Experimental assessment of vapour chamber heat spreader implementation in avionic cooling

Avionic thermal management is quickly becoming the limiting factor of aircraft performance and reliability, particularly prevalent with ageing airframes. While the increasing power density of avionic components requires a greater heat removal capacity for a given geometric module size, supplementary generation of cooling airflow is detrimental to engine and aircraft performance. This paper looks at improving the heat removal efficiency of forced convection cooled avionic modules by reducing the thermal resistance between the avionic component and module heat exchanger. The implementation of two-phase high thermal conductivity materials, such as Vapour Chamber Heat Spreaders (VCHS), embedded within the avionic module chassis act to improve heat exchanger isothermalisation, improving the effective heat transfer area. A bespoke test rig has been manufactured to experimentally compare a pure aluminium and embedded VCHS avionic chassis for heat removal capability. When considering a single circuit card, a direct mass flow rate reduction of between 22% and 65% is achieved with embedded VCHS over a pure aluminium chassis. Base plate isothermalisation is improved by 9%, generating a reduction in component temperature of 8% to 12%. As the number of heat sources increase, the performance improvements decrease. When testing with three circuit cards mass flow rate savings are reduced to between 14% and 26%. The concluding performance characteristic of the embedded VCHS avionic base plate is the insensitivity to the way thermal energy is coupled to it. Across all testing, the localised heat removal was never further than 3.5% from the averaged plate performance.