14.11.2022How does a Thermal Shroud work?
In conventional (atmospheric pressure) environmental chambers, hot air is used to transfer heat into the hardware being tested/processed. This is usually performed by a heating element and a flow enhancing system such as a fan (this is how convection ovens work). As it is the air that is heated and then circulated, the heating element can be mounted safely away from the chamber walls.
When we consider a vacuum chamber, there isn’t any air inside the chamber, so there’s no air to transfer the heat into the hardware. We need a different kind of heating element -this is a thermal shroud.
Thermal Shrouds in Action
Thermal shrouds operate by way of radiation rather than convection; energy flows from the heat source in the form of photons and most effectively in the infrared spectrum. Radiation is emitted perpendicular (at 90°) to the surface of the heat source because light tends to travel in straight lines. The energy in each photon is small compared to convection and conduction, so typically it takes much longer to heat any hardware facing the thermal shroud. Oddly, this is exactly the reason that vacuum-insulated thermoses are able to hold hot liquids for so long, because they are insulated with a vacuum!
The thermal shrouds tend to line the inside of a chamber, rather than be situated at the rear or in a separate heating unit. They tend to ‘point’ toward the centre of the chamber so that they heat hardware uniformly from all sides. They are large (usually metal) panels made from vacuum compatible materials, such as stainless steel, or a suitable aluminium alloy.
By attaching electrical resistance heaters to these panels, they will get hot and emit radiation toward the hardware in the chamber. Conversely, it is possible to attach Peltier devices or cooling lines (cryolines) to thermal shrouds to give them the ability to cool hardware.
At AEON’s in-house test chamber, we use four independently controlled thermal shrouds to provide thermal control during thermal bakeout processes or environmental simulation. We’re able to elevate the temperature inside the chamber to promote outgassing of the hardware.
The increase in kinetic energy due to heating and the absence of atmospheric pressure provides the required conditions for volatile molecules to be ejected from the Item-Under-Test (IUT), and by using our “AETHER” TQCM, we’re able to monitor the status of a bakeout.
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To lean more about AEON’s thermal vacuum testing process or any of our other capabilities please contact us directly and lets see how we can turn your challenges into solutions.