I. design of natural convection heat sink
-- preliminary design of the heat sink can be made on the envelope volume, and then detailed design on the details of the heat sink such as fins and bottom size
1. Envelope volume
General criteria for fin design general criteria for fin design
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2, heat sink bottom thickness
Good bottom thickness design must be from the heat source part of the thick to the edge part of the thinning, so that the heat sink from the heat source part to absorb enough heat to the surrounding thinner part of the rapid transfer.
General criteria for fin design general criteria for fin design
Bottom thickness relation//bottom thickness relation to input power
 aluminum heat sink chart |  aluminum radiator |
3. Fin shape
The thickness of the air layer is about 2mm, and the spacing between fins should be more than 4mm to ensure smooth natural convection. But it will reduce the number of fins and reduce the heat sink area.
A. Narrowing of fin interlatation - natural convection is reduced and heat dissipation efficiency is reduced.
Larger interfins - fewer fins, less surface area.
B. fin Angle the fin Angle is about three degrees.
General guidelines for fin design
Fins shape
General guidelines for fin design
Fin shape reference value
C. Fin thickness
When the fin shape is fixed, the balance of thickness and height becomes very important, especially when the fin thickness is thin and high, which will cause difficulties in heat transfer at the front end, making the fin unable to increase efficiency even if the volume increases
Fin thinning - the ability of the fin to transfer heat to the tip becomes weaker
Fin thickening - reduction in fin number (surface area)
Fin augmentation - decreased ability of fin to reach the tip (decreased volume efficiency)
Fin shortens - surface area decreases
4, heat sink surface treatment
The surface of the fin can be treated with acid-resistant aluminum (Alumite) or anodized to increase the radiation performance and increase the heat dissipation efficiency of the fin. Generally speaking, it has little to do with the color of white or black. The processing of surface protuberance can increase heat dissipation area, but in the case of natural convection, may cause the obstruction of air layer instead, reduce efficiency.
Second, forced convection fin design
-- increase the thermal conductivity
(1) increasing the air flow velocity is a very direct method, which can be combined with the fan with high wind speed to achieve the purpose.
(2) the flat fin is crosscutting and the flat fin is cut into many short parts. In this way, although the heat dissipation is reduced, the heat conductivity is increased and the pressure is also increased. This design is more appropriate when the wind direction is variable. (e.g. heat sink on motorcycle)
General guidelines for fin design
The fin is crosscutting
(3) needle-fin fin design needle-fin fin fin has the advantages of lighter and smaller size, higher volume efficiency, and more importantly, isodirectional, so it is suitable for forced convection fin, as shown in FIG. 9. The shape of fins can be divided into rectangle, circle and ellipse. The rectangular fin is made of aluminum extruded cross-cutting, while the circle can be forged or cast. The oval or droplet shaped fin has high heat transfer coefficient, but it is difficult to shape.
(4) impingement cooling USES airflow to impact from the tip of fins to the bottom. This cooling method can increase the heat conductivity, but it should be noted that the flow direction of the wind is in line with the overall design.
General criteria for fin design general criteria for fin design
Needle-fin fin radiating fin fin radiating fin
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5) for the common fan blow down design above the radiator fin, due to the need to cooperate with the fan characteristics, more accurate design is needed. Due to the rotation effect of the axial flow fan, and the position of the axial wind is not easy to blow, so many radiating fins are designed as shown in figure 10. There are also fin tips designed to be short or curved to guide the wind. The other way is to use side blowing. Generally speaking, side blowing radiator can blow through the fin due to the air flow, and the flow resistance is less, so for high and dense fin, with the top cover design to avoid bypass, side blowing can have better effect than side blowing.
Design specification/experience of radiator in baoan district, shenzhen
Heat sink design considerations
1: the larger the surface area, the better the cooling effect.
2: if the heat sink placed conducive to air circulation, can improve the heat dissipation effect.
3: copper. Aluminum has high thermal conductivity and is the first choice for heat dissipation materials.
4: it is more effective to increase the thickness of heat sink than to increase the length (our experience).
5: surface anodic oxidation treatment can resist oxidation corrosion, improve radiation capacity, stable heat dissipation effect.
6: economic practicality of processing.
Comparison of heat dissipation effects under the same conditions:
The quality of light
Long oxidation life
Short service life without oxidation
Slotted heat dissipation effect is good
No slot heat dissipation effect is poor
High blade density, good heat dissipation effect (better with fan)
Low blade density, poor heat dissipation effect (plus fans)
High blade height, good heat dissipation effect (better with fan)
Low blade height, good heat dissipation effect (plus fans)
The bottom thickness of the thick heat absorption, heat loss is not necessarily. It's a little bit better.
Bottom thickness thin heat absorption smaller, heat loss is not necessarily. Relative would be less.
Four, radiator choice principle
Users must consider the following factors when selecting a radiator:
Module working current size, to determine the required cooling area;
(2) the use of the environment, which can be determined to take what kind of cooling mode -- natural cooling, forced air cooling, or water cooling;
The shape of the device, volume, the size of the space reserved for the radiator, which can determine what shape of the radiator. In general, most users will choose aluminum radiator.
Five, radiator design steps
The design of radiator is usually divided into three steps:
1:Design the radiator profile according to relevant constraints.
2: according to the relevant design criteria of the radiator, the radiator tooth thickness, tooth shape, tooth spacing, substrate thickness were optimized.
3: check calculation.
Design method of natural cooling radiator
Considering the natural cooling when the temperature boundary layer thicker, if tooth spacing is too small, easy to cross two tooth thermal boundary layer, the influence of tooth surface of convection, so usually, suggested that natural cooling radiator tooth spacing greater than 12 mm, if the radiator depth less than 10 mm, according to the tooth spacing of 1.2 times the depth to determine the radiator or tooth spacing.
Natural cooling radiator surface heat transfer ability is weak, in the heat dissipation tooth surface increase ripple will not have too much influence on the natural convection effect, so it is recommended that heat dissipation tooth surface without corrugated teeth.
The radiator surface of natural convection generally USES blackening treatment, in order to increase the radiation coefficient of heat dissipation surface, strengthen radiation heat transfer.
Since it takes a long time for natural convection to reach the heat balance, the substrate and tooth thickness of the natural convection radiator should be enough to resist the impact of instantaneous heat load, and it is recommended to be more than 5mm.
Add corrugated tooth in radiator surface, the depth of corrugated tooth should be less than 0.5mm commonly.
Increase the number of teeth on the radiator. At present, the advanced international extrusion equipment and technology can reach the aspect ratio of 23, while the maximum aspect ratio in China can only reach 8. For the occasions that can provide sufficient concentrated air cooling, it is recommended to use low-temperature vacuum brazing forming cold plate, whose tooth spacing can be as small as 2mm.
The design method of needle tooth is adopted to increase the fluid disturbance and improve the convection heat transfer coefficient between the heat dissipating teeth.
When the wind speed is greater than 1m/s(200CFM), the influence of buoyancy on surface heat transfer can be completely ignored.