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Title: Sub-grid drag model for immersed vertical cylinders in fluidized beds

Abstract

Immersed vertical cylinders are often used as heat exchanger in gas-solid fluidized beds. Computational Fluid Dynamics (CFD) simulations are computationally expensive for large scale systems with bundles of cylinders. Therefore sub-grid models are required to facilitate simulations on a coarse grid, where internal cylinders are treated as a porous medium. The influence of cylinders on the gas-solid flow tends to enhance segregation and affect the gas-solid drag. A correction to gas-solid drag must be modeled using a suitable sub-grid constitutive relationship. In the past, Sarkar et al. have developed a sub-grid drag model for horizontal cylinder arrays based on 2D simulations. However, the effect of a vertical cylinder arrangement was not considered due to computational complexities. In this study, highly resolved 3D simulations with vertical cylinders were performed in small periodic domains. These simulations were filtered to construct a sub-grid drag model which can then be implemented in coarse-grid simulations. Gas-solid drag was filtered for different solids fractions and a significant reduction in drag was identified when compared with simulation without cylinders and simulation with horizontal cylinders. Slip velocities significantly increase when vertical cylinders are present. Lastly, vertical suspension drag due to vertical cylinders is insignificant however substantial horizontal suspensionmore » drag is observed which is consistent to the finding for horizontal cylinders.« less

Authors:
 [1];  [2];  [3];  [1]
  1. National Energy Technology Lab. (NETL), Morgantown, WV (United States)
  2. National Energy Technology Lab. (NETL), Morgantown, WV (United States); AECOM, Morgantown, WV (United States)
  3. National Energy Technology Lab. (NETL), Morgantown, WV (United States); West Virginia Univ. Research Corp., Morgantown, WV (United States)
Publication Date:
Research Org.:
National Energy Technology Lab. (NETL), Morgantown, WV (United States)
Sponsoring Org.:
USDOE Office of Fossil Energy (FE)
OSTI Identifier:
1415470
Alternate Identifier(s):
OSTI ID: 1396865
Report Number(s):
A-CONTR-PUB-053
Journal ID: ISSN 0032-5910; PII: S0032591016309214
Grant/Contract Number:
FE0004000
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Powder Technology
Additional Journal Information:
Journal Volume: 316; Journal Issue: C; Journal ID: ISSN 0032-5910
Publisher:
Elsevier
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; 97 MATHEMATICS AND COMPUTING; Two-fluid model; Filtered model; Fluidized bed; Cylinders; Drag force

Citation Formats

Verma, Vikrant, Li, Tingwen, Dietiker, Jean -Francois, and Rogers, William A. Sub-grid drag model for immersed vertical cylinders in fluidized beds. United States: N. p., 2017. Web. doi:10.1016/j.powtec.2016.12.044.
Verma, Vikrant, Li, Tingwen, Dietiker, Jean -Francois, & Rogers, William A. Sub-grid drag model for immersed vertical cylinders in fluidized beds. United States. doi:10.1016/j.powtec.2016.12.044.
Verma, Vikrant, Li, Tingwen, Dietiker, Jean -Francois, and Rogers, William A. Tue . "Sub-grid drag model for immersed vertical cylinders in fluidized beds". United States. doi:10.1016/j.powtec.2016.12.044. https://www.osti.gov/servlets/purl/1415470.
@article{osti_1415470,
title = {Sub-grid drag model for immersed vertical cylinders in fluidized beds},
author = {Verma, Vikrant and Li, Tingwen and Dietiker, Jean -Francois and Rogers, William A.},
abstractNote = {Immersed vertical cylinders are often used as heat exchanger in gas-solid fluidized beds. Computational Fluid Dynamics (CFD) simulations are computationally expensive for large scale systems with bundles of cylinders. Therefore sub-grid models are required to facilitate simulations on a coarse grid, where internal cylinders are treated as a porous medium. The influence of cylinders on the gas-solid flow tends to enhance segregation and affect the gas-solid drag. A correction to gas-solid drag must be modeled using a suitable sub-grid constitutive relationship. In the past, Sarkar et al. have developed a sub-grid drag model for horizontal cylinder arrays based on 2D simulations. However, the effect of a vertical cylinder arrangement was not considered due to computational complexities. In this study, highly resolved 3D simulations with vertical cylinders were performed in small periodic domains. These simulations were filtered to construct a sub-grid drag model which can then be implemented in coarse-grid simulations. Gas-solid drag was filtered for different solids fractions and a significant reduction in drag was identified when compared with simulation without cylinders and simulation with horizontal cylinders. Slip velocities significantly increase when vertical cylinders are present. Lastly, vertical suspension drag due to vertical cylinders is insignificant however substantial horizontal suspension drag is observed which is consistent to the finding for horizontal cylinders.},
doi = {10.1016/j.powtec.2016.12.044},
journal = {Powder Technology},
number = C,
volume = 316,
place = {United States},
year = {Tue Jan 03 00:00:00 EST 2017},
month = {Tue Jan 03 00:00:00 EST 2017}
}

Journal Article:
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  • The accuracy of coarse-grid multiphase CFD simulations of fluidized beds may be improved via the inclusion of filtered constitutive models. In our previous study (Sarkar et al., Chem. Eng. Sci., 104, 399-412), we developed such a set of filtered drag relationships for beds with immersed arrays of cooling tubes. Verification of these filtered drag models is addressed in this work. Predictions from coarse-grid simulations with the sub-grid filtered corrections are compared against accurate, highly-resolved simulations of full-scale turbulent and bubbling fluidized beds. The filtered drag models offer a computationally efficient yet accurate alternative for obtaining macroscopic predictions, but the spatialmore » resolution of meso-scale clustering heterogeneities is sacrificed.« less
  • Immersed cylindrical tube arrays often are used as heat exchangers in gas-particle fluidized beds. In multiphase computational fluid dynamics (CFD) simulations of large fluidized beds, explicit resolution of small cylinders is computationally infeasible. Instead, the cylinder array may be viewed as an effective porous medium in coarse-grid simulations. The cylinders' influence on the suspension as a whole, manifested as an effective drag force, and on the relative motion between gas and particles, manifested as a correction to the gas-particle drag, must be modeled via suitable sub-grid constitutive relationships. In this work, highly resolved unit-cell simulations of flow around an arraymore » of horizontal cylinders, arranged in a staggered configuration, are filtered to construct sub-grid, or `filtered', drag models, which can be implemented in coarse-grid simulations. The force on the suspension exerted by the cylinders is comprised of, as expected, a buoyancy contribution, and a kinetic component analogous to fluid drag on a single cylinder. Furthermore, the introduction of tubes also is found to enhance segregation at the scale of the cylinder size, which, in turn, leads to a reduction in the filtered gas-particle drag.« less
  • Cited by 2
  • A model for local heat transfer between a gas-fluidized bed and a submerged tube is proposed based on combined dense-phase and lean-phase transport. The heat transfer process during dense-phase contact at the tube surface is modeled by packet renewal mechanism and the transfer process during lean-phase contact by fluid convection mechanism. The model predictions show good agreement with experimental local and average heat transfer coefficient data for horizontal tubes.