Performance evaluation of controllable separate heat pipes

•A controllable separate heat pipe (CSHP) is designed and tested.•The start–stop performance of CSHP is investigated and confirmed.•CSHP starts up quickly in approximately 15 seconds.•The quickest stopping time of CSHP approximates to 80 seconds.

A controllable separate heat pipe (CSHP) combined with cool storage can be an efficient and low-cost solution to release the necessary cool power and to improve the precision in the temperature control of cool-storage refrigerators powered by solar energy or electricity with time-of-use price policy. However, the precise temperature control performance of separate heat pipes under active control depends on system design and thus should be confirmed. In this study, a CSHP was developed and an active control method was achieved by interrupting its two-phase natural circulation flow. A one-dimensional steady-state model was used to calculate the critical fill ratio, heat transfer rate, and average working temperature of CSHP. A series of experiments was conducted to analyze the start–stop and heat transfer performances of CSHP at various R134a fill ratios and heat sink temperatures. Under different test conditions, the optimum working points were obtained through fitting. The most suitable control mode was determined and the start–stop performance of CSHP was examined in detail. CSHP starts up quickly in approximately 15 seconds and the quickest stopping time of CSHP approximates to 80 seconds. Therefore, the performance of CSHP under active control can be applied to cool-storage refrigerators.