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Subambient full submersion phase change cooled pc - Page 2

post #11 of 333
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Okay I've just done 3 sketches which explains in more detail how this system is proposed to operate, again sorry for the sketch quality.



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The first sketch above illustrates the chamber filling procedure prior to using the computer.

The freezer is off so that the gas bottle is at ambient temps and the contained gas at high pressure.

Line 2 is opened intermittently to allow gas into the chamber which is condensed out by the ac unit to form the liquid gas pool. Once sufficient gas is pooled line 2 is closed and the pc is ready to use.



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This sketch represents the situation while the pc is being used, both lines to the gas bottle are turned off, there is no interchange between the chamber and gas bottle/freezer.

Cooling is via evaporation of the liquid at the pc components and re condensation of the vapor produced at the ac unit evap....I may additionally pump liquid over the evap to further lower the liquid temp or perhaps spray it into the chilled gas above...sort of "bong cooling" fashion, as this would allow for greater sub boiling point cooling of the liquid.

Also importantly during this phase the freezer is turned on and both lines/valves are closed. This lowers the temp of the gas bottle to below the boiling point of the gas contained in the bottle and so lowers the sealed bottles pressure below atmospheric in readiness to recover the liquid from the chamber.



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This last sketch shows the turning off process, the pc is turned off, the ac unit re condenses all the refrigerant gas to liquid and then line/valve 1 is opened to the gas bottle.

The chamber is still at atmospheric pressure due to the expansion sac and the fact that the chamber contains sufficient non volatile gas to fill it (from bottled nitrogen).

The gas bottle is however at lower than atmospheric pressure as it is now at a temp lower than the boiling point of the contained refrigerant, so the gas bottle will actively suck a certain amount of the fluid back into the bottle because of the pressure difference.

Hopefully it will suck back all the liquid but if back pressure builds before that occurs I'm quite confident from what limited experimentation I've done that the remainder will drain back via gravity.

I can maximize the suck back by using a larger bottle as a low pressure in a larger bottle will suck back more volume before pressure builds sufficiently to stop the flow.

Also, again from what I've learned through experimentation agitating the bottle and pipe will cause the fluid to flow back by gravity.....It may be that opening line/valve 2 may also assist the pressure in escaping even though they share the same route as they enter the bottle.

Once the liquid is returned to the bottle the valves are closed and the bottle and freezer are allowed to return to ambient ready for the next run.
post #12 of 333
Thread Starter 
*sigh*........getting bored now.....tech news is all pretty static.....bored bored bored.

Gonna have to spend my hard earned on something......so I've been working out exactly what materials I'm going have to order to make a start on this.

So think I'm going to make a start on this now...just trying to find a cheaper source of the HFC 227ea /FM-200....messaging a Chinese supplier on alibaba.com
post #13 of 333
I like your thermosiphon idea the best so far. Actually it would be a gravity fed heat pipe in this situation. I think if you can keep the inlets to the water blocks/boilers flooded then there won't be any problems with proper vapor return to the condenser.

My suggestion would be to have a self contained AIO(all in one) type system inside the chillbox. It would consist of a thin horizontal condenser above the pc compartment and that will gravity feed the water blocks with liquid refrigerant. Vapor return back up to the top rows of the condenser. The beauty of this system would be that you could use r134a by tuning the pipe for around 9psi/-15c at zero load.

Your latest plan would require a whole rework of the chamber right? I guess the pump would make or break this setup. Any loss of pump at high oc and load could kill your hardware. It would probably have to be a diagram type pump with a float switch.
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post #14 of 333
I would advise you to look up how a common meat cooler works with the compressor compressing the gas into the liquid form of the coolant and pushing it through the system. It would help you avoid the gas pressure problem because those are completely closed loops with regulators and expansion valves to help balance the liquid to gas pressure ratio.
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post #15 of 333
Thread Starter 
Thanks Terrere, I've been looking for links to how a meat cooler system works but not found anything specific as yet....If you could give me a link or elaborate I'd be grateful......I'm always open to new ideas.

Having said that I'm pretty certain I've thought out the process to fill the chamber and recover the liquid now...at least in my mind.

I'd simply use a standard bottle upside-down linked to the chamber by a single pipe bottom filling/emptying from the chamber sump. A freezer would be used to create the pressure differences to move the liquid.

I know your not meant to store pressure cylinders upside-down but as far as I can ascertain that is only because the liquid phase in the bottle would be covering the pressure release valve rather than the gas phase, so if any excess pressure did develop in the bottle then liquid would be ejected from the safety release valve rather than vapor...which obviously once in the open would expand to a much greater volume of gas and be a more significant loss.

Excess pressure is not going to be a problem as the gas bottle is going to be in a freezer and I will ensure it is not overfilled with liquid so there is plenty of vapor space in the bottle.....the majority of the times the bottle will be at negative pressures.

The revised fill and recovery cycle is really quite simple.

From the starting point with the bottle in the freezer obviously first chill the chamber down so you don't get explosive decompression, then remove the bottle from the freezer in and place in an upside-down position allow it to warm so that the bottle pressure starts to build, open the tap valve and the bottle pressure will push the liquid phase which is obviously covering the valve opening along the hose into to chamber sump.
Once filled, close the valve and replace the bottle in the freezer.

The recovery is a little more complicated because of the way the tap valve works, the sealing piston is not directly connected to the valve screw, so I anticipate that when the bottle is under negative pressure that unscrewing the the tap will not release the valve piston as the negative pressure will hold it closed.
So the initial stage of recovery will strangely involve again allowing the bottle to warm to build some pressure and pop the piston seal open, once opened the bottle would again be place upside-down in the freezer this time with the valve open.

In this situation the vapor phase in the bottle would be separated from the vapor in the chamber by the liquid phase in the bottle/hose/chamber sump all of which would be in a continuous "U" shaped bend.

The pressure in the chamber would be at atmospheric due to the expansion sac and the fact that it also contains sufficient volume of non volatile gas to fill the chamber (from bottled nitrogen....well non volatile in the temp range I'm considering....lol) while the pressure in the bottle vapor chamber would be below atmospheric as the temperature would be below the boiling point of the liquid and this vapor phase would only contain volatile vapor (no nitrogen).

So the pressure difference would be equalized by liquid being pushed into the bottle. This of course would then mean that the bottle vapor pressure would become the same as atmospheric, but as the temperature is still below the atmospheric pressures boiling point then vapor would phase change back to liquid so restoring the bottles negative pressure again to below atmospheric. The heat given off by the phase change back to liquid would be absorbed by the freezer and buffering ice packs and this energy would essentially be what is driving the liquid movement.

From an energy consideration standpoint the max volume of vapor that would be needed to re-condense would be 15 liters of vapor which equated to about 63ml of refrigerant liquid, the heat of vaporization per ml of liquid is about 200 joules so a total energy of 12600 joules.....If a freezer can deliver 100w of cooling or 100 joules per sec then it would take just over 2 minutes for this process to occur......in any event the freezer will also contain ice packs that will buffer this energy absorption requirement (and any loss of freezer function at a critical moment which may otherwise prevent liquid recovery).

So as you can see this would be a continuous process that would occur without any back pressure build up until all the liquid is recovered at which point you turn the tap valve off.

The only other problem I can envisage would be if nitrogen were to get into the bottle vapor space, that may affect the bottle pressures....but that would be easily removed just by purging the bottle at the chamber fill stage. Initially rather than having the bottle upside-down just put it the correct way up, the boiling liquid phase would then push the vapor and nitrogen out of the bottle, probably the nitrogen first as it is less dense and would be at the top of the vapor space, once purged like this simply turn upside-down and the liquid will then be pushed out.
Edited by technogiant - 3/22/13 at 1:51am
post #16 of 333
Try this,slide 6, if you are familiar with common cooling setups. You wouldn't need the condenser fan, defrost timer, or anything really to defrost the system since you aren't using Freon or anything to drop it below freezing temps. You are just wanting subambient temps correct? If you use some other coolant all you will need is a compressor and assembly plus the actual lines. Normally with high power compressors you need copper tubing to avoid line pressure issues, but if your compressor doesn't have an extra strong pump you can settle for less rigid line material. You can look at industrial HVAC systems as well for a sample workflow for a compressor style cooling example. Also, if you want to use the least restrictive style vapor/liquid system. This wikipedia article has some good tidbits about vapor compression. Basically, instead of a normal radiator, you use a set of condenser coils, can get these off of an old refrigerator in a junk yard. Hope this helps you see whether or not this is an option. If you have an old AC unit you can make the compressor work for this, I think.

EDIT: Even without freon you will still need condenser and evaporator coils. Just asked a family member who knows the industrial cooling method. He did say that even just a little bit of high level coolant will probably freeze all of your components. So just a word of warning, treat it as Nitrogen or dry ice cooling and insulate all of your components to prevent damage.
Edited by Terrere - 3/22/13 at 7:31am
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post #17 of 333
Thread Starter 
Thanks for those links Terrere, some good info in those.

I'm not really sure what I'm suggesting is covered by traditional refrigeration techniques though. Perhaps I didn't fully explain the setup.....I'm going for substantially sub-ambient temps, I'm currently running a fully sealed and insulated chillbox which consists of a window style ac unit with the evap enclosed in the chillbox and getting temps of -30c to -22c dependent on load, The chillbox contains air to cool the pc components which are also contained within the chill box.

My proposal involves replacing the air with a refrigerant gas that will liquify at those temperatures and so form a pool of liquified refrigerant I can submerge my mobo in.

I'm not considering any further compression/decompression stages, the liquid pool will solely be formed by the temperature within the chillbox which will be below the boiling point of the refrigerant gas.

The pc components will be cooled by direct evaporation of the refrigerant liquid which will be re-condensed in the cold temp of the chillbox caused by the ac units evap.

Much of the discussion above has simply been about how to safely remove the liquified refrigerant from the chamber into a pressure bottle between uses when the chillbox will return to ambient temps, not being a pressure bearing vessel it could not contain the refrigerant liquid which would boil off to form a huge volume of gas.

I think the system I've worked out to recover the liquid to the pressure bottle is actually used within industry and is called "cold line transfer"...so I've probably just reinvented the wheel again...but not being qualified in these subjects I'm just trying to brainstorm my way through as I go.

I'm unsure from your comments if I have made the proposed setup clear or perhaps I've not understood you. smile.gif
post #18 of 333
Quote:
Originally Posted by technogiant View Post

Thanks for those links Terrere, some good info in those.

I'm not really sure what I'm suggesting is covered by traditional refrigeration techniques though. Perhaps I didn't fully explain the setup.....I'm going for substantially sub-ambient temps, I'm currently running a fully sealed and insulated chillbox which consists of a window style ac unit with the evap enclosed in the chillbox and getting temps of -30c to -22c dependent on load, The chillbox contains air to cool the pc components which are also contained within the chill box.

My proposal involves replacing the air with a refrigerant gas that will liquify at those temperatures and so form a pool of liquified refrigerant I can submerge my mobo in.

I'm not considering any further compression/decompression stages, the liquid pool will solely be formed by the temperature within the chillbox which will be below the boiling point of the refrigerant gas.

The pc components will be cooled by direct evaporation of the refrigerant liquid which will be re-condensed in the cold temp of the chillbox caused by the ac units evap.

Much of the discussion above has simply been about how to safely remove the liquified refrigerant from the chamber into a pressure bottle between uses when the chillbox will return to ambient temps, not being a pressure bearing vessel it could not contain the refrigerant liquid which would boil off to form a huge volume of gas.

I think the system I've worked out to recover the liquid to the pressure bottle is actually used within industry and is called "cold line transfer"...so I've probably just reinvented the wheel again...but not being qualified in these subjects I'm just trying to brainstorm my way through as I go.

I'm unsure from your comments if I have made the proposed setup clear or perhaps I've not understood you. smile.gif

I misunderstood your intentions. biggrin.gif It's fine, I now get that you aren't looking for a subambient cooling system to create a component contained loop. thumb.gif After rereading your posts, I see that I just took the wrong impression from the initial post and it more or less "biased" my other readings. I will be watching to see how this turns out. biggrin.gif

BTW you have a self-contained version of what I was meaning. biggrin.gif The air conditioner does the compression, condensing, and evaporation methods of the coolant for you.
Edited by Terrere - 3/22/13 at 10:54am
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post #19 of 333
Thread Starter 
No problem Terrere.....I've changed my mind and considered so many different methods while thinking this one out I've confused everyone ....including myself....lol

But now I've thought out what I believe to be a fool proof way of recovering the liquid refrigerant I'm confident to go ahead with my favored method which is the full submersion one.

It eliminates many of the problems of the other methods I've considered and the only real drawback was the large volume of liquid refrigerant it would require....which I'm now sure I can safely contain.

Thanks for your input anyway Terrere....please feel free if you think of anything else. smile.gif
post #20 of 333
Thread Starter 
Quote:
Originally Posted by Terrere View Post

BTW you have a self-contained version of what I was meaning. biggrin.gif The air conditioner does the compression, condensing, and evaporation methods of the coolant for you.

Absolutely correct........the additional stuff I'm trying to work out is really just a method of delivering that cooling power as directly, effectively, simply and reliably as I possibly can to my pc components.
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