Earth-bound heatsinks loose most of their heat by convection – a luxury not available to heatsinks on satellites which can only use radiation. And spacecraft heatsinks cannot be heavy.
The research project is looking into situations were heat is not generated continuously, where the thermal mass of a heatsink can be used to spread the time available for radiation – allowing the radiant structure to deal with average rather than peak power.
But how to increase thermal mass without increasing actual mass?
In this case, by using a hollow heatsink filled with a material that temporarily changes phase within the range of temperatures encountered.
Paraffin wax was chosen, a lightweight material with a melting point between 53 and 58°C, that absorbs a large amount of heat (~170kJ/kg) as it melts, re-emitting it when it solidifies.
Its disadvantage is that it has poor thermal conductivity, so a series of fins were created inside the heatsink’s cavity to improve internal heat transfer.
Not only was this tested on the ground, but the experiment has also been orbiting in a CubeSat for almost a year.
“We alternate our experiments with those of the other payloads,” said Professor Mickey Clemon (pictured). “We’re testing different duty cycles and cooling regimes with the fixed heat sinks that we’ve put up there. The idea is for this to inform design and operating sequences for other electronics and computing in space.”
The team’s results thus far are promising, according to the university, with the melting wax significantly increasing the time that the electronics can operate within its safe temperature range, and the wax behaving the same with and without gravity.
“We’ve developed some simplified models to predict the performance of these heat sinks that may provide a first direction for designers to test their designs against rather than having to build something and test it physically,” added Clemon.
Next, the effects of cyclic solar heating during the spacecraft’s 90 minute orbit will be added into the study.
The University of Illinois Urbana-Champaign worked with the University of Technology Sydney, the University of Sydney and Mawson Rovers.
Two ScienceDirect papers cover the research:
