Experimental Investigation of the Operating Characteristics of a Pulsating Heat Pipe with Ultra-Pure Water and Micro Encapsulated Phase Change Material Suspension

The specific heat capacity of working fluid is an important influence factor on heat transfer characteristic of the pulsating heat pipe (PHP). Due to the relatively large specific heat capacity of micro encapsulated phase change material (MEPCM) suspension, a heat transfer performance experimental facility of the PHP was established. The heat transfer characteristic with MEPCM suspension of different mass concentrations (0.5% and 1.0%) and ultra-pure water were compared experimentally. It was found that when the PHP uses MEPCM suspension as its working fluid, operating stability is impoverished under lower heating power and the operating stability is better under higher heating power. At the inclination angle of 90°, the temperature at heating side decreases compared to ultra-pure water and the temperature at heating side decreases with the raising of MEPCM suspension mass concentration. The heat transfer characteristic of the PHP is positively correlated with the inclination angle and the 90° is optimum. The unfavorable effect of the inclination angle decreases with heating power increasing. When the inclination angle is 90°, the PHP with MEPCM suspension at 1.0% of mass concentration has the lowest thermal transfer resistance and followed by ultra-pure water and MEPCM suspension at 0.5% of mass concentration has the highest thermal transfer resistance. When the inclination angles are 60° and 30°, the effect of gravity on the flow direction is reduced to 86.6% and 50% of that on the inclination angle of 90°, respectively, and the promoting effect of gravity on the working fluid is further weakened as the inclination angle further decreases. Due to the high viscosity of MEPCM suspension, the PHP with ultra-pure water has the lowest heat transfer resistance. When the inclination angles is 60°, the thermal resistance with MEPCM suspension at 0.5% of the mass concentration is lower than that at 1.0% at the heating power below 230 W. The thermal resistance of MEPCM suspension tends to be similar for heating power of 230–250 W. At the heating power above 270 W, the thermal resistance with MEPCM suspension at 1.0% of the mass concentration is lower than that at 0.5%.