Ice distillation is a thermal water purification method that utilizes freezing as a means of concentrating salt in a salt-water solution. The method can be used to produce very high concentrations of waste, i.e., brine, and yields high quality water, depending on the freezing rate among other factors. This method is distinct from traditional freeze purification methods, in that ice is used only for its ability to separate ions from water and where the ice is not used per se as the source of pure water. As such, with proper thermal design, the method can potentially operate at efficiencies comparable to those of reverse osmosis at low infinite dilution. A prototype water desalting apparatus is built and tested to verify a 1-D theoretical model. Using control volume analysis, equations that account for all the species present in an electrolytic solution (salt, water, ice) were developed. A set of assumptions were made considering a steady-state 1-D flow, i.e., a continuously well-mixed solution moves axially, ice and brine are formed transversely and brine is being rejected transversely. Three equations for the solution density, flow velocity and volume fraction of ice are obtained that form a coupled set of first-order evolution equations. The equations are solved numerically in non-dimensional form for different input functions for ice generation rate and rejected solution velocities in the axial direction. Underlying this process is the ability of ice, when frozen in a salt-water solution, to reject salt ions from the ice structure. The partitioning of solute and water during freezing on a polymer surface is key to concentrating salt in ice-liquid solution. The aim is to concentrate salt in solution via thin-film ice formation to nearly the precipitation limit, without entraining salt within the ice itself. The hypothesis is that ice with thickness below 100 μm prevents dendritic ice from forming, thus limiting entrainment of salt. We report on the generation of ice on a polymer at frequencies from 1 to 100 Hz which varies the thickness of the ice sheet on detachment. The concentration of salt-in-solution will be reported for different thicknesses of ice. The goal is to optimize the prototype that leads to a low-cost, high efficiency, fouling-resistant desalinator.
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