This report describes the MFIX (Multiphase Flow with Interphase eXchanges) compurer model. MFIX is a general-purpose hydrodynamic model that describes chemical reactions and heat transfer in dense or dilute fluid-solids flows, flows typically occurring in energy conversion and chemical processing reactors. MFIX calculations give detailed infor-" marion on pressure, temperature, composition, and velocity distributions in the reactors. With such information, the engineer can visualize the conditions in the reactor, conduct parametric • studies and what-if experiments, and, thereby, assist in the dessgn process. The MHX model, developed at the Morgantown Energy Technology Center (METC), has the following capabilities: mass and momentum balance equations for gas and multiple solids phases; a gas phase and two solids phase energy equations; an arbitrarynumber of species balance equations for each of the phases; granular stress equations based on kinetic theory and frictional flow theory; a user-defined chemistry subroutine; three-dimensional Cartesian or cylindrical coordinate systems; nonuniform mesh size; impermeable and semipermeable internal surfaces; user-_endly input data file; multiple, single-precision, binary, direct-access, output f'desthat minimize disk storage and accelerate data retrieval; and extensive error reporting. This report, which is Volume I of the code documentation, describes the hydrodynamic theory used in the model: the conservation equations, constitutive relations, and the initial and boundary conditions. The literatureon the hydrodynamic theory is briefly surveyed, and the bases for the different parts of the model are highlighted.

in Wiley InterScience (www.interscience.wiley.com).Starting from a kinetic theory based two-fluid model for gas-particle flows, we first construct filtered two-fluid model equations that average over small scale inhomogeneities that we do not wish to resolve in numerical simulations. We then outline a procedure to extract constitutive models for these filtered two-fluid models through highly resolved simulations of the kinetic theory based model equations in periodic domains. Two-and three-dimensional simulations show that the closure relations for the filtered two-fluid models manifest a definite and systematic dependence on the filter size. Linear stability analysis of the filtered two-fluid model equations reveals that filtering does indeed remove small scale structures that are afforded by the microscopic twofluid model.

No abstract

in Wiley InterScience (www.interscience.wiley.com).We use the well established core-annulus flow regime as a numerical benchmark to evaluate the sensitivity of gas-solids continuum models and boundary conditions to model formalisms and parameters. By using transient, 1D, grid-independent numerical solutions, we avoid the use of speculative closure terms and show that the kinetic theory of granular flow (KTGF) is sufficient to model core-annulus regime. That regime arises in the time-average solution as a consequence of the fluctuating motion of regions with high solids concentration. These fluctuations are most sensitive to the gravitational acceleration (g) and granular energy dissipation terms. The fluctuation frequency is a ffiffi ffi g p . The effect of fluctuations is so dominant that decreasing the restitution coefficient (KTGF parameter) actually increases the average granular temperature. The wall boundary conditions for solids momentum and granular energy equations dictate the core-annulus flow regime. They must cause a net dissipation of granular energy at the wall for predicting that regime.

No abstract