Experimental study on the effect of filling ratio on an R141b two-phase thermosyphon loop with a horizontal parallel tube evaporator

A two-phase thermosyphon loop is an ideal heat transfer device to achieve compact and efficient cooling with low energy consumption. In this paper, a two-phase thermosyphon loop with a horizontal parallel tube evaporator for multiple heat source cooling is proposed. The effect of the filling ratio on the transient response of temperature and pressure, heat transfer characteristics, instability issues, as well as flow regimes under different heat loads are investigated experimentally and visually. The filling ratios are divided into three groups according to their unique heat transfer and instability characteristics. The research results show that a too low or too high filling ratio is not conducive to the safe and stable operation of the system. At medium and high filling ratios, temperature and pressure overshoot are prone to occur, threatening the safe operation of the system; geyser boiling is another unstable phenomenon that can be inhibited as the heat load increases. Gravity will lead to uneven distribution of working fluid in the evaporator and further affect the temperature uniformity and heat transfer capability. From the perspective of temperature control performance and heat transfer capability, 30% is the optimal filling ratio in this study, with a minimum thermal resistance of 0.12 degrees C center dot W-1 and a maximum heat transfer coefficient of 1345.36 W center dot m(-2)center dot degrees C-1. This paper provides a basis for designing and applying a two-phase thermosyphon loop for multiple heat source cooling in confined spaces.