For microfluidic systems, interfacial phenomena in micro-reactors are of great importance because they control the transfer and reaction characteristics. This paper dwells on how the surface property and geometry influence the mass flux in a complex microchannel. The lattice Boltzmann method(LBM) with a pseudo potential model and the Shan–Chen model for the interaction between fluid and hydrophobic surface were built up, so a boundary slip effect was added and verified. On this basis, a microchannel with variable-section geometry was simulated. The results indicate that the optimal design and the flow pattern are quite different under hydrophilic and hydrophobic conditions. A microchannel with sequential hydrophilic and hydrophobic surface was also simulated. The numerical results indicate that the hydrophobic wall can improve the mass flux, irrespective of microchannel geometry. Particularly, an empirical correlation with a linearly relationship between length of hydrophobic segment and mass flux was obtained for the straight microchannel.
This work presents a numerical investigation on steady internal, external and surface flows of a liquid sphere immersed in a simple shear flow at low and intermediate Reynolds numbers. The control volume formulation is adopted to solve the governing equations of two-phase flow in a 3-D spherical coordinate system. Numerical results show that the streamlines for Re = 0 are closed Jeffery orbits on the surface of the liquid sphere, and also closed curves outside and inside the liquid sphere. However, the streamlines have intricate and non-closed structures for Re ≠ 0. The flow structure is dependent on the values of Reynolds number and interior-to-exterior viscosity ratio.
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.
