Anyone gone down the quite large reservoir road?

JonJ678

JonJ678

JonJ678

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I can remember, quite some time ago, proposing a water butt as a reservoir on here. Sadly I'm still not on the ground floor, don't trust the windowsill with 100kg, and for the sake of an easy life have to hide my insanity under a desk.

So, I've just ordered this, on the basis that it's fairly large, but will fit under a desk. It'll take a week to get here, sadly shops only stock the smaller ones.

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Stated capacity is 84 litres, and as it's polypropylene I'm fairly sure it'll be waterproof. The plan is to make a couple of holes in the lid and route my cooling loop through it. As I'm not willing to buy 80 litres of deionised water, I think it's going to have to be the tap. Bath is an exceptionally hard water area, so I'm going to jury rig a spare radiator to act as a heat exchanger.

Neglecting evaporation, and switching off my fans, I think at 350W I can get nearly three hours before the water temp goes up by ten degrees. It's not great I know. However at an average wattage of 200 (plucked from thin air) and including evaporation, I think around seven hours is plausible. There's definitely a chance of making it through the working day before the temperatures reach the point where switching fans becomes important, and it can then cool down overnight.

So, there's my plan. I should be able to determine conclusively whether this is viable or not within a fortnight or so. Any guesses?
 
well I wouldn't fill one of them with water, more than likely it will break with the force on the sides, good luck though
 
That's an interesting point. Can't say I'd thought of that.

Still, 44cm compares sufficiently favourably with the dimensions of my bathtub that I can fill it in relative safety, and it'll do me good trying to work out the force exerted on the sides.

edit: About 20kg acting on the longer sides, 12kg on the shorter ones. I can't say I'm entirely confident about that.
 
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Warn downstairs.

If you really want to try something with a massive reservoir then a fish tank would be more suited surely?
 
Biffa said:
I'd take the laundry out first mind..
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lol


I've seen someone do it on another forum and had a pond pump inside the tub.

It worked well but i would buy some proper water for it. Its not expensive.

Or if your going to use tap water boil it first and add Milton to it. Will kill anything that.
 
Yes. It ill take ages to pump all that water round. Eventually it will be just the same as having a small res. But for a few hour you will not even need a rad.
 
I think if I'm reading it right the op plans to immerse a radiator into the tub filled with water rather than use the big tub as a res

If your going to thT extent why not run some tubing to the nearest sink and keep the cold tap flowing ? With the plug that is heat will rise and escape via the overflow and you have a constant temp
 
Foxtrot26 said:
I think if I'm reading it right the op plans to immerse a radiator into the tub filled with water rather than use the big tub as a res

If your going to thT extent why not run some tubing to the nearest sink and keep the cold tap flowing ? With the plug that is heat will rise and escape via the overflow and you have a constant temp
Click to expand...

must not of read it properly im on my phone.

Total waste of time then.

My room is 28c when its warm so the water will be that to start off with.

turn on your computer and play a game and the water will just heat right up.

You could make a cup of tea if you used a small tub.

What a great idea computer that makes tea. Dragons den here i come lol
 
Regarding amount of water and cooling performance. Generally more is not better. A loop with no reservoir at all has the lowest resistance to flow, and the flow rate is consequently as high as possible. This is part of the popularity of T lines. A small reservoir helps remove bubbles. Beyond that, every litre you add significantly increases the thermal inertia of the system, it'll reach the same equilibrium temperature but it'll take longer to get there. That's where the cunning bit lies though. If your computer isn't under 100% load all the time, say the cpu is heavily loaded for a while then the gpu, the changes in wattage are damped somewhat by the water. You can have the fans spinning slowly all the time, rather than ramping them up under load. This concept extends this, currently my computer is on for less than 8 hours a day. If the reservoir is big enough, the water wont heat up enough while its on to be an issue, and it can cool down overnight. Evaporative cooling should help, but my estimates for this are rather crude.


I'm looking for a very cheap way of greatly increasing the thermal inertia of the system. It looks like I've gone for too cheap, and bought a box that'll break if filled with water, which would be a shame. Aside from that rather weak link (potentially solved by fish tanks, or a water butt) there is sense to the idea.

The radiator submerged in the water will be cooled very effectively to nearly the overall water temperature. I'm expecting less than a degrees difference between them, the water between the fins warms up and moves upwards to be replaced by cooler water from below like using a fanless radiator mounted horizontally in air. The much greater heat capacity of water is why I believe the temperture gap will be small.

I'm hoping that from a thermal point of view a heat exchanger in a static reservoir is the same as pumping directly through the large reservoir. One advantage is then that anything can be in the reservoir, tap water, chunks of ice etc, as long as it doesn't attack copper, brass or solder. Indeed one could run tap water through it straight from the tap. The second is that the computer pump doesn't need to be anything special, as it isn't dealing with accelerating static water in order to move it around the loop. This means the pump can be placed anywhere relative to the reservoir, and doesn't for example need to be lower than it. It also wont lose any more pressure than it would going through a radiator anyway.
 
only problem you have is that the water will always be room temp so the water going round the computer to start off with will be room temp. then will get hotter and hotter as you dont have anything to cool it.

would be better if you just use the water in the tub/tank as the water for the res and not just to cool the rad that you are putting into it.
 
Ah. Water cistern appears to be the magic word, the pictures on your link look like exactly the thing I was after when I ordered the box in the OP. Do you know roughly how thick the plastic sides are? Pleased to hear it works for you, improves the chance it'll work for me.

The water is always at room temp to start with, unless you're going the subambient route. The water inside the loop will warm up, and then lose heat to the large reservoir, which then warms up. It's the same wattage into the same mass of water when plumbed in directly as when there is a heat exchanger involved. I'll accept the temperature difference across the submerged radiator in order to avoid running tap water through my computer.

edit: your first paragraph says there's nothing to cool it, the second says it's cooled by the reservoir. I don't think I follow
 
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there is nothing to cool the loop other than the tank.

the heat will not transfer that fast.

its going to be a fail i think.

now if you use the tank as a res and not a cooler then i think it will work
 
Then I guess we'll wait and see. I think the box will break, but the water-through-radiator-fins will work fine.

I just dont get what you're saying. If the tank is a reservoir, and there's "nothing to cool the loop other than the tank", then there's exactly the same problem regardless of whether there's a heat exchanger involved or not.
 
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