Building your PC:
Thermal Control with Fans
Introduction
Modern computers generate lots of heat. They are electronic devices and one of the natural consequences of having an electrical field flowing through any medium with a modicum of resistance is the generation of heat as a consequences. This is why copper wire s warm up and the tungsten wire in a lightbulb glows. Of course, the modern computer relies on silicone devices which are termed semiconductors. These are not even very good conductors of electricity, which indicates that they have a very high resistance. As such they will produce a considerable amount of heat. Increased heat means increased motion of the atoms in the semiconductor which means decreased efficiency of operation and increased resistance... Which means more heat. The whole process becomes a vicious cycle until something gives. This is why some form of cooling is critical in modern computers.
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Computer Cooling: Fans
CPU Cooling:
As a semiconductor device, the CPU generates heat whilst operating. Without some form of cooling the temperature of the CPU will continue to rise until temperature generated by the flow of electricity into the CPU matches the heat loss of the CPU to the atmosphere. In real terms, for modern CPUs this state of equilibrium can be as high as 260°C well above the temperature at which the CPU itself will suffer damage. This temperature, of course, is dependent on the technology used in the CPU's construction, its operational frequency and the voltage at which it operates.
For reliable operation of the CPU the temperature at which it reaches thermal equilibrium with the outside air must be sufficiently low for the structure of the CPU to survive. Most modern CPUs contain thermal sensors incorporated into their design and internal logic within the CPU and the motherboard is intended to shut down the CPU if reasonable bounds are exceeded. However, this can be extremely inconvenient on a hot day when the CPU shuts your computer down every half an hour or so and it is probably unwise to rely on this as it is not universally implemented, and even if implemented is intended as a damage limitation feature and may not prevent the CPU temperature from reaching dangerous levels such that repeated incidents will cause premature failure of the CPU.
As a result some means of lowering the temperature at which the CPU reaches thermal equilibrium with the atmosphere is needed. This can be done passively by a heatsink which improves the thermal coupling between the CPU and the surrounding air which may be combined with positive airflow through the computer case driven by the fans in the power supply.
The heatsink is generally thermally coupled to the CPU with some kind of thermal transfer medium which maximizes the flow of heat from the CPU to the heatsink. This is shaped as a series of metal flanges that maximize the surface area of the heatsink, and thus optimize the contact between the heatsink and the air. This is generally an efficient means of heat transfer. However, in the enclosed confines of a computer case there is little air movement across the heatsink so that the CPU may still over-heat dangerously.
The way to overcome this is with a combination of a heatsink for optimal thermal transfer and a fan so that fresh, cool, air is constantly moving across the surface of the heatsink. As a result cool air is always in contact with the heatsink, maximizing the thermal transfer from the CPU to the air. This is by far the commonest means for cooling modern CPUs and most OEM (original equipment manufacturer) CPUs are provided with a heatsink and a fan. However, these integral cooling devices may be nowhere near as efficient as modern third-party cooling devices such as the one pictured left. These may well be quieter, have greater thermal capacity and efficiency as those supplied with the CPU.
The latest generation of cooling devices can be controlled by the motherboard's bios (increasing the fan speed as necessary) or they can have external controls so that the fan's rotational speed can be increased. Modern designs also include horizontal rather than vertical air flow so that the through-put of cold air across the heatsink is maximized. You should also note that if you're sourcing your own CPU cooling system it must match your CPU's socket design otherwise the heatsink will not fit properly over the CPU. You will also need to buy an appropriate thermal compound. This is important as it is the primary means of contact between the CPU and the heatsink. You will now have efficient cooling of the CPU but as a result the overall temperature inside your case which means that for efficient cooling you need to reduce the temperature inside the case itself.
Case Cooling
Your power supply provides a modicum of cooling for your system but, as modern components such as the graphics card also generate a considerable amount of heat which is all being pumped into the interior of your case.
Most modern cases have fixings within them for at least two case fans such as the one pictured on the left. These are large fans that direct a flow of air from the inside of the computer to the outside. There are usually holes on the opposite side so that cold air is drawn in as the warm air is expelled. This maintains the temperature inside the computer at a lower temperature than that of thermal equilibrium thus increasing the efficiency of component cooling. Use of more than one case fan increases the effective volume of air that moves across the components and increases the overall cooling efficiency.
Auxiliary or Additional Cooling
Dependent on the overall configuration of your system you may need additional cooling. One option for such a cooling device is a slot cooling system. This fits into a free expansion bay, and plugs into a free power cable from the power supply. It directly channels air from the inside of the case to the outside via the back of the computer.
