Abstract:
Efficient and effective cooling of aircraft avionics is required to achieve optimized
performance, reliable & extended operation. Thus, rated temperature ranges for safe
operation of avionics are ensured by employing Environmental Control System (ECS) in
aircraft, which uses ram air in closed circuits to cool avionics Line Replaceable Units
(LRUs). Heat is dissipated into the closed circuit ram air stream (sink) from the PCB cards
(source) via forced convective heat exchange. During this process, heated components
leave soot particles into the downstream which are subsequently condensed & accumulated
in the ECS components (in the form of black soot). Being a good insulator of heat, it
reduces efficiency of ECS system by decreasing heat transfer. Overheating of avionics due
to black soot deposition was calculated using empirical, experimental and simulation on
FLUENT & results were compared. 10 to 11% of temperature rise was observed at PCBs
inside housings of avionics LRUs due to 1g/cm2 deposited black soot. Whereas, a 30%
reduction in reliability of avionics can be associated to thermal failures of avionics. SPMPs
does not include inspections of avionics LRUs for black soot depositions & it is
recommended that commercial and fighter jet avionics should be removed after every 500
hours flying for inspections of ECS ducts for possible deposition of black soot & other
contaminations.
