28.03.2022What is a Thermal Shroud?
Simply put, a thermal shroud is a large panel, typically made from stainless-steel (or other vacuum compatible material), that is situated within the vacuum environment and that can be heated (and possibly cooled).
Shroud surface coating
Non-contact heating of flight hardware within a vacuum environment can be challenging as all heat transfer must be done radiatively rather than through conduction or convection, the biggest effect on the efficiency of the thermal shrouds is the surface coating Aeroglaze Z306 applied to the shrouds (a characteristic known as emissivity). The surface coating is specifically chosen to increase the emissivity of the shrouds and therefore increase the radiative heat transfer to the item under test (IUT). It's important to monitor the cryogenics of the material throughout.
It's worth noting that the IUTs ability to absorb this radiative heat is also dependent on the surface characteristic, in this case named absorptivity.
Where are thermal shrouds used?
The process of baking out flight hardware is an essential part of a product assurance programme for any critical project. The bakeout process is performed to accelerate the outgassing of volatile compounds from an IUT, which otherwise might affect the in-service performance of the IUT. These volatile compounds typically originate from painted surfaces or are measured for the purposes of characterising and qualifying new materials.
Outgassing can occur naturally over time, however, this can be accelerated by placing the IUT into a vacuum and elevating its temperature. AEON's thermal testing facility creates a controlled environment for the bake out process, allowing it to be monitored by a suite of sensors including; TQCM to monitor the rate of outgassing, RGA to identify the elemental compounds being outgassed in real-time or with post-bakeout analysis of a Molecular Contamination (MoC) plate by Fourier Transform Infrared Spectroscopy (FTIR analysis).
One of the key contributors to accelerating the outgassing process is an elevated temperature. One way this can be achieved is using thermal shrouds within the vacuum chamber.
Independent Shrouds
AEON’s CERES bakeout facility utilises four independently controlled thermal shrouds with a closed loop feedback. This ensures that each shroud can be programmed to a specific customers requirement for bespoke bakeout temperature profiles. Control over the rate of temperature change for each shroud ensures the temperature gradient across the IUT can be controlled either to provide a slow uniform heating or to deliberately maintain regions of varying temperature. Independent shrouds also provide a level of redundancy so if a power supply to a single shroud were to fail during a bakeout the remaining shrouds would be able to compensate and the bakeout would not be affected.
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