Krishnaswamy Nandakumar

Louisiana State University | LSU · Cain Department of Chemical Engineering

Direct Numerical Simulations (DNS) are performed on single and multiple particles freely falling in a fluid confined between two closely spaced parallel plates [Hele-Shaw cell (HSC)]. Simulations were carried out in the range of Reynolds numbers from 100 to 1000 (Rep based on particle terminal settling velocity and particle diameter) for understand...

Through periodic introspection and assessment, the chemical engineering field has developed a mature undergraduate curriculum built on a strong science background in mathematics, physics, and chemistry. This brings a unique set of skills in transport, reaction engineering, and thermodynamics coupled with suitable process systems engineering and pro...

The authors discuss the opportunities for achieving rapid innovation cycles in the chemical manufacturing space, a field that is traditionally slow to evolve compared to other industries like automotive, aerospace, and IT industries. The main reason is the enormously complex heterogeneous multiphase, multiscale, reactive mixtures that are handled i...

Microfluidic technology has been highly useful in nanovolume sample preparation, separation, synthesis, purification, detection and assay, which are advantageous in drug development. This review highlights the recent developments and trends in microfluidic applications in two areas of drug development. First, we focus on how microfluidics has been...

We evaluate a Toroidal Helical Pipe (THP) for the extent of process intensification that it can offer over an equivalent length of straight pipe by providing continuous curvature changes resulting in complex secondary flows in a compact space. The present study is a radical departure from traditional curved and helical tubes with constant curvature...

In this study, the dynamic response of a neutrally buoyant elliptical cylinder is investigated for a two-dimensional shear flow over a wide range of aspect ratios (, where, ra and rb are the major and minor axis radii, respectively). Parametric studies were carried out for confinement ratios () that vary the distance between the particle and the do...

In the present study, the impingement process of alginate droplet on an immiscible liquid is investigated using experimental and numerical approaches. The results reveal that the intensity of interaction between the two immiscible liquids leads to formation of different droplet shapes after impingement. The droplet yield stress, Ohnesorge number (O...

This simulation study explores the two‐fluid model's (TFM) capability to reproduce the alternating bubble patterns in a sinusoidal pulsed fluidized bed (PFB). Simulations were performed with frictional limits ranging between 0.58‐0.62 with the inlet gas frequency being varied in the range of 3‐6 Hz. The preliminary investigations showed that the Jo...

Direct Numerical Simulations (DNS) were carried out for a freely falling/rising rigid particle in an otherwise quiescent fluid, using a non-Lagrangian multiplier based fictitious domain (FD) method. Validation studies showed that the proposed FD based DNS are in good agreement with the existing experimental results in the transition regime of falli...

Dimples can break all symmetries in the law of reflection and make the bouncing of droplets on super‐repellent surfaces non‐specular, reported by Liqiu Wang and co‐workers (article number 2006695), and thus functioning as a “magic” hand to enable various on‐demand droplet manipulations including trapping, shedding, antigravitational transporting, t...

The bouncing of droplets on super‐repellent surfaces normally resembles specular reflection that obeys the law of reflection. Here, the nonspecular reflection of droplet impingement onto solid surfaces with a dimple for energy‐efficient, omnidirectional droplet transport is reported. With the dimple of the radius being comparable to that of the dro...

Early detection and accurate diagnosis of Alzheimer’s disease (AD) is essential for patient care and disease treatment. Microfluidic technology is emerging as an economical and versatile platform in disease detection and diagnosis. It can be conveniently integrated with nanotechnology and/or biological models for biomedical functional and pre-clini...

In the present study, the sedimentation of a swarm of mono-sized particles is investigated using the Computational Fluid Dynamics–Discrete Element Model (CFD-DEM) approach. The computational approach employed was able to accurately predict the breakup pattern of the swarm of particles into secondary clusters. The rate of leakage of the particles fr...

Magnetic particles are widely used in medical diagnosis and treatment owing to their ever-increasing magnetic targeting ability and superparamagnetism. However, small particle size and low magnetic saturation (MS) are disadvantageous for targeted delivery of magnetic particles. In this study, Fe3O4@polyvinyl alcohol (PVA) microspheres were prepared...

Computational Fluid Dynamics and Discrete Element Method are used to study the dynamics of a pseudo-2D pulsed fluidized bed, consisting of Geldart B particles. The focus is on the response of the system to variations in the mean gas velocity, VM, and the amplitude of oscillations, VA, at an imposed frequency of 3.5 Hz. Distinctive flow patterns are...

The understanding of the dynamics of arbitrary shaped particle(s) under shear flow is of great importance in design and scale-up Chemical Engineering equipment. In this study, we have carried out a series of numerical experiments on an elliptical cylinder particle, subjected to a 2D shear flow for moderate shear-based Reynolds number. The simulatio...

The physical understanding of separating flows which exhibit critical phenomena under various flow conditions, have helped in designing various drag-reduction devices, turbulence generators, controllers, etc. Direct Numerical Simulation (DNS) of such separating flows helps to identify the flow structures and decipher the corresponding effects they...

High fidelity numerical models help in understanding complicated multiphase flow physics. The knowledge generated from such simulations can be utilized for designing energy efficient, optimized industrial scale reactors.

Vascular stenosis is always associated with hemodynamic changes, especially shear stress alterations. Herein, bi-conical shaped microvessels were developed through flexibly and precisely controlled templated methods for hydrogel blood-vessel-like microchip. The blood-vessel-like microvessels demonstrated tunable dimensions, perfusable ability, and...

Direct Numerical Simulation (DNS) has been carried out in the sub critical regime (Re = 10000) for the flow past a stationary sphere. The critical parameters affecting the accuracy of DNS lies in the degree of accuracy which ultimately is governed by two important parameters, the grid sizing and the temporal resolution. Moreover, for simulating unb...

We examine the effectiveness of the forced convective heat transfer in a toroidal helical pipe (THP), as a compact process intensification device for use in heat exchangers. Earlier, we showed that mixing was enhanced significantly in such devices due to continuously changing curvature along the length of the pipe while retaining its compactness. I...

In this work, we applied discrete element method (DEM) based simulations to investigate the granular organization phenomenon recently observed in an orbital shaker. The simulation results capture the complex motion and self-organizing patterns of particles. When a single particle descends along the wall of an orbiting cylinder, the centrifugal and...

In nuclear reactors, heat is generated in the fission process which is harnessed by transferring it to fluid. The transfer also maintains the integrity of the fuel. The subject of nuclear reactor heat transfer and thermal hydraulic is crucial as it establishes the relation between the heat generated in fission and its transfer to the coolant. The h...

The effect of Schmidt number (Sc) and D/d ratio on mass transfer through gas-solid and liquid-solid packed beds was studied. The parameters investigated in this study were Sc = 1, 10, 100 and 1000, Re ≤ 100, D/d = 6 and 11, and the void fraction was kept constant at 0.57. DEM-CFD simulations were conducted to create the random geometry of the packe...

The effect of Schmidt number (Sc) and D/d ratio on mass transfer through gas-solid and liquid-solid packed beds was studied. The parameters investigated in this study were Sc = 1, 10, 100 and 1000, Re ≤ 100, D/d = 6 and 11, and the void fraction was kept constant at 0.57. DEM-CFD simulations were conducted to create the random geometry of the packe...

This review presents a systematic analysis of the published literature on flow regime mapping and effects of external disturbances for flow past a single stationary sphere. Various experimental and numerical investigations have been performed over the past years on such flows over a wide range of Re. The first part of this review (Tiwari et al. [1]...

Direct numerical simulations are carried out for an incompressible flow past a stationary sphere, in the range of 100 ≤ Re ≤ 1000. It is found that the first instability occurs as the axisymmetric wake undergoes breakage at Re ≥ 250. Adding small perturbations to the flow showed that the preferred direction of breakage of the axisymmetric wake and...

A Multiphysics numerical model was developed using COMSOL Multiphysics to study the effect of size, shape and position of catalyst bed within the microwave reactor (2450 MHz). The dielectric properties of HZSM-5 catalyst were measured at different frequencies and nine different temperatures ranging from 25 °C to 370 °C. The heat transfer in porous...

Flow separation across bluff bodies has been a fascinating area of fluid mechanics since 1851. A large number of computational and experimental studies have been performed in the last several decades which have enabled the understanding and hence helped in distinguishing the flow regimes based on the characteristics exhibited by different flow para...

Chemical Engineering operations involve single and multiphase flows which can be categorized into internal and external flows depending on the boundedness of domain through which the fluid flows. Design procedures of such systems have gone through some extraordinary developments in last couple of decades with advancements in the field of Computatio...

Direct Numerical Simulations (DNS) are performed for three dimensional stationary bluff body at two different flow regimes (unsteady non-axisymmetry regime and shear layer instability regime). The purpose is to examine the similarity and differences in the formation of flow structures in the transition of the flow towards turbulence. The subject of...

In this paper we present the design of a novel, passive mixer, to enhance mixing and residence time distribution for promoting transport and reaction mechanisms in such devices. The goal is to understand and optimize the flow patterns for enhancing mixing in laminar flows through toroidal helical pipes, inspired by the coiled flow inverter (CFI) (S...

We present three algorithms for robust and efficient geometric calculations in the context of immersed boundary method (IBM), including classification of mesh cells as inside/outside of a closed surface, projection of points onto a surface, and accurate calculation of the solid volume fraction field created by a closed surface overlapping with a ba...

Fluid flow in microchannels has wide industrial and scientific applications. Hence, it is important to explore different driving mechanisms. In this paper, we study the net transport or fluid pumping in a two-dimensional channel induced by a travelling temperature wave applied at the bottom wall. The Navier–Stokes equations with the Boussinesq appr...

Direct Numerical Simulation (DNS) was performed to investigate the end effects on mass transfer in a packed bed for Reynolds number (Re) ≤ 100. The system considered in this study was naphthalene-air with a Schmidt number (Sc) ∼ 2.52. The location of the spheres’ centers in a randomly packed bed were obtained from Discrete Element Method – Computat...

Evaluating the order of accuracy (order) is an integral part of the development and application of numerical algorithms. Apart from theoretical functional analysis to place bounds on error estimates, numerical experiments are often essential for nonlinear problems to validate the estimates in a reliable answer. The common workflow is to apply the a...

The present work reports the experimental and CFD investigations of a Novel Down-flow bubble column to understand the flow characteristics. A novel mechanism of gas-liquid injection has been used to generate a high concentration of micro-bubbles with uniform distribution in a column of large cross-section (0.3 m diameter). Gas hold-up is obtained u...

The spontaneous production of meso-scale flow features such as bubbles and slugs during gas-solid fluidization is well known. This has direct impact on chemical engineering design issues such as conversion rates during catalyst regeneration. However, controlling the size and frequency of appearance of such bubbles during fluidization is not well-un...

Catalyst regeneration process has recently been the subject of comprehensive research investigations focusing mainly on the chemistry of the regeneration while overlooking the bed hydrodynamics and its effects on the regeneration performance. For this purpose, an industrial Fluid Catalytic Cracking (FCC) regenerator is simulated using a Multi-Phase...

In this paper, Direct Numerical Simulation (DNS) was performed to understand the effects of confining walls on mass transfer through a packed bed for laminar regime (Re ≤ 100). The X, Y and Z coordinates of the center of the spheres in a randomly packed bed with varying ratios D/d (D is the diameter of the column and d is the diameter of the partic...

The causes and ad-hoc remedies associated with the formation of slugs that result in pump power fluctuation inside slurry loop reactors have been discussed in several patent literature, but studied in few research publications. The circulation of large polymer slugs inside loop reactors can induce violent fluctuations of pump power that can lead to...

In this paper, mixing in an oscillating column was experimentally and numerically studied as a function of power applied through vibrations. The mixing experiments were performed using phenolphthalein and NaOH solution, and the mixing time was computed using a simple image processing algorithm to track intensity changes implemented in MATLAB. Numer...

During deepwater oil spill events, oil is released into a relatively stagnant environment (ocean water) in an uncontrolled manner. The oil phase initially emerges as jet and the gushing oil loses its momentum energy and results in entrainment of surrounding water. The shear interaction between the oil mass and the ambient fluid results in generatio...

Gas-liquid two phase flows are widely encountered in industry. The design parameters include two phase pressure drop, mixing and axial mixing in both the phases, effective interfacial area, heat and mass transfer coefficients. Currently, there is a high degree of empiricism in the design process of such reactors owing to the complexity of coupled f...

Among the discoveries of the Deepwater Horizon blowout was the so-called "sub-surface plume"; herein termed the "oil-trapping layer". Hydrocarbons were found positioned at ~1100-1300m with thickness ~100-150m and moving horizontally to the SW in a vertically stratified layer at the junction of the cold abyssal water and the permanent thermocline. T...

The growing energy demand across the globe has resulted in an increase in the deep water oil exploration activities which in turn has increased the risk of occurrence of associated accidental oil releases. Oil and Gas offshore businesses are important to Qatar's economy. Further, the country is heavily dependent on its marine water resources for fu...

The discrete particle model (DPM) in OpenFOAM was used to study the turbulent solid particle suspension flows through the porous media of a natural dual-permeability rock. The 2D and 3D pore geometries of the porous media were generated by sphere packing with the radius ratio of 3. The porosity is about 38{\%} same as the natural dual-permeability...

The Discrete Particle Model (DPM) based on OpenFOAM was established at the high performance computing (HPC) platform (SuperMIC in LSU with Intel Xeon Phi Coprocessor). It coupled a multiphysics simulation algorithm for both fundamental physics needs as well as efficient usage of HPC resources.

In this work we demonstrate the utility of a new computational algorithm, based on the finite volume method, for simulating the motility of microorganisms. The approach is adopted from our work on discrete particle modeling. The shape of a swimming cell is reconstructed as a contiguous sequence of spherical particles at discrete locations on the su...

Multiphase reactors are very common in chemical industry, and numerous review articles exist that are focused on types of reactors, such as bubble columns, trickle beds, fluid catalytic beds, etc. Currently, there is a high degree of empiricism in the design process of such reactors owing to the complexity of coupled flow and reaction mechanisms. H...

This is a first of its kind study demonstrating that oil weathering can result in its sinking. Although a controversial proposition, oil's appearance on the sea floor following the 2010 Macondo 252 spill in the Gulf of Mexico and its large unaccountable volume has raised awareness of possible alternative explanations. Drag-down by settling particle...

Sperm cell activation plays a critical role in a range of biological and engineering processes, from fertilization to cryopreservation protocol evaluation. Across a range of species, ionic and osmotic effects have been discovered that lead to activation. Sperm cells of zebrafish (Danio rerio) initiate motility in a hypoosmotic environment. In this...

Computational Methods for Engineers: Modeling, Algorithms and Analysis

Droplet-based microfluidic devices have received extensive attention in the fields of chemical synthesis, biochemical analysis, lab-on-chip devices etc. Conventional passive microfluidic hydrodynamic flow–focusing devices (HFFD) control the droplet breakup process by manipulating the flow ratios of the continuous phase to the dispersed phase. They...

Experimental and numerical investigations were conducted to study the effect of unsteady mass transfer on the dynamics of an organic droplet released in quiescent water. The situation is important and relevant to deep sea oil spill scenario. The droplet contains two components, one is heavier (immiscible) than water and other is lighter (miscible)....

In this study we have investigated the effect of surfactant, sodium dodecyl sulfate (SDS), on the dynamics of a single crude oil droplet, rising in a quiescent water column. Experiments were conducted in a tank, in which an oil droplet was released into a stagnant water column through a nozzle. The droplets ranging from 0.3 to 0.85 cm were produced...

We consider the case of transient three-dimensional, incompressible and isothermal channel ow of a newtonian uid past a symmetrically confined obstacle of square cross section at zero incidence. The blockage ratio (ratio of cylinder diameter to channel width) is fixed at 1/4. Results from both Laser Doppler (LDV) experiments and direct simulations...

The laminar flow in microfluidic devices has shown promise as an effective delivery mechanism for cryoprotective agents to biological cells. For this method to gain more prevalence, its potential for use with more realistic and more complicated mixtures of cryoprotectants requires further exploration. In this work, we investigate the transport phen...

We present a numerical investigation of the simultaneous loading of a cocktail of propanediol and dimethyl sulfoxide into human sperm cells inside of a microchannel. The microchannel simulated has one central upstream inlet for cells, two upstream sheath inlets with one of the cryoprotective agents, and two downstream sheath inlets with the other c...

The Canadian Journal of Chemical Engineering has had a long record of assessing, disseminating and archiving outstanding contributions to the field of chemical engineering. Many distinguished Canadian and International chemical engineers have contributed and continue to contribute to its development and stature today. It is a distinct pleasure to a...

Droplet-based microfluidics has gained extensive research interest as it overcomes several challenges confronted by conventional single-phase microfluidics. The mixing performance inside droplets/slugs is critical in many applications such as advanced material syntheses and in situ kinetic measurements. In order to understand the effects of operati...

This chapter (i) documents scantily available data on the 2010 Gulf of Mexico (GoM) deepwater horizon (DWH) oil spill and the sources of such data; (ii) identifies the various mechanisms for transport and physicochemical change of the oil-gas mixture as it interacts with the seawater; (iii) summarizes the mechanistic models available in the literat...

Computational Methods for Process Engineers

The sedimentation of a swarm (cloud) of particles in a viscous fluid at low and moderate Reynolds numbers has been studied using an Eulerian-Lagrangian multiphase flow approach. We looked at the volume fraction dependence of the settling cloud and find a similar dependence in the simulations as in the theoretical predictions of Nitsche and Batche...

The performance of a homogeneous T-mixer can be enhanced significantly by the stimulation of secondary/transverse flows in the microchannel. The groove-based micromixers generate helical flows within the microchannel to augment the mixing performance. These micromixers are extensively studied with respect to planar geometric parameters such as groo...

Cryopreservation of cells and tissues is critical to long term storage and off the shelf availability of biomaterials for a variety of disciplines[1]. Typical cryopreservation protocols aim to remove intracellular water by exposing the sample to a cryoprotective agent (CPA) to create an osmotic pressure gradient[2]. While CPAs are useful in prevent...

The freshwater fish, Danio rerio (zebrafish), have become widely used as a model organism for vertebrate development, DNA mutation, and human disease studies [1]. Maintaining live colonies of the numerous developed strains of zebrafish under investigation can be prohibitively costly. As such, there is a growing need to catalog their reproductive ce...

Particle image velocimetry measurements have been performed in a solid–liquid fluidized bed in the Reynolds number range 51–759. To do this, the refractive indexes of the solid and liquid phases were matched at approximately 1.47 using 3 mm diameter borosilicate glass beads and a solution of turpentine and tetra-hydronaphthalene. Paraffin oil was a...

In this work, we conduct a computational study on the loading of cryoprotective agents into cells in preparation for cryopreservation. The advantages of microfluidics in cryopreserving cells include control of fluid flow parameters for reliable cryoprotectant loading and reproducible streamlined processing of samples. A 0.25 m long, three inlet T-j...

With recent increasing trend towards development of “easy to fabricate” and simple millifluidic systems that could provide required control as well as high throughput, we present here a demonstration of potential opportunities for controlled droplet/slug formation within a flow-focusing millifluidic chip. Numerical simulations supported by experime...

Micromixing is a key step in realizing fast analysis time in many bio-chemical, biological and detection applications of lab-on-a-chip (LOC) devices. The conventional T-mixer design requires longer channel lengths and times to achieve complete mixing owing to its dependence on transverse diffusion. As the surface properties of the microchannel gove...

Chemical dispersants are widely used to counter the adverse effects of oil spills on the environment. Surfactants are the active ingredients in dispersants which cause reduction in interfacial tension resulting in the production of smaller oil droplets. Surfactant distributes between the bulk phase (water) and the interface to achieve equilibrium b...

Cryopreservation of reproductive cells offers scientists a cost-effective alternative to maintaining a live strain of a genetically modified species. Prior to cryopreservation, it is desirable to remove intracellular water to prevent ice crystal formation. This is done by loading a cryoprotectant, such as glycerol, into the cell. Microfluidic devic...