Heatsink Design and Selection
Design factors which influence the thermal performance of a heat sink
The heat transfer from the heatsink occurs by convection of the surrounding air, conduction through the air, and radiation. Heat transfer by radiation is a function of both the heat sink temperature, and the temperature of the surroundings that the heat sink is optically coupled with. When both of these temperatures are on the order of 0 °C to 100 °C, the contribution of radiation compared to convection is generally small, and this factor is often neglected. In this case, finned heat sinks operating in either natural-convection or forced-flow will not be effected significantly by surface emissivity.
In situations where convection is low, such as a flat non-finned panel with low airflow, radiative cooling can be a significant factor. Here the surface properties may be an important design factor. Matte-black surfaces will radiate much more efficiently than shiny bare metal in the visible spectrum. A shiny metal surface has low effective emissivity due to its low surface area. While the emissivity of a material is tremendously energy (frequency) dependent, the noble metals demonstrate very low emissivity in the NIR spectrum. The emissivity in the visible spectrum is closely related to color. For most materials, the emissivity in the visible spectrum is similar to the emissivity in the infrared spectrum; however there are exceptions, notably certain metal oxides that are used as "selective surfaces".
The vast majority of ABL Components' Heatsinks - single piece extrusion, customised extrusion, BGA and board mount - are black anodised on-site at ABL to assist performance. High powered extrusions - because of their unique manufacturing process - are not black anodised because the performance of these heatsinks has been optomised by the excellent surface area created by the high fin ratios utilised in these designs.