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Sankaran Sundaresan

Bio: Sankaran Sundaresan is an academic researcher from Princeton University. The author has contributed to research in topics: Catalysis & Particle. The author has an hindex of 58, co-authored 241 publications receiving 10083 citations. Previous affiliations of Sankaran Sundaresan include University of Houston & St. John's Medical College.


Papers
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Journal ArticleDOI
TL;DR: In this paper, it is shown that the meso-scale structures are too small, and hence too expensive, to be resolved completely in simulation of gas-particle flows in large process vessels.
Abstract: Meso-scale structures that take the form of clusters and streamers are commonly observed in dilute gas–particle flows, such as those encountered in risers. Continuum equations for gas–particle flows, coupled with constitutive equations for particle-phase stress deduced from kinetic theory of granular materials, can capture the formation of such meso-scale structures. These structures arise as a result of an inertial instability associated with the relative motion between the gas and particle phases, and an instability due to damping of the fluctuating motion of particles by the interstitial fluid and inelastic collisions between particles. It is demonstrated that the meso-scale structures are too small, and hence too expensive, to be resolved completely in simulation of gas–particle flows in large process vessels. At the same time, failure to resolve completely the meso-scale structures in a simulation leads to grossly inaccurate estimates of inter-phase drag, production/dissipation of pseudo-thermal energy associated with particle fluctuations, the effective particle-phase pressure and the effective viscosities. It is established that coarse-grid simulation of gas–particle flows must include sub-grid models, to account for the effects of the unresolved meso-scale structures. An approach to developing a plausible sub-grid model is proposed.

685 citations

Journal ArticleDOI
TL;DR: In this paper, a two-fluid model for gas-particle flows is constructed from a kinetic theory-based model, and a procedure to extract constitutive models for these models through highly resolved simulations of the kinetic theory based model equations in periodic domains is presented.
Abstract: Starting from a kinetic theory based two-fluid model for gas-particle flows, we first construct filtered two-fluid model equations that average over small scale inhomogeneities that we do not wish to resolve in numerical simulations. We then outline a procedure to extract constitutive models for these filtered two-fluid models through highly resolved simulations of the kinetic theory based model equations in periodic domains. Two- and three-dimensional simulations show that the closure relations for the filtered two-fluid models manifest a definite and systematic dependence on the filter size. Linear stability analysis of the filtered two-fluid model equations reveals that filtering does indeed remove small scale structures that are afforded by the microscopic twofluid model. 2008 American Institute of Chemical Engineers AIChE J, 54: 1431–1448, 2008

416 citations

Journal ArticleDOI
TL;DR: In this article, a frictional-kinetic rheological model for dense assemblies of solids in a gas-particle mixture is described, which treats the kinetic and frictional stresses additively.

363 citations

Book ChapterDOI
TL;DR: In this article, the authors describe a hierarchy of models at different length scales, where the particle-particle and fluidparticle interactions are taken into account with different levels of detail, and the results and insights obtained from the more fundamental models are used to feed continuum models which can be used to compute the flow structures on a much larger scale.
Abstract: Numerical models of gas-fluidized beds have become an important tool in the design and scale up of gas-solid chemical reactors. However, a single numerical model which includes the solid-solid and solid-fluid interaction in full detail is not feasible for industrial-scale equipment, and for this reason one has to resort to a multiscale approach. The idea is that gas-solid flow is described by a hierarchy of models at different length scales, where the particle-particle and fluid-particle interactions are taken into account with different levels of detail. The results and insights obtained from the more fundamental models are used to develop closure laws to feed continuum models which can be used to compute the flow structures on a much larger (engineering) scale. Our multi-scale approach involves the lattice Boltzmann model, the discrete particle model, and the continuum model based on the kinetic theory of granular flow. In this chapter we give a detailed account of each of these models as they are employed at the University of Twente, accompanied by some illustrative computational results. Finally, we discuss two promising approaches for modeling industrial-size gas-fluidized beds, which are currently being explored independently at the Princeton University and the University of Twente.

295 citations

Journal ArticleDOI
TL;DR: In this article, the results obtained in coarse-grid integration of the microscopic equations for gas-particle flows change appreciably if subgrid corrections to account for the effects of unresolved structures are included.
Abstract: Continuum model equations for unsteady gas-particle flows in devices such as fluidized beds and circulating fluidized bed risers contain unstable modes whose length scale is of the order of 10 particle diameters. Yet, because of limited computational resources, these flows are routinely simulated by solving the discretized version of continuum models over coarse spatial grids. These simulations resolve the large-scale flow structures but not the finer scale structures. In most industrial applications involving large devices, it is impractical to resolve all the fine-scale structures, and therefore the effects of the unresolved structures must be addressed through suitable subgrid models. Using gas-particle flows in a wide and very tall vertical channel as an example, we have demonstrated in this study that the results obtained in coarse-grid integration of the microscopic equations for gas-particle flows change appreciably if subgrid corrections to account for the effects of unresolved structures are incl...

260 citations


Cited by
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01 May 1993
TL;DR: Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems.
Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

29,323 citations

01 Jan 2007
TL;DR: The Third edition of the Kirk-Othmer encyclopedia of chemical technology as mentioned in this paper was published in 1989, with the title "Kirk's Encyclopedia of Chemical Technology: Chemical Technology".
Abstract: 介绍了Kirk—Othmer Encyclopedia of Chemical Technology(化工技术百科全书)(第五版)电子图书网络版数据库,并对该数据库使用方法和检索途径作出了说明,且结合实例简单地介绍了该数据库的检索方法。

2,666 citations

Journal ArticleDOI
TL;DR: In this article, an improved method for computing incompressible viscous flow around suspended rigid particles using a fixed and uniform computational grid is presented. But the main idea is to incorporate Peskin's regularized delta function approach into a direct formulation of the fluid-solid interaction force in order to allow for a smooth transfer between Eulerian and Lagrangian representations.

1,399 citations

Journal ArticleDOI
TL;DR: In this paper, the limitations of the Fick's law for describing diffusion are discussed and it is argued that the Maxwell-Stefan formulation provides the most general and convenient approach for describing mass transport which takes proper account of thermodynamic non-idealities and influence of external force fields.

1,323 citations

Journal ArticleDOI
TL;DR: Zhu et al. as discussed by the authors provided a summary of the studies based on discrete particle simulation in the past two decades or so, with emphasis on the microdynamics including packing/flow structure and particle-particle, particle-fluid and particle wall interaction forces.

1,253 citations