Evaluation of a solar-powered spray-assisted low-temperature desalination technology

The use of solar energy has huge potential for desalination application due to the geographical coincidence between high solar irradiance and fresh water scarcity. This paper investigates the performance of a spray-assisted low-temperature desalination system powered by solar thermal energy. The proposed system applies a spray evaporator and a coil condenser that operate under low-pressure conditions, which increases evaporation rate and promotes productivity. A numerical model was developed to predict the dynamical system performance. Concurrently, an experimental setup was designed and commissioned to demonstrate the feasibility of the spray-assisted low-temperature desalination system and to validate the model. Applying the developed model, the long-term desalination performance of the system coupled with a flat plate solar thermal collector was evaluated under Singapore's climatic conditions. Additionally, the energy flow inside the system is analyzed in order to highlight the sources of energy losses. Results revealed that the inefficiency of the system is attributed to the losses of both the solar thermal collector and the desalination unit. There exists an optimal feed flowrate that promotes the solar collector performance while minimizing the inefficiency of the desalination unit. The system is able to provide uninterrupted fresh water supply of 30 L per day with a solar collector area of 7.6 m² and a water storage tank of 305 L. The contributions of this paper include: (1) the development of a validated non-steady-state model via the dual experimental and numerical approach; (2) identifying the sources of inefficiencies inside the system through a detail energy flow analysis; and (3) evaluating and optimizing the system based on long-term performance calculated from annual weather data, which provides a more accurate and robust design basis for this type of standalone solar desalination system.