Research

The use of acoustic fields for manipulating inhomogeneous fluids in a microchannel has given rise to an interesting phenomenon called acoustic relocation. It is a process in which inhomogeneous fluids in a microchannel, initially at an unstable fluid profile relocate due to acoustic fields to a stable profile. We have proposed a theory governing this motion of fluids and that impedance gradient is one of the necessary conditions for acoustic relocation in addition to an unstable configuration and a sufficient acoustic energy density to overcome interfacial tension. We have outlined a stability theory that defines the behavior of these fluids (both miscible and immiscible) and agrees with previous experimental results. Also, digging a little further into the process, an alternate passive method for quick and effective acoustic relocation has been put forward.

As a medium is homogeneous with suspended microbeads, with induced acoustic fields in the microchannel, the particles tend to stream in the (move in trajectories resembling rolls). On the other hand, when the medium is inhomogeneous, these rolls can be suppressed, thus showing no circulation in the bulk of the fluid. There are extensive opportunities on understanding these rolls experimentally and studying the sensitive as well as multiple variations in those profiles with the aid of mathematical and computational analysis.

It is well-known that fluids relocate to achieve a stable configuration when exposed to acoustic fields. Consequently, when the case is miscible fluids, they tend to mix due to diffusion with the acoustic phenomena accelerating this process by creating multiple interfaces and convection. We have iterated over several wave and flow configurations and proposed the case where maximum mixing occurs in a short duration. Such studies evince applications in the mixing of bio-fluids and other biological research. Working on improvising this process with geometrical modification of microchannel and proposing the optimal set of the parameters used for the acoustic mixing process are a few more current areas of work in our group.

Droplet microfluidics has a wide range of applications including biological assays cell synthesis, and drug administration to name a few. Here we use bulk acoustic wave (BAW) to shape, deform, squeeze, and fuse droplets. Subsequently, these acoustic fields can be implemented to relocate and stratify the droplets against gravity. Our team works on experimental and numerical analysis of these phenomena, diving in deeper to get more comprehensive insights into the happenings.

When heated inhomogeneous fluid is subjected to acoustic fields, the resulting acoustic body force which is proportional to the impedance gradient induces fluid convection and enhances the heat transfer. It was found that acoustic forces can enhance heat transfer up to 2.5 times compared to natural convection and up to 11.2 times compared to pure conduction. It has also been observed that the heat transfer and fluid motion vary significantly with respect to thermal boundary conditions, wavenumber (quarter, half, and full-wave), and direction of the standing wave, attributed to the dependency of acoustic body force on the position of inhomogeneity.

When a dielectric liquid medium is subjected to alternating Electric Field and a temperature gradient, it induces dielectrophoretic body force which creates circulating flows that enhances convection. This heat transfer enhancement technique through convection under microgravity conditions can be used for efficient cooling of space-electronic devices.

On-a-chip devices have been caught substantial interest in recent times. Such minuscale devices accomplishing this task efficaciously are a booming area of research, consistently looking for improvisations and new possible methods and subsystems. We take pleasure to mention our contribution for a Lab-on-chip device, in collaboration and funded by Agappe Foundation, India for a nucleic acid amplification device. The device makes use of the LAMP (Loop-mediated Isothermal Amplification) for the process, where we have made progress in maintaining the ideal temperature conditions using a feedback loop mechanism and designed the device.