Experimental investigation of double-diffusive convection in a quasi-two-dimensional chamber during the unidirectional solidification of binary solutions*

Importance of double diffusive convection during unidirectional solidification of binary solutions has been realized in the literature. The present experimental work, conducted using a combination of non-intrusive measurement techniques, pertains to the study of the onset and further development of double diffusive layers (DDLs) during unidirectional solidification of Succinonitrile-ethanol binary solution. The associated flow (PIV) and transported parameters (temperature and species concentration through dual-wavelength interferometry) have been mapped in real-time. In addition, rainbow-schlieren deflectometry has been used for recording the real-time convection transients, plumes and DDLs, which, in turn, lead to the creation of stepped structure of composition and temperature in the fluid domain. The experimental observations from different techniques revealed the continuous evolution of convective rolls inside DDLs along with several key characteristics e.g., size, shape, inclination, sense of rotation, downward movement etc. A combination of solutal and thermal Rayleigh numbers have been quantified to characterize the double-diffusive convection. The experimental results are additionally supported with analytical scales of length, time, velocities etc.