Bidisperse Suspension Pinch-off
Generation of droplets of suspensions is relevant for processes such as bioprinting, which consists of cells as particles. The presence of particles in a liquid increases its viscosity, and modifies the process of droplet generation. Past studies on monodisperse suspensions have reported an accelerated pinch-off dynamics when compared to liquids of equivalent viscosities. Our study adds more complexity to past work. We studied the pinch-off dynamics of bidisperse suspensions, which consist of particles of two different diameters. Using rheological principles, our studies revealed that because of better packing efficiency, bidisperse suspensions have a lower viscosity, and hence faster pinch-off dynamics than monodisperse suspensions.
Coil-stretch transition
Liquid fragmentation is ubiquitous, from the break-up of the droplets when the ocean strikes a sea rock to the atomization of liquid propellants. On a smaller scale, some examples of pure extensional flows are droplet pinch-off or stretching of a liquid bridge. When a drop or liquid bridge of Newtonian droplet breaks, it is abrupt and the strain-rate diverges before the breaks up. But in solutions of polymers, the abrupt break-up is delayed. When the flow reaches a certain maximum strain-rate, the dissolved polymers uncoil from their equilibrium state. Macroscopically, this is seen through the formation of cylindrical ligaments, and the thinning goes from a Newtonian, (weak interaction of polymer coils with the flow) to a viscoelastic regime (strong interaction of uncoiled polymers with the flow). Using high-speed imaging, our study characterized the macroscopic properties of a droplet of polymer solution during this transition.
Bubble pinch-off
Bubbles are encountered in a range of industrial processes such as froth flotation and mixing flows, or as contrast agents for ultrasound scanning. Because of the potential damage bubbles can cause, it is important to study the dynamics of their formation. The formation and detachment of bubbles is an ultra-fast process, happening over the order of a few µs, which makes them difficult to study. Despite these difficulties, the last two decades have produced several studies characterizing their formation and break-up in Newtonian liquids. However, most of the fluids in real life are more complex, often exhibiting, non-Newtonian behavior. Using high-speed imaging at over 100,000 frames per second and image processing routines, our study characterizes the formation and break-up dynamics of gas bubbles in a rheologically complex polymer solution.
Microplastic Transport
Every year, over 8 million tons of plastic end up in the ocean. These plastic undergoes various weathering process on their journey and break down into particles that are smaller than 5 mm in diameter, termed microplastics. Such microplastic particles can be consumed as food by aquatic organisms and enter the food chain. Hence, the presence of microplastics in the ocean poses a threat not only to aquatic life but also to life higher up on the food chain. Therefore, it is important to appropriately describe the flow of such microplastics in aquatic bodies. Further, microplastic transport can also be modified due to biofilm formation on their surface. The biofilms, composed of biopolymers, can bind together the microplastic particles and modify their transport by forming an effectively larger mass. Using image processing and custom Python routines, we propose a study to elucidate the role of biopolymers in the sedimentation of microplastics in a stationary fluid.
Axial liquid bridges
Liquid bridges are encountered ubiquitously in nature. A pile of dry sand is difficult to be held together. However, moist sand can easily clump together, with liquid bridges between adhering the sand. Depending on the physical properties of the fluid, the resistive forces can be inertial, viscous, or capillary. Such adhesive forces are also responsible for the clumping or aggregation of powders or granular materials. This is a problem frequently encountered in industries due to the condensation of vapors between particles in a humid environment, resulting in liquid bridges. While the effect of such liquid bridges formed by Newtonian solvents has already been investigated in past studies, my work focuses on elucidating the effect of polymer solutions.
Spreading dynamics of fibers
When a drop of fiber suspension impacts a solid surface, what does the final size and distribution of the fibers look like? We use experiments to investigate the spreading dynamics of fiber suspensions of different mass fractions on a hydrophilic solid surface.
Mechanical Engineering Grad Slam 2021 (came 1st!)
Sreeram Rajesh- ME Grad Slam 2021 Submission.mp4My submission to the 2021 UCSB Mechanical Engineering Grad Slam, a summary of my work on droplet break-up dynamics
Mechanical Engineering Grad Slam 2023 (1st again!)
Grad Slam 2023 Recording.mov