Dynamic of centrifugal step emulsification and prediction of droplet diameter

Studies show that centrifugal step emulsification is an effective method for high throughput droplet generation and has been widely used over the past ten years. However, there is no in-depth understanding of the physics underlying emulsification and the effect of centrifugal force on the droplet volume. Aiming at resolving this shortcoming, this article is focused on the dynamics of the droplet formation process subjected to centrifugal acceleration, and a theoretical model is proposed for accurately predicting the droplet size. A critical time and a critical bulb length are introduced to describe the droplet formation and divide this process into stable and rapid filling regimes. It is worth noting that the centrifugal force was considered in the dispersed phase profile. Finally, a theoretical model was established to predict the droplet size. Numerical simulation and high-speed measurements demonstrate that there is a critical time and bulb length, and the critical bulb length is in good agreement with the proposed theory. To evaluate the performance of the model, experiments with different centrifugal accelerations, terrace heights, and terrace lengths were carried out. The obtained results are in excellent agreement with the experiments, and the relative diameter error was less than 4%. The performed analyses demonstrate that the established model can be applied to accurately calculate the droplet size and obtain the correlation between the droplet size and different parameters, such as terrace height, terrace length, and centrifugal acceleration. This model has great potential in guiding the designs of centrifugal step emulsification systems.