Research on the refrigerant distribution and distinctive flow phenomena in a two-phase loop thermosyphon through a holistic visualization method

Abstract A two-phase loop thermosyphon (TPLT) was studied by conducting visualization experiments. All the TPLT system components, except for its condenser, were visualized. This study investigated the effects of working conditions on the operating states of the TPLT, particularly in terms of the variation in the flow characteristics. The filling ratio was varied from 20% to 140% in steps of 20%, and the heating temperature was set as 20 °C, 30 °C, or 40 °C under each filling ratio condition. Some distinctive flow phenomena occurred because of the strong influence of gravity, which were found to affect the performance. In addition, the experimental results indicated that increasing the filling ratio beyond 60% at a heating temperature of 30 °C does not affect the flow patterns and heat transfer capacity of the evaporator. However, it changes the refrigerant distribution and increases the pressure drop throughout the cycle, which suggests that the effect of the working conditions on the flow characteristics should be considered. The operating states of the TPLT under the different working conditions were divided into four stages, and the ideal working conditions were qualitatively analyzed. The results of this study could serve as a reference for the design of a TPLT for practical applications.