Ice crystal growth in the freezing desalination process of binary water-NaCl system

Abstract

In this study, ice crystal growth in the freezing desalination process of binary water-NaCl system is investigated. The phase field method is used to conduct simulation and predict dendrite growth behaviour during the crystallization of sea ice. An experimental setup focusing on the directional crystallization of binary water-NaCl solutions on the horizontal wall is established to verify the e theoretical model. The results show that the crystal with single nucleus obtains obvious six-fold symmetry, while in the competitive crystallization of multiple crystal nuclei, spindle growth is inhibited. Brine channels and salt cells are formed in the directional crystallization, seawater consists of higher Mg2+and SO42− get more difficult in freezing desalination. The degree of subcooling significantly affects the salt cell concentration at the roots, the solid phase ratio, and the height of the planar crystal, while the heat flux significantly affects dendrite growth rate. The experimental average tip growth rate is 9.15 × 10−5 m/s, and the experimental average tip radius is 5.16 × 10−6 m. Peclet number of both simulation and experiment have the same order of magnitudes, with 0.1–0.2 and 0.3–0.6, respectively, which suggests the three-field coupling model established is reasonable for desalination simulation.