Experiments and insights of desalination by a freezing/thawing method at low subcooling

摘要

Desalination by freezing/thawing method was a very important method to obtain fresh water from seawater.In this work,desalination by freezing/thawing method was conducted with initial sodium chloride of 3.5 wt% in consideration of stirring speed,freezing time and subcooling.The subcooling ranged from 1.2 K to 4 K.The optimum conditions for desalination in this work were stirring speed of 200 r·min^−1,freezing time of 120 min,and subcooling of 3 K.The results also showed that sodiumchloride cannot be effectively removed by once freezing/thawing process.The maximumremoval efficiency of sodiumchloride was 64.3%.Two major reasons resulting in the impurity of obtained melted water by freezing/thawing method were proposed.The first reason was the inevitable adhesion of salt solution to the surface of ice,which could be removed easily by distilled water flushing.The second reason was that salt solution was heterogeneously wrapped in the accumulated ice,which was difficult to be removed by distilled water flushing.The liquid flushing method was proposed to verify the conjecture,and the results were in accordance with the two reasons mentioned above.Additional method,such as multiple flushing liquid method,was suggested to be used during the freezing/thawing process for effectively removing sodium chloride,and obtaining fresh water.