Emmisivity in Passive Thermal Management - Acktar black coatings

Emmisivity in Passive Thermal Management

metallic tube coated with ultra black coating from the inside
By David Alster

All devices generate waste heat as a by-product of their operation. This heat needs to be dissipated in order to avoid the generation of undesirable high temperatures and damage to the devices.

The waste heat can be dissipated from a device by one of several mechanisms

Conduction to a housing or any other larger heat-sink
Conduction to a cooling heat-transfer liquid and from there to a heat transfer unit operating thru convection or radiation
Natural or forced convection to the atmosphere As thermal infra-red radiation

Ultra Black
Black Coating for MWIR and LWIR (medium and low infra red wavelength) with extremely low reflectance.

The two conduction options can only serve as interim measures because they cannot store ever increasing amounts of heat and it must eventually be dissipated by convection or radiation.

When the device to be cooled or the heat-sink is located where there is no possibility of convection because there is no atmosphere – such as in a vacuum enclosure or on a satellite in space – the only available mechanism is thermal infra-red radiation.

ACKTAR_Optomechanics_2
Fractal BlackTM is the coating of choice where low reflectance / high emissivity is required across the spectrum from the UV through LWlR — typically for stray light suppression.

The amount of heat which can be radiated from a surface is a direct function of the surface temperature and of the emissivity of the radiating surface.

It is in the context of the management of this passive thermal process that the extremely high emissivity of  Acktar Black Coatings play a decisive roll.

In space applications radiation is especially effective because radiation is to a zero Kelvin background.

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