(566d) Hydrodynamics and Mass Transfer of Gas-Liquid Flow in a Tree-Shaped Parallel Microchannel with T-Type Bifurcations

Gas-liquid systems are widely encountered in various chemical processes. However, the process efficiency is usually insufficient in traditional equipment. As an effective approach for process intensification, micro-chemical technology has received increasing attention. It has been verified that the mass transfer efficiency of a single microchannel is much higher than that of the conventional reactors. To maintain the merit of micro-scale, the numbering-up strategy has been adopted to implement industrial throughputs. Nevertheless, the numbering-up strategy could cause negative effects on hydrodynamics and mass transfer. Therefore, the study of the dependence of hydrodynamics and mass transfer of gas-liquid two-phase flow on the operating conditions in parallel microchannels is indispensable for the optimization of design and operation of commercial microreactor.

In this study, the hydrodynamics and mass transfer of gas-liquid two-phase flow in a tree-shaped parallel microchannel constructed by T-type bifurcations are investigated experimentally. The results show that the flow distribution is corporately determined by the capillary number Ca at the T-type bifurcation and the hydrodynamic feedback effect of the end of branches. At a fixed absorbent concentration, there exists a critical ratio of gas flow rate to liquid flow rate for an optimal flow distribution. Before the critical point, the uniformity of flow distribution becomes better with increasing the ratio, but it would gradually deteriorate beyond the critical point. Meanwhile, the operating condition also determines the flow regime in each branch, thereby influences the mass transfer performance. Before the critical ratio, bubbly flow or slug flow occurs in the branch, and the specific surface area extends with the increase of the ratio. However, beyond the point, the flow regime evolves into the compact slug flow, the specific surface area only decreases slightly with the increase of the ratio, and the liquid slug in the branch almost disappears, consequently the mass transfer depends mainly on the liquid film surrounding the main body of bubble instead of the liquid slug. Due to the change of hydrodynamics in the microchannel, the volumetric mass transfer coefficient decreases with the increase of the gas-liquid flow rate ratio after the critical point.

In conclusion, the hydrodynamics in the tree-shaped parallel microchannel is much different between before and after critical point. Therefore, the determination of the critical point of the gas-liquid flow rate ratio could effectively avoid the negative effect and thereby maintain the excellent performance like in a single microchannel.