Numerical Simulation Of Droplet Formation Process In A T-shaped Micro-channel

Microfluidic chips can be used as a specific method in many fields, including infrequent cell sorting, ribonucleic acid messenger extraction and purification, single cell analysis, protein crystallization, and preparation of nano-particles and micro-emulsion. For these applications, as main control cells, well dispersed and even microdrop flow is very important, and the controllability of drop volume is also a key problem. This study focuses on the numerical simulation of droplet formation in a wide T-shaped microchannel . Water and oil are used respectively as dispersed phase and continuous phase, and their property parameters are defined based on real case. The research in this paper include following five parts:1. T-shaped microchannel model is set up, and reasonable boundary conditions are given according to relevant experimental research results; numerical simulation of droplet formation process in micrometer-scaled is realized; droplet diameters in Fluent images are obtained through Matlab programs.2. The accuracy of our numerical simulation is proved through the comparison between experimental and simulation results. Then droplet formation conditions are studied, and numerical simulation results showed that wetting property of the microchannel walls are the first important condition, ideal droplet can be formed only when wall contact angle smaller than 90°; additionally, the velocity and viscosity of continuous phase and interfacial tension between two flows are three important factors that influence the droplet formation process; capillary number ( , is viscosity of continuous phase and is velocity of continuous phase, is interface tension between two phases)is used for bulk analysis; a critical is resulted.3. Our numerical simulation results showed that, droplets form at different positions in microchannels when use fluids with different properties. For low number, droplet breakup at the junction of the T channel; with increases, the droplet formation position far awy from the junction and when reaches a critical value 0.16, the two flows can not form droplet longer.4. For a single droplet, the whole process of its formation was observed. Under the conditions of droplet formation, the whole formation process can be divided into three phases: droplet growth, droplet breakup from dispersed phase and droplet detachment from microchannel wall. Detailed analysis for each phase showed that the formation of droplet was mainly resulted from the shear force of continuous phase on dispersed phase and the interfacial tension between two fluids.5. The factors that influence the droplet volume forms in T-shaped microchannel are studied, and the quantitative effect of each factor on droplet diameter was obtained. For microchannel, we found that the contact angle of channel wall has definite effect on droplet volume, and bigger droplet corresponds to bigger contact angle. This is due to the stronger adhesive force between dispersed phase and wall which resulting in longer + . When the velocity of continuous phase is constant, theaccumulative amount of dispersed phase in droplet increased. For flow property, droplet diameter increases in a logarithmic trend with the increase of interfacial tension and decreases in a exponent form with then increase of velocity and viscosity of continuous phase.6. The relation between droplet diameter D and the capillary number is analyzed, and the results show that there is a definite liner relation between them, but not just a simple liner relation. As the existence of droplet influence the shear stress, the capillary number is corrected as , and based on which a better liner relation is obtained: .