In the natural exchange of heat energy, heat is transferred from higher to lower temperatures, a phenomenon known as heat transfer. There are three types of heat transfer: heat conduction, heat convection and heat radiation. Among which, heat convection is the movement of molecules in a fluid and often occurs when there is a temperature difference in the fluid or between the fluid and the solid. Differences in temperature can cause differences in density between fluids. When a liquid or gaseous substance is heated, the volume expands, causing the density to decrease and the substance gradually rises, with the original position replenished by the surrounding low-temperature and high-density substance, before the substance is then heated and rises again, with the surrounding substance adding to it, so that the cycle spreads the heat from the fluid to everywhere, i.e. heat convection.
In heat transfer, convection is classified into natural convection and forced convection. Natural convection is a phenomenon that occurs when there is a temperature difference between fluids, such as hot air rising and cold air falling (because hot air is less dense than cold air so it rises whereas cold air is more dense than hot air so it falls). Forced convection is the phenomenon of convection caused when a fluid is driven by an external force (e.g. by a pump or fan). For example, in an electric fan heater, the air is heated when the wind blows over the heating element, or when a person blows on food, the temperature of the food is lowered because the air is cooler and forced convection is used.

The local heat flux can be written as
 

where h is the coefficient of heat convection, the higher the h the better the heat convection effect.
Factors affecting the heat convection coefficient include the state of fluid movement (velocity and direction), the type of fluid and its physical properties, the shape and surface condition of the heat transfer of solid, etc. In the case of heat sink fins, fins with tighter fin spacing are more effective in dissipating heat, but if the fin spacing is so small that air cannot enter between the fins for heat exchange, the effect is reduced. A thermal simulation can be performed to identify the optimum fin spacing.
Generally speaking, heat sources below 10W can be cooled by natural convection using fins with holes in the casing to increase air convection, while heat sources above 10W need to be cooled by forced convection.

Editorial staff T-Global Marketing

Author T-Global R&D team Team introduction – A team of professional heat flow engineers, with independent and innovative research and development, provides customers with preliminary thermal simulation planning and institutional heat dissipation design consulting. In the face of evolving market trends, they can quickly respond and continue to provide innovative anti-heat solutions.