Yumei Yong

Mixing Characteristics and Bubble Behavior in an Airlift Internal Loop Reactor with Low Aspect Ratio

The present study summarizes the results of macro-and micro-mixing characteristics in an airlift internal loop reactor with low aspect ratio (H/D <= 5) using the electrolytic tracer response technique and the method of parallel competing reactions respectively. The micro-mixing has never been investigated in airlift loop reactors. The dual-tip electrical conductivity probe technique is used for measurement of local bubble behavior in the reactor. The effects of several operating parameters and geometric variables are investigated. It is found that the increase in superficial gas velocity corresponds to the increase in energy input, liquid circulation velocity and shear rate, decreasing the macro-mixing time and segregation index. Moreover, it is shown that top clearance and draft diameter affect flow resistance. However, the bubble redistribution with a screen mesh on the perforated plate distributor for macro-mixing is insignificant. The top region with a high energy dissipation rate is a suitable location for feeding reactants. The analysis of present experimental data provides a valuable insight into the interaction between gas and liquid phases for mixing and improves the understanding of intrinsic roles of hydrodynamics upon the reactor design and operating parameter selection.

Direct simulation of the influence of the pore structure on the diffusion process in porous media

In this paper, we numerically study the influence of pore structures on diffusion processes in porous media. The porous media geometry models are constructed based on two-dimensional Voronoi diagrams, and they feature randomly connected channels with large pores embedded to simulate the heterogeneity of porous media. A link-type two-relaxation-time (LTRT) lattice Boltzmann (LB) method is employed to solve the diffusion equation. The tortuosity is characterized as a function of porosity and pore structure. From numerical results, a correlation for the tortuosity as a function of porosity is derived for Voronoi geometries without large pores. Geometries with large pores at the same total porosity have higher tortuosity, which indicates that geometric heterogeneity slows down the diffusion.

Transport of Wetting and Nonwetting Liquid Plugs in a T-shaped Microchannel

The transport of liquid plugs in microchannels is very important for many applications such as in medical treatments in airways and in extraction of oil from porous rocks. A plug of wetting and non-wetting liquids driven by a constant pressure difference through a T-shaped microchannel is studied numerically with lattice Boltzmann (LB) method. A two-phase flow LB model based on field mediators is built. Three typical flow patterns (blocking, rupture and splitting flow) of plug flow are obtained with different driving pressures. It is found that it becomes difficult for a plug with short initial plug length to leave the microchannel; the flow pattern of plug transport varies with the contact angle, especially from wetting to nonwetting; with the increase of interfacial tension, the front interface of plug moves faster; the front and rear interfaces of the plug with small viscosity ratio move faster in the microchannel than those of the plug with large viscosity ratio. The study is helpful to provide theoretical data for the design and scale-up of liquid-liquid reactors and separators.