Convection cooling is the mechanism where heat is transferred from the hot device by the flow of the fluid surrounding the object. The fluid can either air, which is the most common, or another suitable liquid.
During the cooling process the heat causes an expansion of the fluid and a reduction in its density. The difference in density causes the fluid to flow and as this happens, the hotter, expanded, and less dense fluid carries with it some thermal energy. This results into the energy transfer from the hot object into the surrounding air or liquid.
The effectiveness of the cooling depend factors such as:
- Temperature difference between the surrounding and the hot object
- Viscosity of the fluid (air or liquid)
- Rate of the fluid’s thermal expansion
- Shape, size and surface texture of the object
- Ability of the fluid to move in response to the density difference
Most enclosed electronic equipment are made with several vents on their enclosures or casings to allow for the natural exchange of air. A heat sink may be attached to the power devices to increase their heat dissipation area. This allows more heat to be being transferred away from the device, first by conduction from the device to the heat sink, and then by convection cooling from the heat sink to the ambient air.
There are two types of convectional cooling, namely the natural convection cooling and the forced air convection cooling.
Natural convection cooling
In the natural cooling, the air surrounding the object transfers the heat away from the object and does not use any fans or blowers. Most electronic components are rated for natural convection cooling with the assumption that the surrounding air is always cooler and remains within a certain temperature range.
Advantages include being cheap, and easy to implement as well as maintain due to the fact that it does not use fans which may require regularly maintenance and replacements. The other advantage is the reduction in acoustic noise and vibrations.
Forced air convection cooling
This is used in designs where the enclosures or environment do not offer an effective natural cooling performance, in high power applications, and other areas where natural cooling is not effective.
The forced air convectional cooling uses a cooling fan to blow and direct air towards the electronic components with or without heat sinks. Most power supply units have built-in fans that provide the require forced-air convectional cooling.
Type of fan may be determined by the heat to be dissipated, space available and in some instances the required amount of air flow for the device as specified by the manufacturer, usually in cubic feet per minute that guarantees maximum rated out power from the device.
The forced air convection cooling is the most effective cooling method used in power supplies. It can be customized to provide the required cooling performance and increase the efficiency of the components and hence that of the whole.