sounds a lot like "cerrosafe" which is used to cast chambers on firearms, to see what round they use. in the 1/2" or so diameter pieces that come out of the chamber they only expand a couple thousandths [0.002"] over a few weeks...
 

EdZ

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best [486];1034082014 said:
It sounds a lot like "cerrosafe" which is used to cast chambers on firearms, to see what round they use. in the 1/2" or so diameter pieces that come out of the chamber they only expand a couple thousandths [0.002"] over a few weeks...
That's exactly what it is. Cerrolow is simply a lower melting point version of Cerrosafe (Cerrolow has some Indium in it that Cerrosafe does not).
what are the advantages to using Cerrolow 136 vs water? (heat conductivity? specific heat capacity?)
Massive advantages in conductivity and heat capacity, at the expense that it must be kept heated.


Given the cost of the Danamics LM10, they're probably using Galinstan as the 'liquid metal'. It's molten at room temperature (all the way down to −19°C), but is VERY expensive, and rather aggressive. Put a drop of Galinstan on a sheet of Aluminium foil, and it will eat it's way through, and you'll be left with a drop of useless contaminated Galinstan. If you want to run it through tubing, you need to either run it though a non-metal tube (e.g.glass), or coat the inside with Gallium oxide (not cheap, or easy to to), and this goes for the 'water' block too.
Mercury, while a lot cheaper, also has these problems. And the additional pressure problems from sublimation, and the toxicity of it's fumes.
 

best [486]

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Mercury, while a lot cheaper, also has these problems. And the additional pressure problems from sublimation, and the toxicity of it's fumes.

Make your waterblocks out of iron/steel [it doesn't amalgamate with them], and use rubber tubing, dunno what you'd use for a radiator though...
 

serpretetsky

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Massive advantages in conductivity and heat capacity, at the expense that it must be kept heated.
i know, you've said that in your original post, however, i cannot find any sources for this. In fact, googling "Cerrolow 136 heat capacity" or "Cerrolow heat capacity" simply brings me to my post as the first hit. The manufacturer website doesn't have much info on this (not surprising, since this isn't their target)

Mercury, while a lot cheaper, also has these problems
mercury also has much lower heat capacity than water.
 

Tigerbiten

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It's not going to work.

A neat formula to size peltiers:

Delta T = (1 - (heat load/max cooling power))*max temp difference

where heat load = CPU's heat output in watts, max cooling power = Maximum peltier rating in watts and max temp = Peltier's maximum temperature rating, in degrees C.
So DeltaT = (1-(250/1,000))*68= 50C.
If your hot side is at ~70C to keep your metal liquid, then your cold side will be at ~20C.
You'll be running your cold side around ambient temps.

Luck .............. :D
 

EdZ

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It's not going to work.

A neat formula to size peltiers:

Delta T = (1 - (heat load/max cooling power))*max temp difference

where heat load = CPU's heat output in watts, max cooling power = Maximum peltier rating in watts and max temp = Peltier's maximum temperature rating, in degrees C.
So DeltaT = (1-(250/1,000))*68= 50C.
If your hot side is at ~70C to keep your metal liquid, then your cold side will be at ~20C.
You'll be running your cold side around ambient temps.

Luck .............. :D
That appears to assume a single 1kW peltier cooling a 250W CPU. Peltiers exist with greater maximum temperature ratings (sure, they won't be cheap, but nothing else in this is anyway). It should also be remembered that peltier delta-t increases with hot-side temperature (though not efficiency). Stacking multiple peltiers with multiple stacks in parallel could also work.

As for Cerrolow's heat capacity: I'd need to experimentally verify it (expensive, I don't have the equipment or any Cerrolow), and I can't make a ballpark guess just from it's composition. It's mostly Bismuth, which gives it a somewhat lower heat capacity per mole than water (damn that lack of Hydrogen and it's excellent heat capacity), but it's greater density should compensate somewhat. This is definitely the fuzziest aspect of the idea.
 

BrainEater

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I'm not sure 'cerralow' is what you really want.

Most of the companies that have tried this use 'Galinstan' ( 68.5 % Gallium , 21.5 % Indium and 10% tin... melts at ~ -19c.)

Galinstan ain't cheap , and has major issues to overcome.

There is a reason this isn't making it to market.

Galinstan is an incredible solvent for nearly all metals....Refractory metals are basically the only ones that are not affected.......Try pricing out a custom machined 'liquid block' made from molybdenum or tungsten.

Pumps are an issue too.MHD pumps have been used , but the galinstan dissilves the electrodes........this leaves basically only peristaltic pumps......more $$$$....

-------

It's certainly possible , but I would expect the cost to run into the thousands....

:D
 

EdZ

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I'd mentioned Galinstan and it's problems previously. All the low melting point metals (Mercury, Wood's Metal, Field's Metal, etc) have similar problems.
 

BrainEater

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Yep....I know ya did.

I think the problems associated with running galinstan would be less of a pain to overcome , than running a higher M.P. metal , so I wanted to reiterate...

The biggest issue I see is the whole 'preheating' thing , although , the pump would be difficult too.....I think you would still have dissolving issues with a MHD pump , and other pumps for high shear liquids are never cheap.

gl ! , and be safe , liquid metal cooling can be dangerous..

:D
 
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Concentric

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This is the most audacious cooling plan i've ever heard.
I haven't entirely understood the ideas but apart from anything else it looks like you would have problems with the Cerrolow solidifying in the pipes with a melting point that high.
 

arentol

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As you kind of said earlier, if possible this would only be for the "cool" factor of seeing metal moving through the cooling system, because there is simply no way this would ever be an "effective" cooling solution (as in more effective than water cooling).

'tis a silly idea.
 

ghost6303

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because there is simply no way this would ever be an "effective" cooling solution (as in more effective than water cooling).

maybe not "effective" for the purpose of computer cooling, but liquid metal cooling loops are used in manufacturing all the time. they can transfer a monsterous amount of heat energy very efficiently. much more so then water. but usual operating temperatures of those loops are 500*-1000*+ F. using liquid metal on something as relatively "cool" as a 100*-150* F computer is not really practical.
 

Archmage

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The melting point is too high... definitely.

If you used water on the hot-side, you could easily keep the coolant 20C lower, which already negates the benefits of using a "coolant" of superior thermal conductivity and heat capacity.

Furthermore, TECs don't exactly have a large Delta-T when used at a reasonably efficient voltage. Any successful TEC chiller will use multiple TECs in parallel, and generally at a lower voltage (but not necessarily - if you're a madman you can waste all the power you want and force the need to run multiple large radiators).

Neat idea though.

Edit: echo what ghost6303 said as well. Good point.
 

RadRob

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I would do some research into this cooler. I don't know any more about it than what is on their website, but it looks interesting. Take your basic tower style air cooler, put liquid metal in the heat pipes, connect the ends of the heat pipes to form a loop over the top of the heat sink, and put an electromagnetic pump there. No idea what materials they are using for the liquid metal coolant or the heat pipes. The electromagnetic pumping is rather ingenious though.

After a little research on their site and hence googling NaK I found this:
http://www.frigprim.com/articels4/LiqMetal.html

It seems to be useful in comparing some of the different metals that have been mentioned here. Given the properties, if I were designing/making this, I would just have a loop with NaK in it.

But the idea of an electromagnetic pump would work to correct one of the original problems - solids in the pump.
 

arentol

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maybe not "effective" for the purpose of computer cooling, but liquid metal cooling loops are used in manufacturing all the time. they can transfer a monsterous amount of heat energy very efficiently. much more so then water. but usual operating temperatures of those loops are 500*-1000*+ F. using liquid metal on something as relatively "cool" as a 100*-150* F computer is not really practical.

Yeah, but we are talking about PCs, and for PCs it is a silly idea that is only for cool factor.
 

flogge

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Maybe a vertical cooling tower with fins on the side would work well. Just put a heat-sink on the bottom inside of the tower, then fill up the tower with the liquid metal. When you start the peltier, it will melt the metal from the bottom up, then set up a convection where the cool fluid falls along the sides and the hot fluid rises in the center. That should give an interesting visual. Get some of the fluid, then put it in a saucepan on the oven to get an idea what it will do.
 

Hallis

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Too many mechanics would have to go into it to make it work for a PC. While transition metals are awesome and some dangerous ;) I think i'll stick with good ol air and water mixtures for cooling.

A big problem i see is, how long would it take to heat the entire loop? I'd forsee a hot spot where it's liquid right over the pelt and then it taking some time to heat up the rest if at all. Might even be akin to a "steam void" which is a term that you NEVER want to hear if you happen to be near a nuclear reactor lol. And since you'd have to use peltiers anyway then it's just pelt cooling and you're wasting so much electricity.

I did have a little techno-chubby going there at the idea though :)
 

Emission

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The expense and the cooling (or heating, however you look at it) issues totally kill the feasibility. I would research more cost-effective options or just go with water or another liquid.
 
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