RESUMO

This paper presents an experimental investigation of passive cooling of instruments using phase change material and heat pipe. Instruments for defence and surveillance consist of one or more electro-optical sensors, which generate heat continuously or/and intermittently. Heat generated by these sensors is required to be dissipated from sealed enclosure to ambient. To simulate the actual condition for intermittent heat generating unit, a constant heat source is applied inside enclosure. Heat pipe is connected to heat source for heat transfer to ambient. Since performance of heat pipe is greatly dependent on the cooling mechanism at condenser side, active fan is required for better performance. For passive cooling PCM may be a substitute of active fan for intermittent heat source as molten PCM needs to be re-solidified by dissipating heat to surrounding while. PCM which is stored between the fins of heat sink is applied outside the enclosure. Properties of PCM including the melting temperature of 48-50°C, latent heat, sensible heat, thermal conductivity and density are based on a commercially available paraffin wax. The experimental result shows that PCM is also very useful to enhance duty cycle of intermittent use as well as it restricts maximum temperature at condenser end. To achieve effective cooling it is important to ensure that the operating duration of the electronic devices does not exceed the time of full melting.