Salinity signaled by trapped air bubbles during freezing desalination

With its low cost and low energy consumption, seawater desalination is expected to become an effective approach to alleviating freshwater scarcity. Existing research has largely focused on freezing methods and desalination devices at the macroscopic level, while insufficient attention has been paid to the microscopic mechanisms, particularly trapped bubbles that affect heat and mass transfer processes. To address this gap, this study employed a Hele-Shaw cell to freeze a single-layer saline solution, with a focus on analyzing the influence of salinity on the freezing process and trapped air bubble behavior. The results show that the freezing rate gradually decreases with increasing salinity, leading to a reduction in the number of trapped air bubbles and an increase in their average size. As salinity increases from 10⁻⁴% to 3.5%, bubbles almost completely disappear in the ice formed from solutions with a salinity of 10⁻¹%. This study reveals the quantitative relationship and influence patterns between salinity and the formation and distribution characteristics of trapped air bubbles. On this basis, trapped air bubbles working as an indicator of desalination performance is innovatively proposed and its feasibility theoretically validated. This provides theoretical support for improving the efficiency of freezing desalination.