Cryo-powered desalination: Experimental investigations on brine droplets freezing in a natural convection environment

Abstract

Freeze desalination (FD) is an energy-efficient desalination method that shows promise over traditional thermal-based approaches. FD requires minimal energy by utilizing latent heat of fusion during the phase transition of saltwater from liquid to solid state. However, the stochastic nature of nucleation and salt trapping in the formed ice has hindered industrial implementation. This study focuses on experimental investigations of ice nucleation during the freezing of brine droplets. The effects of droplet size (3–9 μL), salinity (0–70 g/L), and freezing temperature (−15 °C to −40 °C) on nucleation behavior are examined. Results showed that smaller droplets exhibit faster cooling rates, reduced supercooling degrees (SD) (12.00 to 9.81 °C), and quicker nucleation onset (117.95 to 72.7 s). Higher droplet salinity leads to decreased nucleation temperatures (from −13.89 to −15.32 °C) while lower freezing temperatures enhance cooling rates and reduce nucleation times (from 123.6 to 48.2 s). The analytical model has accurately predicted nucleation times and temperature evolution. Simulation results suggest that freezing at extremely low temperatures, i.e., −40 °C, yields to shorter nucleation time, i.e., 50 s for 5μL brine droplet. Varying initial temperatures (20–50 °C) showed faster precooling but delayed nucleation, while nucleation temperatures remain consistent. These insights contribute to optimizing FD for energy-efficient desalination.