Effect of Filling Ratio and Tilt Angle on the Performance of a Mini-Loop Thermosyphon

The thermal behavior of a compact mini-loop thermosyphon is experimentally studied at different filling ratios (20%, 30%, 40%, 50%, and 70%) and tilt angles (0 deg, 30 deg, 45 deg, 60 deg, and 90 deg) for the heat loads of 20–300 W using distilled water as the heat pipe fluid. The presence of microfins at the evaporator results in an average decrease of 37.4% and 15.3% in thermal resistance and evaporator wall temperature, respectively, compared with the evaporator with a plain surface. Both filling ratio (FR) and tilt angle influence the heat transfer performance significantly, and the best performance of the mini-loop thermosyphon is obtained at their optimum values. The thermal resistance and thermal efficiency values lie in the ranges of 0.73–0.076 K/W and 65–88.3% for different filling ratios and tilt angles. Similarly, evaporator heat transfer coefficient and evaporator wall temperature show significant variation with changes in filling ratio and tilt angle. A combination of the optimum filling ratio and tilt angle shows a lowest thermal resistance of 0.076 K/W and a highest evaporator wall temperature of 68.6 °C, which are obtained at 300 W. The experimental results recommend the use of mini-loop thermosyphon at an optimum filling ratio for electronics cooling applications, which have a heat dissipation of 20–300 W.