Idea for ACing your PC using Alcohol

[klosterdev]

I came up with an idea on how it might be possible to air condition a PC without need for a compressor. I took a look at alcohol evaporation tempretures, and they were in the perfect range of what you would need to make it work. Any pump system creates pressure, so boiling points will most likely be lower, so it might be smarter to use Isopropal or Ethanol instead. Another issue is that alcohols can corrode certain metals, but putting a thin non-reactive metal lining inside of the copper pipes might solve the problem.

I know those CPU temp ranges aren't incredibly accurate, but I inserted that in the picture because I was sending it to a mechanical engineer who doesn't know much about CPU temps so I just hedged a rough guess.

Alternitivly, I could make the pump a compressor by putting it after the CPU but before the cooler, then re-widening the pipes after it runs through the cooler.

 

[crazywheels]

try it and let us know how it turned out.

 

[jnjkele]

Nice idea - it will be problematic though for a few reasons. ..

First - you are talking about a two-phase system (liquid-vapor) and as such, boiling point is not the only parameter to be considered. The vapor pressure vs. temperature as well as specific heat vs temperature properties of the working fluid must be considered when designing the system.

Second - you will probably find that the alcohols, while they do boil at approximately the right temp, have very little heat capacity (low specific heat) which means they vaporize readily with little heat applied (unless they are run at high pressures, thus necessitating a compressor). So what happens is that the alcohol vaporizes quite happliy in your CPU heat exchanger, but the heat load (>100W in the case of prescott) overwhelms the capacity of the cooling loop, and the net result is you end up needing to pump tens of gallons of alcohol per hour (far more than is practicable for an enclosed system running on a home PC). to keep up with the heat produced in the CPU

Third - even if a system of this nature were sucessfully implemented, you would find the danger factor prohibitive. . . I'm sure I would not want to be sitting next to a PC that is a virtual bomb waiting to go off. . the slightest leak and that alcohol will be more than happy to burn very violently, reacting poorly with the PC hardware, and the user in close proximity to the burning PC. . .

For more details, and to get the proper mathematics to investigate further, I would google 'two phase cooling systems' and see what you can find.



J. Keller
BS - Mechanical Engineering
MS - Mechanical Engieering

 

[badge]

Nice idea - it will be problematic though for a few reasons. ..

First - you are talking about a two-phase system (liquid-vapor) and as such, boiling point is not the only parameter to be considered. The vapor pressure vs. temperature as well as specific heat vs temperature properties of the working fluid must be considered when designing the system.

Second - you will probably find that the alcohols, while they do boil at approximately the right temp, have very little heat capacity (low specific heat) which means they vaporize readily with little heat applied (unless they are run at high pressures, thus necessitating a compressor). So what happens is that the alcohol vaporizes quite happliy in your CPU heat exchanger, but the heat load (>100W in the case of prescott) overwhelms the capacity of the cooling loop, and the net result is you end up needing to pump tens of gallons of alcohol per hour (far more than is practicable for an enclosed system running on a home PC). to keep up with the heat produced in the CPU

Third - even if a system of this nature were sucessfully implemented, you would find the danger factor prohibitive. . . I'm sure I would not want to be sitting next to a PC that is a virtual bomb waiting to go off. . the slightest leak and that alcohol will be more than happy to burn very violently, reacting poorly with the PC hardware, and the user in close proximity to the burning PC. . .

For more details, and to get the proper mathematics to investigate further, I would google 'two phase cooling systems' and see what you can find.



J. Keller
BS - Mechanical Engineering
MS - Mechanical Engieering

I noticed he didn't answer. You don't think.... No...couldn't be...

 

[badge]

try it and let us know how it turned out.

How creul.

 

[klosterdev]

Yeah, I'm still alive. Thanks for the tips. It occured to me after I posted the idea that if I use a gear pump, I can just narrow the output valve and make the pump the compressor itself. The problem with that though is that in that case I would need to put the pump between the CPU and the cooling section, but in that case the gear pump would be pushing vapor. This could be solvable by leaving the gear pump as is, but narrowing the valve after the CPU.

That would create a higher pressure enviorment, while still allowing the pump to push liquid instead of gas. I still have the problem with the selection of chemicals though. Since it's (now) going to be pressurized, what chemicals are commonly used in phase-change cooling?

 

[Kholonar]

I really like this kind of inventiveness as it is simple to understand to the layman while the engineer in me likes the pumping mechanism. If I separate myself from this though, and put on my marketing goggles, what advantages does this system have over the more conventional water cooling?

One of the reasons why distilled water is used is because it is non-reactive, inflammable, relatively non-conductive and as someone else pointed out - has a high heat capacity. I think you've jumped on alcohol because it tends to evaporate at temperatures not alot over what a processor runs at. If indeed you were trying to exploit this evaporation capability then it is generally not required to have a pump in the system (since evaporation usually causes transportation). Take the vapochill heatsinks, they have a chemical inside that evoprates near the cpu and rises up to the cooling fins. Once it condenses, it falls back down and the cycle continues.

Don't stop your designing though, I may be completely wrong as designs can work better in practice than in theory.

Goodluck with it.

 

[QuietFreek]

Hi thaught id add my ideas on this althought i am by no means an expert.
increaceing the pressure of the working fluid in the cpu bock would increace the boiling point meaning that the block would run hotter in order to acheave the desired liquid - vapour change which would extract the energy so much more effectively than a liquid only system.

If you were to use a gas pump down-stream of the block to reduce the pressure in the cpu block the BP would drop and you would force the liquid - vapour phase change with the assoicated enthalpy change required to do that you could then quite easyly return the vapour to its liquid state in a radiator / heater matix and run the liquid back into the cpu block.

this is my interpritation based on my 2nd & 3rd year thermo lectures

 

[QuietFreek]

further thaughts:

assumeing that the pressure drop is small because you would be running the working fluid near its atmospheric boiling point anyway doing some rough ballparking estimates.

two choices of fluid:
Acetone : 29 kj/mol enthalpy of vapourisation @ 56 deg C
Methyl alcohol : 35 kj/mol elthalpy of vapurisation @ 64 deg C

to cool 125w processor need a flow of aprox:

0.0043 mol / second acetone
0.0035 mol / second methyl alcohol

which is

0.371 m3 / hour of vapour for acetone
0.302 m3 / hour of vapour for methyl alcohol

or:

1.145 L/hour liquid acetone
0.512 L/hour liquid methyl alcohol

notes:

methyl alcohol would require a larger pressure drop in block to acheave satisfactory BP for cpu temp than the acetone and therefore a highter volumertic flow rate due to drop in density of the gass - not accounted for here. everything is verry rough and assumed to be at room pressure i have no real way without doing lots of complicated sums to tell if these assumptions are valid.

good luck and try not to kill yourself

 

[jnjkele]

If I separate myself from this though, and put on my marketing goggles, what advantages does this system have over the more conventional water cooling?

The biggest advantage over typical water cooling setups would be the cooling capacity of this system. Most water coolers won't take a cpu very far below air cooling - I think the best h20 systems basically bring the cpu down to around 25-35C. With a system like this, if you expand and condense the working fluid properly (in this case the alcohol) you can concievably COOL the cpu to temperatures below room temp, allowing more extreme overclocking. A well designed two-phase system with the right working fluid, expansion block, compressor and condensor could conceivably bring the temperature down below freezing without using exotic things like liquid nitrogen. They do it all the time with two-phase systems in the aerospace industry - they're called cryo-coolers, and they use these very same principles to cool things down to cryogenic temperatures.

The only question remaining would be whether or not the power requirements for this system would be lower than that of using watercooling with peltier coolers attached to a heat exchanger. I saw a setup that would cool the system to 32F (yes, freezing) using 1kw of peltier coolers - hardly economical to run.

This would be very interesting to get working!! Keep it up!

An afterthough on acetone - this is an extrememly caustic substance and should not be used casually or you could get seriously hurt. For some additional ideas, look into what working fluids are used in heat pipes, they are basically passive two-phase cooling devices. I know that ammonia is frequently used, but again, not exactly a user-friendly substance.

I'll mention again concern with using alcohols - they are highly flamable, somewhat dangerous and burn without making much of a visible flame, making them that much more dangerous.

J. Keller

 

[QuietFreek]

Isnt acetone (IUPAC propanone) just nail varnish remover and therefore not caustic ? - i appologise if ive got tis mixed up Mr Keller.

anyway on a more progressive note:

acording to the NIST data sheet if you could hold 0.098 bar abs in the evaporator you could acheive 288K or 15 degC ish with alcohol.

you could go sub zero (if the relationship holds outside stated range) if you could hold a pressure of 0.04 bar abs in the bloc.

this is based on the assumption that the block would cool down to roughly the boiling point of the liquid for the vapour pressure generated based on the antoine equations

if acetone were a viable working fluid; for it to go sub zero it would only require a pressure of 0.093 bar abs to be maintained.

unfortunatly i have no experience with vacuum pumps so couldnt tell u if thats feasable or not? - let us know if you do

 

[n3zyd]

what about using ammonia, besides the horible smell if it leaked I think there would be less chance of a nasty fire.

 

[QuietFreek]

I think ammonia is a reasonable choice for profesional aplications and for use in passive heatpipes, however here it has three draw backs.

1) avalability - ive never scene a cylnder of the stuff as pure compressed gass rater than as the aquious solution commonly labled ammonia avalable in the shops.

2) at Room Temperature Ppressure (RTP) its a gas and would require the contruction of gass refrigeration cycle almost identical to that in your frige at home and the assocated high pressures and difficulties in engineering it - it would possibly be easyer to modify a refrigerator evaporator to bolt onto the cpu (a la promithia mach 3 et al) and run that (if you couold put up with the noise)

3) it has a nasty habbit of blinding people if it gets in their eyes.

 

[allhell]

You are a bright guy,,, its good to see some one with sense posting here.. congrats!!!! Good post.
DAMN fanboyz need to get a life or learn to help old ladies cross the street.

 

[Jak_Sparra]

i agree with what that other fella said about the danger factor. if i was you i would keep a fire exstiguisher (or however you spell it) attached to your case, you can get them small ones for cars quite cheap....

Also handy for when your brother sets his goaty beard and neck on fire while trying to down a flaming sambuca on his 20th birthday.....

... or the time he set my carpet on fire while trying to show me some dumb 'freezing beer trick' with lighter gas and beer in my front room....whilst smoking... :roll:

 

[silentcoercion]

Isnt acetone (IUPAC propanone) just nail varnish remover and therefore not caustic ?

Yes; no.

Yes, acetone is used as a nail polish remover, but it also is caustic and rather impressively flammable, same as the alcohols suggested.

 

[TheMaster]

As impressive as that looks theres only a couple of substances that have a higher heat capacity than water... in increasing order:

Ammonia
Helium
Hydrogen

Ammonia, as it turns out is really supposed to be a gas at room temp.
The stuff that is available commercially is ammonium hydroxide solution.

So there's no liquid that has more heat capacity than water.

As far as using Ammonia in heatpipes:

Anhydrous ammonia corrodes copper- and zinc-containing alloys, and so brass fittings should not be used for handling the gas. Liquid ammonia can also attack rubber and certain plastics.

You definately don't want to be handling this stuff.

 

[jnjkele]

Ok, while the theory and engineering involved with a two-phase PC cooling system is facinating, it is somewhat academic as it really becomes a matter of heat capacity - and safety. The alcohols have such low heat capacity that any disturbance in the system would cause the alcohol to evaporate back into the pump, bringing the whole system down and frying the CPU. The precarious nature of vaporizing in the CPU cooling blocks leavs me thinking it would be pretty unstable as minor variations in pressure drop across the block could potentially trigger the scenario mentioned above. You would be better off with a classical refrigeration cycle and expand the gas right before the cooling block (essentially put the evaporator from an AC unit on the CPU. That would be more efficient and safer.

More pragmatic yet - take the benefits of existing water cooling solutions and improve upon their cooling capacity by adding a heat exchanger to the fluid loop that has a peltier cooler attached. You could put a 100W cooler on that heat exchanger and drop the temp on the CPU nearly to freezing (most pelts will do about 70F temp delta for the 100W or higher models). Add a bit of glycol to the water solution in the cooler and you could get below freezing without the water in the loop freezing up. That would be less troublesome, safer and more easily accomplished than a completely custom two phase system that is potentially unstable in its operation.

That modification on a water cooling loop could probably be done much cheaper too - I may just have to try that one!!

Cheers!!

J. Keller

 

[allhell]

I have a water cooler with 2 200 WATTS peltier sandwiched external water block,,, instead of a radiator & fan,,,,, but I start to encounter condensation problems once the temps reach 25 deg c. Its very nice tho but I have to use a 500 Watts PSU to run it & I guess you can imagine that additional expense for very little gain in performance.

I have a Venice @ 2.8 on air & if I use this peltier water cooling rig I can only get to 2.9 stable even tho the temps asr low... I think that might be the max for this individual cpu core I have,,,, others may get better milage from theirs. My 2.8 Venice set up on air is very quiet so I'm happy.

Mercury is probably the only other thing I would want to experiment with but that liquid/metal posesses it own major health hazards as well.

Next I will be experimenting with a small peltier (@ about 12 watts) with a cold plate & HS "atop" a heat pipe type HS assembly & see what milage I can get from it.