Freeze desalination of drops of saline solutions

Abstract This study investigates freeze desalination achieved through partial freezing of drops of saline solutions. Firstly, a parametric study is performed to determine the ice recovery (%) and salinity reduction (%) for drops of NaCl solutions as a function of drop size, NaCl concentration and freezing temperature. It was shown that desalination can be achieved in millimetric drops at freezing temperatures pertinent to their partial freezing state. Overall, greater supercooling degrees were required for higher salt concentrations, leading to a higher ice recovery (%) in smaller drops for a given salt concentration. The salinity reduction (%), however, reduced linearly as the ice recovery (%) increased, with drops of greater salt concentrations showing the least salinity reduction. The higher ice growth rate experienced by such drops is believed to be responsible for the observed lower salinity reduction (%). A map of freezing state is developed for drops of 1, 3.5 and 6 wt% NaCl solution. The map identifies the drop's state of freezing in terms of unfrozen, partially frozen, and fully frozen state. This map can be employed to identify the temperature range required for achieving partial freezing of saline drops, the pre-requisite for drop-based freeze desalination processes.