General guidelines for heat sink design
1. Natural convection heat sink design
——The design of the heat sink can make a preliminary design on the envelope volume, and then make a detailed design on the details of the heat sink such as fins and bottom dimensions
1. Envelope volume
2. The bottom thickness of the heat sink
A good bottom thickness design must be from the heat source part thick and thin to the edge part, so that the heat sink can absorb enough heat from the heat source part to quickly transfer to the surrounding thinner part.
3. Fin shape
The thickness of the air layer is about 2mm, and the grid between the fins needs to be above 4mm to ensure smooth natural convection. But it will reduce the number of fins and reduce the area of the heat sink. A. The grid between the fins becomes narrower-the occurrence of natural convection is reduced and the heat dissipation efficiency is reduced. The fin space becomes larger-the fins become smaller and the surface area is reduced.
Fin thickness
When the shape of the fin is fixed, the balance of thickness and height becomes very important, especially when the thickness of the fin is thin and high, it will cause difficulty in heat transfer at the front end, so that even if the volume of the heat sink increases, the efficiency cannot be increased.
Thinning of the fins-the ability of the fins to transfer heat to the top becomes weaker
Thicker fins-fewer fins (reduced surface area) Increased fins-the ability of the fins to reach the tip becomes weaker (the volumetric efficiency becomes weaker) Shorter fins-reduced surface area.
4. Surface treatment of heat sink
Alumite or anode treatment on the surface of the heat sink can increase the radiation performance and increase the heat dissipation efficiency of the heat sink. Generally speaking, it has little to do with the color of white or black. The sudden drop of the surface can increase the heat dissipation area, but in the case of natural convection, it may cause the obstruction of the air layer and reduce the efficiency.
2. Forced convection heat sink design
——Increase the thermal conductivity
(1) Increasing the air velocity is a very straightforward method. It can be used with a fan with a high wind speed to achieve the goal.
(2) The flat fin is cross-cut to cut the flat fin into multiple short parts. Although this will reduce the heat sink surface, it will increase the thermal conductivity and increase the pressure. When the wind direction is indeterminate, this design is more appropriate. (Such as the heat sink on a motorcycle)
(3) Needle fin design. Needle fin heat sinks have lighter and smaller n-points, as well as higher volumetric efficiency, and more importantly, they are isodirectional, so they are suitable for forced convection heat sinks, such as As shown in Figure 9. The shape of the fins can be divided into rectangular, circular and oval. The rectangular heat sink is made of aluminum extrusion cross-cut, and the round can be forged or cast. The heat transfer of the elliptical or droplet-shaped heat sink The coefficient is higher, but it is not easy to form.
(4) Impinging flow cooling utilizes air flow from the top of the fins to the bottom. This cooling method can increase thermal conductivity, but attention must be paid to the direction of the wind to match the overall design.
For the common down-blowing design where the fan is placed above the heat sink, a more precise design is required because the fan characteristics must be matched. Due to the rotation effect of the axial fan, the position of the shaft is not easy to be blown by the wind, so many heat sinks are designed to be radial, and the top of some heat sinks are designed to be different in length or curved to guide the wind. Another way is to use side blowing. Generally speaking, side blowing heat sinks can blow through the fins and have less flow resistance. Therefore, for high and dense fins, the top cover design is used. In order to prevent the air flow from bypassing, the side-blowing type can have a better effect than the down-blowing type.
