INTERFACIAL INSTABILITY ON BUBBLE SURFACE DURING CHEMOSORPTION
Advancing the chemical engineering fundamentals
Interfacial & Colloidal Phenomena - I (T2-6a)
Keywords: interfacial instebility, bubble, chemosorption
The problem of generation and time evolution of convective structures arisen due to chemical reactions became a subject of numerous studies in connection with the search for more intensive mass transfer mechanisms than simple molecular diffusion. The phenomena of chemo-gravitational and chemo-capillary instability manifest itself in the appearance of simultaneous convective flows near the gas-liquid interface due to gravitation and surface tension forces. This happens during chemosorption when the density of the reaction product differs from that of medium.
With the use of interference microscope we could visualized at a real time scale the evolution of interfacial instability near a spherical bubble of carbon dioxide formed on the end of microsyringe needle and mounted in the water solution of a base. This gave the possibility to describe in detail the principle stages of instability, to estimate its duration and to suggest a physical interpretation of the experimental pattern.
The appearance of the reaction product at the bubble surface is observed only after some period which may last several seconds after the inert gas is substituted by carbon dioxide. One can clearly see the elevating convective flows of the liquid heated due to the heat of reaction. At this stage the chemical reaction seems to proceed via the diffusion-kinetic mechanism. Approximately at the same time the movement of the liquid along the interface is detected. Such behavior is inherent in chemo-capillary instability which intensifies heat and mass transfer near the interface. Later on, the film of reaction product becomes more and more thick and starts to precipitate along the bubble surface to its bottom as if it is a separate quasi phase, possessing its own surface tension. This corresponds to the chemo-gravitational mechanism of instability. At the last stage, droplets of reaction product are formed at the bottom part of the bubble. The size of droplets is defined by the chemical composition of the water solution. Periodically droplets leave the surface and precipitate into the surrounding liquid without intermixing.
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Presented Wednesday 19, 16:20 to 16:40, in session Interfacial & Colloidal Phenomena - I (T2-6a).
