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Arvind Pattamatta
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Arvind Pattamatta
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Arvind Pattamatta
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Pattamatta, Arvind
Pattamattaa, Arvind
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9 results
Now showing 1 - 9 of 9
- PublicationPercolation network dynamicity and sheet dynamics governed viscous behavior of polydispersed graphene nanosheet suspensions(01-01-2013)
;Dhar, Purbarun ;Ansari, Mohammad Hasan Dad ;Gupta, Soujit Sen ;Siva, V. Manoj; ; The viscosity of polydispersed graphene nanosheet (5 nm-1.5 μm) suspensions (GNS) and its behavior with temperature and concentration have been experimentally determined. A physical mechanism for the enhanced viscosity over the base fluids has been proposed for the polydispersed GNSs. Experimental data reveal that enhancement of viscosity for GNSs lies in between those of carbon nanotube suspensions (CNTSs) and nano-alumina suspensions, indicating the hybrid mechanism of percolation (like CNTs) and Brownian motion-assisted sheet dynamics (like alumina particles). Sheet dynamics and percolation, along with a proposed percolation network dynamicity factor, have been used to determine a dimensionally consistent analytic model to accurately determine and explain the viscosity of polydispersed GNSs. The model also provides insight into the mechanisms of viscous behavior of different dilute nanoparticle suspensions. The model has been found to be in agreement with the GNS experimental data, and even for CNT (diameter 20 nm, length 10 lm) and nano-alumina (45 nm) suspensions. © Springer Science+Business Media 2013. - PublicationCascaded collision lattice Boltzmann model (CLBM) for simulating fluid and heat transport in porous media(02-09-2017)
;Shah, Nimit ;Dhar, Purbarun ;Chinige, Sampath Kumar ;Geier, MartinThe present paper reports a cascaded collision lattice Boltzmann model for the simulation of an incompressible two-dimensional fluid flow in a porous media regime. The cascaded model is first validated for the nonporous regime using limiting conditions against previous finite element model reports. Subsequently, the cascaded collision model is applied to the lid-driven porous-filled cavity to demonstrate the largely augmented numerical stability of the model against the more common Bhatnagar–Gross–Krook and multiple relaxation time collision models. Finally, the cascaded model is applied to an inflow–outflow case of flow and heat transfer over a porous bluff body to showcase its efficiency in capturing the complex fluid and heat transport phenomenon through porous media. - PublicationBridging Thermal and Electrical Transport in Dielectric Nanostructure-Based Polar Colloids(01-09-2015)
;Dhar, Purbarun ;Sengupta, Soujit; Heat and charge transport characteristics of nanocolloids have been bridged from fundamental analysis. The relationship between the two transport phenomena in dielectric nanostructure-based polar colloids has been quantitatively presented. An extensional intuitive analogy to the Wiedemann-Franz law has been drawn. Derived from the fact that mobile electrons transport both heat and charge within metallic crystal structure, the analogy can be extended to nanocolloids, wherein the dispersed population act as the major transporter. The analogy allows modeling of the relationship between the two phenomena, and sheds more insight and conclusive evidence that nanoparticle traversal within the fluid domain is the main source of augmented transport phenomena exhibit by nanocolloids. Important factors, such as the thermal and dielectric responses of the nanocolloid can be quantified and bridged through the semianalytical formalism. The theoretical analysis has been validated against experimental data and variant scientific literature, and good accuracy has been observed. - PublicationThe role of percolation and sheet dynamics during heat conduction in poly-dispersed graphene nanofluids(22-04-2013)
;Dhar, Purbarun ;Sen Gupta, Soujit ;Chakraborty, Saikat; A thermal transport mechanism leading to the enhanced thermal conductivity of graphene nanofluids has been proposed. The graphene sheet size is postulated to be the key to the underlying mechanism. Based on a critical sheet size derived from Stokes-Einstein equation for the poly-dispersed nanofluid, sheet percolation and Brownian motion assisted sheet collisions are used to explain the heat conduction. A collision dependant dynamic conductivity considering Debye approximated volumetric specific heat due to phonon transport in graphene has been incorporated. The model has been found to be in good agreement with experimental data. © 2013 AIP Publishing LLC. - PublicationParticle–fluid interactivity reduces buoyancy-driven thermal transport in nanosuspensions: A multi-component Lattice Boltzmann approach(02-08-2016)
;Savithiri, S. ;Dhar, Purbarun; ABSTRACT: Severe contradictions exist between experimental observations and computational predictions regarding natural convective thermal transport in nanosuspensions. The approach treating nanosuspensions as homogeneous fluids in computations has been pinpointed as the major contributor to such contradictions. To fill the void, inter-particle and particle–fluid interactivities (slip mechanisms), in addition to effective thermophysical properties, have been incorporated within the present formulation. Through thorough scaling analysis, the dominant slip mechanisms have been identified. A Multi-Component Lattice Boltzmann Model (MCLBM) approach is proposed, wherein the suspension has been treated as a non-homogeneous twin component mixture with the governing slip mechanisms incorporated. The computations based on the mathematical model can accurately predict and quantify natural convection thermal transport in nanosuspensions. The role of slip mechanisms such as Brownian diffusion, thermophoresis, drag, Saffman lift, Magnus effect, particle rotation, and gravitational effects has been accurately described. A comprehensive study on the effects of Rayleigh number, particle size, and concentration revealed that the drag force experienced by the particles is primarily responsible for the reduction of natural convective thermal transport. In essence, the dominance of Stokesian mechanics in such thermofluidic systems is established in the present study. For the first time, as revealed though a thorough survey of the literature, a numerical formulation explains the contradictions observed, rectifies the approach, predicts accurately, and reveals the crucial mechanisms and physics of buoyancy-driven thermal transport in nanosuspensions. - PublicationTrimodal charge transport in polar liquid-based dilute nanoparticulate colloidal dispersions(01-10-2014)
;Dhar, Purbarun; Abstract: The dominant modes of charge transport in variant polar liquid-based nanoparticulate colloidal dispersions (dilute) have been theorized. Theories formulating electrical characteristics of colloids have often been found to over- or under-predict charge transport in dilute suspensions of nanoparticles in polar fluids owing to grossly different mechanistic behaviors of concentrated systems. Three major interacting modes with independent yet simultaneous existence have been proposed and found to be consistent with analyses of experimental data. Electric double layer (EDL) formation at nanoparticle–fluid interface-conjugated electrophoresis under the influence of the electric field has been determined as one important mode of charge transport. Nanoparticle polarization due to short-range field non-uniformity caused by the EDL with consequent particle motion due to inter-particle electrostatic interactions acts as another mode of transport. Coupled electro-thermal diffusion arising out of Brownian randomization in the presence of the electric field has been determined as the third dominant mode. An analytical model based on discrete interactions of the charged particle–fluid domains explains the various behavioral aspects of such dispersions, as observed and validated from detailed experimental analysis. The analysis is also predictive of the dominance and behavior of the three modes with important nanocolloidal parameters such as temperature and concentration. - PublicationSuperior dielectric breakdown strength of graphene and carbon nanotube infused nano-oils(01-04-2016)
;Dhar, Purbarun ;Katiyar, Ajay ;Maganti, Lakshmi Sirisha; Nano-oils comprising stable and dilute dispersions of synthesized Graphene (Gr) nanoflakes and carbon nanotubes (CNT) have been experimentally observed for the first time to exhibit augmented dielectric breakdown strengths compared to the base transformer oils. Variant nano-oils comprising different Gr and CNT samples suspended in two different grades of transformer oils have yielded consistent and high degrees of enhancement in the breakdown strength. The apparent counter-intuitive phenomenon of enhancing insulating caliber of fluids utilizing nanostructures of high electronic conductance has been shown to be physically consistent thorough theoretical analysis. The crux mechanism has been pin pointed as efficient charge scavenging leading to hampered streamer growth and development, thereby delaying probability of complete ionization. The mathematical analysis presented provides a comprehensive picture of the mechanisms and physics of the electrohydrodynamics involved in the phenomena of enhanced breakdown strengths. Furthermore, the analysis is able to physically explain the various breakdown characteristics observed as functions of system parameters, viz. nanostructure type, size distribution, relative permittivity, base fluid dielectric properties, nanomaterial concentration and nano-oil temperature. The mathematical analyses have been extended to propose a physically and dimensionally consistent analytical model to predict the enhanced breakdown strengths of such nano-oils from involved constituent material properties and characteristics. The model has been observed to accurately predict the augmented insulating property, thereby rendering it as an extremely useful tool for efficient design and prediction of breakdown characteristics of nanostructure infused insulating fluids. The present study, involving experimental investigations backed by theoretical analyses and models for an important dielectric phenomenon such as electrical breakdown can find utility in design of safer and more efficient high operating voltage electrical drives, transformers and machines. - PublicationAnomalous room temperature magnetorheological behavior of colloidal graphene nanogels(05-10-2017)
;Dhar, Purbarun ;Katiyar, Ajay; Weak magnetism is known to exist in graphene systems, yet, as of now, it remains unharnessed for bulk scale applications. Weak ferromagnetic response from chemically exfoliated graphene samples has been employed to harness appreciable magnetorheological effects via the use of novel graphene nanogels. Chemically exfoliated graphene samples have been synthesized and ferromagnetic response has been registered (in tune with scarce reports in literature). Characterizations reveal that presence of magnetic impurities would be unable to yield magnetic moments as obtained and hence the response is innate to the vacancy and defects in the graphenic structure. Polymer based nanogels with infused graphene nanoplatelets has been synthesized and the colloidal gel phase enables harnessing of magnetorheology from such weak moment systems. Strong magnetorheological response is obtained from the colloidal gel phase due to the compact texture which aids in fibrillation of the nanoplatelets. Largely enhanced magnetoviscosity and yield stress have been observed from the gels in similitude to conventional magnetorheological nanocolloids. The presence of dispersed phase with platelet morphology as well as surface lubrication behavior of graphene has been found responsible for certain anomalous behavior such as magnetic shear thickening in the gels which has been explained based on order to disorder transitions under field influence. Transient response of the gels show good modulation caliber in field actuated viscous control as well as minute magnetoviscous hysteresis. The present colloids show novel promise in use of graphene as potential magnetic material in magnetic field governed actuation, control and tuning MEMS/NEMS and allied devices. - PublicationLarge electrorheological phenomena in graphene nano-gels(20-01-2017)
;Dhar, Purbarun ;Katiyar, Ajay; Large-scale electrorheology (ER) response has been reported for dilute graphene nanoflake-based ER fluids that have been engineered as novel, readily synthesizable polymeric gels. Polyethylene glycol (PEG 400) based graphene gels have been synthesized and a very high ER response (∼125 000% enhancement in viscosity under influence of an electric field) has been observed for low concentration systems (∼2 wt.%). The gels overcome several drawbacks innate to ER fluids. The gels exhibit long term stability, a high graphene packing ratio which ensures very high ER response, and the microstructure of the gels ensures that fibrillation of the graphene nanoflakes under an electric field is undisturbed by thermal fluctuations, further leading to mega ER. The gels exhibit a large yield stress handling caliber with a yield stress observed as high as ∼13 kPa at 2 wt.% for graphene. Detailed investigations on the effects of graphene concentration, electric field strength, imposed shear resistance, transients of electric field actuation on the ER response and ER hysteresis of the gels have been performed. In-depth analyses with explanations have been provided for the observations and effects, such as inter flake lubrication/slip induced augmented ER response. The present gels show great promise as potential ER gels for various smart applications.