Aluminum alloys are popular for extruding as heat sinks because they provide both malleability and formability. They can be easily machined and are as little as one-third the density of steel. This results in extrusions that are both strong and stable, at a reduced cost relative to other materials.
The aluminum extrusion process starts with designing and creating the die that will shape the [url=
http://www.sindathermal.com/heatsink-extrusion/]heatsink extrusion.[/url] Once this has been done, a cylindrical billet of aluminum is heated up in a forge to high temperatures, generally between 800-925°F (427-496°C). Next, a lubricant is added to the aluminum to prevent it from sticking to any of the machinery. It is then placed on a loader and pressure is applied with a ram to push heated aluminum through the die.
During this process, nitrogen is added in order to prevent oxidation. The extruded part will pass completely through the die and out the other side. It has now been elongated in the shape of the die opening. The finished extrusion is then cooled, and if necessary, a process of straightening and hardening creates the finished product.
They can be cut to the desired lengths, drilled and machined, and undergo a final aging process before being ready for market. [4]
Finished heat sinks typically come with anodized surfaces, which can enhance their thermal performance. Alternatively, a chromate finish provides some corrosion protection, or can be used as a primer before a final paint or powder coating is applied. [5]
Shapes of Extruded Heat Sinks
[url=
http://www.sindathermal.com/heatsink-extrusion/extrusions-tooling-heat-sink/]Extrusions tooling heat sink[/url] profiles range from simple flat back fin structures to complex geometries for optimized cooling. They can be used for natural (passive) or forced convection (active) with an added fan or blower. Extruded profiles can also include special geometries and groove patterns for use with clip or push pin attachment systems.
6063 aluminum alloy has a thermal conductivity of 201-218 W/(mK). Higher tensile strength 6061 aluminum’s thermal conductivity ranges from 151-202 W/(mK).
Besides choosing the aluminum alloy, selecting an optimal extruded heat sink should factor in its overall dimensions and weight, the specified thermal resistance, and the extrusion shape (flat-back, flat-back with gap, hollow, double-sided, etc.). [7]
Extruded heat sinks can be designed with very thin, and thus more, fins than other sink types. They can be extruded with aspect ratios of around 8:1, which can greatly optimize heat sink performance. A heat sink’s aspect ratio is basically the comparison of its fin height to the distance between its fins.
Linear Cellular Alloys (LCAs) are metal honeycombs that are extruded using powder metal-oxide precursors and chemical reactions to obtain near fully dense metallic cell walls. Either ordered periodic or graded cell structures can be formed. In this work, the performance of heat sinks fabricated from stochastic cellular metals is compared to that of LCA heat sinks. Flash diffusivity experiments are performed to determine the in situ thermal properties of cell wall material. The pressure drop for unidirectional fluid flow in the honeycomb channels and the total heat transfer rate of LCA heat sinks are experimentally measured. These measurements are compared to values predicted from a finite difference code and commercial computational fluid dynamics (CFD) software.
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