Experimental approach to study mass transfer in liquid–liquid systems under vertical piston oscillations

In the paper, a novel experimental setup is introduced that is designed to investigate the dynamics of two-layer liquid–liquid systems under vertical piston oscillations. It can operate within a wide range of fluid properties, including miscible and immiscible, reactive, and non-reactive pairs of liquids. The oscillations are driven by the motion of a high-precision linear motor, whose forcing is transmitted to fluids via membranes and a hydraulic circuit. The system’s flexibility allows for precise adjustment of vibration parameters (frequency and amplitude), facilitating a detailed examination of their effects on fluid dynamics. The setup developed is used in the present work for experiments on a two-layer system composed of aqueous sugar and salt solutions, focusing on the study of double-diffusive convection dynamics. Under oscillatory conditions, experimental results demonstrate a significant reduction in the mixing time between the salt and sugar solutions in the zone of contact between the layers, with nearly one order of magnitude enhancement in the mixing rate compared to non-vibrational experiments. Meanwhile, the oscillations have little impact on the development of finger patterns within the considered duration of experiments. This acceleration in mass transfer processes is attributed to the disruptive effect of oscillations on stable layer stratification, promoting efficient interlayer mixing. The findings underscore the potential applications of controlled vibrations in enhancing fluid mixing dynamics across various scientific and engineering disciplines, especially in real-world marine environments, such as improving oceanic productivity through enhanced mixing strategies.