Reseearch On Micro-scale Liquid Flow Mass Transfer And Vortex Mixing Technology

As an important branch of the microfluidic chip,the micromixer has achieved great development in medicine,biology,chemistry and other fields,and has been widely applied for its unique advantages.Influenced by the change of characteristic scale,many new problems have arisen in the flow and mass transfer in micro-scale liquids.It is very important for the development of microfluidic devices to understand the change rules in micro-scale liquid flow mass transfer.This paper focuses on the systematically study the mechanism of the flow and mass transfer of microchannel liquids under the effect of wall roughness,the fluid flow and mass transfer laws under the influence of roughness effects were obtained.Taking the development of liquid liquid passive mixer with simple structure and high efficiency and stable mixing performance in a large Re range,a new passive vortex micromixer is constructed by using Coanda effect in fluid mechanics.And the application of the micromixer for related experimental research.The main research contents are as follows:(1)In order to study the influence of the random roughness of the microchannel surface on liquid flow and mass transfer characteristics,random wall roughnesses of micro-channels were constructed using typical roughness elements based on the random arrangement criteria.Finite element analysis method was used to analysed the influence of factors such as the type,height and spacing of the near-wall surface roughness on the flow rate,pressure gradient,flow resistance,mass transfer mechanism and other factors in the microchannel.The study shows that the presence of roughness in the near-wall region of the microchannel has a significant effect on the fluid flow field,and there are obvious vortices and flow separation phenomena in the fluid near the wall.The pressure drop and flow resistance at each location in the random rough microchannel increase approximately linearly with the increase of the relative height of the roughness elements,and the amplitude near the outlet is more obvious.The existence of the microchannel wall roughness accelerates the diffusion rate of fluid molecules mass transfer,but it is greatly affected by roughness type and relative roughness height.(2)The mixing mechanism of the vortex-type passive micromixer based on the Coanda effect was described using the finite element analysis method.Two mixing mechanisms of the vortex-type passive micromixer were revealed: eddy current mixing and chaotic mixing induced by secondary flow.The effects of two important parameters of the vortex-type passive micromixer channel structure,the depth H of the microchannel and the mixed element arc labyrinth cavity K,are analyzed in detail,and the values of the optimal structure parameters are given.(3)Through the intermixing experiments of liquids,the two mixing mechanisms in the vortex-type passive micromixer are verified: eddy current mixing and chaotic mixing induced by secondary flow;The significance of vortex flow for improving the mixing performance of passive micromixer is analyzed.The mixed performance has been quantitatively verified by digital image processing method,demonstrating the wide application prospects of the vortextype passive micromixer in the fields of high Re number and high flux.