CFD Numerical Simulation Of Droplet Formation In A Microfluidic Chip Base On The Shear Method Of T-junction Channel

Microfluidic technology is a newly-developing interdisciplinary subject that involves in chemistry, fluid physics, micro-electronics, new materials, biology and biomedical engineering. Nowadays, microfluidic technology is widely applied in biomedicine, material synthesis and drug screening, etc., fields and is promising in these fields. As everyone knows that micro-droplet is an important brand of microfluidic technology. In recent years, micro-droplet that utilizes micro-fluidic chips to make preparations for it is increasingly concerned for its good monodispersity, high degree of uniformization, and accurate and controllable size. Micro-channel T-junction is the commonest method to prepare for micro-droplet, but research on mechanism of generating micro-droplet by micro-channel T-junction is not common, and research makes slow progress. Now, it mainly concentrates on the experimental research stage, but it has no uniform theoretical model. The numerical analog simulation experiment is an essential and effective research. CFD technology can be used to do numerical simulation on the formulation process of micro-droplet in micro-channel T-junction in micro-fluidic chips, reveal forming criterion of micro-droplet under microscale, and provide a theoretical basis for applications of micro-biochemical analysis, etc., fields. This will have extremely important significance on enriching micro-droplet and broadening theoretical system of microfluidics.Aiming at characteristics of two-phase flow and beginning with actual application demands, a theoretical equation of forming process for micro-droplet is established, namely VOF equation and flow control equation. A numerical modeling experiment of forming process for micro-droplet is achieved by solving the established mathematical model. The method overcomes limitations of traditional experimental research and analyzes influences of relevant parameters on micro-droplet formation systematically.Image processing method is used to calculate the size of micro-droplet, while bitmap conversion process and MATLAB are utilized to do size analysis. First of all, the paper conducts bitmap processing, introduces them into Matlab, establishes pixel matrix, utilizes RGB to distinguish from oil phase, water phase and other pixel points, as well as adopts k-means algorithm to classify independent drops, and finally calculates the size of drops through procedures.Based on the simulation analysis, an influence rule of channel wall forming drops can be drawn in the paper. The research shows that wettability of channel wall plays a certain influence on the micro-droplet formation. When channel wall evacuates dispersed phase, it only has the possibility to form micro-droplet. At the moment, changes of contact angle have a smaller influence on the micro-droplet size. The paper further draws some conclusions on influence rules of continuous-phase viscosity and speed on micro-droplet size, namely the formed micro-droplet size will be reduced with the increase of continuous-phase viscosity, and the formed micro-droplet size also will be reduced with the increase of continuous-phase speed. At last, the paper draws an influence rule of interfacial tension between phases on micro-droplet size, namely, the formed micro-droplet size will be increased with the increase of interfacial tension between phases, demonstrating that the micro-droplet size is reduced with the increase of capillary number, and micro-droplet will not be generated when capillary number reaches a specific value.In order to further explore an influence rule of shear force on micro-droplet formation, the paper designs a multichannel micro-pressure inspection system. The system conducts multi-node measurement on pressure in fluid flow passages of PMMA micro-fluidic chips on the basis of the MEMS micro-pressure sensor MPXV7002, adopts an external silicone tube connection method to install micro-pressure sensors on different micro-channel nodes, and carries out filtering and smoothing pressure data. Moreover, the paper conducts a testing experiment on multi-node pressure, analyzes experimental data, and carries out system calibration and error analysis. The research result shows that the system has higher test precision.The paper conducts an experimental research on micro-droplet. The research result shows that micro-droplet size is related to continuous-phase viscosity, continuous-phase velocity, interfacial tension, micro-pipe size, pipe wall property. The experimental result is similar to CFD numerical simulation and has good consistency. On the one hand, it proves the correction of CFD numerical simulation. On the other hand, CFD numerical simulation also guides the formation of microfluidic micro-droplet.