The energy efficiency of multistage interfacial desalination: Comprehensive analysis and further improvement strategy

Multistage interfacial desalination is a promising strategy to address global freshwater scarcity due to its ultrahigh energy conversion efficiency. While numerous researches focus on materials improvement and system design, the underlying mechanisms of energy efficiency improvement are less explored. In this work, we establish a theoretical framework based on energy conservation and heat and mass transfer to comprehensively analyze the energy efficiency of multistage interfacial desalination. We demonstrate that there is an efficiency upper limit of 894 % under ideal conditions, which is mainly limited by the unavoidable sensible heat loss from the fresh water. Furthermore, we show that a typical ten-stage desalination system with a lab scale (10 cm x 10 cm) can reach a calculated efficiency of 232 %. An energy loss analysis allows us to identify another important heat transfer term, the wick where the evaporator takes seawater, which also causes significant heat loss. Experiments are conducted to show that better thermal insulation on wick can enhance energy efficiency. Moreover, we found that the system efficiency can be improved by enhancing the internal convective heat and mass transfer. This work provides insights into physical processes involved in multistage interfacial desalination and offers important guidance for further performance improvement towards its application.