Thermal Management of an Ultra Light-weight RPV FLIR Payload

A Forward Looking Infrared (FLIR) laser designator system has been designed for airborne application on a remotely piloted vehicle. The system consists of a sealed elevation assembly, which houses the inner gimbal and the FLIR cryocooler unit with associated optics. The sealed elevation assembly is cooled primarily by recirculation of internal air and is the subject of this paper. A detailed heat transfer analysis was carried out to demonstrate that adequate thermal management could be attained. Several key parameters had to be determined including the flow resistance of the internal air passages, the internal and external heat transfer coefficients, and the optimum recirculation fan size. Methods of evaluating these parameters are described and verification is provided using data inferred from comprehensive flow and thermal tests. In general, measured component temperatures were slightly less than predicted values, reflecting the conservative approach used in the analysis. More importantly, the test results indicate that the thermal design meets the system requirements.