Air – Is it Running Out of Gas?
When I first started working on electronics cooling it was at the end of what people sometimes refer to as the ‘bipolar age’. CMOS had become established, paving the way for PCs with very low power consumption. The cooling challenge was just to get the heat out of the box, making sure there were no major dead spots in the flow that would lead to overheating. Typical problems tended to be quite obvious, such as the air flow being blocked by a flat 25-pin strip cable used to connect up peripherals like floppy and IDE drives. Otherwise the cooling task was fairly straightforward.
Fast-forward to the present day and processor power consumption has increased almost a hundred-fold. The cooling solution is very different – from no heat sink to a massive air-cooled heat sink, often with integral heat pipes, and yes, in some cases liquid cooling. A whole liquid cooling sub-culture has grown up around overclocking PCs, games consoles etc. – for those who don’t value manufacturer warranties.
Apple’s dual 2.5GHz Power Mac G5 was liquid cooled, and first shipped in 2004 – almost 5 years ago. What I find interesting is that liquid-cooled systems aren’t more common today and I wonder why that is. I can think of several possible reasons.
From a purely technical standpoint using a liquid cooling system is much akin to using a heat pipe. It’s a very efficient means of moving heat from where it’s generated to somewhere it can be more conveniently removed – but the heat still needs to be removed. That means dumping it to the ambient air, which requires a radiator and a fan. This is much like a conventional car, where the engine is liquid cooled, but the car is air cooled.
Liquid cooling makes it possible to remove several hundred Watts per square centimeter at the package level. The limiting factor is the size of the radiator needed to dump the heat to the ambient air, and the fan (or fans!) needed to cool it.
Perhaps the added performance made possible by liquid cooling just isn’t enough to warrant the additional design complexity. Maybe consumers simply aren’t prepared to pay the necessary premium for the added performance and more expensive cooling solution. Or maybe the general public is just too concerned about leaks. What’s your opinion?
The next 5 years will be interesting, but until volumes of liquid cooled systems increase substantially, costs are going to remain relatively high. So it seems likely that the vast majority of CPUs and GPUs in consumer PCs will be air cooled for some time yet.
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