Transport phenomena during saline water solidification under top-cooling configuration for desalination purpose

Abstract

Water is essential for life, yet its scarcity is a growing concern due to population growth, climate change, and pollution. Freeze desalination can give salt-free ice, offering energy efficiency and reduced scaling compared to thermal desalination. This study investigates a top cooling solidification of the binary salt system for desalination. During the top freezing of saline solutions, influenced by thermal and solutal effects, transport phenomena contribute to reduced salinity in the resulting ice. A parametric study, varying initial liquid temperatures, top plate freezing temperatures, and initial solute concentrations, identifies optimal conditions for achieving low salinity and efficient ice formation. Thermal and solutal plumes, solute-rejecting channels, and the solidifying interface during top cooling solidification are observed using experiments (shadowgraph, Digital single-lens reflex (DSLR) imaging, and thermocouple measurement history) and two-dimensional numerical simulation. Real-time liquid salinity, ice salinity (measured after the experiment), and ice generation rate give the overall idea of freeze desalination. A close match between experimental and numerical trends of ice salinity with solid height fraction is obtained. Additionally, the thermal history of the bottom copper plate in a rectangular cavity highlights three distinct time regimes of mass and heat transfer within the bulk liquid. A notable temperature rise in thermal history, indicating restricted localized flow, occurs as the solid interface reaches the bottom plate.