Study on the steady-state operation characteristics of open loop heat pipe desalination

Open loop heat pipe desalination (OHLPD) can achieve a high water production rate with a small temperature difference, without consuming additional mechanical power. In this study, a steady-state model of the OLHPD system was established to investigate its water-production performance, operating modes, pressure-drop distribution, and the effects of compensation-chamber position and vapor-line geometry. The simulation results demonstrate that the system can effectively utilize low-grade waste heat at 33-37 °C (such as thermal discharge from coastal power plants, resulting in near-zero thermal energy cost) achieving a water production rate of 10-45 kg/(m 2 ·h). The overall flow resistance is identified as the primary factor limiting system performance, with the vapor line contributing approximately 45% of the total pressure drop. Consequently, shortening the vapor line or enlarging its inner diameter can significantly enhance the water production. The driving temperature difference also exerts a marked influence: within the investigated heat-source temperature range of 33-37 °C, the water production rate increases by approximately 46% on average for each 1 °C increase in the heat-source temperature, whereas a 1 °C decrease in the heat-sink temperature yields an approximate 4% improvement. Positioning the compensation chamber above the evaporator allows gravity to assist the capillary driving force, thereby enhancing water production. In this configuration, the system operates in either a gravity-driven or a capillary-gravity co-driven regime, with the former to be avoided to prevent seawater breakthrough.