Investigations on Heat Pipe Heat Exchanger

Abstract

Waste heat recovery is extremely important and necessary for saving energy, which is an important parameter for the world economy and can result in lowering future energy consumptions. As the global energy resources are decreasing, the energy costs increase and hence efficient heat transfer/dissipation play an important role. In industries such as textiles, substantial energy is wasted with the exhaust gases which are used for maintaining the fabric moisture and hence in order to recover waste heat from exhausted gases, the heat pipe heat exchanger can be used. The heat pipe heat exchanger comprises of a large number of heat pipes which function as individual units in transferring heat. The objective of the present study is to study the effects of various parameters on a copper heat pipe such as filling ratio (30%, 35%, 40%, 45%), heat input (150 to 510 W), gravity-assisted angle of orientation of heat pipe (0°, 45°, 90°), wick mesh size (50, 100, 150) and the number of wick layers (0, 1, 2). Also in order to enhance the performance of heat pipe, techniques such as increased roughness (average roughness of 6.905 microns) on evaporator surface and TFE (tetrafuoroethylene) coating on condenser surface were used and the performance compared with the untreated heat pipe. From the experimental results, an optimum angle of heat pipe orientation was observed to be 45° (gravity assisted with condenser upwards) and best result was found with 50 mesh size. Among the different filling ratio, least resistances (Re, Rc and Rth) and hence and higher efficiency were observed with a 35 % filling ratio. Due to surface enhancement techniques, the heat pipe performance was substantially improved in all the cases and the maximum improvement was obtained with 2 wick layers. The surface enhanced heat pipe at 35 % Filling ratio and 2 wick layers of 50 mesh size led to a 27.94 % reduction in resistance. An improvement of 38.9 % and 5.52 % in the heat transfer coeficient and efficiency respectively was observed for the enhanced surface heat pipe as compared to the untreated (bare) heat pipe. The study concludes that for an improved heat pipe performance, the application of surface enhancement techniques can make a substantial difference and lead to efficient heat transfer.