Prototype Development of a Two-Stage Hydrogel–CaCl₂ Absorption–Desorption Device for Atmospheric Water Harvesting

Freshwater scarcity has become a pressing global challenge, driving the need for innovative and sustainable water production technologies. Atmospheric water harvesting offers a promising solution by exploiting the vast reservoir of water vapor in the air, particularly for arid and remote regions. In this study, we developed a novel two-stage moisture absorption–desorption system using a highly hygroscopic hydrogel–CaCl₂ composite (7.4% hydrogel, 92.6% CaCl₂). The device comprises an absorption compartment equipped with 10 trays (0.675 kg of the composite per tray) for capturing atmospheric moisture and a condensation–recovery compartment integrated with a refrigeration system for efficient desorbed vapor condensation. The system operates in cyclic absorption and thermally driven desorption phases, with each phase offering fully programmable and controllable duration. The desorbed vapor is subsequently directed into a condensation chamber, where it is recovered through an integrated refrigeration unit, and discharged from the system. Experimental results demonstrated a freshwater production capacity of approximately 1 L per day, under air relative humidity of approximately 33%. This integrated approach highlights the potential of hydrogel–salt composites coupled with active condensation for atmospheric water harvesting applications.