Numerical simulation and experimental analysis of ice crystal growth and freezing-centrifugal desalination for seawater with different compositions

Abstract

In this study, numerical and experimental studies of ice directional crystallization for the NaCl, Na2SO4, MgCl2, and MgSO4 solutions were investigated. The comparison of energy consumption between freezing-centrifugal desalination and the conventional method was discussed. The phase-field method was employed to simulate the ice directional crystallization process. A microscope experimental setup was established to observe the morphology of dendrites and verify the theoretical model in the directional crystallization process. The absolute deviations of the average width of the brine channel between numerical and experimental results are less than 15%, which indicates that the phase-field method can present the performance of ice directional crystallization well. The results also showed that in the directional crystallization process, the solutions with SO42- (Na2SO4 and MgSO4 solutions, and their mixtures) form narrower brine channels than that of NaCl and MgCl2 solutions due to their low diffusion coefficient. Moreover, the impacts of ions and brine channel on the freezing-centrifugal desalination were investigated by the experiments. When the rotation speed and centrifugal time were set at 5000 rpm and 2.0 min, respectively, the salt removal efficiency of NaCl and MgCl2 was higher than 96%, while they were less than 13% for the Na2SO4 and MgSO4 solutions. Hence, the SO42- ion plays a significant role in preventing sea ice desalination due to narrower brine channels.