Enhancing freeze desalination via stirring-induced modulation of thermal and solute transport at the ice-liquid interface

• Integrated experiments and CFD to analyze ice/solute dynamics in freezing brine. • Mechanical stirring enhances salt removal efficiency. • Identified preferential ice growth at the top of the brine. • Discovered that ice purity increases over time. • Provided design guidance for optimizing freeze desalination systems. Optimizing crystallization dynamics and solute separation in freeze desalination (FD) remains challenging due to non-uniform thermal gradients and complex fluid behavior. This study investigates the effect of mechanical stirring on FD performance using a custom-designed, jacketed cylindrical crystallizer. A synthetic NaCl solution (35 g/L) was subjected to radial directional freezing under varied stirring conditions to evaluate changes in desalination efficiency. Experimental measurements of brine temperature and ice salinity were complemented by a validated computational fluid dynamics (CFD) model simulating thermal and solute transport during freezing. The model captured key trends observed experimentally, including ice growth patterns and salinity evolution, with minor deviations attributed to heat losses. Initially, ice nucleated along the cooled wall, driven by the imposed radial temperature gradient. Over time, salt rejection increased brine density, inducing buoyancy-driven stratification and shifting ice accumulation toward the top of the crystallizer, where salinity was lower. Stirring disrupted these gradients, homogenizing temperature and concentration fields. Sensitivity analysis revealed that stirring at 60 rpm improved salt removal efficiency to 67 %, compared to 59 % under static conditions, without reducing ice yield. Stirring moderated thermal and solutal boundary layers, delayed salinity buildup at the ice–liquid interface, and promoted more uniform crystal growth. These findings demonstrate that mechanical stirring can be used strategically to enhance desalination performance of FD technology. The insights gained offer guidance for optimizing FD systems through informed control of hydrodynamics and crystallization behavior, contributing to the development of energy-efficient separation technologies for sustainable water resource management.