Effects of filling ratio, geometry parameters and coolant temperature on the heat transfer performance of a wraparound heat pipe

The present work focuses mainly on the effects of heat input, filling ratio, inclination angle, tube diameter and coolant temperature on the thermal performance of a wraparound heat pipe charged with R134a. Results show that thermal resistance decreases with the increase of heat input when the filling ratio is larger than 40%. An optimal filling ratio for the heat pipe with the best performance exists between 50% and 60%. The pressure of working fluid in the heat pipe exceeds 1.6 MPa in the 70% and 80% filling ratios experiments. For larger inclination angles (θ > 10°), the thermal resistance decreases with increasing the heat input and finally tends to a stable value. For heat loads of 420 W and greater, the values of thermal resistance are 0.056, 0.07, 0.034 and 0.027 K/W for outer diameters of 8, 10, 12 and 16 mm, respectively. No significant difference in thermal resistance at different coolant temperatures is observed for heat inputs greater than 300 W. In all experiments, for a 22° inclination angle, an outer diameter of 16 mm, and a filling ratio of 50%, the best performance of heat pipe is observed and the lowest value of thermal resistance is 0.027 K/W.