Research highlights
Particle-laden polymeric fluid flows
When a particle-laden polymeric fluid is allowed to flow through a suitably designed flow geometry, it is observed that particles can undergo irreversible aggregation in the form of long, thread like, flexible structures known as streamers. The name streamer is inspired from a morphologically similar structure obtained in bacteria laden flows.
The underlying mechanism behind the formation of particle-polymer aggregate is the mechanism of polymeric bridging. According to this mechanism, a long polymeric molecule can adsorb on two or more particles and act as a bridge to draw them together. Particle-laden polymeric flows find its application in many natural and industrial processes. Despite their wide occurrence the mechanism of polymeric bridging is not completely understood.
Some of the interesting findings from my research work related to particle-laden polymeric fluid has been published as a part of technical paper publication in an interenational conference (ASME-ICNMM 2020).
Oily rod-climbing effect
Our experiments on rod-climbing effect with an oil coated rod revealed two key differences compared to bare rod. First, an increase in height of climb for a given rod rotation speed. Second, there exist an interfacial-condition dependent threshold rod rotation speed below which climbing height is zero. Introduction of oil-coated rod decreases this threshold speed. As per our hypothesis, all these observations can be explained by accounting for the behavior of three-phase contact line at the rod-fluid interface.
Our cover art has been selected as the front cover for the volume 37, issue 51 of the Langmuir publications.
To read more about this work click here.
Shock-induced aerobreakup of a polymeric droplet
Droplet atomization through aerobreakup is omnipresent in various natural and industrial processes. Atomization of Newtonian droplets is a well-studied area; however, non-Newtonian droplets have received less attention despite their frequent encounters. By subjecting polymeric droplets of different concentrations to the induced airflow behind a moving shock wave, we explore the role of elasticity in modulating the aerobreakup of viscoelastic droplets. Three distinct modes of aerobreakup are identified for a wide range of Weber number (∼ 10^2 − 10^4) and Elasticity number (∼ 10^{−4} − 10^2) variation; these modes are- vibrational, shear-induced entrainment, and catastrophic breakup mode. Each mode is described as a three-stage process (shown in the movie below). Stage-I is the droplet deformation, stage-II is the appearance and growth of hydrodynamic instabilities (Kelvin-Helmholtz and Rayleigh-Taylor), and stage-III is the evolution of liquid mass morphology. It is observed that elasticity plays an insignificant role in the first two stages, but a dominant role in the final stage. The results are described with the support of adequate mathematical analysis.
To read more about this work click here. Related to this research, we also wrote a review article titled- "Advance in droplet aerobreakup."
Movie4.mp4This video illustrates the three stages in the shock-induced aerobreakup of a liquid droplet
Figure-14_multimedia_view.mp4Above a certain rod rotation speed, the oil-water interface becomes unstable, and emulsification happens through sheet breakup and ring instability.
The Newtonian rod climbing effect
If a rotating rod is introduced vertically in a pool of Newtonian liquid, then a dip in the liquid free-surface profile near the rod is observed. This happens because the centrifugal force is balanced by the pressure force in the liquid and gets manifested as a dip in the free-surface profile. However, if the same experiment is performed at the interface of two immiscible Newtonian liquids (silicone oil and water in the present case), then a climb in the interface profile is observed. This is known as the Newtonian rod climbing effect. Although the climbing profile looks similar to the Viscoelastic rod climbing, the governing mechanism is completely different in the two cases.
Our research revealed that the contact angle hysteresis at the liquid-liquid-rod interface plays an important role in the Newtonian rod climbing effect. The details of this research can be found here.
aerodynamic bag breakup of a polymeric droplet
combined_bag_breakup.mp4The aerodynamic breakup of a polymeric droplet in the bag breakup regime is investigated experimentally and compared with the result of the Newtonian droplet. To understand the effect of liquid elasticity, the Weber number is kept fixed (~12.5) while the elasticity number is varied in the range of ~10^{-4}-10^{-2}. Experiments are performed by allowing a liquid droplet to fall in a horizontal, continuously flowing air stream. It is observed that the initial deformation dynamics of a polymeric droplet is similar to the Newtonian droplet. However, in the later stages, the actual fragmentation of liquid mass is resisted by the presence of polymers. Depending upon the liquid elasticity, fragmentation can be completely inhibited in the timescale of experimental observation. We provide a framework to study this problem, identify the stages where the role of liquid elasticity can be neglected and where it must be considered, and finally, establish a criterion that governs the occurrence or the absence of fragmentation in a specified time period.
To read more about this work, click on the link below-