Cooling by Reservoir only?

Pumps and reservoirs
EtrnlFlux
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Cooling by Reservoir only?

Postby EtrnlFlux » Sun Nov 13, 2011 10:05 am

Sorry, just created an account, and going to be building my first water cooling system. Their is huge amounts of data I have been reading all over the internet about water cooling, and also looking into chemical solutions to further enhance cooling.

Anyways, my question is this. I plan to have a setup of:

Reservoir > Pump > CPU > Reservoir

How this setup I "believe" will work is a plastic or all metal box containing possibly two liters of water, in which will have an air tube dispersing bubbles throughout the water. I am kind of taking this on as more of a fun "science" project rather then trying to do some insane setup so I can overclock my system (Don't care to anyways, too much hassle and maintenance) :P

So this passive setup with no Rad, what do you guys see in it?

I am also looking into buying a pond pump for my pumping purposes, unless someone has a better idea? The pumps out on the market for things like this are extremely over inflated in price, hence my choice in a home depot variant. I also have noticed that computer pumps are plugged into the PSU rather than a typical wall socket, which I believe makes it more difficult to do a stand alone test of the water system for leaks before setup occurs.

Anyways, just some thoughts. Thoughts? Flames?

Izerous
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Re: Cooling by Reservoir only?

Postby Izerous » Mon Nov 14, 2011 6:14 pm

If you look at tests with massive passive radiators that are for more efficient than a large a ultra large res even they can't keep up over time. The problem your going to experience is that it might work in the beginning but the overall temperature of the res is going to continuously increase and eventually reach a point where it can no longer keep up. The better the passive equipment the longer this take.

As for testing a pump for leaks etc... you jump the a PSU with nothing but the pump connected and your done, or there are power bricks with molex connectors specifically designed to run molex power to a component strait from the wall.

And strait water even distilled water will eventually get bio contaminants without proper additives.
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Ace0751
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Re: Cooling by Reservoir only?

Postby Ace0751 » Tue Nov 15, 2011 9:05 am

My bet is your setup will fail within a couple of days. Buying a pump at your local depot store will not do any good, I say that cause you need to find the right tubing for that pump and install it on the PC component and the requires modding the blocks and fittings. Plain water will not do the trick, PC components get very hot and with the improper setup the water will boil and melt the tubing. And chemical solutions you have to be very careful on what you put in cause one slight mess up and it will not work.

Having a radiator in a setup is much needed not only will it dispense the hot air it will also keep the liquid from getting hot and melting the tubing and also leaks. Water cooling is not something to really mess around with especially if your components are expensive. Best bet is to read up on it a little more and see what beginners setup would be right and take the time to sit down and figure out what you want to get. I might come off sounding harsh but its better to be safe than sorry.
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schamp
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Re: Cooling by Reservoir only?

Postby schamp » Tue Nov 15, 2011 11:04 am

It sounds like you want cool the system by passing air through the cooling fluid. This may be a problem because increasing the amount of air dissolved in the fluid will increase resistance to flow and cause cavitation on the pump. It will definitely be a problem because contaminates from the air will dissolve into the coolant, and the presence of air and dust will facilitate both oxidation and microbe growth. For these reasons, the primary cooling loop needs to be closed - air is something we normally try to purge from our loops.

Of course, this does not rule out running a closed primary loop into an exchanger which transfers heat into a secondary exchange system. This can be as simple as a metal pipe or radiator assembly immersed in the liquid of a secondary cooling system - or use a plate exchanger to transfer heat to a separate loop. So drop a radiator into a water filled aquarium, and pump some air into the aquarium... But how much air? This is largely a function of mass.

To give you an idea bout the air mass required : I would estimate that my system idles with about 40cfm over the radiator, and at full load, it's about 200cfm. Do the math for atmospheric pressure and composition to find the mass involved. Heat transfer via bubbling air may be more or less efficient - I bet it depends on the size of the bubbles (smaller is better), and is actually less efficient even with tiny bubbles, so more air would be needed.

The holy grail is a passive system. As Izerous noted, large passive radiators can not keep up because they have insufficient ability to dissipate heat. They can -absorb- huge amounts of energy because of the large mass of metal and coolant they contain, but even though the amount of energy they dissipate increases with the coolant temp, they are still inadequate to keep the coolant at operating temperature over longer periods of operation.

To give you an idea, I tried to get my system simply to *idle* passively. I used an oversized radiator mounted in a hole cut into the top of my case, and have few restrictions to vertical air flow. This is a 1300W rated 4x120mm radiator and my system peaks at about 500W with an idle under 100W. With a 22c ambient and the system completely idle, it is stable using natural convection and a coolant temp of about 42c. But the pump's max operating temperature is 50c, and I needed to handle loads too, so I ended up spinning the fans at 20% under idle and scale their speed to max out at 40c under load.

Based on that experience, for a full passive system, I would expect to need a heat exchanger the size of a small cabinet to achieve sufficient heat dissipation to accommodate a mid range gaming rig.

Oh - and as far as chemicals go... Water is the baseline, and nothing you dump into it is going to radically change the specific thermal capacity or conductivity - and who cares if it does? No matter what the thermal capacity of the loop is, it's still finite, so the principle concern is still the dissipation rate, which the chemicals have a negligible effect on. The function of chemical additives is to reduce corrosion, kill microbes, and (optionally) look cool.

As for pumps on the primary loop... Some of the questions to ask in picking up pump are:

What is the flow rate vs head?
How will you connect it to the loop?
What is the MTBF?
What metals are used in the construction (a matter of Galvanic corrosion)?
How will you detect and shutdown on pump failure?
What is the fluid operating temperature range?
Is it fluid cooled or air cooled - and, if fluid cooled, how much additional heat is it dumping into the system?
How loud is it : will you still be sane 30 minutes after you turn it on?

As for system design - you should plan for at least two failsafes : pump speed / measured flow rate (flow rate is what matters, but pump speed is an acceptable proxy), and - unless you are absolutely 100% completely and totally sure that your system will maintain coolant temperatures below failure range in all imaginable circumstances - you need a failsafe based on coolant temperature. Mine is set to shut down via ATX off at 50c coolant temp.
If for any reason the coolant boiled, the tubing would get soft from the heat and the pressure would blow out one of the fittings, if not outright burst the tubing. A toasted PC that hit a thermal shutdown and maybe doesn't work anymore is something I could handle... I just *really* don't want to come home from work and find my carpet has been dyed red and the house smells like glycol.

And FYI, running a 12v pump manually is easy peasy. Just hot wire an ATX power supply with a paper clip. I have an old power supply I keep around so I don't have to go to the "massive trouble" of disconnecting the main supply to hot wire it and run my pump. If you don't have a spare, pick up a used / stupid cheap new one.


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