EXPLORING THE IMPACT OF DROPLET SIZE AND VISCOSITY RATIO ON THE CRITICAL CAPILLARY NUMBER FOR DROPLET BREAKUP IN T-JUNCTION MICROCHANNELS

Understanding droplet behavior and accurately predicting the conditions for droplet breakup are fundamental for effective droplet control and manipulation in microchannels. In this study, three-dimensional numerical simulations were conducted to investigate droplet breakup behavior at a T-junction under the combined influence of three factors: droplet size ratio (<i>D/W</i>), viscosity ratio (λ), and capillary number (Ca). The results revealed that droplets with smaller size ratios and viscosity ratios are more resistant to breakup. A theoretical model was proposed to predict the critical capillary number (<i>Ca<sub>cr</sub></i>) for droplet breakup based on the two key parameters, namely, the droplet size ratio and the viscosity ratio, expressed as <i>Ca<sub>cr</sub></i> > a<sub>1</sub>[(0.28λ + 1)/(3λ + 2)] (<i>D/W</i> + a<sub>2</sub>). Our findings show that <i>Ca<sub>cr</sub></i> ranges from 0.04 to 0.37 for <i>D/W</i> between 0.5 and 1.0, and λ between 0.05 and 30. Unlike existing models, this new model incorporates the viscosity ratio as a key parameter, providing a more comprehensive and accurate prediction of breakup conditions. The high accuracy and reliability of this model were validated by comparing its predictions with numerical simulation results. Furthermore, the breakup process for different droplet size ratios was explored, showing that smaller droplets require more time to break compared to larger ones. These insights not only advance the understanding of droplet breakup mechanisms but also pave the way for more precise and efficient droplet manipulation techniques in microfluidic applications.