Coastal nuclear power plants discharge large amounts of warm cooling water, releasing low-grade heat to the marine environment. Using part of this heat for seawater desalination can reduce thermal discharge while producing freshwater. This study experimentally evaluated a low-temperature flow-flash desalination system with passive natural circulation in the main loop (PFFD-NCF). Seven tests were conducted near a separator temperature of 40 °C, covering flash superheat of 7.5-12.5 °C, make-up-water subcooling of 5-11 °C, and brine-discharge ratios of 50-200%. Natural circulation, flow flashing, vapor-liquid separation, condensation, and freshwater production were maintained without a main circulation pump. A representative setting combined a 40 °C separator temperature, 7.5 °C flash superheat, 5 °C make-up-water subcooling, and a 50% brine-discharge ratio. Under this setting, mean circulation mass flow rate was 0.396 kg/s and separator pressure was 6.97 kPa. Repeated tests confirmed reproducible operation. Product-water salinity readings were 1-5 ppm, compared with approximately 35 g/kg for the feed. Based on main-heater heat absorption, the preliminary specific thermal energy consumption ranged from 2486 to 2750 kJ/kg, with a corresponding gain-output ratio of 0.88-0.97. At the representative setting, the specific thermal energy consumption was 2486 kJ/kg and the gain-output ratio was 0.97, close to the previously predicted ranges of 2471-2484 kJ/kg and 0.96-0.97. The selected auxiliary electricity consumption was 6.53-7.90 kWh/t and was mainly caused by the laboratory cooling-water pump. The close agreement between experiment and theory demonstrates the capability of PFFD-NCF to use low-temperature waste heat from nuclear power plants efficiently.

Keywords: low-temperature desalination; nuclear waste heat; natural circulation; flow flashing; experimental investigation; energy consumption