The Modular Model: Sapa Develops New Method to Manufacture High Ratio Air Cooled Heat Sinks
Sapa's North America Technical Center (NATC)—a research, design and development center within Sapa Extrusions North America works to provide innovative solutions and products—has developed a new method of manufacturing high ratio air cooled heat sinks that are approximately eight percent more thermally efficient than the industry standard.
Leveraging Sapa's expertise in aluminum extrusion manufacturing and Friction Stir Welding technology, the new method utilizes a modular concept that enables maximum flexibility with fin geometry, fin ratio and heat sink footprint, yielding heat sink ratios in excess of 40:1. Not only does this method allow for the production of large-scale heat sinks up to 20" in width, it is also well-suited for serial production, making these types of heat sinks a competitive product in the marketplace.
The objective of the study was to develop and improve a product that would provide a savings in cost, a decrease in lead time and a solution to the needs and requirements of customers. The heat sinks are intended for high power applications, as well as LED forced convection applications.
Friction Stir Welding (FSW) is a mechanical joining method that produces high strength, porosity free, homogenous joints that will not degrade over time. Because no filler metal is used, parent metal thermal conductivity is maintained through the joint line. Additionally, the joint line can be face-milled to ensure required surface roughness or flatness tolerances are met.
The FSW welds joining individual profiles in the heat sink were examined through metallographic sections, all of which showed a fully consolidated weld (see Figure 1).
Figure 1: Cross weld sections of Sapa's FSW heat sink
Sapa's NATC conducted this study in conjunction with its European counterpart, Sapa Technology, part of Sapa Group, the parent company of Sapa Extrusion North America.
Two heat sinks were sent to Sapa Technology from the NATC for experimental testing to benchmark thermal performance during forced convection. One heat sink was a Sapa NATC designed FSW heat sink and the other was a competitor heat sink with bonded fins (see Figure 2).
Figure 2: FSW and Bonded Fin Heat Sinks
Both heat sinks had an identical cross-section (see Figure 3).
Figure 3: Cross Sections
The heat sinks were individually placed in a test chamber with foam plastic used to create a duct surrounding the heat sinks.
The study was conducted with four different airflow rates over the heat sink, with an applied constant power on a 4 mm copper plate mounted to the base of each heat sink.
To measure the temperature of the heat sinks, small grooves were milled in the copper plates in order to mount thermocouples to each heat sink. Thermocouples were also mounted to measure the air temperature at the inlet and outlet of the duct. Temperature readings were taken after reaching a steady state condition.
A summary of the test conditions and performance curves include the following:
- Heat load – 360W
- Airflow rates – 90, 110, 130, and 150 m^3/hr
- Ambient temp – 20°C
- Thermal resistance is calculated based on the measured maximum surface temperature, inlet air temperature and the applied load.
- A uniform load was assured during testing using a copper thermal spreader.
- Surface temperature measerements were taken at eight positions.
When compared to one another, the Sapa designed FSW heat sink shows a slightly lower thermal resistance while maintaining an equivalent pressure drop, resulting in an approximate eight percent better thermal performance than the bonded heat sink (see Figure 4).
Figure 4: Thermal Resistance and Pressure Drop Charts