<p>Microdroplet generators are used in many lab-on-a-chip devices for biological and chemical applications. Generating precise droplets with the required size and frequency has been a focus of interest by many. As a result, numerous actuation and control mechanisms are developed to achieve controllable droplet generation. Among those, the T-junction-based droplet generator has been popular because of its design simplicity and controllability. The droplet fluid termed as the dispersed fluid flows perpendicularly with respect to the continuous fluid until they meet at the T-junction. At the junction, the dispersed fluid forms droplets of a particular size depending on the relative flow rate between the two fluids. In contrast to flow-based control, we recently developed a T-junction microdroplet generator equipped with a pneumatic actuation for controlling the droplet size. It is a multi-layer device that can be fabricated using rapid manufacturing tools such as a desktop-based laser cutter. In our design, a T-junction fluidic layer sits at the bottom and the pneumatic control layer consists of a pneumatic chamber, as well as inlet and outlet channels at the top. In this presentation, we will detail the numerical modeling techniques used to design and optimize the device. The model developed in this research solves for Laminar Two-Phase Flow together with Level Set to predict droplet generation. Our results showed that the model produces a consistent droplet of 3.5 mm in size with a capillary number of 0.007 at a flow rate of 0.1 ml/min for both fluids and a channel aspect ratio of 1.11:1. Results with pneumatic control showed that the pressure inside the pneumatic chamber has an inverse relationship with the size of the droplets generated. Working pneumatic pressures of up to 0.4 MPa can be achieved, resulting in a droplet size reduction of 38%&nbsp;compared to a reference droplet. Alternatively, the droplet size can be regulated by controlling the relative flow rates of the continuous and dispersed fluids, as in the conventional method. An increase in the continuous fluid flow rate compared to the dispersed fluid resulted in a decrease in the droplet size. While comparing the continuous fluid usage for the same size of a regulated droplet between conventional and our model, it is noticed that the flow rate in a conventional method for continuous fluid increased significantly, whereas in our model it remained constant throughout. The continuous fluid used in our model was 0.1 ml/min, whereas the conventional method was 0.19 ml/min, resulting in a 38 percent reduction in droplet size. This indicates an additional 0.09 ml usage for every minute to maintain the regulated droplet size in the conventional method, which is not the case in our model. Pneumatic actuation is more advantageous, as it does not require additional fluid usage and the flow rate does not need to be ramped up to decrease the droplet size. The pneumatic control, rapid manufacturing, and fabrication ease of the design provide an attractive alternative method for a microdroplet generator in microfluidics.</p><p>Keywords: T-junction, Multi-layer, Pneumatic actuation, Numerical simulation, and Capillary number.</p>

Modeling and Experimental Analysis of Pneumatically Controllable T-Junction-Based Droplet Generation

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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