arXiv subjects

Pranab Kumar Mondal

Publications and source records attributed to Pranab Kumar Mondal.

11 recordsLinked to original sources

arXiv2026

Correlative effects of induced magnetic field-buoyancy on reactive solute dispersion dynamics in couple-stress fluids

We investigate the dispersion of a reactive solute in a couple-stress fluid flowing between two parallel plates under the combined effects of pressure-driven flow, buoyancy, and an induced magnetic field. The model incorporates first-order heterogeneous reactions at both channel walls alongside a bulk reaction. Using Mei's multiscale homogenization technique accurate to third order, we develop a higher-order asymptotic formulation to determine the effective longitudinal dispersion coefficient and concentration field. Analytical predictions are complemented by Brownian dynamics simulations and finite-difference solutions, while the Aris method of moments quantifies transient mean displacement, spatial variance, and effective dispersivity. The hydrodynamic analysis reveals a singular branch in the velocity solution when the Hartmann number equals half the couple-stress parameter and identifies a characteristic quarter-power scaling between the Hartmann number and couple-stress parameter, separating couple-stress- and magnetically dominated regimes. The model recovers classical Taylor-dispersion behavior in the non-reactive Newtonian limit and agrees well with experimental measurements. Couple-stress rheology and magnetic damping suppress shear-induced dispersion, whereas buoyancy enhances dispersion through additional transverse velocity gradients. A distinct saturation regime of the dispersion coefficient emerges with an increasing couple-stress parameter, while unequal wall absorption induces persistent transverse asymmetry, and stronger absorption enhances solute removal near the source. Numerical and stochastic results validate the analytical framework while resolving higher-order concentration structures and particle-scale wall adsorption.

physics.flu-dyn↗

arXiv2026

Plant-On-a-Disc (POD): A Phytofluidic platform enabling In Situ Root Analysis

Phytofluidic platforms have enabled controlled studies of plant roots, however, most existing systems either impose geometric confinement without flow or introduce hydrodynamics in single-channel devices that limit throughput and disrupt downstream analysis. New experimental platforms are therefore needed to investigate how roots integrate mechanical confinement and hydrodynamic nutrient transport, two defining features of the rhizosphere that remain difficult to reproduce under controlled laboratory conditions. Here, we present the Plant-on-a-Disc (POD), a phytofluidic platform that enables the parallel cultivation of eight seedlings under controlled hydrodynamic conditions while allowing non-invasive, in situ multimodal analysis of the intact root-shoot system. The device is fabricated in PDMS using a cost-effective wire-drawing technique to generate radial microchannels that converge into a central sump beneath an optical window. This design enables sequential bright-field, fluorescence, and Raman measurements using a single microscope objective without disturbing neighbouring seedlings. Dimensionless transport analysis and finite-element modelling confirm that the radial architecture equalizes hydraulic resistance across channels, establishing creeping laminar flow with convection-dominated nutrient transport under physiologically safe shear conditions. Using Brassica seedlings, we show that hydrodynamic flow drives coordinated root responses across multiple scales. Roots grown in flow condition exhibit accelerated elongation, substantial ROS generation and anisotropic cortical cell expansion, accompanied by carotenoid signatures detected by Raman spectroscopy.

physics.bio-ph↗

arXiv2025

Phytoscale Transport Physics: Insights into Xylem Flow Homeostasis and Drought Stress

We investigate the flow dynamics of nutrient solution through the xylem vessels of Brassica juncea under drought stress. To this end, we perform experiments to obtain morphological traits of xylem vessels under drought-stressed conditions, and develop a mathematical framework to model the underlying flow through the xylem, considering several features relevant to the plant system. Performing experiments using state of the art instruments, we measure the morphology of xylem vessels, physicochemical and mechanical properties of xylem walls under drought stressed conditions. Our experimental results unveil that drought reduces both xylem diameter and pit aperture size, implicating hydraulic adaptations of plants to drought stress. We find that the reduced cellulose content in drought stressed xylem vessels lowers the zeta potential and decreases elasticity of the vascular region. Additionally, drought stress alters metabolite activity, increases reactive oxygen species, reduces chlorophyll content, and limits the uptake of essential metallic nutrients. Besides, we perform three-dimensional numerical simulations to evaluate local flow field, mechanical stress, hydraulic conductivity, and radial transport efficiency of xylem vessels under drought stressed conditions. Simulated results reveal that under drought conditions, resistance to axial flow through xylem vessels increases significantly, which in turn, promotes radial transport of nutrients, allowing plants to survive even in drought stress. We show that the radial flow efficiency of xylem vessels becomes notably higher under drought stress than in well-watered control plants. Overall, results of this endeavor provide new insights into how geometric adaptations of xylem vessels modify flow behavior under water deficient conditions, enhancing the plants ability to survive environmental stress.

physics.bio-ph↗

arXiv2024

Unveiling nutrient flow mediated stress in the plant roots using on-chip phytofluidic device

The initial emergence of the primary root from a germinating seed is a pivotal phase that influences a plant's survival. Abiotic factors such as pH, nutrient availability, and soil composition significantly affect root morphology and architecture. Of particular interest is the impact of nutrient flow on thigmomorphogenesis, a response to mechanical stimulation in early root growth, which remains largely unexplored. This study explores the intricate factors influencing early root system development, with a focus on the cooperative correlation between nutrient uptake and its flow dynamics. Using physiologically relevant, portable, and cost-effective microfluidic system for the controlled fluid environments offering hydraulic conductivity comparable to that of the soil, this study analyzes the interplay between nutrient flow and root growth post-germination. Emphasizing the relationship between root growth and nitrogen uptake, the findings reveal that nutrient flow significantly influences early root morphology, leading to increased length and improved nutrient uptake, varying with the flow rate. The experimental findings are supported by stress-related fluid flow-root interaction simulations and quantitative determination of nitrogen uptake using the Total Kjeldahl Nitrogen (TKN) method. The microfluidic approach offers novel insights into plant root dynamics under controlled flow conditions, filling a critical research gap. By providing a high-resolution platform, this study contributes to the understanding of how fluid-flow assisted nutrient uptake and pressure affect root-cell behavior, which, in turn, induces mechanical stress leading to thigmomorphogenesis. The findings hold implications for comprehending root responses to changing environmental conditions, paving the way for innovative agricultural and environmental management strategies.

physics.bio-ph↗

arXiv2023

Chemiosomotic flow in a narrow fluidic channel

A liquid volume containing dissolved solutes moves through a charged nanofluidic channel under the influence of the concentration gradient of the solutes, non-trivially modulated by the electrostatic interaction between ionic liquid and charged surface. The available studies in this paradigm primarily focus on either of diffusioosmosis or electrodiffusioosmosis modulated physicochemical hydrodynamical phenomenon, essentially to obtain a net throughput at the overlapping scales. Here, we develop a theoretical model that accounts for the induced pressure gradient stemming from the concentration gradient of the solutes alongside the axially varying electrical double layer effect in tandem and characterizes the chemiosmotic flow in a reservoir-connected nanofluidic system. Starting from the potential distribution developed due to the solute gradient modulated electrical double layer effect, we look at the effect of pertinent physicochemical parameters and their eventual manifestations onto the purely chemiosmotic transport, aptly described in this endeavor. We analytically establish a chemiosmotic velocity scale from a macroscopic viewpoint, relating flow velocity with the relevant parameters, and uniquely measuring the magnitude of chemiosmotic velocity. A closer as well as consistent agreement on theoretical predictions with the corresponding full-scale simulated results, both in the limit and beyond the Debye-Huckel approximation, substantiates the efficacy of our theory.

physics.flu-dyn↗

arXiv2021

Magnetofluidic based controlled droplet breakup: effect of non-uniform force field

We report the breakup dynamics of a magnetically active droplet (ferrofluid droplet) in a T-shaped LOC device under the modulation of a non-uniform magnetic field. We adhere to high-speed imaging modalities for the experimental quantification of the droplet splitting phenomena in the presence of a non-uniform force field gradient, while the underlying phenomena is supported by the numerical results in a qualitative manner as well. On reaching the T-junction divergence, the droplet engulfs the intersection fully and eventually deforms into the dumbbell-shaped form making its bulges to move towards the branches of the junction. We observe that the asymmetric distribution of the magnetic force lines, acting over the T-junction divergence, induces an accelerating motion to the left moving bulge (since the magnet is placed adjacent to the left branch). We show that the non-uniform force field gradient allows the formation of a hump-like structure inside the left moving bulge which triggers the onset of augmented convection in its flow field. We reveal that this augmented internal convection developed in the left moving volume/bulge, on getting coupled with the various involved time scales of the flow field, lead to the asymmetric splitting of the droplet into two sister droplets. Our analysis establishes that at the critical strength of the applied forcing, as realized by the critical magnetic Bond number, the flow time scale becomes minimum at the left branch of the channel, leading to the formation of larger sized sister droplet therein. Inferences of the present analysis, which focuses on the simple, wireless, robust and low-cost droplet splitting mechanism, will provide a potential solution for rapid droplet breakup, typically finds significant importance in point-of-care diagnostics.

physics.flu-dyn↗

arXiv2021

Investigations into the complete spreading dynamics of a viscoelastic drop on a spherical substrate

We study the spreading dynamics of a sphere-shaped elastic non-Newtonian liquid drop on a spherical substrate in the capillary driven regime. We use the simplified Phan Thien Tanner model to represent the rheology of the elastic non-Newtonian drop. We consider the drop to be a crater on a flat substrate to calculate the viscous dissipation near the contact line. Following the approach compatible with the capillary-viscous force balance, we establish the evolution equation for describing the temporal evolution of the contact line during spreading. We show that the contact line velocity obtained from the theoretical calculation matches well with our experimental observations. Also, as confirmed by the present experimental observations, our analysis deems efficient to capture the phenomenon during the late-stage of spreading for which the effect of line tension becomes dominant. An increment in the viscoelastic parameter of the fluid increases the viscous dissipation effect at the contact line. It is seen that the higher dissipation effect leads to an enhancement in the wetting time of the drop on the spherical substrate. Also, we have shown that the elastic nature of fluid leads to an increment in the dynamic contact angle at any temporal instant as compared to its Newtonian counterpart. Finally, we unveil that the phenomenon of increasing contact angle results in the time required for the complete wetting of drop becomes higher with increasing viscoelasticity of the fluid. This article will fill a gap still affecting the existing literature due to the unavailability of experimental investigations of the spreading of the elastic non-Newtonian drop on a spherical substrate.

physics.flu-dyn↗

arXiv2020

Tutorial Review of Mixing in a Rotating Soft Microchannel under Electrical Double Layer Effect: A Variational Calculus Approach

We study the effect of the grafted polyelectrolyte layer on the flow dynamics, and its consequences on underlying mixing in the rotating microfluidic channel. For this analysis, the method used by Sadeghi et al. (J. Fluid Mech., vol. 887, 2020, pp. A13; Phys. Rev. Fluids., vol. 4 (6), 2019, 063701-23), is modified by incorporating the non-linear effect stemming from the polyelectrolyte layer induced electrostatics to solve the coupled system of equations, integrated with the non-homogeneous boundary conditions. This method is used to obtain the velocity distribution in the asymptotic limit of geostrophic plug flow under the framework of variational calculus approach. We analyze the mixing dynamics from the perspective of both qualitative assessment and quantitative evaluation. For the qualitative estimation, we focus on the Poincaré map analysis, while the entropy of mixing approach is used for the mixing quantification. Results show that the grafted polyelectrolyte layer in contact with the ionic solution leads to the development of an electrical double layer, which upon interacting with the external electric field, strengthens the electroosmotic pumping in the fluidic channel. Such polyelectrolyte layer modulated strong electroosmotic pumping together with its intrinsic feature of offering a frictional drag to the underlying transport helps to modulate the primary as well as the secondary flows in the channel under the influence of rotational forces. With an alteration in the electroosmotic pumping and frictional drag force, tuneable through the thickness of the grafted polyelectrolyte layer, we obtain different types of secondary flow vortex configurations viz., a standard double-vortex, dumbbell-shaped vortex and the transition state between the formers. A significant change in the structure and strengths of these vortices modulates the chaotic mixing in the present configuration

physics.flu-dyn↗

arXiv2020

Magnetofluidic mixing of a ferrofluid droplet under the influence of time-dependent external field

We report the experimental investigations on the mixing of a ferrofluid droplet with a non-magnetic fluid in the presence of a time-dependent magnetic field on an open surface microfluidic platform. The bright field visualization technique, in combination with the micro-PIV analysis, is carried out to explore the internal hydrodynamics of the ferrofluid droplet. Also, using the Laser-induced fluorescence (micro-LIF) technique, we quantify the mass transfer occurring between the two droplets, which in effect, determines the underlying mixing performance under the modulation of the frequency of the applied magnetic field. We show that the magnetic nanoparticles exhibit complex spatio-temporal movement inside the ferrofluid droplet domain under the influence of a time-dependent magnetic field, which, in turn, promotes the mixing efficiency in the convective mixing regime. Our analysis establishes that the movement of magnetic nanoparticles in presence of the time-periodic field strengthens the interfacial instability, which acts like a sparking agent to initiate an augmented mixing in the present scenario. By performing numerical simulations, we also review the onset of interfacial instability, mainly stemming from the susceptibility mismatch between the magnetic and non-magnetic fluids. Inferences of the present analysis, which focuses on the simple, wireless, robust, and low-cost open surface micromixing mechanism, will provide a potential solution for rapid droplets mixing without requiring pH level or ion concentration dependency of the fluids.

physics.flu-dyn↗

arXiv2020

Marangoni instability in a viscoelastic binary film with cross-diffusive effect

The viscoelastic fluids are usually the blends of a polymeric solute and a Newtonian solvent. In the presence of a temperature gradient, stratification of these solutes can take place via the Soret effect. Here, we investigate the classical Marangoni instability problem for a thin viscoelastic film considering this binary aspect of the fluid. The film, bounded above by a deformable free surface, is subjected to heating from below by a solid substrate. Linear stability analysis performed numerically for perturbations of finite wavelength (short-wave perturbations) reveals that both monotonic and oscillatory instabilities can emerge in this system. The interaction between the thermocapillary and solutocapillary forces in the presence of Soret diffusion is found to give rise to two different oscillatory instabilities, of which one mode was overlooked previously, even for the Newtonian binary mixtures. As a principal result of this work, we provide a complete picture of the susceptibility to different instability modes based on the model parameter values. Finally, an approximate model is developed under the framework of long-wave analysis, which can qualitatively depict the stability behaviour of the system without numerically solving the problem.

physics.flu-dyn↗

arXiv2020

Thermosolutal Marangoni instability in a viscoelastic liquid film: Effect of heating from the free surface

We study the Marangoni instability in a thin polymeric liquid film heated from the free surface. Polymeric solutions are usually the binary mixture of a Newtonian solvent with polymeric solute and exhibit viscoelastic behaviour. In the presence of a temperature gradient, stratification of these polymeric solutes can take place via the Soret effect, which may give rise to the solutocapillary effect at the free surface. Considering the Soret effect and incorporating the effects of gravity, here we analyse the stability characteristics of this polymeric thin film bounded between its deformable free surface and a poorly conductive rigid substrate from below. A linear stability analysis around the quiescent base state reveals that under the combined influences of thermo-solutocapillarity, apart from the monotonic disturbance, two different oscillatory instabilities can emerge in the system. The characteristics of each instability mode are discussed, and a complete stability picture is perceived in terms of the phase diagrams, identifying the model parameter space wherein a particular instability mode can get dominant.

physics.flu-dyn↗