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Continuous-flow microchannels are widely employed for synthesizing various materials, including nanoparticles, polymers, and metal-organic frameworks (MOFs), to name a few. Microsystem technology allows precise control over reaction parameters, resulting in purer, more uniform, and structurally stable products due to more effective mass transfer manipulation. However, continuous-flow synthesis processes may be accompanied by the emergence of spatial convective structures initiating convective flows. On the one hand, convection can accelerate reactions by intensifying mass transfer. On the other hand, it may lead to non-uniformity in the final product or defects, especially in MOF microcrystal synthesis. The ability to distinguish regions of convective and diffusive mass transfer may be the key to performing higher-quality reactions and obtaining purer products. In this study, we investigate, for the first time, the possibility of using the information complexity measure as a criterion for assessing the intensity of mass transfer in microchannels, considering both spatial and temporal non-uniformities of liquid's distributions resulting from convection formation. We calculate the complexity using shearlet transform based on a local approach. In contrast to existing methods for calculating complexity, the shearlet transform based approach provides a more detailed representation of local heterogeneities. Our analysis involves experimental images illustrating the mixing process of two non-reactive liquids in a Y-type continuous-flow microchannel under conditions of double-diffusive convection formation. The obtained complexity fields characterize the mixing process and structure formation, revealing variations in mass transfer intensity along the microchannel. We compare the results with cases of liquid mixing via a pure diffusive mechanism. Upon analysis, it was revealed that the complexity measure exhibits sensitivity to variations in the type of mass transfer, establishing its feasibility as an indirect criterion for assessing mass transfer intensity. The method presented can extend beyond flow analysis, finding application in the controlling of microstructures of various materials (porosity, for instance) or surface defects in metals, optical systems and other materials that hold significant relevance in materials science and engineering. Graphic Abstract [ABSTRACT FROM AUTHOR]

This paper focuses on experimental investigations of the spatio-temporal distributions of fluid velocity and temperature and the concentration of reagents and reaction products. We study concentration-dependent diffusion (CDD) convection driven by the neutralization reaction in a two-layer miscible system in a vertical Hele-Shaw cell using the original experimental complex. A comprehensive understanding of the physical mechanisms of convective motion and instabilities requires employing various experimental methods simultaneously. The proposed experimental complex provides simultaneous visualization and facilitates identification of the location of the reaction front, which is of importance to the study of its characteristics.

This study is devoted to the investigation of the chemoconvection in a two-layer miscible system caused by the neutralisation reaction proceeding in the convective-controlled (CC) regime under the influence of vertical vibrations. The CC regime without vibrational influence is characterized by the development of a density wave and vigorous convection in the upper layer, ensuring a high reaction rate and forcing the reaction front to move downwards more rapidly than in the well-known diffusive-controlled (DC) regime. It is shown that vibrations lead to some deceleration of the convection that depends both on the magnitude of the vibrational acceleration and on the initial concentrations of the reagents. Analysis of the system behaviour depending on the dimensionless parameters is carried out. It is demonstrated that the theory of thermal vibrational convection may be applied for reacting systems on quasi-steady time intervals. [ABSTRACT FROM AUTHOR]