4.1. Model Setup

The Model pane is used to specify global project settings. Depending on what is selected, other panes are enabled or disabled.

  • Description allows for a short model description to be provided. This is written in the .OUT file by the solver.

  • Solver specifies the model solver.

    • Single phase is the MFiX fluid solver. This disables all solids model inputs.

    • Two-Fluid Model (MFiX-TFM) treats both the fluid and solids as interpenetrating continua.

    • Discrete Element Model (MFiX-DEM) treats the fluid as a continuum while modeling individual particles and collisions.

    • Particle in Cell Model (MFiX-PIC) treats the fluid as a continuum while using “parcels” to represent groups of real particles with similar physical characteristics.

  • Disable the fluid phase turns off the fluid solver for MFiX-TFM and MFiX-DEM simulations for pure granular flows. The fluid solver cannot be disabled for single phase flows.

  • Enable thermal energy equations solves thermal transport equations for all phases.

  • Turbulence Model incorporates the selected turbulence model.

    • None

    • L-Scale Mixing - Do not include turbulence.

      • Requires a turbulent length scale definition for all initial condition regions.

    • K-Epsilon - Do not include turbulence.

      • Requires turbulent kinetic energy and turbulent dissipation definitions for all initial condition regions and all mass and pressure inflow boundary conditions.

  • Max turbulent viscosity has units of \((Pa \cdot sec)\) and is used to bound turbulent viscosity.

  • Gravity has units of \(({m}/{sec^2})\) and defines gravitational acceleration in the x, y, and z directions.

  • Drag model specifies the fluid-particle drag model. This option is only available with the MFiX-TFM and MFiX-DEM solvers.

    • Syamlal-O’Brien [SB1988]

      • Requires the specification of the C1 tuning parameter, 0.8 by default.

      • Requires the specification of the D1 tuning parameter, 2.65 by default.

    • Beestra-van der Hoef-Kuipers [BVK2007]

    • Gidaspow [DG1990]

    • Gidaspow Blend [LB2000]

    • Holloway-Yin-Sundaresan [HYS2010]

      • Requires the specification of the lubrication cutoff distance, 1e-6 meters by default.

    • Koch-Hill [HKL2001]

    • Wen-Yu [WY1966]

    • User-Defined Function (UDF)

      • A custom drag model must be provided in the usr_drag.f file

      • A custom solver must be built.


The polydisperse tag following a specified drag model indicates that the polydisperse correction factor is available. For additional details see [HBK2005], [BVK2007a], and [BVK2007b].

Other advanced options that can be selected include:

  • Momentum formulation (Model A, Model B, Jackson, or Ishii)

    • Model A

    • Model B

    • Jackson

    • Ishii

  • Select sub-grid model

  • Sub-grid filter size

  • Sub-grid wall correction


There are some restrictions to when using sub-grid models. They are only available with MFiX-TFM simulations using the Wen-Yu drag law, and without turbulence model. Additional restrictions apply.


Syamlal, M, and O’Brien, T.J. (1988). Simulation of granular layer inversion in liquid fluidized beds, International Journal of Multiphase Flow, Volume 14, Issue 4, Pages 473-481, https://doi.org/10.1016/0301-9322(88)90023-7.


Hill, R., Koch, D., and Ladd, A. (2001). Moderate-Reynolds-number flows in ordered and random arrays of spheres. Journal of Fluid Mechanics, Volume 448, Pages 243-278. https://doi.org/10.1017/S0022112001005936


Ding, J. and Gidaspow, D. (1990). A bubbling fluidization model using kinetic theory of granular flow, AIChE Journal, Volume 36, Issue 4, Pages 523-538, https://doi.org/10.1002/aic.690360404


Lathouwers, D. and Bellan J. (2000). Modeling of dense gas-solid reactive mixtures applied to biomass pyrolysis in a fluidized bed, Proceedings of the 2000 U.S. DOE Hydrogen Program Review, https://www.nrel.gov/docs/fy01osti/28890.pdf


Wen C.Y., and Yu Y.H. (1966). Mechanics of fluidization, The Chemical Engineering Progress Symposium Series, Volume 62, Pages 100-111.


Beetstra, R., van der Hoef, M.A., and Kuipers, J.A.M. (2007). Numerical study of segregation using a new drag force correlation for polydisperse systems derived from lattice-Boltzmann simulations, Chemical Engineering Science, Volume 62, Issues 1–2, Pages 246-255. https://doi.org/10.1016/j.ces.2006.08.054.


Holloway, W., Yin, X., and Sundaresan, S. (2010). Fluid‐particle drag in inertial polydisperse gas–solid suspensions, AIChE Journal, Volume 56, Issue 8, Pages 1995-2004. https://doi.org/10.1002/aic.12127


Hoef, M., Beetstra, R., and Kuipers, J. (2005). Lattice-Boltzmann simulations of low-Reynolds-number flow past mono- and bidisperse arrays of spheres: Results for the permeability and drag force. Journal of Fluid Mechanics, Volume 528, Pages 233-254. https://doi.org/10.1017/S0022112004003295


Beetstra, R. , van der Hoef, M. A. and Kuipers, J. A. (2007), Drag force of intermediate Reynolds number flow past mono‐ and bidisperse arrays of spheres. AIChE J., 53: 489-501. https://doi.org/10.1002/aic.11065


(2007), Erratum. AIChE J., 53: 3020-3020. https://doi.org/10.1002/aic.11330


Igci, Y., Pannala, S., Benyahia, S., and Sundaresan, S. (2012). Validation studies on filtered model equations for gas-particle flows in risers, Industrial & Engineering Chemistry Research, Volume 54, Issue 4, Pages 2094-2103. https://doi.org/10.1021/ie2007278


Milioli, C.C., Milioli, F.E., Holloway, W., Agrawal, K. and Sundaresan, S. (2013), Filtered two‐fluid models of fluidized gas‐particle flows: New constitutive relations. AIChE J., Volume 59, Issue 9, Pages 3265-3275. https://doi.org/10.1002/aic.14130