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 multi-fluid model to capture segregation caused by density difference is demonstrated by simulating grain-chaff biomass flows in a laboratory-scale air column and in a combine harvester. The multi-fluid 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 gas-fluidized 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. Large-scale 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):
- IS-T 2434
TRN: US200724%%53
- DOE Contract Number:
- AC02-07CH11358; PS07-01ID14039
- 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 multi-fluid model to capture segregation caused by density difference is demonstrated by simulating grain-chaff biomass flows in a laboratory-scale air column and in a combine harvester. The multi-fluid 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 gas-fluidized 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. Large-scale force networks bearing larger-than-average forces are found with the presence of wall friction. The role of force networks in assisting rising of the large particle is analyzed. Single-point force distribution and two-point spatial force correlation are computed. The results show the heterogeneity of forces and a short-range 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 two-fluid (TF) equations for the gas phase. Multi-particle contacts are found in defluidized regions away from bubbles in fluidized beds. The multi-particle contacts invalidate the binary-collision 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}
}
-
This thesis is concerned with developing kinetic and turbulence models for granular and two-phase flows. A kinetic model is introduced and the kinetic equation governing the evolution of the first-order distribution function including the fluid drag force is presented. The particle-fluid interactions are analyzed and the first-order particulate distribution function is determined. The system of equations governing the mean granular velocity, solid volume fraction, and fluctuation energy are developed. The special case of a simple shear flow is studied, and the predictions of the present model are compared with those of other models and the available experimental data. A discrete-elementmore »
-
Mathematical modeling of solute segregation and redistribution during freezing in peat and overlying water
Freezing of the water in a peatland causes the redistribution of existing solutes in both the shallow water and the peat zone. Such solute redistribution phenomena are of interest for establishing the geochronology of deposits and determining the nature of pollutant burial. Understanding these phenomena is important for the consideration of peatlands as multi-use resources. This work presents the theoretical analyses and mathematical models to describe the solute redistribution processes during freezing in overlying water and interstitial water in the porous peat. The analyses include the segregation of the solute at the ice-water interface in both the overlying water andmore » -
Three-dimensional constitutive modeling of a granular mine tailings material
A three-dimensional soil testing system was developed to provide a convenient and accurate testing environment and to provide the capability of exploring the stress-strain-strength behavior of a fine-grained coal mine tailings material (or other types of soil) along general three-dimensional stress paths. This testing system was used to generate stress-strain-strength information for the fine coal refuse along several stress paths, i.e., Conventional Triaxial Compression (CTC), Reduced Triaxial Extension (RTE), Hydrostatic Compression (HC), and Constant Pressure (CP) stress paths. In all, 24 cubical tests were performed. In order to compare the results obtained from this cubical device to those obtained frommore » -
Measurements and analytical modeling of heat transfer in flowing granular media
An investigation was conducted of the heat-transfer characteristics of a variety of flowing-particulate solid media. Five different granular materials were studied in a vertical gravity-driven flow through an electrically heated circular stainless steel tube test section. From measurements of wall temperature distribution, particle bulk-inlet temperature, radial temperature distribution of the particle flow at the test section exit, and mass flow rate, determination of local and average heat-transfer coefficients along the test section were made. Comparison of the experimental results with predictions of various models appearing in the literature were made. A more physically realistic theoretical model was developed to improvemore » -
Low-Reynolds-numbers modeling of complex flows with and without density variation
Design of modern combustors and gas turbines require detailed analysis of near-wall flow because complex effects due to geometry, external forces and boundary conditions play dominant roles in the development of the wall boundary layers. Analysis of the near-wall flow behavior reveals the importance of viscous effects and forms the basis of a modified model to calculate the entire flow field including the near-wall region. Based on a near-wall flow analysis, a low-Reynolds-number full Reynolds stress model was developed and tested against fully developed flow. The model is further applied to calculate complex turbulent flows, such as developing pipe flowmore »