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So the hardcore solution is simply 4x 5970s/6990s watercooled each taking up 2 slots. If you want to do it w/ 4x 6950 you can however it is a lot of expense for roughly half the hashing power.
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Hardcore?
This is hardcore (sorry Jarvis) - rip the whole badly-designed BS off these cards and install them single-slot-style, in a logic board suitably modded to accept 4 cards without bumping into heatsinks etc. (or remove the heatsinks from the logic board).
Then dunk the entire logic board and cards into a tub full of some liquid that has both *incredibly* low electrical conductivity and *incredibly* high heat conductivity. Some pipes, a pump, a feck-off big heat exchanger and a very large, quiet fan (or multiple fans - whatever is required to pull air through the heat exchanger *quietly* but efficiently and, importantly, move a LOT of air) - job's a carrot's second cousin.
It could be that the heat density of both the CPU and GPU cores, plus certain components on the graphics boards that I'm *sure* cause me all the aggro (e.g. XFX put a nice heatsink on the GPU, but the bits that overheat are bare, uncooled RAM chips or VRMs) is simply too high for convection in a bath of inert fluid to be adequate cooling.
Would this be so? Hell - even with a broken fan, the components will hit over 100˚C but have logic built in to prevent 400˚C accidents. I'm not talking about using water (polar, too conductive even if 5 9s pure), or burn-the-house-down diethyl ether (hehehehehe) - but something that boils significantly over 100˚C and doesn't conduct electricity even when hot.
Even if the heat density causes hotspots, this can be solved easily enough because with the cards perpendicular to the logic board, a fluid pump positioned sensibly should cause a steady flow of cool (straight from the heat exchanger) fluid over the cards.
I'm not talking cryogenic fluids here (that'd be *extreme*, not *hardcore*
) - the entire rig should work at room temperature. High boiling point for the inert coolant is desirable to minimise evaporation - but a sealed system is also more feasible if the fluid isn't prone to high vapour pressure in the computation tubs - if the coolant isn't anywhere near boiling, a sealed system would be a LOT easier since pressurisation isn't anywhere near as high in the engineering problems to solve.
Apart from the warranty issues - the whole idea of home-brew water-cooling using waterblocks, home-made piping and domestic pumps / heat exchangers seems insane to me. Some of the biggest hot-spots on GPUs are small components like VRMs and capacitors. Most water-cooling systems put copper waterblocks over the GPU and memory. None of them can give a cool surface to ALL components, especially not the small but high-heat-density ones. So I'm bemused as to why the hardcore haven't tried to use the full-immersion cooling system more frequently.
Is it *really* that hard to find a suitable liquid coolant that is both electrically non-conductive (even accounting for potential contaminants, e.g. if the fluid is hygroscopic) and conducts heat well enough to serve as a coolant in a heat engine?
I've seen the few *extreme* types with bare PCs inside tubs of liquid nitrogen, etc. but those tend to be built 'because I can' rather than because the system really needed it. One of the old Cray supercomputers actually *had* the requirement for full immersion liquid cooling, rather than just the CPU. High-density computing such as bitcoin mining with lots of modern GPUs consuming many kilowatts in less than a cubic metre... I'd say that is getting very close to the point where full-immersion cooling would present *real* benefits.
Is anyone doing this in anger? Are there kits available, and have the bugs been worked out? I'd be keen to remove all the heatsinks and fans off my GPUs and put the *whole lot* into a tub full of inert coolant if the job was feasible. There's more heat capacity in a tub of coolant too... if the pump were to fail then I'd have more time for the machines to shut down before the coolant boiled off - it's not like our GPUs are nuclear fuel rods, but with just convected air, a powered GPU will burn out before software can stop it (hence the panic switches *on the silicon*)...
Bit of a hardcore option, but if these are *dedicated* miners.... Just chucking some ideas around, given my problems with cooling at the moment...