Natural convection is one of the most effective cooling solutions for cooling electronics.The heat sinks commonly used in this area are extruded heat sinks, which are cutted and machined according to the assembly of electronic components. The main inconvenience of this kind of natural convection heat sink is that the heat transfer rate is very low, so this heat sink performance is not particularly good, how to design heat sink to improve the performance of natural convection heat sink? The following is the introdution to natural convection heat sink design. 

The fluid velocity in natural convection is very low, which limits the ability of heat sink to transfer heat to the environment. In order to improve the performance of the heat sink, the surface area of the natural convection heat sink should be as large as permitted in the application.

A good base thickness design must be thickened by the heat source part and thinned to the edge, so that the natural convection heat sinks can absorb enough heat from the heat source part to transfer rapidly to the surrounding thinner part.

Direct proportional relationship between heat transfer rate and free surface of heat sink. Increase this area, the performance of the natural convection heat sink is better, therefore the natural convection heat sink usually has complex profile and structures that calls heat sink shape.

Radiation also plays a major role in the performance of the heat sink, and surface finish will affect the emissivity of a surface and its ability to dissipate heat through radiation, so the heat sink should be treated, alumite, anodized or painted. This surface treatment improves the heat sink radiation performance and increase the heat dissipation efficiency of the heat sink, or its ability to radiate heat to other objects in the environment. The surface protrusion can increase the heat dissipation area, but when designing a heat sink for natural convection,it may cause the obstruction of the air layer and reduce the efficiency

Under natural convection cooling, the thermalresistance value (°C/W) will  change according to the power dissipation of the heat source. Higher power dissipation results in more heat and larger natural convection air flow. This will improve the performance of the natural convection heat sink and reduce thermal resistance.

1. 1. Considering that the temperature boundary layer is thicker under natural cooling, if the heat sink fin spacing natural convection is too small, the thermal boundary layer of the two fins is easy to cross, affecting the convection on the fin surface. Therefore, in general, it is recommended that the heat sink fin spacing for natural convection should be greater than 12mm, if the height of the heat sink fin is less than 10mm, the heat sink fin spacing of the natural convection heat sink can be determined according to the heat sink fin spacing ≥1.2 times the heat sink fin height.

2. The heat transfer capacity of the surface of the natural convection heat sink is weak, and the increase of ripple on the surface of the cooling heat sink fin will not produce the effect of natural convection, so it is recommended that the surface of the cooling heat sink fin without corrugated heat sink fin.

3. Because the time that natural convection achieves heat balance is longer, so the base of natural convection heat sink and heat sink fin thickness should be enough, in order to resist the impact of instantaneous heat load, suggest more than 5mm above.