Abstract
Continuous-flow microreactors are an important development in chemical engineering technology, since pharmaceutical production needs flexibility in reconfiguring the synthesis system rather than large volumes of product yield. Microreactors of this type have a special vessel, in which the convective vortices are organized to mix the reagents to increase the product output. We propose a new type of micromixer based on the intensive relaxation oscillations induced by a fundamental effect discovered recently. The mechanism of these oscillations was found to be a coupling of the solutal Marangoni effect, buoyancy and diffusion. The phenomenon can be observed in the vicinity of an air–liquid (or liquid–liquid) interface with inhomogeneous concentration of a surface-active solute. Important features of the oscillations are demonstrated experimentally and numerically. The periodicity of the oscillations is a result of the repeated regeneration of the Marangoni driving force. This feature is used in our design of a micromixer with a single air bubble inside the reaction zone. We show that the micromixer does not consume external energy and adapts to the medium state due to feedback. It switches on automatically each time when a concentration inhomogeneity in the reaction zone occurs, and stops mixing when the solution becomes sufficiently uniform.
Highlights
In the last decades, the interaction between reaction–diffusion phenomena and hydrodynamics has attracted increasing interests both from the fundamental point of view of nonlinear science and from application-oriented aspects in chemical engineering [1,2,3,4]
The interaction between reaction–diffusion phenomena and hydrodynamics has attracted increasing interests both from the fundamental point of view of nonlinear science and from application-oriented aspects in chemical engineering [1,2,3,4]. This arises from the fact that the chemically-induced changes of fluid properties such as density, viscosity, thermal conductivity or surface tension may result in flow instabilities, which exhibit a large variety of convective patterns
It is subjected to high solute concentration at the upper side, implying low interfacial tension since isopropyl alcohol makes the surface tension lower, and low concentration at the bottom, i.e., high interfacial tension
Summary
The interaction between reaction–diffusion phenomena and hydrodynamics has attracted increasing interests both from the fundamental point of view of nonlinear science and from application-oriented aspects in chemical engineering [1,2,3,4] This arises from the fact that the chemically-induced changes of fluid properties such as density, viscosity, thermal conductivity or surface tension may result in flow instabilities, which exhibit a large variety of convective patterns. Since the pharmaceutical production needs flexibility in reconfiguring the synthesis system rather than high throughput, increasingly miniature reactor design concepts are established [5,6]. This new reactor type provides several advantages with respect to the traditional batch-reactor. The different design and operation mode leads to following features:
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