Development of a Freeze Resistant Heat Pipe with Water as Working Fluid for Automotive Applications

Abstract

Abstract In this paper, we present a heat pipe with ethylene glycol and water as working fluid that can prevent any damage to the copper container on exposure to cyclic freezing and thaw. Different mass concentrations of water and ethylene glycol have been tested for freeze protection of heat pipes in this research. Experimental investigations have shown that 3.5% by mass concentration of ethylene glycol with water is able to sustain the cyclic freezing and avoid any damage to the copper pipe. For this research the freezing and heating cycle is set to operate between -40°C to 90°C. Heat pipes used for testing in this research are 6mm in diameter and 150mm long with copper fibre spiral wick. Thermal performance tests have been carried out on these heat pipes with charging ratio of working fluid varying between 10%-30% by volume. It is observed that the thermal resistance of heat pipe with working fluid charging ratio in range of 10%-25% by volume varies from 0.6°C/W-0.2°C/W for the rate of heat transfer of 10W-50W. While the charging ratios beyond 25% have shown the higher thermal resistance in the range (0.8-1.0°C/W) for similar rate of heat transfer. Accelerated life tests are performed on these heat pipes for up to 500 hours and have not shown any signs of degradation in its thermal performance.