Experimental study on the thermal performance of a closed loop pulsating heat pipe with various angle

Abstract

The performance of a closed-loop pulsating heat pipe (CLPHP) was investigated using different parameters such as filling ratio, working fluid, and angle. The results showed higher filling ratios reduced thermal resistance, indicating more efficient heat transfer. Among the studied configurations, the CLPHP filled with ethanol at an 50% ratio and inclined at a 45° angle demonstrated the best performance, with a thermal resistance of 1.38 °C/W. On the other hand, ethanol at a 50% filling ratio and an angle of 180° exhibited the poorest performance, with a thermal resistance of 2.75 °C/W, indicating reduced heat transfer efficiency. The choice of working fluid also played a significant role, with ethanol consistently displaying lower thermal resistances than methanol. The impact of the angle on thermal resistance varied depending on the filling ratio and working fluid. The research findings deviated from the optimal range reported in previous studies, indicating the possibility of dry-out conditions due to fewer turns in the CLPHP and the operation at a 180° angle. This discrepancy could be attributed to the increased liquid phase viscosity, resulting in higher frictional surface shear stress. Additionally, the absence of body force in the horizontal operation mode hindered fluid motion. Overall, the study highlights the importance of considering various parameters in CLPHP design to achieve optimal thermal performance and emphasizes the influence of filling ratio, working fluid, and angle on thermal resistance and heat transfer efficiency.