Effects of Aspect Ratios and Number of Meandering Turns on Performance Limit of an Inclined Closed-Loop Oscillating Heat Pipe

Problem statement: The purpose of this research was to determine the effects of aspect ratios and number of meandering turns on performance limit of an inclined closed-loop oscillating heat pipe. Approach: The Closed-Loop Oscillating Heat Pipe (CLOHP) was made of a long copper capillary tube. The geometrical sizes, which were the variable parameters of this study, were as follows; the internal diameter of 0.66, 1.06 and 2.03 mm, the evaporator section length of 50, 100 and 150 mm, the adiabatic and condenser section length of each set was equaled to the evaporator length and the numbers of meandering turn of 5, 10 and 15 turns. The experiments were conducted by setting the inclination angles at 0-90° adjusted by 10°, there totally were 9 sets and each set was tested with R123 as working fluid. The adiabatic temperature was controlled at 50±5°C. The low-voltage and high-current power transformer was used as the heat source and heat transfer rate was obtained by using calorific method at the condenser section. Results: It was found from the experiments that, in case of the CLOHP with 10 turns and the internal diameter of 2.03 mm, the maximum heat flux increases from 10-35.5 kW m^-2 when the aspect ratio decreases from 151.5-49.26 and the highest maximum heat flux occurs at inclination angle about 70-90°.Conclusion: The result indicated that the aspect ratio, the ratio of evaporator length by internal diameter and number of meandering turns significantly affect the maximum heat flux and inclination angle.