Simultaneous measurement of thermal and solutal diffusivities of salt-water solutions from a single-shot dual wavelength interferometric image

The present study is concerned with the simultaneous estimation of thermal and solutal diffusivities of salt-water solutions from a single-shot dual-color interferometric image recorded using real-time dual wavelength interferometric technique. The experimental scheme consists of a two-layered salt stratified medium created in a quartz cell while diffusing thermal conditions have been created by imposing stabilizing temperature boundary conditions at the two horizontal surfaces. The line-of-sight projection data of variations in the refractive index field caused due to changes in the thermal and solutal fields have been recorded using a dual wavelength Mach-Zehnder interferometer. Two distinct monochromatic laser sources i.e. He-Ne (λ1 = 632.8 nm) and Ar-ion (λ2 = 457.9 nm) have been employed for recording the changes in the density field and the corresponding phase changes in the path of the traversing beam have been recorded simultaneously by using Bayer mosaic color CCD sensor. The experiments have been performed with an initial concentration step of ΔCi = 0.25 (wt/wt)% and a temperature gradient of ΔT = 1.2 °C. The results have been presented in the form of dual-color interferometric images, contours of two-dimensional temperature and concentration fields, corresponding profiles of temperatures and concentrations along the central vertical axis at various time instants. The temporal fringe shifts observed in the fringe patterns of two colors enable the simultaneous measurements of solutal and thermal diffusivities in real time. The thermal and solutal diffusion coefficients have been estimated by ensuring the fidelity between the experimentally determined respective fields with the analytical solutions and the values estimated in the present work are in close agreement with the standard values reported in the literature.