FORCED-AIR COOLING

Figure 1-3.—Forced-air coding. FORCED-AIR COOLING The increase the cooling effect over that provided by convection cooling, forced-air cooling (fig. 1-3) uses a blower to provide air movement instead of the natural convection currents. Cool air is drawn into the equipment enclosure and flows past the heat producing part, picking up the heat. The air is then exhausted out of the equipment. An air filter is provided at the air inlet to remove dust and dirt that otherwise would settle on the internal parts of the equipment. The air filter must be kept clean according to the equipment’s maintenance requirements. This will ensure maximum air movement and cooling. In some equipment, a honeycomb rf interference filter is installed on both input and outlet to prevent stray rf from entering or leaving the equipment cabinet. This filter can also collect dirt that can reduce the airflow. Failure of a bearing in the blower motor is not an uncommon problem. A replacement of both blower motor bearings or blower assembly is warranted at the first sign of abnormal operation, such as excessive noise or vibration. It is better to replace the bearings than to risk damage to the equipment that the blower motor is designed to protect. AIR-TO-AIR COOLING Some units of electronic equipment are hermetically sealed to prevent the entrance of moisture. For equipment of this type, an air-to-air heat exchanger (fig. 14) is used to prevent the air inside the equipment enclosure from mixing with the outside air and still allow cooling to take place. Air moving past the heat producing part absorbs heat and is forced through a heat exchanger by an internal blower. The heat in the internal air is absorbed by the heat exchanger. The cooled internal air is then returned to the equipment interior to continue the cycle. Figure 1-4.—Air-to-air cooling. 1-2