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Having talked about energy, we should also talk a little about temperatures. Heat transfer is a one-way street. Heat only flows from regions of higher temperature to regions of lower temperature. Applying this concept to computer cooling is not difficult. In the computer, items that generate heat will be hotter than items that cool them. If we ignore refrigeration, peltiers, and other low-temperature alternatives for a moment, then everything we are cooling can never be cooler than our room air.
This fact is so crucial that it’s worth repeating again. If we ignore refrigeration, peltiers, and other low-temperature alternatives, then everything we are cooling can never be cooler than our room air.
In typical water cooling, air is blown through a radiator to cool water. The water can never be cooler than the air flowing through the radiator. If the radiator is inside a poorly ventilated case, then the air going through the radiator may be five or more degrees Celcius warmer than room air. An additional temperature differential between the air and water is needed to transfer heat from the water to the air. In similar fashion, the CPU can never be cooler than the water flowing through the block. A temperature differential must exist to transfer heat from the CPU to the water block.
In this way we can consider the relative temperature differentials to be a measure of our cooling system’s performance. This also allows us to evaluate how well (or poorly) a given component within our system is performing. It should come as no surprise that shrinking temperature differentials to a minimum is both desirable and difficult. As we carry our discussion on to individual components, we’ll take temperature differentials into account for each one. This will allow us the power to evaluate each component on its own merits and help choose the right ones for our purposes.