Ever since our ape ancestors picked up the first bone, the first stick, the first flint, turning it over, tentatively weighing it in their hands and examining its potential use as a tool, an important question has haunted us throughout time, and plagued the smartest minds of humanity. That question is: “Can I watercool this? And if so, will it perform better?” This article aims to inform you of the basic fundamentals of water cooling. This is so you can expand your PC modding horizons, acquire street-cred with the modding crowd, and achieve a Zen-like state of enlightenment. And so you can stop spamming in the Exteme Cooling forums. The Principle. Anyone who has sat in front of a fan knows that moving air cools. This is because the breeze constantly replaces the air around your body, which has been absorbing the heat you radiate, with fresh, cooler air. Heatsinks and fans work in this way: the heatsink absorbs the heat from the CPU, GPU, whatever, and the fan creates a constant breeze of fresh, cooler air to take that heat away from the sink. Of course this process works better when more air can make contact with the surface of the heatsink, so heatsinks are generally built to have as large a surface area as possible. Hence all those fins and spikes. The problem is of course, that higher performing hardware has more heat to get rid of, and at some point: - air just isn’t cool enough anymore (both literally and figuratively); - the heatsink is so large that its weight threatens to snap your motherboard in two (if it will fit at all), causes you massive trauma when you try to lift the case, and requires enough copper for manufacture to supply a medium-sized economy with change; - the fan needs to be so powerful that it can lift an Airbus 380, and will shatter your eardrums and turn your insides to pulp with the noise it generates. OK, here comes the science bit. Concentrate… The issue is one of thermal conductivity, which is expressed in watts per metre-kelvin, or W/(m•K), or simply, k. I won’t bore you with what this all means, because then it gets way too complicated (and believe me, it is). All you need to know is that although a copper heatsink has a thermal conductivity of 385 k, which is good, air (at sea level) only has a thermal conductivity of a piffling 0.025 k. Which is bad --but hey, the heatsink has to lose its heat to something, and radiation just isn’t enough. However water has a thermal conductivity of roughly 0.60 k, which is 24 times better than air. Another way of looking at it is in terms of "specific heat". This refers to the amount of heat needed to raise a substance's temperature relative to water. Now air consists (roughly) of 80% nitrogen and 20% oxygen. In the case of nitrogen, its specific heat is approximately 0.25 so nitrogen needs 0.25 times the amount of heat that water needs to raise its temperature by one degree, that is 0.25 calories. In the case of oxygen this figure is about 0.22. So for air as a whole, this figure is roughly 0.24. That’s right, it takes four times as much heat to raise the temperature of water by one degree, as it does air. So what do we get? Not only does water conduct heat better, it also can absorb more of it in one pass. So you see the solution: replace air flow over the heatsink with water flow, and presto! Killer cooling. Science applied: Of course people have known about this for centuries. Back to sitting in front of a fan on a warm summer day: nice, huh? Now take a dip in a swimming pool. Which cools you down quicker? Engineers also know this (but in a much more technical way, involving lots more numbers), and applications of water cooling can be found everywhere, like for instance, in a car engine. We’re going to take a good look at that example because the principle is in fact very similar to what goes on in PC water cooling. What you see when you pop the bonnet (or hood, depending on your country of origin) is the following: a header tank containing coolant, traditionally a mixture of water and an anti-corrosive. The anti-corrosive is added to discourage rust and corrosion from forming on the metal components that the coolant gets into contact with. From the header tank tubes lead to a pump (usually driven by the engine, but sometimes also electric) which pushes the coolant through channels in the engine block. This cools the engine. That’s good, but the coolant now needs to get rid of the heat somewhere. As such it carries on to the car radiator, which is exposed to a stream of cool air. The coolant gets cooled down again, and flows from the radiator back to the header tank where the whole cycle starts all over again. Now there are some important points here and we’ll tackle them one by one. - The header tank is there for a good reason. Not only does it make it more convenient to fill the loop, but when coolant warms up, and expands in volume (as warm things do) it has somewhere to expand to. As such you will note that the tank usually has a “maximum” fill level somewhere below the filler cap, which you are not supposed to exceed. The header tank is also useful for trapping air bubbles that may get caught in the loop; - The engine block has channels running through it, which conduct the coolant and allow it to carry heat away from the engine. As such the engine block is also a waterblock… - Like with a heatsink, the effectiveness of the radiator is determined by its surface area. As such it has a large number of fins to make maximum contact with the cool air stream, but also a large number of long, winding channels to allow warm coolant to make maximum contact with the radiator (so it can pass on the heat to the radiator, which in turn passes it on to the air stream); - Normally a car moving forward at a fair clip produces a decent air stream (as any dog with its head out the window can tell you). This is why the radiator generally sits right in the front of the car. However if you drive, you will no doubt know the frustrations of rush hour, during which your car will often not move forward at all, or only very slowly. As such radiators often have a huge thermostat-controlled fan mounted behind them which will kick in and suck air through when the passive air stream by itself just isn’t sufficient. Now if you have been reading all this (as I’m sure you have…), you should now realise that a radiator sounds, in fact, just a glorified heatsink, not mounted on the heat source, but away from it, with water acting as a go-between. It is. But it’s a truly huge heatsink, much bigger than what could be created by just slapping some fins onto a rather compact heat source (like the engine, or a CPU). Some engines do, in fact, go that route (think of motorcycle engines or the engines of some propeller airplanes), but if you want efficient cooling that is not restricted by the dimensions or location of the heat source, water cooling is the way to go.