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Fan assemblies with this control input provide the ability to adjust the rotational speed of the fan without changing the input voltage delivered to the cooling fan assembly. A variable rotation speed allows the cooling rate to be adjusted to meet demand, quietening the fan and saving energy when full speed is not required.
A finned air cooled heatsink with fan clipped onto a CPU, with a smaller passive heatsink without fan in the background A 3-fan heatsink mounted on a video card to maximize cooling efficiency of the GPU and surrounding components Commodore 128DCR computer's switch-mode power supply, with a user-installed 60 mm cooling fan.
Where noise is an issue, larger, slower-turning fans are quieter than smaller, faster fans that can move the same airflow. Fan noise has been found to be roughly proportional to the fifth power of fan speed; halving the speed reduces the noise by about 15 dB. [22] Axial fans may rotate at speeds of up to around 38,000 rpm for smaller sizes. [23]
A centrifugal fan is a mechanical device for moving air or other gases in a direction at an angle to the incoming fluid. Centrifugal fans often contain a ducted housing to direct outgoing air in a specific direction or across a heat sink; such a fan is also called a blower, blower fan, or squirrel-cage fan (because it looks like a hamster wheel).
An axial fan is a type of fan that causes gas to flow through it in an axial direction, parallel to the shaft about which the blades rotate. The flow is axial at entry and exit. The fan is designed to produce a pressure difference, and hence force, to cause a flow through the fan. Factors which determine the performance of the fan include the ...
For a heat sink in a duct, where air flows through the duct, the heat-sink base will usually be hotter than the air flowing through the duct. Applying the conservation of energy, for steady-state conditions, and Newton's law of cooling to the temperature nodes shown in the diagram gives the following set of equations:
Hence, once we know the thermal power to be dissipated (Pd), the maximum allowed case temperature (Tc) of the CPU and the maximum expected ambient temperature (Ta) of the air entering the cooling fans, we can determine the fundamental characteristics of the required Heat sink, i.e. its thermal resistance Rca, as:
When the CPU uses power management features to reduce energy use, other components, such as the motherboard and chipset, take up a larger proportion of the computer's energy. In applications where the computer is often heavily loaded, such as scientific computing, performance per watt (how much computing the CPU does per unit of energy) becomes ...