Salt-finger convection generated by lateral heating of a solute gradient

When a tank of fluid with a solute gradient is subjected to lateral heating, a series of horizontal convection cells is generated when the critical condition is exceeded. This phenomenon has been observed experimentally and simulated by two-dimensional numerical schemes by a number of previous investigators. In each of the convection cells, relatively warm and solute-rich fluid flows from the hot to the cold wall along the top of the cell while the return of the relatively cool and solute-poor fluid is along the bottom of the cell. This situation is conducive to the onset of salt fingers. We recently performed a series of such experiments with salt-water and ethanol-water solutions. By using flow visualization techniques, salt fingers in longitudinal rolls typical of those occurring in shear flows were observed. Salt fingers were observed as soon as convection was initiated, and they advanced with the convection front. Experiments with an ethanol-water solution showed that salt fingers can be generated by flows driven by a surface tension gradient and that the effect of solute concentration on surface tension plays an important role in the process.