Study on formation of unstable clathrate-like water molecules at freezing/melting temperatures of water and salty water

SMF Sh and M Foroutan, FLUID PHASE EQUILIBRIA, 384, 73-81 (2014).

DOI: 10.1016/j.fluid.2014.10.007

Having performed simulations for the pure waterand water-NaCl salt mixture at several temperatures, we reveal new aspects of the formation of unstable clathrate-like water molecules in coexistence with ice molecules. Interestingly, the maximum numbers of water molecules in clathrate hydrate phase are recorded at freezing/melting points of the pure water and water-salt mixture. In the presence of NaCl salt, the number of water molecules in the unstable formed clathrate phase decreases. We first perform molecular dynamics simulations using the coarse-grain model to study the freezing/melting behavior of the pure water and 14% water-salt mixture at several temperatures, For both systems, the freezing/melting behavior of water molecules is studied using some qualities such as density, number of ice molecules, coordination number, and liquid fraction. From the results of our study, we also show that calculating the coordination numbers of water, sodium and chloride ions at different temperatures can serve as a useful method for determining the freezing/melting temperature for the pure water and salty water, and also for the brine rejection process for water-salt mixture. In the pure water, large changes occur at the freezing/melting point for the coordination numbers both for the first and higher coordination shells. (C) 2014 Elsevier B.V. All rights reserved.

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