Sankaran Sundaresan

Sankaran Sundaresan
Princeton University | PU · Department of Chemical and Biological Engineering

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301
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Introduction
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Publications

Publications (301)
Article
Full-text available
We present a semi-analytic model for a novel plasma-assisted chemical conversion pathway using triboplasmas generated in granular flows. Triboelectric charge relaxation is a well known phenomena where the potential generated from contact charging of particles exceeds the breakdown voltage of the background gas. In this work, we extend the triboelec...
Preprint
Full-text available
We present a semi-analytic model for a novel plasma-assisted chemical conversion pathway using triboplasmas generated in granular flows. Triboelectric charge relaxation is a well known phenomena where the potential generated from contact charging of particles exceeds the breakdown voltage of the background gas. In this work, we extend the triboelec...
Article
Full-text available
Gas-particle flows are commonly simulated through a twofluid model at the industrial scale. However, these simulations need a very fine grid to have accurate flow predictions, which is prohibitively demanding in terms of computational resources. To circumvent this problem, the filtered two-fluid model has been developed, where the large-scale flow...
Article
Full-text available
Contact electrification, or contact charging, refers to the process of static charge accumulation after rubbing, or even simple touching, of two materials. Despite its relevance in static electricity, various natural phenomena, and numerous technologies, contact charging remains poorly understood. For insulating materials, even the species of charg...
Preprint
Full-text available
Gas-particle flows are commonly simulated through two-fluid model at industrial-scale. However, these simulations need very fine grid to have accurate flow predictions, which is prohibitively demanding in terms of computational resources. To circumvent this problem, the filtered two-fluid model has been developed, where large-scale flow field is nu...
Article
Full-text available
Ammonia (NH 3 ) is an attractive low-carbon fuel and hydrogen carrier. However, losses and inefficiencies across the value chain could result in reactive nitrogen emissions (NH 3 , NO x , and N 2 O), negatively impacting air quality, the environment, human health, and climate. A relatively robust ammonia economy (30 EJ/y) could perturb the global n...
Article
Full-text available
The accuracy of filtered two‐fluid model simulations critically depends on constitutive models for corrections that account for the effects of inhomogeneous structures at the sub‐grid level. The complexity of accounting these structures increases with cohesion. In the present study, a dataset from filtered Euler‐Lagrange simulations with systematic...
Article
The wettability of a polymer surface─related to its hydrophobicity or tendency to repel water─can be crucial for determining its utility, such as for a coating or a purification membrane. While wettability is commonly associated with the macroscopic measurement of a contact angle between surface, water, and air, the molecular physics that underlie...
Preprint
Full-text available
The wettability of a polymer surface--related to its hydrophobicity or tendency to repel water--can be crucial for determining its utility, such as for a coating or a purification membrane. While wettability is commonly associated with the macroscopic measurement of a contact angle between surface, water, and air, the molecular physics that underli...
Preprint
Full-text available
The wettability of a polymer surface--related to its hydrophobicity or tendency to repel water--can be crucial for determining its utility, such as for a coating or a purification membrane. While wettability is commonly associated with the macroscopic measurement of a contact angle between surface, water, and air, the molecular physics that underli...
Article
We report on the effect of catalyst support particle porosity on the conversion of NH3 synthesis from N2 and H2 in a coaxial dielectric barrier discharge (DBD) plasma reactor. The discharge was created using an AC applied voltage with the reactor at room temperature and near atmospheric pressure (550 Torr). Two different particles of almost equal d...
Article
Full-text available
Principal Component Analysis can be used to reduce the cost of Computational Fluid Dynamics simulations of turbulent reacting flows by reducing the dimensionality of the transported variables through projection of the thermochemical state onto a lower-dimensional manifold. However, because of the nonlinearity of the principal component source terms...
Article
We have performed Computational Fluid Dynamics-Discrete Element Method (CFD-DEM) simulations of air and particles in a commercial ELLIPTA® inhaler. We simulated the fluidization, deagglomeration and transport of carrier and API particles, with two realistic inhalation profiles that are representative of moderate asthma and very severe COPD patients...
Article
The charges acquired by polyethylene and glass particles fluidized by argon, nitrogen, and air at different humidity levels in acrylic and steel columns have been measured. Increased bed expansion at higher fluidization gas velocities lowered the space charge effect, allowing the particles to acquire more charges. The low dielectric strength of arg...
Article
This article reviews recent developments in computational modeling of dry powder inhalers (DPIs). DPIs deliver drug formulations (sometimes blended with larger carrier particles) to a patient’s lungs via inhalation. Inhaler design is complicated by the need for maximum aerosolization efficiency, which is favored by high levels of turbulence near th...
Article
The total charges acquired by soda-lime glass particles and polyethylene particles were measured in a vibrated bed under a nitrogen or argon environment. The charge magnitudes were lower in argon compared to nitrogen. Complementary Discrete Element Method simulations using the gaseous dielectric strength as a constraint largely reproduce the experi...
Preprint
Full-text available
A fundamental understanding of plasma-catalyst interactions is important for understanding reaction mechanisms, optimizing the catalyst, and increasing the efficiency of plasma-assisted catalytic process for ammonia (\ce{NH3}) synthesis. We report on the effect of the surface porosity of the catalyst support on this reaction carried out in a coaxia...
Article
Full-text available
Ammonia synthesis experiments were carried out in a coaxial dielectric barrier discharge (DBD) reactor packed with several different supports and metal catalysts. There was a marked increase in the reaction rate, over that obtained in an empty DBD plasma reactor, upon introduction of a packed bed of γ-Al2O3, Ru/γ-Al2O3, or SiO2 particles. The diffe...
Article
The transport and aerosolization of particles are studied in several different dry powder inhaler geometries via Computational Fluid Dynamics-Discrete Element Method (CFD-DEM) simulations. These simulations combine Large Eddy Simulation of gas with Discrete Element Model simulation of all the carrier particles and a representative subset of the act...
Article
Drug delivery via dry powder inhaler (DPI) is a complex process affected by multiple factors involving gas and particles. The performance of a carrier-based formulation depends on the release of active pharmaceutical ingredient (API) particles, typically characterized by fine particle fraction (FPF) and dispersion fraction (DF). Computational Fluid...
Article
The energy efficiency of heterogeneous catalytic processes may be improved by using mid-infrared light to excite gas-phase reactants during the reaction, since vibrational excitation of molecules has been shown to increase their reactivity at the gas-catalyst interface. A primary challenge for such light-enabled catalysis is the need to ensure clos...
Data
This is a package to demonstrate drift flux prediction using neural network model in C++. The model and implementation is part of the supplementary material to the publication: Yundi Jiang, Xiao Chen, Jari Kolehmainen, Ioannis G. Kevrekidis, Ali Ozel, Sankaran Sundaresan, "Development of Data-Driven Filtered Drag Model for Industrial-Scale Fluidi...
Article
Simulations of large-scale gas-particle flows using coarse meshes and the filtered two-fluid model approach depend critically on the constitutive model that accounts for the effects of sub-grid scale inhomogeneous structures. In an earlier study (Jiang et al., 2019), we had demonstrated that an artificial neural network (ANN) model for drag correct...
Article
Total charge acquired by soda-lime glass particles of two different sizes in nitrogen environment were measured in vibrated beds. A systematic difference of surface charge density was observed. Complementary Discrete Element Method simulations were performed to examine how this size dependence could be captured in a tribocharging model. Neither die...
Article
On modelling shear layers in dense granular flows - Volume 892 - Sankaran Sundaresan
Article
Although Euler-Lagrange simulations can be performed with millions of particles, particle coarsening where particles are replaced by parcels is necessary for simulation of large particulate and fluid-particle flows. The present study examines coarsening strategies for cohesive particles, where cohesion arises through either van der Waals interactio...
Article
We study wall-induced triboelectrification of particles by analyzing a continuum model for charge transport. We first consider an idealized case of homogeneous distribution of granular materials in a periodic channel and show that the domain-average charge per particle is inversely proportional to channel size. We then perform three-dimensional sim...
Article
Full-text available
Contact charging between insulators is one of the most basic, yet least well understood, of physical processes. For example we have no clear theory for how insulators recruit enough charge carriers to deposit charge but not enough to discharge. In this paper we note that charging and discharging kinetics may be distinct, and from this observation w...
Article
Full-text available
Filtered two-fluid model (fTFM) for gas-particle flows require closures for the sub-filter scale corrections to interphase drag force and the stresses, the former being more significant. In this study, we have formulated a neural-network-based model to predict the sub-grid drift velocity, which is then used to estimate the drag correction. As a par...
Article
Full-text available
Developing constitutive models for particle phase rheology in gas-fluidized suspensions through rigorous statistical mechanical methods is very difficult when complex inter-particle forces are present. In the present study, we pursue a computational approach based on results obtained through Eulerian-Lagrangian simulations of the fluidized state. S...
Preprint
Contact charging between insulators is one of the most basic, yet least well understood, of physical processes. For example we have no clear theory for how insulators recruit enough charge carriers to deposit charge but not enough to discharge. In this letter we note that charging and discharging kinetics may be distinct, and from this observation...
Article
Simulations of particle-laden flow with dielectric particles are carried out with varying levels of electrical charging and particle polarization. Simulation results reveal three distinct flow regions. For low particle charge and polarizability, flow is nearly symmetric and nonmeandering. For strong charging and polarization, particles form a conti...
Article
Full-text available
Particles subjected to flow are known to acquire electrostatic charges through repeated contacts with each other and with other surfaces. These charges alter gas–particle flow behaviour at different scales. In this work, we present a continuum framework for analysing the interplay between tribocharging and the flow of a monodisperse assembly of par...
Article
Full-text available
The effects of triboelectricity in a small-scale fluidized bed of polyethylene particles were investigated by imaging the particle layer in the vicinity of the column wall and by measuring the pressure drop across the bed. The average charge on the particles was altered by changing the relative humidity of the gas. A triboelectric charging model co...
Article
As multiscale structures are inherent in multiphase flows, constitutive models employed in conjunction with transport equations for momentum, species, and energy are scale dependent. We suggest that this scale dependency can be better quantified through deep learning techniques and formulation of transport equations for additional quantities such a...
Article
Full-text available
The formation of inhomogeneities within fluidized beds, both in terms of the particle configurations and flow structures, have a pronounced effect on the interaction force between the fluid and particles. While recent numerical studies have begun to probe the effects of inhomogeneities on the drag force at the particle scale, the applicability of p...
Article
Full-text available
Euler-Lagrange simulations of gas-solid flows in unbounded domains have been performed to study sub-grid modeling of the filtered drag force for non-cohesive and cohesive particles. The filtered drag forces under various microstructures and flow conditions were analyzed in terms of various sub-grid quantities: the sub-grid drift velocity, which ste...
Article
This article, and this entire issue of the AIChE Journal, are meant to honor Professor Roy Jackson, whose contributions to chemical engineering have been profound and exceptionally broad. It is often said of Roy Jackson that few, if any, scholars have so deep a command of the full range of highly varied subjects that comprise the chemical engineeri...
Article
Aligned fibers of extracellular matrix (ECM) affect the direction, efficiency, and persistence of migrating cells. To uncover the mechanisms by which multicellular tissues align their surrounding ECM before migration, we used an engineered three-dimensional culture model to investigate the dynamics of ECM alignment around tissues of defined geometr...
Article
Polyethylene particles were tribocharged in a glass container subjected to vertical vibration and the resulting charge per unit mass was measured. The experimental data in conjunction with discrete element method simulations coupled with a tribocharging model were used to deduce effective work function differences between the particles and the glas...
Article
Gas-solid fluidization involving small amounts of liquid is simulated using a CFD-DEM model. The model tracks the amount of liquid on each particle and wall element and incorporates finite rates of liquid transfer between particles and pendular liquid bridges which form between two particles as well as between a particle and a wall element. Viscous...
Article
Desalination via forward osmosis using draw agents whose regeneration is aided via liquid-liquid phase separation has gained much attention in recent years. In the present study, mixtures of two different glycol ethers, tripropylene glycol methyl ether and tripropylene glycol n-butyl ether, have been studied as potential draw agents. Water activity...
Article
Significance Using CFD‐DEM simulations, a wet agglomerate of particles was placed in a void region of a dry vigorously fluidized bed to understand how wet agglomerates grow or breakup and how liquid spreads when agglomerates interact with dry fluidized particles. In the CFD‐DEM model, cohesive and viscous forces arising from liquid bridges between...
Article
CFD-DEM simulations were conducted and compared with magnetic resonance imaging (MRI) measurements1 of gas and particle motion in a 3D cylindrical bubbling fluidized bed. Experimental particles had a kidney-bean-like shape, while particles were simulated as being spherical; to account for non-sphericity, “effective” diameters were introduced to cal...
Article
Full-text available
Relative flow between granular material and gas can create phenomena in which particles behave like a liquid with bubbles rising through them. In this paper, magnetic resonance imaging is used to measure the velocities of the gas and solid phases in a bubbling fluidized bed. Comparison with theory shows that the average velocity of gas through the...
Article
Relative flow between granular material and gas can create phenomena in which particles behave like a liquid with bubbles rising through them. In this paper, magnetic resonance imaging is used to measure the velocities of the gas and solid phases in a bubbling fluidized bed. Comparison with theory shows that the average velocity of gas through the...
Article
To investigate the interplay between particle charging and hydrodynamics in fluidized beds, models for triboelectric charging and electrostatic forces were built into a CFD-DEM model. Charge transfer was governed by the difference in effective work function between contacting materials as well as the electric field at the point of contact. Monodisp...
Article
The intrusion of a droplet of liquid into a hexagonal closed packed array of spheres under gravity is investigated using analytical methods and volume-of-fluid simulations. Four regimes of ultimate fluid behavior are identified: (A) no liquid imbibition into the bed, (B) trapping of liquid high in the bed, (C) liquid descent to the bottom of the be...
Article
The accuracy of fluidized-bed CFD predictions using the two-fluid model can be improved significantly, even when using coarse grids, by replacing the microscopic kinetic-theory-based closures with coarse-grained constitutive models. These coarse-grained constitutive relationships, called filtered models, account for the unresolved gas-particle stru...
Article
Simulating full-scale heated fluidized bed reactors can provide invaluable insight to the design process. Such simulations are typically computationally intractable due to their complex multi-physics and various length-scales. While it may be possible to simulate some large-scale systems, they require significant computing resources and do not lend...
Article
In particulate flow devices particles acquire electric charge through triboelectric charging, and resulting electrostatic forces can alter hydrodynamics. To capture this effect, the electrostatic force acting on individual particles in the device should be computed accurately. We present a hybrid approach to determine the electrostatic force, which...
Article
Euler-Lagrange simulations of fluidized beds of Geldart Group A particles containing different levels of fines are performed in periodic domains with various domain-averaged solid volume fractions. Bubble-like voids readily form when no fines are added. Introducing fines does not reduce bubble sizes if van der Waals force between particles is not a...
Article
In a fluidized bed, the drag force acts to oppose the downward force of gravity on a particle, and thus provides the main mechanism for fluidization. Drag models that are employed in large-scale simulations of fluidized beds are typically based on either fixed-particle beds or the sedimentation of particles in liquids. In low-Reynolds-number ( $Re...
Article
Simulations of wet fluidized beds of particles in small periodic domains have been carried out using a CFD-DEM approach. A liquid bridge forms upon particle-particle collision, which then ruptures when the particle separation exceeds a critical distance. The simulations take into account only the surface tension force of attraction due to the liqui...
Conference Paper
Full-text available
We present a new approach for the closure of the effective drag force appearing in the filtered two-fluid model (TFM) for gas-solid flow. In particular, we show that the effective drag can be systematically described by using the filtered volume fraction and the kinetic energy of the meso-scale velocity fluctuations, ks. Characterizing the effectiv...
Article
Predictions of simulations based on filtered Two-Fluid Models (TFMs) with constitutive relations for filtered fluid–particle drag coefficient and filtered stresses proposed by Igci and Sundaresan [Ind. Eng. Chem. Res. 50 (2011) 13190–13201] and Milioli et al. [AIChE J. 59 (2013) 3265–3275] were compared against experimental data from a bubbling flu...
Article
Building on a our previous study on the kinetics of formation of cyclopentane (CP)-methane binary sII-type hydrate in well-agitated fresh water, analogous experiments have been performed in brine solutions at two salinities (3.5% and 7.0% NaCl, w/w) to investigate how salt affects this formation process thermodynamically and kinetically. The hydrat...
Conference Paper
Discrete element simulations of simple shear flows of dense and homogeneous assemblies of uniform, spherical, soft and dry particles reveal three regimes: (i) a quasi-static regime, where the stress is independent of shear rate, (ii) an inertial regime where the stress varies quadratically with shear rate and (iii) an intermediate regime where the...
Conference Paper
In order to effectively study fluid-particle systems on a large scale, it is vital to accurately model the fluid-particle interaction force on a microscopic level. In a fluidized bed, the drag force, which is the most dominant contribution to the interactions between the fluid and particles, acts to oppose the downward force of gravity on a particl...
Conference Paper
It is well known that addition of fines improves quality of fluidization [1,2]. However, the mechanism through which the fines affect fluidization quality is not fully understood. Addition of fines not only introduces particle size distribution, but also makes the system more cohesive. It is unclear which property of fines is responsible for its be...
Conference Paper
Wet granular materials are widely used in numerous industrial processes such as mixing, granulation, coating and coking. Previous research in the area of wet granular flows mainly focused on forces involved in the formation of liquid bridges. Unfortunately, much less theory is available to describe liquid transfer upon particle-particle collisions....
Conference Paper
Full-text available
Wet fluidized beds in which the solids are wetted by a liquid prior to or during fluidization by a gas are common in energy, chemical, food and pharmaceutical industries. Colliding wet particles form liquid bridges, promoting agglomeration, which is desirable in some contexts such as granulation, but is undesirable in others. When a gas fluidizes...
Conference Paper
Sub-grid models improve considerably the quantitative accuracy of coarse-grid CFD simulations of gas-particle flows. Earlier efforts on sub-grid models by Igci et al. [AlChE J., 54(6), 1431-1448, 2008] focused on one-marker models, where the sub-grid corrections were correlated in terms of filtered particle fraction (in addition to filter size). Th...
Conference Paper
Full-text available
Euler-Lagrange simulations, where the locally averaged equations of motion for the fluid phase are solved in an Eulerian framework (often denoted as CFD of the gas phase) and the particles are tracked in a Lagrangian fashion (using the Discrete Element Method, i.e., DEM), are widely used to investigate gas-solid flow behavior in fluidized beds. The...
Conference Paper
Simulations provide a convenient approach for the study of multiphase fluidized beds due to their ability to probe flow details, such as individual particle velocities and solid volume fraction profiles, that are difficult to measure in experiments. Yet, one shortcoming of simulation studies is their ability to model flow behavior at the large leng...
Article
Adequately resolving the hydrodynamics and heat transfer in gas-solid flow simulations typically requires computational grids on the order of 1-10 particle diameters. This requirement is not feasible for most full-scale applications. To overcome these impracticalities, we consider a sub-grid filtering approach where the microscopic heat transfer me...
Article
Full-text available
Fluidized gas-particle systems are inherently unstable and they manifest structures on a wide range of length and time scales. In this article we present for the first time in the literature a coarse-grained drag force model for Euler-Lagrange (EL) based simulations of fluidized gas-particle suspensions. Two types of coarse graining enter into cons...
Article
Full-text available
We investigate the dense-flow rheology of cohesive granular materials through discrete element simulations of homogeneous, simple shear flows of frictional, cohesive, spherical particles. Dense shear flows of noncohesive granular materials exhibit three regimes: quasistatic, inertial, and intermediate, which persist for cohesive materials as well....
Article
The accuracy of coarse-grid multiphase CFD simulations of fluidized beds may be improved via the inclusion of filtered constitutive models. In our previous study (Sarkar et al., 2013 Chem. Eng. Sci., 104, pp. 399–412), we developed such a set of filtered drag relationships for beds with immersed arrays of cooling tubes. Verification of these filter...
Article
Advanced multiscale modeling and simulation have the potential to dramatically reduce the time and cost to develop new carbon capture technologies. The Carbon Capture Simulation Initiative is a partnership among national laboratories, industry, and universities that is developing, demonstrating, and deploying a suite of such tools, including basic...
Article
Using the microscopic multi-fluid model as a starting point we perform fine grid simulations of bidisperse gas–particle flows to examine the dependence of the filtered fluid–particle drag coefficient, particle–particle drag coefficient, and particle phase stress on the volume fractions and sizes of the particles and the filter size. Scalings are id...
Article
Immersed cylindrical tube arrays often are used as heat exchangers in gas-particle fluidized beds. In multiphase computational fluid dynamics (CFD) simulations of large fluidized beds, explicit resolution of small cylinders is computationally infeasible. Instead, the cylinder array may be viewed as an effective porous medium in coarse-grid simulati...
Conference Paper
Filtered two-fluid models offer a promising practical alternative to microscopic two-fluid model for the simulation of gas-particle flows in industrial systems generally characterized by heterogeneous structures ranging from micro-scale to macro-scale. In our prior studies [1,2] we performed highly resolved simulations of gas-particle flows using m...
Conference Paper
Gas-fluidized beds of dry particles exhibit complex behavior with instabilities giving rise to inhomogeneities that span a wide range of time and length scales. Adding liquid to the system such that particles support a liquid film coating introduces further complexity, allowing for the fluidization of both particles and agglomerates. Constitutive m...
Conference Paper
Previous research in the area of wet granular flows mainly focused on forces connected to liquid bridges. However, there is much less theory concerned with the process of liquid transfer upon particle-particle and particle-wall collisions. To study the liquid transfer upon bridge formation and rupture, the Navier-Stokes equation can be simulated, i...
Conference Paper
Understanding flows of granular matter is essential for the design of particulate and gas-solid flow processes, and much research attention has been devoted to studying granular flows of non-cohesive particles. However, cohesive particles are ubiquitous in nature and industrial processes and exhibit behaviors unseen in non-cohesive materials, inclu...
Conference Paper
While previous research in the area of wet granular flows mainly focused on forces connected to liquid bridges, there is much less theory concerned with the process of liquid transfer upon particle-particle or particle-wall collision. For example, to study the liquid transfer upon bridge rupture, solution of the Navier-Stokes equation (i.e., direct...
Article
Full-text available
A lattice Boltzmann (LB) method is presented for solving the energy conservation equation in two phases when the phase change effects are included in the model. This approach employs multiple distribution functions, one for a pseudotemperature scalar variable and the rest for the various species. A nonideal equation of state (EOS) is introduced by...
Article
New constitutive relations for filtered two‐fluid models (TFM) of gas‐particle flows are obtained by systematically filtering results generated through highly resolved simulations of a kinetic theory‐based TFM. It was found in our earlier studies that the residual correlations appearing in the filtered TFM equations depended principally on the filt...
Article
Many different types of multiphase flow chemical r