Experimental and Numerical Investigation of Thermosyphon Heat Pipe Performance at Various Inclination Angles

Abstract

Interest in the use of heat pipes in solar applications is increasing due to their role in improving the heat transfer performance of solar collectors. In order to effectively utilise heat pipes, their performance under various operating conditions and inclination angles need to be investigated. In this work, numerical and experimental studies were carried out to investigate the effects of heat input and inclination angle on the wall temperature distributions and thermal resistance of thermosyphon heat pipe. A Computational Fluid Dynamics (CFD) model was developed using ANSYS Fluent to simulate the flow and mass transfer using volume of fluid (VOF) approach together with user - defined function (UDF) to simulate the phase change processes at various inclination angles. Experiments were carried out to validate the CFD model at heat inputs of 81.69W and 101.55W with temperature distribution results showing good agreement of ±4.2% average deviation. Also the predicted thermal resistance at different inclination angles showed good agreement with the experimental ones with maximum deviation of ±5.7%. Results showed that as the heat input increases, the heat pipe wall temperature increases and the thermal resistance decreases. Experimental and numerical results showed that increasing the inclination angle will improve the thermosyphon heat pipe performance to reach its maximum value at 90o, but this effect decreases as the heat input increases.