Mutiscale Modeling of Segregation in Granular Flows
Abstract
Modeling and simulation of segregation phenomena in granular flows are investigated. Computational models at different scales ranging from particle level (microscale) to continuum level (macroscale) are employed in order to determine the important microscale physics relevant to macroscale modeling. The capability of a multifluid model to capture segregation caused by density difference is demonstrated by simulating grainchaff biomass flows in a laboratoryscale air column and in a combine harvester. The multifluid model treats gas and solid phases as interpenetrating continua in an Eulerian frame. This model is further improved by incorporating particle rotation using kinetic theory for rapid granular flow of slightly frictional spheres. A simplified model is implemented without changing the current kinetic theory framework by introducing an effective coefficient of restitution to account for additional energy dissipation due to frictional collisions. The accuracy of predicting segregation rate in a gasfluidized bed is improved by the implementation. This result indicates that particle rotation is important microscopic physics to be incorporated into the hydrodynamic model. Segregation of a large particle in a dense granular bed of small particles under vertical. vibration is studied using molecular dynamics simulations. Wall friction is identified as a necessary condition for the segregation. Largescale forcemore »
 Authors:
 Iowa State Univ., Ames, IA (United States)
 Publication Date:
 Research Org.:
 Ames Lab., Ames, IA (United States)
 Sponsoring Org.:
 USDOE Office of Science (SC)
 OSTI Identifier:
 910301
 Report Number(s):
 IST 2434
TRN: US200724%%53
 DOE Contract Number:
 AC0207CH11358; PS0701ID14039
 Resource Type:
 Thesis/Dissertation
 Country of Publication:
 United States
 Language:
 English
 Subject:
 42 ENGINEERING; ENERGY LOSSES; FLUIDIZED BEDS; HYDRODYNAMIC MODEL; SEGREGATION; KINETICS; PHYSICS; BIOMASS; SIMULATION
Citation Formats
Sun, Jin. Mutiscale Modeling of Segregation in Granular Flows. United States: N. p., 2007.
Web. doi:10.2172/910301.
Sun, Jin. Mutiscale Modeling of Segregation in Granular Flows. United States. doi:10.2172/910301.
Sun, Jin. Mon .
"Mutiscale Modeling of Segregation in Granular Flows". United States.
doi:10.2172/910301. https://www.osti.gov/servlets/purl/910301.
@article{osti_910301,
title = {Mutiscale Modeling of Segregation in Granular Flows},
author = {Sun, Jin},
abstractNote = {Modeling and simulation of segregation phenomena in granular flows are investigated. Computational models at different scales ranging from particle level (microscale) to continuum level (macroscale) are employed in order to determine the important microscale physics relevant to macroscale modeling. The capability of a multifluid model to capture segregation caused by density difference is demonstrated by simulating grainchaff biomass flows in a laboratoryscale air column and in a combine harvester. The multifluid model treats gas and solid phases as interpenetrating continua in an Eulerian frame. This model is further improved by incorporating particle rotation using kinetic theory for rapid granular flow of slightly frictional spheres. A simplified model is implemented without changing the current kinetic theory framework by introducing an effective coefficient of restitution to account for additional energy dissipation due to frictional collisions. The accuracy of predicting segregation rate in a gasfluidized bed is improved by the implementation. This result indicates that particle rotation is important microscopic physics to be incorporated into the hydrodynamic model. Segregation of a large particle in a dense granular bed of small particles under vertical. vibration is studied using molecular dynamics simulations. Wall friction is identified as a necessary condition for the segregation. Largescale force networks bearing largerthanaverage forces are found with the presence of wall friction. The role of force networks in assisting rising of the large particle is analyzed. Singlepoint force distribution and twopoint spatial force correlation are computed. The results show the heterogeneity of forces and a shortrange correlation. The short correlation length implies that even dense granular flows may admit local constitutive relations. A modified minimum spanning tree (MST) algorithm is developed to asymptotically recover the force statistics in the force networks. This algorithm provides a possible route to constructing a continuum model with microstructural information supplied from it. Microstructures in gas fluidized beds are also analyzed using a hybrid method, which couples the discrete element method (DEM) for particle dynamics with the averaged twofluid (TF) equations for the gas phase. Multiparticle contacts are found in defluidized regions away from bubbles in fluidized beds. The multiparticle contacts invalidate the binarycollision assumption made in the kinetic theory of granular flows for the defluidized regions. Large ratios of contact forces to drag forces are found in the same regions, which confirms the relative importance of contact forces in determining particle dynamics in the defluidized regions.},
doi = {10.2172/910301},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}

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