Real-time two-color interferometric technique for simultaneous measurements of temperature and solutal fields

Development of a real-time Mach-Zehnder based dual wavelength interferometry technique for studying the double-diffusive convection phenomena is presented. The interferometer employs two different monochromatic light sources with wavelengths of λ1 = 632.8 nm and λ2 = 457.9 nm. A high resolution color CCD sensor has been employed to record the interferograms that carry phase information pertaining to the coupled effects of the two wavelengths used. Phenomenon of double-diffusive convection has been set up in a two-layered salt-stratified solution that is destabilized by isothermal heating at the bottom wall of the test cell. The resultant changes in the thermal and solutal fields have been simultaneously captured using the developed interferometric technique. Experiments have been performed at a stability ratio of Rρ = 1.02 and thermal Rayleigh number of RaT = 6.0 × 105. The work presents a detailed methodology for quantitative determination of temperature and/or concentration fields from a single dual wavelength interferogram. Results have been presented in the form of dual color interferometric images and contours of whole-field temperature distribution as a function of experimental run time. The two-dimensional contours of concentration field at time instant t = 0 min have been presented. The observed variations in the fringe patterns are primarily due to thermal gradients prevailing in the fluid layer. In addition to the quantitative studies, interferometer also acts as a flow visualization tool and fringe patterns give qualitative insights into the flow field. The fringe patterns indicate towards the possibility of the existence of mechanical coupling between the two fluid layers wherein the direction of circulatory movement of fluids in each layer is oppositely oriented.