The Study On The Mechanism Of Droplet Generation In Flow Focusing Microchannels

Micro-fluidic system has a wide range of application in biomedical, chemical industry and petroleum, the research on the governing law of the fluid flow in microchannels has drawn more and more attention. The characteristics of the flow in a microchannel are different from conventional ones, as the surface tension and wet ability have great impact on the flow, therefore it is of importance to study the underlying mechanism, which is still unclear.The main contents for the paper:(1) the effects of viscosity and surface intension on the size and frequency of droplets in a cross microchannel with different width; (2) the effects of the geometry of the microchannel on the size of droplets; (3) develop a model based on the Shan -Chen model to study the formation of bubbles in the microchannels. The results showed that (1) the sizes of droplets decreased with the increasing of viscosity, velocity of continuous phase or the surface intension, and the parameters can be described by the capillary number, the sizes of droplets decreased with the increasing of capillary number; (2) the sizes of droplets decreased with the increasing of degrees, and the degrees have great impact s on the size of droplets when the mechanisms of generating droplets are squeezing or dripping,but the difference of size is very small when jetting. There are no much difference when the degree is bigger than 60°, but significant difference when less than 60°; (3) an equilibrium distribution is introduced into lattice Boltzmann and verified by poiseuille flow. After then, the equilibrium distribution is introduced into multiphase flow and developed the code for solubility, interfacial tension and contact angles. The outflow boundary condition was optimized to be consistent with CBC-AV to understand the formation of bubbles.