Like most electronic circuits, computers generate a lot of heat. As semiconductors get hot, their operating characteristics change, making them work erratically, or even not at all. Computers are especially sensitive to heat because the chips used in them are very dense CPUs, chipsets, and graphics processing units (GPU) are especially dense and therefore usually require heat sinks and dedicated fans to keep them cool. As these component coolers operate, hot air builds up inside the computer case, setting the stage for further harmful operating conditions. Other heat sources inside the computer such as the hard drive and expansion cards contribute to the heat problem. An AC axial cooling fan is often used to combat heat inside a computer.
An AC axial cooling fan works by flowing air along its axis. An axial fan is effective for cooling electronics because the shaft can be aligned with the heat source to either blow air on it or pull air past it. Because it is axial, the flow of air is very concentrated. When mounted in a computer case, an AC axial cooling fan will typically pull air into the unit from the front of the unit and past heat sinks that are attached to hot components, dissipating the heat. The hot air is then forced out of the computer as new, cooler air continues to enter from the front.
AC axial cooling fans are manufactured to operate well in hot environments, usually in the 70°C (158°F) range. With the harshness of the environment in mind, these fans are available with different types of bearings. Cheaper fans are likely to be equipped with sleeve bearings, which don’t last as long in high temperatures; for the fans used most often in computer cases use either ball bearing or fluid bearing fans. These are more expensive, but provide for longer life and consistent operation.
Computer power supplies usually have their own AC axial cooling fan that is build into the power supply unit (PSU). The placement of this fan helps to ensure that the critical power components don’t get too hot, reducing the life of the unit. Together with the axial fans mounted in the computer’s case, the system temperature can be prevented from reaching dangerous levels. Sometimes PSUs will have two fans, one for sucking in air and the other for expelling air.
In the computer case itself, a fan is usually mounted at a vented intake point in front of the case. This helps ensure that an adequate supply of cool air is always available as it pulls air from outside and blows it into the case. On the rear of the case, a second axial cooling fan is mounted that blows air out of the case. This makes sure that a strong flow of air is available to dissipate the heat generated by the computer’s components. Occasionally a third fan will be mounted on top of the case to help draw air away from the CPU.