Micro-scale Transport Group
Welcome to MisT Lab!
Numerous transport processes in natural and industrial settings involve particulate suspensions which are moved passively by external flows. We are interested in transport of such passive systems along with enthusiasm in `active' particulate matter, which consist of self-propelling systems represented by motile microorganisms and chemically powered colloids. Our research group aims to model such systems at two length scales:
(i) Microscopic view: How do these additional time scales alter the hydromechanics and navigation strategies of motile pathogens and colloids?
(ii) Macroscopic view: What is the impact of these competing time scales on the rheological response, suspension stability, and spatiotemporal patterns?
Below we have listed our ongoing research interests:
Eric Lauga, Bacterial Hydrodynamics, ARFM 2016
Active suspensions in complex flows
One of our interests is in studying how microswimmers or active particles (ex: bacteria in fig. on top-left) navigate flows that are rendered complex due to confinement or inherent non-linearities like inertia and non-Newtonianness i.e., departures from Stokesian assumptions.
We intuitively know that the addition of particles in fluid & flows only makes the fluid thicker. That is why coffee/tea is thicker than water.
Active microscopic particles, however, are capable of reducing the apparent viscosity and making the fluid appear thinner due to active disturbances generated while swimming. Recently, we studied how the activity of such elongated microswimmers can yield fundamental modifications to the orientational dynamics in viscoelastic fluids (top-right schematic). These alterations are found to be activity-specific (whether it is E.coli or Chlamydomonas) and strong enough to sustain the biological noise, and hence substantially impact the bulk suspension viscosity.
Publications:
1. A. Choudhary, S. Paul, F. Ruhle, and H. Stark., How inertial lift affects the dynamics of a microswimmer in Poiseuille flow, Communications Physics
2. A. Choudhary and H. Stark., On the cross-streamline lift of microswimmers in viscoelastic flows, Soft Matter
3. M. Eberhard ,A. Choudhary, and H. Stark.
Why the reciprocal two-sphere swimmer moves in a viscoelastic environment, Physics of Fluids
4. A. Choudhary, S. Nambiar, and H. Stark.
Orientational dynamics and rheology of active suspensions in weakly viscoelastic flows, Communications Physics
Lay summary:
https://twitter.com/TheoBiophysics/status/1678292299782955012
Evolution of suspension microstrucutre (with noise) with increasing shear
Pusher Microsructure
Mass transport in microcreactors
Although microchannels offer a high surface area to volume ratio, several reaction processes are limited due to sole reliance on slow diffusion, which causes the formation of undesired products and safety hazards. One of our interests is in intensification methods and modeling of such systems through CFD simulations. For instance, a gently curved channel produces vortices, which generate cross-section mixing and enhancement in heat and mass transport.
Publications:
1. A. Choudhary and S. Pushpavanam. Process intensification by exploiting Dean vortices in catalytic membrane microreactors,
Chemical Engineering Science 174
2. C. Sun, Z. Luo, A. Choudhary, P. Pfeifer and R. Dittmeyer. Influence of the Condensable Hydrocarbons on an Integrated Fischer-Tropsch Synthesis and Hydrocracking Process: Simulation and Experimental Validation, Industrial & Engineering Chemistry Research 56.45
Self-diffusiophoresis in complex environments
Synthetic swimmers such as Janus particles and rods can propel themselves by generating concentration gradients along their surface. This results in a 'diffusio-osmotic' slip which consequently propels the particle autonomously. A significant portion of the potential applications lies in drug-delivery and biological fluid systems which exhibit non-Newtonian behavior, which motivated us to study the changes in the slip and swimming of Janus particles in complex fluids. We also developed a semi-analytical framework to model the hydrodynamic interaction of such swimmers with confinements and externally applied chemical gradients.
Publications:
1. A. Choudhary, T. Renganathan and S. Pushpavanam. Non-Newtonian effects on the slip and mobility of a self-propelling active particle, Journal of Fluid Mechanics 899
2. P.M. Vinze, A. Choudhary, and S. Pushpavanam. Motion of an active particle in a linear concentration gradient, Physics of Fluids 33
3. A. Choudhary, K.V.S. Chaithanya, Sebastien Michelin, and S. Pushpavanam. Self-propulsion in 2D Confinement: Phoretic and Hydrodynamic Interactions, European Physical Journal E (Article)
Electrophoretic particles in confined and non-Stokesian flows
Cross-stream migration of particles suspended in fluid flows occurs due to inherent non-linearity: inertia or polymeric stresses. This physics, in the past, has been utilized in microfluidics to focus cells in biological fluids. Recent experimental studies, towards the manipulation of focusing via external fields, have drawn our attention to ask: how electrokinetics affects the particle migration in non-Stokesian flow conditions? The use of classical mathematical techniques (such as perturbation theory and asymptotics in conjunction with reciprocal theorem) has helped us gain fundamental insights into the migration of charged particles and reveal the primary source behind the breaking of symmetry in weakly inertial and viscoelastic flows.
Publications:
1. A. Choudhary, T. Renganathan and S. Pushpavanam., Inertial migration of an electrophoretic rigid sphere in a 2D Poiseuille flow, Journal of Fluid Mechanics 874
2. A. Choudhary, Di Li, T. Renganathan, X. Xuan and S. Pushpavanam. Electrokinetically enhanced cross-stream particle migration in viscoelastic flows, Journal of Fluid Mechanics 898
3. A. Choudhary, T. Renganathan and S. Pushpavanam. Comment on "Migration of an electrophoretic particle in a weakly inertial or viscoelastic shear flow", Physical Review Fluids 6 (doi.org/10.1103/PhysRevFluids.6.036701 )
