Measurement of the Diffusion Coefficient of Miscible Fluids using Moiré Deflectometry

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Addis Ababa University


Measurements of the diffusion coefficient of two miscible liquids are reported. The liquids are various combinations of sodium chloride (NaCl) and pure water. The liquids were placed in a diffusion cell such that the interface is initially horizontal. As the fluids diffuse, the profile of the index of refraction near the interface is time dependent and is related to the local concentration of the diffusing fluids. The concentration gradient profile was measured, the experimental details and theoretical analysis for obtaining the magnitude of diffusion coefficient using the Moiré fringe patterns are described. In this report the Moiré defelectometery method is applied for measuring the diffusion coefficient of NaCl in pure water at room temperature. The average diffusion coefficient was obtained by analysis of the measured concentration gradient profile, assuming that the diffusion process is one-dimensional and is characterized by a constant value of the diffusion coefficient (D). The value of s D m 2 9 1.58( 0.05) 10    is obtained for diffusion of NaCl molecules in pure water and it is in good agreement with the reported value in literatures



Using Moiré Deflectometry