Antarip Poddar, PhD

Our research interests include but are not limited to

(i) Biomedical flows,

(ii) Multiphase Flow,

(iii) Complex Fluids,

(iv) Active Matter Flow,

(v) Electrokinetic flows,

(vi) Granular Flows (Discrete Element Modeling)

We use both computational and experimental tools to investigate various interesting problems in the above fields. For computations, we employ a wide range of techniques, ranging from pure analytical calculations, combined analytical-numerical approach to pure Computational Fluid Dynamics (CFD) using FEM, FVM or BEM techniques. We develop our own code (in MATLAB, Python or Fortran90) or use open-source/commercial packages (e.g. OpenFOAM, Basilisk, AnsysFLUENT, COMSOL) as demanded by the problem statement.

The research problems have close links with different practical applications, such as lab-on-a-chip devices, drug delivery, disease prevention, environmental remediation, biosensing, hotspot cooling, inkjet printing & nuclear reactor thermal hydraulics, etc.

We welcome collaboration and joint projects.

Overview of research areas:

Abnormal hemorheology in eccentric stenosis

Microswimmers in complex environments

(i) Artificial microswimmer propulsion in complex biofluids

(ii) Locomotion of micro-organisms near slippery substrates

(iii) Slippery rheotaxis of microswimmers

How surfactants alter droplet electrohydrodynamics (EHD)?

Electrokinetics

(i) The ion partitioning effect in a soft nanochannel

(ii) Electroosmosis of nematic liquid crystals

Thermal optimization for Nuclear Reactor Thermal Hydraulics

(i) Optimum number of adjuster rods to be inserted during fuel rod cooling

(ii) Second law analysis of a nuclear fuel rod in an annular channel

(iii) Performance assessment of rod bundles in central subchannels

Abnormal hemorheology in eccentric stenosis

Background and Objective: Stenosis or narrowing of arteries due to the buildup of plaque is a common occurrence in atherosclerosis and coronary artery disease (CAD), limiting blood flow to the heart and posing substantial cardiovascular risk. While the role of geometric irregularities in arterial stenosis is well-documented, the complex interplay between the abnormal hemorheology and asymmetric shape in flow characteristics remains unexplored.

Methods: This study investigates the influence of varying hematocrit (Hct) levels, often caused by conditions such as diabetes and anemia, on flow patterns in an idealized eccentric stenotic artery using computational fluid dynamics simulations. We consider three physiological levels of Hct, 25%, 45%, and 65%, representing anemia, healthy, and diabetic conditions, respectively. The numerical simulations are performed for different combinations of shape eccentricity and blood rheological parameters, and hemodynamic indicators such as wall shear stress (WSS), oscillatory shear index (OSI), are relative residence time (RRT) are calculated to assess the arterial health.

Results: Our results reveal the significant influence of Hct level on stenosis progression. CAD patients with anemia are exposed to lower WSS and higher OSI, which may increase the propensity for plaque progression and rupture. However, for CAD patients with high Hct level — as is often the case in diabetes — the WSS at the minimal lumen area increases rapidly, which may also lead to plaque rupture and cause adverse events such as heart attacks. These disturbances promote endothelial dysfunction, inflammation, and thrombus formation, thereby intensifying cardiovascular risk.

Conclusions: Our findings underscore the significance of incorporating hemorheological parameters, such as Hct into computational models for accurate assessment of flow dynamics. We envision that insights gained from this study will inform the development of tailored treatment strategies and interventions in CAD patients with common comorbidities such as diabetes and anemia, thus mitigating the adverse effects of abnormal hemorheology and reducing the ever-growing burden of cardiovascular diseases.

Microswimmers in complex environments

Bio-inspired synthetic microbots that are artificially designed self-actuated micro - or nano - structures have shown a great promise towards various human-friendly applications such as targeted drug delivery, diagnostics, biochemical sensing, water purification, environmental remediation and thus emerged as a rapidly evolving research topic worldwide. The subject of studying both natural and artificial microswimmers is popularly categorized as the active matter systems. These are identified as physical systems whose constituents can extract the energy stored within their body or in the surrounding environment for some purposeful activity, viz. responding to stimuli, growth, preying, and nutrient transport. This theme concerns the locomotion characteristics of biological or man-made microswimmers through complex surroundings, specifically near a confining solid substrate and a non-Newtonian fluid rheology.

(i) Artificial microswimmer propulsion in complex biofluids

Reference: Poddar, A., Bandopadhyay, A. and Chakraborty, S., 2019. Activated micromotor propulsion by enzyme catalysis in a biofluid medium. Applied Physics Letters, 114(5), 053701.

(ii) Locomotion of micro-organisms near slippery substrates

Reference: Poddar, A., Bandopadhyay, A. and Chakraborty, S., 2020. Near-wall hydrodynamic slip triggers swimming state transition of microorganisms. Journal of Fluid Mechanics, 894, A11.

(iii) Slippery rheotaxis of microswimmers

How surfactants alter droplet electrohydrodynamics (EHD)?

The droplet based multiphase microfluidic devices have become one of the most vibrant research topics because of its utility in the targeted drug delivery systems using artificial drug carriers. Even though in this emerging area, spectacular advancements have taken place, a host of issues need more understanding. The electrically modulated dynamics of the droplets and their suspension dynamics are thus a topic of paramount importance. Surfactants are essential ingredients of the droplet-based microfluidic technology. However, diffusive transport of surfactants leads to spontaneous gradients in interfacial tension, which in turn, may influence the electrically mediated dynamics of droplets in a rather profound manner. We aim to develop a generic theoretical formalism that can account for different background flow situations, the droplet deformability, and the surface charge convection. Such a unified formulation enables us addressing the unique facets of drop migration and emulsion rheology brought in by the critical interplay between the hydrodynamic, Maxwell (electrical), and Marangoni stresses at the drop surface. The interface deformability and the surface charge convection have been implemented within the scope of the small deformation theory and small electric Reynolds number, respectively, while the electrical effects have been modelled with the leaky dielectric model. We developed both axisymmetric and three-dimensional frameworks based on regular perturbation techniques.

Our results revealed that Marangoni effect can arrest an otherwise increment of the drop-settling velocity as attributable to surface charge convection, under gravitational settlement. For specific electrical parameters, the Marangoni flow suppresses the additional secondary vortices observed in a clean drop. For a background Poiseuille flow profile, contrasts in electrical conductivity and permittivity of the drop-surrounding fluid pair, as well as the magnitude and the orientation of the electric field play a significant role in selectively altering the implications of the Marangoni stress, thereby providing a means for selectively controlling the drop velocity in different directions. For a background linear shear flow, we showed that, at a critical value of the shear stress relative to the electrical stress, the Marangoni effects surprisingly vanish, despite the presence of surfactant gradients. Consequently, the bulk emulsion viscosity and the normal stress differences can either enhance or decline, as determined by unique discriminating functions.

References: Poddar, A., Mandal, S., Bandopadhyay, A. and Chakraborty, S., 2019. Electrorheology of a dilute emulsion of surfactant-covered drops. Journal of Fluid Mechanics, 881, 524–550.

Poddar, A., Mandal, S., Bandopadhyay, A. and Chakraborty, S., 2019. Electrical switching of a surfactant coated drop in Poiseuille flow. Journal of Fluid Mechanics, 870, pp. 27–66.

Poddar, A., Mandal, S., Bandopadhyay, A. and Chakraborty, S., 2018. Sedimentation of a surfactant-laden drop under the influence of an electric field. Journal of Fluid Mechanics, 849, pp. 277–311.

Electrokinetics

(i) The ion partitioning effect in a soft nanochannel

We obtained some highly counter-intuitive results in the numerical study of streaming potential phenomenon through a soft nanochannel. Earlier studies in this regard have considered low polyelectrolyte layer (PEL) grafting density at the rigid nanochannel wall and, hence, an equal permittivity inside and outside the grafted layer. In order to overcome this shortcoming, the concept of Born energy is revisited. The coupled system of the modified Poisson–Boltzmann and Navier–Stokes equation is solved numerically, going beyond the widely employed Debye–Huckel linearization and low PEL densities. The complex interplay between the hydrodynamics and charge distribution, modulated by the ion partitioning effect, along with their consequent effects on the streaming potential and electrokinetic energy conversion efficiency (EKEC) have been systemically investigated. It has been observed that the ion partitioning effect reduces the EKEC in comparison to the case with equal permittivity up to a certain electrical double layer thickness after which it increases the EKEC. For a high concentration of mobile charges within the PEL, the net gain in the maximum EKEC due to the ion partitioning effect is about 10 fold that of the case when the ion partitioning effect is not considered. This study also reveals the possibility of improvement in streaming potential mediated energy conversion by the use of polyelectrolyte materials, which possess substantially lower dielectric permittivity than the bulk electrolyte.

Reference: Poddar, A., Maity, D., Bandopadhyay, A. and Chakraborty, S., 2016. Electrokinetics in polyelectrolyte grafted nanofluidic channels modulated by the ion partitioning effect. Soft Matter, 12, pp. 5968–5978.

(ii) Electroosmosis of nematic liquid crystals

Nematic liquid crystals are categorized as a special fluidic state possessing anisotropic behaviour of different physical properties. Their unique transport characteristics have attracted renewed attention in view of microfluidic transport phenomena. In the present study, we explore the electrically actuated flow of an ordered nematic fluid with ionic inclusions, taking into account the influences from surface-induced elasticity and electrical double layer (EDL) phenomena. The present study focuses on the influence of surface charge and elasticity effects in the resulting linear electro-osmosis through a slit-type microchannel whose surfaces are chemically treated to display a homeotropic-type weak anchoring state. We devised the coupled flow governing equations from fundamental free-energy analysis, considering the contributions from first- and second-order elastic, dielectric, flexoelectric, charged surface polarization, ionic and entropic energies. The additional complexity arises from the fourth order angular momentum balance equation, which is not required for isotropic fluids. The complex set of equations was solved using the finite element method (FEM). An optical periodic stripe configuration of the nematic director has been observed, especially for higher electric fields, wherein the Ericksen number for the dynamic study is restricted to the order of unity. Through a systematic investigation, we brought out the fact that the wavelength of the oscillating patterns is dictated mainly by the external field, while the amplitude depends on most of the physical variables ranging from the anchoring strength and the flexoelectric coefficients to the surface charge density and electrical double layer thickness. Contrary to the isotropic electrolytes, the EDL potential in this case was found to be dependent on the external field strength.

Reference: Poddar, A., Dhar, J., and Chakraborty, S., 2017. Electro-osmosis of nematic liquid crystals under weak anchoring and second-order surface effects. Physical Review E, 96, 013114.

Thermal optimization for Nuclear Reactor Thermal Hydraulics

(i) Optimum number of adjuster rods to be inserted during fuel rod cooling

The determination of core temperature distributions and heat transfer rates, namely the thermal analysis of reactor core, plays an important role in reactor design. A core has to be designed to produce the desired thermal power without exceeding temperature limitations on core components that might lead to fuel failure and the release of radioactive material into the coolant. In the present work, the axial power flattening effect with insertion of adjuster rods is modelled. A heat generating single fuel element in an annular channel along with fuel-clad gap, cladding and surrounding coolant flow is characterized under an axially flux flattened condition. The effect of insertion of single adjustor rod at the peak heat generation region has been simulated as two heat sources and one heat sink. The results obtained from the developed model indicate that insertion of adjuster rods beyond a critical number (3 to 4) the flattening effect does not improve much. The peak surface and centerline temperatures of fuel pin are observed to show a cyclic variation and shift towards end as compared to unadjusted profile. Results are in accordance with the numerical simulations and previous experimental observations.

Reference: Poddar, A., Chatterjee, R., Chakravarty, A., Ghosh, K., Sen, S., and Mukhopadhyay, A., 2015. A thermal model to characterize the flattening effect of a nuclear fuel element in an annular channel using simple analytical approach. Progress in Nuclear Energy, 85, pp. 441–453.

(ii) Second law analysis of a nuclear fuel rod in an annular channel

A continuous quest for efficient utilization of energy resources has motivated the researchers to search for optimal design and operating conditions during various energy conversion techniques. These conditions for such systems are often proposed by minimizing the destroyed exergy potential in course of the process. In the present work a second law analysis has been performed for a nuclear fuel element inside a concentric annular coolant passage. The entropy generation analysis has been carried out through a conjugate approach, with steady state temperature profiles within the fuel element and a thermodynamic approach within fluid. The effect of solid core heat generation and the temperature gradients inside solid core, fuel-clad gap and cladding are considered as well along with the irreversibilities arising out of fluid flow under turbulent condition. The effect of Reynolds number, duty parameter, diameter ratio, Biot number, dimensionless heat flux and thermal conductivity ratios on overall entropy generation characteristics have been investigated and interpreted physically. The new thermodynamic design methodology presented in this paper adheres to the safety limits in temperature. The present analysis can be extended for complex fuel pellet arrangements in subchannel structures by an “equivalent annulus model”.

Reference: Poddar, A., Chatterjee, R., Chakravarty, A., Ghosh, K., Sen, S., and Mukhopadhyay, A., 2015. Thermodynamic analysis of a solid nuclear fuel element surrounded by flow of coolant through a concentric annular channel. Progress in Nuclear Energy, 85, pp. 178–191.

(iii) Performance assessment of rod bundles in central subchannels

Longitudinal flow through central subchannel structures in an array of fuel rods in a nuclear reactor plays an important role in removing the heat generated inside these fuel rods. In this problem, an entropy generation analysis has been carried out for assessment of the performance of an infinite triangular as well as a square subchannel for single-phase forced turbulent flow. The performance has been evaluated with the objective function being the overall entropy generation in a central subchannel. Various constraints such as dimensionless flow area subtended by the array of rods, pitch to diameter ratio for the configuration of rod bundles and volumetric heat generation to power density ratio of the subchannel imposed by power restrictions have been considered. The parameters include the dimensionless wall heat flux, duty parameter, length to diameter ratio for fuel rods, Reynolds number, etc.

Reference: Poddar, A., Chatterjee, R., Ghosh, K., Mukhopadhyay, A. and Sen, S., 2015. Performance assessment of longitudinal flow through rod bundle arrangements using entropy generation minimization approach. Energy Conversion and Management, 99, pp. 359–373.

Page updated

Report abuse