# Passively cooled fish tank computer

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Posted · Original PosterOP

Hi everyone,

I'm new here and ready to make an ass out of myself. I've been interested in water cooling for a while, opting to go with an AIO Corsair unit in the interest of budget and safety. After watching some water cooling videos on LTT, specifically the whole-room water cooling, oil cooling, and scrapyard water cooling videos, some gears started turning in my head. My computer doesn't run hot but it is a bit loud and if I can make it quiet and cooler all in one go, all the better.

My solution is using an aquarium as a passively cooled radiator/reservoir combo, the idea being that the surface area of the water would dissipate heat without the need for fans or a separate radiator. I know that it wouldn't be nearly as efficient as an actively cooled system but my goal was for perfect silence and as few moving parts as possible. Following the information in the Watercooling 101 sticky thread and doing some of my own research and number crunching I came up with the following:

To calculate the number of hours it would take to heat the water in the tank you have 3.1 * Gal * ∆F / TDP = Hrs where Gal is the volume of water in gallons, ∆F is the temperature change in Fahrenheit, TDP is the heat generated by the parts being cooled, and Hrs is the number of hours it would take to reach the target change. The first stage of this project would be to just cool the CPU, which is rated at 140W TDP but the goal is to cool the CPU and both GPUs, which is a total TDP of ~440W. (Note: I would be running a submerged pump to reduce noise and haven't taken the pump's TDP into account) To find the right balance of tank size and time the system could be effectively cooled I plugged in the variables and came out with this chart:

(Temperature delta in F, results in hours)

30 degrees F is my baseline (100F/37.8C target - 70F estimated room temperature) with 50 being the upper limit (which would put the water at 120F/48C. I haven't seen any data comparing coolant temperature to CPU/CPU temperature, and I doubt it's 1:1, but 120F seems like a reasonable limit. So now that we have values for everything else we need to decide now long we want to keep the system at full load before hitting these temperature targets which will tell us our tank size. Looking at the 30 and 50 degree rows the 10 gallon column appears to give the best times for my typical usage, 2.1 hours and 3.5 hours respectively.

Another variable, which will either depend on or determine the outer diameter of the tank is heat loss due to evaporation and radiation which is dependent on the surface area of the water. One tank I'm looking at is cylinder with a surface area of 1.07 sq ft. Using this chart as reference we get a BTU/hr loss of 230 which translates to 67.4 watts/hr when the water is at my 100F target and 137 watts at my 120F target. It's not going to dissipate the whole 440w load but it will slow the rate at which the water warms, and it also assumes there's no air moving across the water so the efficiency could be a little higher. If I need to increase the amount of heat being shed I could also run a standard radiator mounted to the top of the PC.

Like I said, I would be starting with just cooling the CPU which is only 140W. The chart for that looks like this:

(Temperature delta in F, results in hours)

6.6 and 11.1 hours at full load, not taking the natural cooling of the water into account, is certainly doable.

With all of that out of the way, does anyone see a reason this wouldn't work? The main issue I see right now is finding a submersible pump that will supply enough flow without adding too much heat to the water.

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Yeah! Numbers! Yeah! Charts! Cool!

But, I have no idea if that would or wouldn't work, but that is a great idea!

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-SNIP-

Welcome to the Forums!

For your idea it will work no problem the main thing in oil cooled PC's is removing the heat from the oil and dissipating it into the air via the rads. Since oil has a low heat capacity it can't carry away heat from the tank into the rads as quickly as water would but water is a whole different story.

For the pump you can submerge a Laing D5 pump into the oil it's more than powerful enough for pushing the oil around.

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If you are thinking you can use water to cool it you are going to have every single component short out and die. Mineral oil is used to cool fishtanks PC's.

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Posted · Original PosterOP

So I think there's some misunderstanding with what my goal is. First, no oil. No oil anywhere. This is 100% water. Second, I'm not submerging my computer in water. Please see this extremely technical diagram I made to illustrate the idea.

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So I think there's some misunderstanding with what my goal is. First, no oil. No oil anywhere. This is 100% water. Second, I'm not submerging my computer in water. Please see this extremely technical diagram I made to illustrate the idea.

-PIC-

The poor fish!!

But yeah don't put anything in the tank, this method of cooling will work but not for extended periods of time since it needs a way of dissipating the heat from the water other than the sides of the tank it won't be super effective.

Also it'll potential get contaminated if it's not a sealed loop and the extra exposure to UV light if it's a fairly bright room will break down the biocidal agent.

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Posted · Original PosterOP

When you say not to add anything, do you mean anything? I was planning on adding colored aquarium rocks, scuba driver, typical aquarium stuff. No fish, obviously, unless I can find a fake one that looks the part. Everything would be washed and sanitized before going in.

I was planning on running a biocide, but I didn't know it brakes down in UV. It won't be hard to keep it away from windows. Is there a way to test effectiveness of the agent? Or should I expect to replace the water and agent periodically?

While thinking about how this system would work I realized it would act as a heat capacitor. I'm typically not using my computer for prolonged periods and if I'm using it for more than 2 hours I'm usually not using it at full load, so it should be okay. If I'm not getting long enough usage periods out of the system I figure I can start investing radiators to passively cool the water before it enters the tank, or worst case I could add a 250mm fan to the top of the tank to actively cool it without adding much, if any, noise.

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When you say not to add anything, do you mean anything? I was planning on adding colored aquarium rocks, scuba driver, typical aquarium stuff. No fish, obviously, unless I can find a fake one that looks the part.

I was planning on running a biocide, but I didn't know it brakes down in UV. It won't be hard to keep it away from windows. Is there a way to test effectiveness of the agent? Or should I expect to replace the water and agent periodically?

While thinking about how this system would work I realized it would act as a heat capacitor. I'm typically not using my computer for prolonged periods and if I'm using it for more than 2 hours I'm usually not using it at full load, so it should be okay. If I'm not getting long enough usage periods out of the system I figure I can start investing radiators to passively cool the water before it enters the tank, or worst case I could add a 250mm fan to the top of the tank to actively cool it without adding much, if any, noise.

I meant anything live but yes fake fish and other things are no problem. The thing with this setup and having a few rads it's just a watercooling loop with a large exterior reservoir which will take longer to heat up. I would not suggest adding a fan to the top of the water since it would cause dust or debris to get in it's best if you can to get an airtight or closed lid for that tank.

For biocide they diminish at different rates depending on the biocide so it's hard to tell, you may need to add some every couple of months but I'm not sure.

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Posted · Original PosterOP

Having it open-air, or at least having a cover that didn't restrict air flow, was part of the passive cooling that would not only keep the water from heating up as quickly but also allow it to cool down once the computer had gone to idle or been shut off. Is the issue that dust or other contaminants would work it's way into the water blocks or auxiliary radiators? Is that something that an aquarium filter would prevent?

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Having it open-air, or at least having a cover that didn't restrict air flow, was part of the passive cooling that would not only keep the water from heating up as quickly but also allow it to cool down once the computer had gone to idle or been shut off. Is the issue that dust or other contaminants would work it's way into the water blocks or auxiliary radiators? Is that something that an aquarium filter would prevent?

Hmm I'm not sure if an aquarium filter would work and it is mostly to ensure no debris gets back into the loop or blocks which can get blocked. Mainly an airtight cover is to prevent evaporation of the tank.

This would be an interesting build to see happen cause I'd be interested to know how long the temps stay around room temp from the water reservoir until it starts to heatup.

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Why not just get a normal loop because moving this thing is going to be a bitch, cleaning it out as well.

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I was getting extremely excited. My ultimate PC goal is to build a PC with fish living inside it.

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Having it open-air, or at least having a cover that didn't restrict air flow, was part of the passive cooling that would not only keep the water from heating up as quickly but also allow it to cool down once the computer had gone to idle or been shut off. Is the issue that dust or other contaminants would work it's way into the water blocks or auxiliary radiators? Is that something that an aquarium filter would prevent?

One thought or suggestion I have, and I have no experience with water cooling mind you, is planting everything in the tank firmly, making sure everything is secure, then get a sheet of acrylic, cut to the size of a lid for the tank, add holes for filling, draining, and of course the to and from the res, and finally completely seal the tank except for the ports. Then to keep it passively cooled with the option to change that, keep two large radiators on the top of the tank for coolant to run through before hitting the tank. If temps get too high, add fans, no prob. You can also use or modify the original top (black cover sorta thing?) to hide the rads.

I dunno if what I'm saying makes sense but I can draw a diagram tomorrow.

And as a suggestion for decor in the tank, throw some dead PC parts in their instead of scuba divers or something. Maybe find the reference cooler to a GTX Titan or something. I think it would be neat lol.

Why not just get a normal loop because moving this thing is going to be a bitch, cleaning it out as well.

From a realistic perspective, a normal loop is just as stupid of an idea considering how much money you'll waste on it for marginal, if any gains, not to mention the extra time in building, maintainence, and risk of leaks. It's an enthusiast thing.
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From a realistic perspective, a normal loop is just as stupid of an idea considering how much money you'll waste on it for marginal, if any gains, not to mention the extra time in building, maintainence, and risk of leaks. It's an enthusiast thing.

-pump

-tubing

-CPU block

-GPU block

-fittings

So honestly the price of adding a rad and a resivour won't be that much more expensive then the cost of a fish tank.

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-pump

-tubing

-CPU block

-GPU block

-fittings

So honestly the price of adding a rad and a resivour won't be that much more expensive then the cost of a fish tank.

Personally I'd just do a normal loop but if he wants to experiment I don't see any problem with that setup as long as he can keep it from going green.

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Personally I'd just do a normal loop but if he wants to experiment I don't see any problem with that setup as long as he can keep it from going green.

Yea I guess to each there own, but computers are heavy enough as is let alone adding a 10 gallons of water.

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Yea I guess to each there own, but computers are heavy enough as is let alone adding a 10 gallons of water.

Yeah don't want to be moving that around.

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Yeah don't want to be moving that around.

Yea that would be a 20 pound PC with 80 pound of water, so nope that's not going to your buddies LAN anytime soon.

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Very cool idea. I'd love to see it happen!

But be sure you use one or two large passive radiators to precool the water. You PC produces around 100 watts at idle, so the tank can alone cann't cool down in idle periods.

Also you are better off sealing the loop what means you cover the tank. This will enlargen the periods between cleaning the loop a lot.

Mineral oil and 40 kg aluminium heat sinks are a perfect combination: 73 cores and a Titan X, Twenty Thousand Leagues Under the Oil

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Posted · Original PosterOP

Hmm I'm not sure if an aquarium filter would work and it is mostly to ensure no debris gets back into the loop or blocks which can get blocked. Mainly an airtight cover is to prevent evaporation of the tank.

This would be an interesting build to see happen cause I'd be interested to know how long the temps stay around room temp from the water reservoir until it starts to heatup.

Not taking evaporation, radiation, or anything else into account this is what the thermals look like over time given a range of heat being introduced into the tank:

..Then to keep it passively cooled with the option to change that, keep two large radiators on the top of the tank for coolant to run through before hitting the tank. If temps get too high, add fans, no prob. You can also use or modify the original top (black cover sorta thing?) to hide the rads.

I get what you mean. The tank is supposed to be aesthetic as well as functional so I'm hesitant to put heat sinks anywhere near or on the tank. If I do use them I'd get a double or tripple 120mm radiator to put on top of the computer case and run the 'exhaust' line to the tank from there. The whole purpose is to have a completely fanless gaming computer, but if it becomes unsustainable I could also put fans on top of the radiator and turn them on above a certain water temperature.

Yea that would be a 20 pound PC with 80 pound of water, so nope that's not going to your buddies LAN anytime soon.

I don't LAN; this machine only moves when it gets new hardware and now the motherboard is completely maxed.

Very cool idea. I'd love to see it happen!

But be sure you use one or two large passive radiators to precool the water. You PC produces around 100 watts at idle, so the tank can alone cann't cool down in idle periods.

Also you are better off sealing the loop what means you cover the tank. This will enlargen the periods between cleaning the loop a lot.

Are there any numbers on watts or BTUs radiators dissipate passively? It'd be nice to be able to add that into my thermal models.

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Are there any numbers on watts or BTUs radiators dissipate passively? It'd be nice to be able to add that into my thermal models.

You can't use "normal" radiators because the finns are to close for natural convection.

Hmmm they don't dare to say how much K/W their but I estimate you can reach 0.5 K/W with a Alphacool Cape Cora HF 642. Or you simply buy a standart extruded heat sink and mount a heat exchanger on it.

Mineral oil and 40 kg aluminium heat sinks are a perfect combination: 73 cores and a Titan X, Twenty Thousand Leagues Under the Oil

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Posted · Original PosterOP

Oh jeez, I didn't know that big, passive radiators were a thing. If it really can cool ~500W that pretty much negates the need for the fish tank as a heat sink and demotes it to a reservoir, making the size virtually irrelevant. Hm...

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I do cool ~450 watts passive: 3 400x300x84mm heat sinks, with a total weigth of 40kg. It's possible, but requires some heavy modding.....

Mineral oil and 40 kg aluminium heat sinks are a perfect combination: 73 cores and a Titan X, Twenty Thousand Leagues Under the Oil

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My 2 cents.

My computer has been running passively with a large plastic bin as the res with both CPU and GPU in loop for close to 2 years now.

CPU: FX 8150

GPU: HD 5770

The plastic bin is the large kind from canadian tire with a lid on it.

Temps are not so great.

Water heats up to about 30C+ over time. GPU stays quite cool though, around 50-60C. CPU temps are quite high, prime95 will knock it out at 80 - 90C, albeit the cpu block is an ebay block. GPU block is EK universal.

So my fx 8150 is underclocked and everything is fine and dandy.

Let me know if you need any more details, because this method is completely feasible.

If youre using a glass aquarium as well, heat transfer will be better than the thick plastic bin.

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Posted · Original PosterOP

What are the dimensions of the container? Funny enough, we don't have Canadian Tire in America so I don't have a reference. Is the container sealed? How often is the system turned off? Idle temperatures?

80-90c is pretty hot; My Phenom II X4 965 is overclocked from 3.4 to 3.8 and doesn't hit 60 under full load on my AIC water loop now.

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