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Coarse-graining approach to infer mesoscale interaction potentials from atomistic interactions for aggregating systems / Sergiy Markutsya in Industrial & engineering chemistry research, Vol. 51 N° 49 (Décembre 2012) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 51 N° 49 (Décembre 2012) . - pp. 16116–16134 Titre : Coarse-graining approach to infer mesoscale interaction potentials from atomistic interactions for aggregating systems Type de document : texte imprimé Auteurs : Sergiy Markutsya, Auteur ; Rodney O. Fox, Auteur ; Shankar Subramaniam, Auteur Année de publication : 2013 Article en page(s) : pp. 16116–16134 Note générale : Industrial chemistry Langues : Anglais (eng) Mots-clés : Aggregating  systems  Atomistic Résumé : A coarse-graining (CG) approach is developed to infer mesoscale interaction potentials in aggregating systems, resulting in an improved potential of mean force for Langevin dynamics (LD) and Brownian dynamics (BD) simulations. Starting from the evolution equation for the solute pair correlation function, this semi-analytical CG approach identifies accurate modeling of the relative acceleration between solute particles in a solvent bath as a reliable route to predicting the time-evolving structural properties of nonequilibrium aggregating systems. Noting that the solute–solvent pair correlation function attains a steady state rapidly as compared to characteristic aggregation time scales, this CG approach derives the effective relative acceleration between a pair of solute particles in the presence of this steady solute–solvent pair correlation by formally integrating the solvent force on each solute particle. This results in an improved potential of mean force that explicitly depends on the solute–solute and solute–solvent pair potentials, with the capability of representing both solvophilic and solvophobic interactions that give rise to solvation forces. This approach overcomes the difficulty in specifying the LD/BD potential of mean force in aggregating systems where the solute pair correlation function evolves in time, and the Kirkwood formula U(r) = −kBT ln g(r) that is applicable in equilibrium diffusion problems cannot be used. LD simulations are compared to molecular dynamics (MD) simulations for a model colloidal system interacting with Lennard-Jones pair potentials to develop and validate the improved potential of mean force. LD simulations using the improved potential of mean force predict a solute pair correlation function that is in excellent match with MD in all aggregation regimes, whereas using the unmodified MD solute–solute pair potential in LD results in a poor match in the reaction-limited aggregation regime. The improved potential also dramatically improves the predicted extent of aggregation and evolution of cluster size distributions that exhibit the same self-similar scaling found in MD. This technique of coarse-graining MD potentials to obtain an improved potential of mean force can be applied in a general multiscale framework for nonequilibrium systems where the evolution of aggregate structure is important. ISSN : 0888-5885 En ligne : http://pubs.acs.org/doi/abs/10.1021/ie3013715 [article] Coarse-graining approach to infer mesoscale interaction potentials from atomistic interactions for aggregating systems [texte imprimé] / Sergiy Markutsya, Auteur ; Rodney O. Fox, Auteur ; Shankar Subramaniam, Auteur . - 2013 . - pp. 16116–16134. Industrial chemistry Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 51 N° 49 (Décembre 2012) . - pp. 16116–16134 Mots-clés : Aggregating  systems  Atomistic Résumé : A coarse-graining (CG) approach is developed to infer mesoscale interaction potentials in aggregating systems, resulting in an improved potential of mean force for Langevin dynamics (LD) and Brownian dynamics (BD) simulations. Starting from the evolution equation for the solute pair correlation function, this semi-analytical CG approach identifies accurate modeling of the relative acceleration between solute particles in a solvent bath as a reliable route to predicting the time-evolving structural properties of nonequilibrium aggregating systems. Noting that the solute–solvent pair correlation function attains a steady state rapidly as compared to characteristic aggregation time scales, this CG approach derives the effective relative acceleration between a pair of solute particles in the presence of this steady solute–solvent pair correlation by formally integrating the solvent force on each solute particle. This results in an improved potential of mean force that explicitly depends on the solute–solute and solute–solvent pair potentials, with the capability of representing both solvophilic and solvophobic interactions that give rise to solvation forces. This approach overcomes the difficulty in specifying the LD/BD potential of mean force in aggregating systems where the solute pair correlation function evolves in time, and the Kirkwood formula U(r) = −kBT ln g(r) that is applicable in equilibrium diffusion problems cannot be used. LD simulations are compared to molecular dynamics (MD) simulations for a model colloidal system interacting with Lennard-Jones pair potentials to develop and validate the improved potential of mean force. LD simulations using the improved potential of mean force predict a solute pair correlation function that is in excellent match with MD in all aggregation regimes, whereas using the unmodified MD solute–solute pair potential in LD results in a poor match in the reaction-limited aggregation regime. The improved potential also dramatically improves the predicted extent of aggregation and evolution of cluster size distributions that exhibit the same self-similar scaling found in MD. This technique of coarse-graining MD potentials to obtain an improved potential of mean force can be applied in a general multiscale framework for nonequilibrium systems where the evolution of aggregate structure is important. ISSN : 0888-5885 En ligne : http://pubs.acs.org/doi/abs/10.1021/ie3013715

Kinetic modeling of nanoprecipitation using CFD coupled with a population balance / Janine Chungyin Cheng in Industrial & engineering chemistry research, Vol. 49 N° 21 (Novembre 2010) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 49 N° 21 (Novembre 2010) . - pp. 10651–10662 Titre : Kinetic modeling of nanoprecipitation using CFD coupled with a population balance Type de document : texte imprimé Auteurs : Janine Chungyin Cheng, Auteur ; Rodney O. Fox, Auteur Année de publication : 2011 Article en page(s) : pp. 10651–10662 Note générale : Chimie industrielle Langues : Anglais (eng) Mots-clés : Kinetic  Nanoprecipitation Résumé : A model study has been conducted for Flash Nanoprecipitation (FNP)—a novel approach to produce functional nanoparticles. A population balance equation with the FNP kinetics has been integrated into a computational fluid dynamics (CFD) simulation of a custom-designed microscale multi-inlet vortex reactor (MIVR) to yield conditions comparable to the real experimental settings. In coping with the complicated aggregation model in the CFD code, a new numerical approach, the conditional quadrature method of moments (CQMOM), has been proposed, which is capable of solving the multivariate system efficiently and accurately. It is shown that the FNP process is highly influenced by mixing effects in the microreactor, and thus coupling CFD with the kinetics model is essential in obtaining valid comparisons with experiments. ISSN : 0888-5885 En ligne : http://pubs.acs.org/doi/abs/10.1021/ie100558n [article] Kinetic modeling of nanoprecipitation using CFD coupled with a population balance [texte imprimé] / Janine Chungyin Cheng, Auteur ; Rodney O. Fox, Auteur . - 2011 . - pp. 10651–10662. Chimie industrielle Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 49 N° 21 (Novembre 2010) . - pp. 10651–10662 Mots-clés : Kinetic  Nanoprecipitation Résumé : A model study has been conducted for Flash Nanoprecipitation (FNP)—a novel approach to produce functional nanoparticles. A population balance equation with the FNP kinetics has been integrated into a computational fluid dynamics (CFD) simulation of a custom-designed microscale multi-inlet vortex reactor (MIVR) to yield conditions comparable to the real experimental settings. In coping with the complicated aggregation model in the CFD code, a new numerical approach, the conditional quadrature method of moments (CQMOM), has been proposed, which is capable of solving the multivariate system efficiently and accurately. It is shown that the FNP process is highly influenced by mixing effects in the microreactor, and thus coupling CFD with the kinetics model is essential in obtaining valid comparisons with experiments. ISSN : 0888-5885 En ligne : http://pubs.acs.org/doi/abs/10.1021/ie100558n

On brownian dynamics simulation of nanoparticle aggregation / Sergiy Markutsya in Industrial & engineering chemistry research, Vol. 47 N°10 (Mai 2008) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 47 N°10 (Mai 2008) . - p. 3338–3345 Titre : On brownian dynamics simulation of nanoparticle aggregation Type de document : texte imprimé Auteurs : Sergiy Markutsya, Auteur ; Shankar Subramaniam, Auteur ; R. Dennis Vigil, Auteur ; Rodney O. Fox, Auteur Année de publication : 2008 Article en page(s) : p. 3338–3345 Note générale : Bibliogr. p. Langues : Anglais (eng) Mots-clés : Nanoparticle  aggregation;  Brownian  dynamics  simulations;  Dimensionless  variable Résumé : Accurate simulation and control of nanoparticle aggregation in chemical reactors requires that population balance equations be solved by using realistic expressions for aggregation and breakage rate kernels. Obtaining such expressions requires that atomistic simulation approaches that can account for microscopic details of particle collisions be used. In principle, molecular dynamics simulations can provide the needed microscopic information, but because of the separation in length scales between the aggregates and solvent molecules, such simulations are too costly. Brownian dynamics simulations provide an alternative to the molecular dynamics approach for simulation of particle aggregation, but there has been no systematic attempt to validate the Brownian dynamics method for this class of problems. In this work we attempt to develop a better understanding of Brownian dynamics simulations of aggregation by (1) developing convergence criteria, (2) determining criteria for aggregation to occur in BD simulations using dimensionless variables, and (3) directly comparing BD and MD simulation predictions for a model aggregation problem. En ligne : http://pubs.acs.org/doi/abs/10.1021/ie0711168 [article] On brownian dynamics simulation of nanoparticle aggregation [texte imprimé] / Sergiy Markutsya, Auteur ; Shankar Subramaniam, Auteur ; R. Dennis Vigil, Auteur ; Rodney O. Fox, Auteur . - 2008 . - p. 3338–3345. Bibliogr. p. Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 47 N°10 (Mai 2008) . - p. 3338–3345 Mots-clés : Nanoparticle  aggregation;  Brownian  dynamics  simulations;  Dimensionless  variable Résumé : Accurate simulation and control of nanoparticle aggregation in chemical reactors requires that population balance equations be solved by using realistic expressions for aggregation and breakage rate kernels. Obtaining such expressions requires that atomistic simulation approaches that can account for microscopic details of particle collisions be used. In principle, molecular dynamics simulations can provide the needed microscopic information, but because of the separation in length scales between the aggregates and solvent molecules, such simulations are too costly. Brownian dynamics simulations provide an alternative to the molecular dynamics approach for simulation of particle aggregation, but there has been no systematic attempt to validate the Brownian dynamics method for this class of problems. In this work we attempt to develop a better understanding of Brownian dynamics simulations of aggregation by (1) developing convergence criteria, (2) determining criteria for aggregation to occur in BD simulations using dimensionless variables, and (3) directly comparing BD and MD simulation predictions for a model aggregation problem. En ligne : http://pubs.acs.org/doi/abs/10.1021/ie0711168

Optimal moment sets for multivariate direct quadrature method of moments / Rodney O. Fox in Industrial & engineering chemistry research, Vol. 48 N° 21 (Novembre 2009) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 48 N° 21 (Novembre 2009) . - pp. 9686–9696 Titre : Optimal moment sets for multivariate direct quadrature method of moments Type de document : texte imprimé Auteurs : Rodney O. Fox, Auteur Année de publication : 2010 Article en page(s) : pp. 9686–9696 Note générale : Chemical engineering Langues : Anglais (eng) Mots-clés : Direct  quadrature  method  of  moments  Population  balance  equations Résumé : The direct quadrature method of moments (DQMOM) can be employed to close population balance equations (PBEs) governing a wide class of multivariate number density functions (NDFs). Such equations occur over a vast range of scientific applications, including aerosol science, kinetic theory, multiphase flows, turbulence modeling, and control theory, to name just a few. As the name implies, DQMOM uses quadrature weights and abscissas to approximate the moments of the NDF, and the number of quadrature nodes determines the accuracy of the closure. For nondegenerate univariate cases (i.e., a sufficiently smooth NDF), the N weights and N abscissas are uniquely determined by the first 2N non-negative integer moments of the NDF. Moreover, an efficient product−difference algorithm exists to compute the weights and abscissas from the moments. In contrast, for a d-dimensional NDF, a total of (1 + d)N multivariate moments are required to determine the weights and abscissas, and poor choices for the moment set can lead to nonunique abscissas and even negative weights. In this work, it is demonstrated that optimal moment sets exist for multivariate DQMOM when N = nd quadrature nodes are employed to represent a d-dimensional NDF with n = 1−3 and d = 1−3. Moreover, this choice is independent of the source terms in the PBE governing the time evolution of the NDF. A multivariate Fokker−Planck equation is used to illustrate the numerical properties of the method for d = 3 with n = 2 and 3. En ligne : http://pubs.acs.org/doi/abs/10.1021/ie801316d [article] Optimal moment sets for multivariate direct quadrature method of moments [texte imprimé] / Rodney O. Fox, Auteur . - 2010 . - pp. 9686–9696. Chemical engineering Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 48 N° 21 (Novembre 2009) . - pp. 9686–9696 Mots-clés : Direct  quadrature  method  of  moments  Population  balance  equations Résumé : The direct quadrature method of moments (DQMOM) can be employed to close population balance equations (PBEs) governing a wide class of multivariate number density functions (NDFs). Such equations occur over a vast range of scientific applications, including aerosol science, kinetic theory, multiphase flows, turbulence modeling, and control theory, to name just a few. As the name implies, DQMOM uses quadrature weights and abscissas to approximate the moments of the NDF, and the number of quadrature nodes determines the accuracy of the closure. For nondegenerate univariate cases (i.e., a sufficiently smooth NDF), the N weights and N abscissas are uniquely determined by the first 2N non-negative integer moments of the NDF. Moreover, an efficient product−difference algorithm exists to compute the weights and abscissas from the moments. In contrast, for a d-dimensional NDF, a total of (1 + d)N multivariate moments are required to determine the weights and abscissas, and poor choices for the moment set can lead to nonunique abscissas and even negative weights. In this work, it is demonstrated that optimal moment sets exist for multivariate DQMOM when N = nd quadrature nodes are employed to represent a d-dimensional NDF with n = 1−3 and d = 1−3. Moreover, this choice is independent of the source terms in the PBE governing the time evolution of the NDF. A multivariate Fokker−Planck equation is used to illustrate the numerical properties of the method for d = 3 with n = 2 and 3. En ligne : http://pubs.acs.org/doi/abs/10.1021/ie801316d

Quadrature - based moment model for moderately dense polydisperse gas − particle flows / Rodney O. Fox in Industrial & engineering chemistry research, Vol. 49 N° 11 (Juin 2010) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 49 N° 11 (Juin 2010) . - pp. 5174–5187 Titre : Quadrature - based moment model for moderately dense polydisperse gas − particle flows Type de document : texte imprimé Auteurs : Rodney O. Fox, Auteur ; Prakash Vedula, Auteur Année de publication : 2010 Article en page(s) : pp. 5174–5187 Note générale : Industrial chemistry Langues : Anglais (eng) Mots-clés : Gas  particle  flows Résumé : A quadrature-based moment model is derived for moderately dense polydisperse gas−particle flows starting from the inelastic Boltzmann−Enskog kinetic equation including terms for particle acceleration (e.g., gravity and fluid drag). The derivation is carried out for the joint number density function, f(t,x,m,u), of particle mass and velocity, and thus, the model can describe the transport of polydisperse particles with size and density differences. The transport equations for the integer moments of the velocity distribution function are derived in exact form for all values of the coefficient of restitution for particle−particle collisions. For particular limiting cases, the moment model is shown to be consistent with hydrodynamic models for gas−particle flows. However, the moment model is more general than the hydrodynamic models because its derivation does not require that the particle Knudsen number (and Mach number) be small. ISSN : 0888-5885 En ligne : http://pubs.acs.org/doi/abs/10.1021/ie9013138 [article] Quadrature - based moment model for moderately dense polydisperse gas − particle flows [texte imprimé] / Rodney O. Fox, Auteur ; Prakash Vedula, Auteur . - 2010 . - pp. 5174–5187. Industrial chemistry Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 49 N° 11 (Juin 2010) . - pp. 5174–5187 Mots-clés : Gas  particle  flows Résumé : A quadrature-based moment model is derived for moderately dense polydisperse gas−particle flows starting from the inelastic Boltzmann−Enskog kinetic equation including terms for particle acceleration (e.g., gravity and fluid drag). The derivation is carried out for the joint number density function, f(t,x,m,u), of particle mass and velocity, and thus, the model can describe the transport of polydisperse particles with size and density differences. The transport equations for the integer moments of the velocity distribution function are derived in exact form for all values of the coefficient of restitution for particle−particle collisions. For particular limiting cases, the moment model is shown to be consistent with hydrodynamic models for gas−particle flows. However, the moment model is more general than the hydrodynamic models because its derivation does not require that the particle Knudsen number (and Mach number) be small. ISSN : 0888-5885 En ligne : http://pubs.acs.org/doi/abs/10.1021/ie9013138

Validation of two-fluid simulations of a pseudo-two-dimensional bubble column with uniform and nonuniform aeration / Sarah M. Monahan in Industrial & engineering chemistry research, Vol. 48 N° 17 (Septembre 2009) 

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