[safemode]

I'm just a little curious as to how big of a radiator is necessary and how big of a pump is necessary to passive cool a athlon / P4 system. If anyone has tried it before and all. When making my system i decided to see how it would run without the heatercore's fans on and it slowly rose into the 60C range before i turned it off. The ambient temp at the time was around 80F and i'm using the standard d-tek heatercore. I figured that if it takes a 120mm fan at ~80cfm to cool a heatercore and keep my processor at it's current temp i'd need an extremely large heatercore to cool at roughly 1-5cfm caused by convection.

The heatercore is about 26026mm^2, and the fan only covers about 14400mm^2, so the cfm of air touching any given part of the heatercore is actually 55% of the cfm of the fan or 44cfm. So it only takes 44cfm to cool my computer. Also, it means for every square mm of heatercore it's dissipating 0.0025 watts from the 66watts my cpu is giving off. The cfm per mm is 0.0017. So we get a ratio of 1.5 of watts to cfm. Now, we know that this ratio is constant so if my cfm per mm is greatly decreased then my watts per mm will have to be greatly decreased to keep the ratio.

We know the watts is constant at 66 and we guess the cfm due to convection is like 1 or 2. So we solve for heatercore size.

looks something like this watts/mm^2 * x / cfm/mm^2 = 1.5 x then gives us the percentage of watts needed to keep the ratio so we set another equation that says
x*watts/mm^2 = watts / y , y is then our new radiator. I got something like 572668mm^2 which if square would be 75.6cm x 75.6cm or 29" x 29" for a 2" deep radiator like the d-tek kind. So according to really bad calculations, to passively cool the computer you would need a heatercore that is 29 inches by 29 inches and a pump that could keep the flow rate the same as if it was 6" by 7". Of course i'm assuming my ratio of 1.5 remains constant if my cpu temp remains constant which it should since i'm not trying to cool more or less, just the same.


so to sum it up, according to theory I would need a heatercore that is 29" x 29" to keep my cpu as cool as it is now with my 6" x 7" heatercore. Does anyone have any real life experimentation with this who has had more success? The kind of pump required to power such a passive system would be huge.

[SkiFletch]

well, I can offer my own experience with passive only cooling. I managed to get my hands on a big Serck radiator of approximately 14x6x2 inches in fan area. the material actually appears to be stainless steel. I can no longer get accurate temperature readings as my frikkin thermal probe broke, but while it was working, I would get temps of around 50c idle and 53c load cooling a tbird running at 1642 with 1.85v, and the chipset of my nforce mobo. the waterblocks used under that configuration were gemini high flow and gemini spiral. and if you check on the wattage per square cm for that overclocked tbird was quite high (in the 90s i think, been a while since I checked). hope this helps out a bit.

oh, and the pump was a via aqua 1300

[JFettig]

heres what iv used for passive cooling rite around room temp, a LARGE 2x3ft container, just run in and out of that, and to keep your water rite at room temp, stick a 25cfm fan in the corner, it works sooo great! just takes up space

[Iron Hawk]

I can hook you up with a huge azz heatercore for $60

[[EG]~NaTz~]

frodo has a huge rad ull need maybe 5 1800gph magdrives to pump though it though and im sure u could pasivley cool wit that bad boy!

[safemode]

Originally posted by maskedgeek
heres what iv used for passive cooling rite around room temp, a LARGE 2x3ft container, just run in and out of that, and to keep your water rite at room temp, stick a 25cfm fan in the corner, it works sooo great! just takes up space

big resevoirs are not passive cooling. The evaporation of the water to the air is active. Basically phase changing.


in passive water cooling systems the water is just a transporter of heat from source to heat dissipator. It's true that you're not using any electricity to cool your computer, but you are using and losing water. which is the same thing.

[safemode]

if you aren't losing anything ie. spending anything to cool then you're passively cooling. If you've got to introduce something to the setup then you're actively cooling. Whether you are introducing water or electricity, it doesn't matter. It's you actively cooling the system. Passive systems should not require anything external to cool the system. A big resevoir requires water as it evaporates or it eventually fails. A fan based system requires electricity. etc etc.

[JFettig]

the only true passive cooling for something like that would be a heatpipe, because you cant stick a massive heatsink on your cpu, and using a pump would mess it all up because thats electricity

[safemode]

well, with a pump you're spending something but that doesn't result in the removal of heat, just helping to move it from point A to point B. For the sake of feasibility i'd be willing to accept tec's and pumps as a heat transport fascilitator. Is there even a way heatpipes can be made to allow for passive cooling? They would have to move heat from the size of a square centimeter to a few thousand square centimeters.

i'm only making the distinction in this case because the energy / fluid is not being used to move heat outside of the cooling system, but stay in the cooling system. If the pump happened to absorb heat then it would not be valid.

[Diggrr]

Have you by chance, a coil of copper tubing available?
A heatercore would make a poor passive cooler because the fin density doesn't allow easy convective air currents to flow through it, almost requiring a fan to force airflow. It does allow some, but not enough as you're seeing.
Almost any passively aircooled system would require air currents to carry away the heat, because air is so poor at absorbing it in the first place, it can't be static...thus the need to have an open design heat exchanger to allow a convective flow, and alot of surface area presented to the air.

Look at the back of a refrigerator, and you'll see the open, passive cooling radiator in use (the refrigeration sytem is active, but the heat radiator is passive).

[grim]

you could just pump your water into an underground tank like bladerunner did

[safemode]

That's valid. but i'm looking for solutions that are somewhat practical. Meaning it is something that can go with the computer and be used in multiple places. Right now the leading idea is a thin radiator that replaces the sides of a computer with dimensions of about 27"x18" . A pump inside the computer could power a fluid through the two radiators and hopefully you get enough convection to create the amount of cfm per area needed to remove the heat per area. which would be around 1-3cfm for such a size radiator. I think that would be feasible. The problem is getting a pump that would be quiet yet powerful enough to get the flow of water through that size of a radiator and waterblock without it slowing to a dribble and frying everything. In fact that would look pretty cool to have anodized black thin radiators making up the sides of yoru case, up on hinges so you can open it without having to disconnect anything. no fans to speak of cept maybe in the power supply. I'm sure a couple maxi-jet 1200's could handle the job.

[papounet]

Have you look at house heating elements ?
The latest design I saw (for a bathroom I am refurbishing ) looks like a steel thin tank (2 sheets seprated by 1cm) plus a lot of fins arranged like T_T_T on the back.

I found one made in steel H 292 mm W 800mm rated at 275 W
but I believe this rating is based on central heating flow and water temp.
Others are made of aluminium or may include more than 1 pannel.

Some radiator are advertised to work with low temperature (like heat-exchanger system).

[wildfrogman]

Are you still going to have the fan in the psu? If so you may be able to duct that air a bit and use it. Maybe that would help temps a bit.

[safemode]

you're gonna try and duct air from 80mm^2 from something like 572668mm^2 heh. Such a duct wouldn't have much of an effect.

[Frodo Baggins]

Originally posted by [EG]~NaTz~
frodo has a huge rad ull need maybe 5 1800gph magdrives to pump though it though and im sure u could pasivley cool wit that bad boy!

nah, I got a car rad I found in the dumpster in front of Yodum's house,. It seems to be leaking at the nozzle near the top of the rad. It's just a normal car rad, bigger then a full tower

If you want to passive cool, tye havin a BIG BIG BIG res, like a fisk tank. The bigger it is,t he mosre heat it'll take to heat it up

[safemode]

that does and means nothing in a closed loop system. Open systems aren't really passive. You leave it alone long enough and you run out of water. I'm talking low density very large radiators. 18"x28" on both sides of the case. Basically we're talking about a fanless system because it's going to be physically impossible to passively cool the processors we use today (athlon / p4). We could even get away with only a couple pumps by using a tec to increase the area we have for a heat source, allowing the use of a larger waterblock to make up for the fact that the flow isn't as high as in normal systems.