Experimental investigation of sustainable solar desalination with pulsed air–water injection: Energy, exergy, and image processing-based analysis

In arid and semi-arid regions, the scarcity of freshwater resources and the high cost of industrial distillation systems have made the supply of clean drinking water challenging. In this context, solar energy as a clean, low-cost, and readily available resource is considered a suitable option for freshwater production. Therefore, the design and optimization of high-efficiency solar desalination systems are essential from both economic and environmental perspectives. This study investigates the combined effects of a solar air heater and a water spray cooling system, both utilizing pulsed injection, on enhancing the condensation rate and efficiency of a solar still desalination system. Series of experiments were conducted over three days on two designed setups. To examine the aforementioned effects in more detail, image processing was used on bubbles created in water. Results show that spraying water on the glass cover at 5-, 10-, and 20-min intervals increases the contact angle of water droplets, shifting condensation from a film to discrete droplets. Increasing airflow through the solar air heater and pulsed flow injection boosted water bubble formation, enhancing evaporation and condensation rates. Applying cold water pulses improved the total internal heat transfer coefficient daily by 14.26 %, 32.43 %, and 54.38 % the 5-, 10-, and 20-min pulses, respectively. Energy efficiency of improved system increased by 37.57 %, 102.36 %, and 187.27 %, while exergy efficiency rose by 42.60 %, 158.57 %, and 306.50 %. Economic analysis showed annual freshwater production increased by 30.47 %, 39.89 %, and 49.52 % for the respective pulse durations. Water spraying reduced glass surface temperature, further enhancing condensation and freshwater production, as confirmed by thermal imaging. The freshwater quality met WHO drinking water standards. These findings demonstrate that integrating solar air heaters, pulse injection, and cooling systems improves energy and exergy efficiency, increases economic profitability, and reduces operational costs.