NEWS - HEAT EXCHANGE / HEATSINK :
27/08/2013

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Comparison of several heat sinks

info:

Alvéotec has realized a comparative test in partnership with Piseo in order to compare performances of different types of radiators. Therefore we have selected the 2 most common types of heat sinks used on lighting market and we compared them with our heat sink made in metal foam. These radiators have the same dimension and they are painted in black. A Citizen Electronics LED has been placed on the heat sinks with thermal past.


  

By measuring directly the junction point temperature between the LED and the radiators, we are able to rank these radiators by their performances of heat dissipation. Consequently we can compare our heat sink made in metal foam and other solutions that already exist on the market.

Measurement equipment

To test these 3 heat sinks, we used a Trister, it is a really particular measurement system based on the LED component behavior theory.

Measurement protocol

Measurement of the junction point temperature between the LED component and the heat sink consists of 3 steps:

  • Characterization of the component alone: it consists on drawing the “K factor” which will be the reference point in order to fin the junction point temperature when the LED will be placed on the heat sinks.

The “K factor is the evolution of the LED’s threshold voltage in function of the temperature. To measure it, the component is placed on a Peltier system; thanks to this system we can change temperature of the heat transfer surface. A past is used to transfer heat between the LED and the heat sink.

Then, we change the heat transfer surface temperature from 15° to 75°C with a steady power supply of 1mA, while we are measuring the LED’s threshold voltage.

On the following picture, you can see the Citizen LED on the Peltier system.

              

  • Once we obtained the threshold voltage data of the heat transfer surface, the LED system is placed on the radiator inside a containment system with a power supply of 1.1A, and then the temperature is stabilized until the equilibrium.When the whole system is stabilized (it can take more than one hour), we start to use the Trister.
  • The power supply of 1.1A is stopped during a few dozen of microseconds and switched to the steady power supply of 1mA (which is the reference) as when we obtained the “K factor” for the component alone.

    By monitoring the threshold voltage we can increase temperature of the junction point in accordance with the “K factor” that we observed before. The first threshold voltage directly measured, when we switched from 1.1A to 1mA, gives us information about the junction point temperature.

    Then by monitoring this threshold voltage during the cooling period of the LED and the heat sink until the containment system temperature (16°), we obtained different thermal resistances for each studied heat transfer surface.

    Results

    With a power supply of 40W for the electronic component, we obtained junction points temperatures, therefore we can draw Cth = f(Rth) curves and deduct from it the Rth of the whole system and each elements separately.

Therefore we have deduced Rth of heat sinks:

  1. Heat sink made with metal foam (by Alvéotec) has a Rth of 1.2K/W
  2. Extruded heat sink (with U cooling fins) has a Rth of 1.3K/W
  3. Casted heat sink (with short cooling fins) has a Rth of 1.4K/W

Conclusion

This test has been realized by a team of experts (Piseo Company) and it demonstrates performances of the heat sink made in metal foam.

This breakthrough innovation, without full optimization, is 10% more efficient than other technology to dissipate heat. Besides, these performances could clearly be improved with complementary studies.

Source: Piseo