CFD Simulation Of Droplet Formation In A T-junction Microchannel

Microfluidic chip is a new detection method becomes a new interdisciplinary research field for its tremendous application potential. In recent years, the interest about microfluidic chip has been focused on the generation of the discrete droplets. In some fields, the dispersed droplets are the basic operating unit in the microfluidic chip. In the configurations adopted to produce droplets, the T- junction Microchannel is the most popular style with a simple structure and enables to generate uniform size droplets easily. And in this work,we have systematically numerical simulation the droplets formation in the T-junction Microfluidic chip by using computational fluid dynamics (CFD) method in three dimensional.In the previous reports , the mechanisms of droplets formation in the T-junction microchannel can be distinguished into three regimes by the continuous phase capillary , the Squeezing regime,Dripping regime,and the Jetting regime. Until now, the regimes and the transition states between them have not been systematically studied and the impacts of the relevant parameters have not been investigated in the droplets formation yet. Because most of the research methods applied currently are experiment,which always leads to a retard to the research process, for the disadvantages that it is difficult to designed and manufactured a microchannel in micron scale, and the operation is fallible and cumbersome with expensive spending, long and endless research cycle.The CFD is able to transform the interaction process of two-phase flows in the microchannel into a specific mathematical model, and then computer is serviced to simulate the droplet formation. With the rapid development of CFD simulation technology, it is able to overcome the traditional experimental research in some specific situation, and it can also avoid the shortages of manual operation easily, study the impact of system parameters without any difficulty and accurately, so that it can accelerate the research process greatly.We have designed two different T-junction configurations to distinguish the three different regimes in the droplet formation, a wide-type T-channel for the dripping regime, and an ordinary configuration with same width T-channel for the squeezing regime. In the wide-type T-channel, we studied the droplet formation of dripping regime. The channel wall wettability is shown by Numerical simulations that, when the channel wall alienates the dispersed phase, the droplet is allowed to be formed. If the continuous phase flow rate and viscosity was increase, the droplet size will decrease gradually; but for the two-phase interfacial tension increasing, the situation is the opposite. There is a decrease of the droplet size as Ca_c increases. More importantly, in a certain range, there is a linear relationship between the droplet diameter and the inverse of Ca_c.In the ordinary channel, there is a transient regime emerging in droplet formation, and the critical Ca_c is about 0.025 in our simulation. The droplet length as same as described by Xu, is about 30μm ~60μm (Wh0.3). When the continuous phase viscosity is increase, the droplet sizes would decrease gradually; When we studied these three factors together as Ca_c, the droplet size can be described by the equation L = 8.2113C a c?0.4876 .Our simulation work would provide a reliable basis for the size prediction of the droplet formation in the T-junction microchannel .