Transient Characteristic and Performance of Novel Loop Heat Pipe

Abstract A novel loop heat pipe (LHP) model was proposed as a passive heat absorption and dissipation technology to address thermal challenges. This LHP featured a wick of copper capillary tubes without a compensation chamber and utilized a reduced-diameter liquid line and casing wick. This study investigated the transient characteristics and performance of the LHP by analyzing the effects of heat load, filling ratio (FR), inclination angle, and mapped natural circulation stability (NCS) in phase-change number–subcooling number space to determine whether the proposed geometry and operating range remained stable. The effectiveness of the LHP as a heat exchanger was also assessed in comparison to conventional heating methods. Experiments were conducted by varying water tank temperatures as a heat load of 35 °C to 65 °C, filling ratios of 40% to 120%, and inclination angles of 0 deg to 5 deg. The condenser was cooled using air at a constant velocity, while the initial pressure of 5332.88 Pa was maintained before the acetone as LHP working fluid charged. Experiment results showed that the optimal configuration at a higher heat load, an 80% filling ratio, and a 5 deg inclination angle with a polyvinyl chloride (PVC) socket achieved the fastest and most stable startup with the lowest thermal resistance (RT) of 0.0338±0.007 °C/W; NCS analysis confirmed stable circulation and achieved efficient and uniform heat distribution with enhanced thermal stability. These findings demonstrate that the proposed LHP achieved rapid, stable startup, stable natural circulation, and effective passive heat exchange.