The sensitivity of filtered Two Fluid Models to the underlying resolved simulation setup

Eulerian-Eulerian modelling based on the Kinetic Theory of Granular Flow has proven to be a promising tool for investigating the hydrodynamic and reactive behaviour inside fluidized beds. The primary limitation of this approach is the very fine grid size necessary to fully resolve the transient solid structures that are typical of fluidized bed reactors. It therefore remains impractical to simulate industrial scale fluidized bed reactors using resolved Two Fluid Model (TFM) simulations. For this reason, there is currently widespread interest in developing sub-grid (filtered) models that allow accurate simulations at coarser grids by correcting for the effects of unresolved solid structures. However, little attention has been paid to the importance of the choice of the underlying TFM closures during the derivation of the filtered models. This paper follows a similar approach to an establish filtered TFM (1) to derive sub-grid closures for the interphase momentum exchange , solids viscosity and solids pressure in 2D periodic simulations. These corrections are obtained for different particle-particle restitution coefficients, frictional pressure models and drag models as a function of the particle phase volume fraction and the filter size. This reveals at which values of the markers the individual resolved TFM model choices have significant effects on the final expressions derived for filtered TFMs. Based on these findings suggestions are made regarding the derivation of new filtered TFMs and the use of the existing models. 1. Y. Igci and S. Sundaresan. Constitutive Models for Filtered Two-Fluid Models of Fluidized Gas–Particle Flows. Ind. Eng. Chem. Res., 50: 13190-13201, 2013

Generalized multirate models for conjugate transfer in heterogeneous materials

We propose a novel macroscopic model for conjugate heat and mass transfer between a mobile region, where advective transport is significant, and a set of immobile regions where diffusive transport is dominant. Applying a spatial averaging operator to the microscopic equations, we obtain a multicontinuum model, where an equation for the average concentration in the mobile region is coupled with a set of equations for the average concentrations in the immobile regions. Subsequently, by mean of spectral decomposition, we derive a set of equations that can be viewed as a generalization of the multirate mass transfer (MRMT) model. This new formulation does not require any assumption on local equilibrium or geometry. We then show that the MRMT can be obtained as the leading order approximation, when the mobile concentration is in local equilibrium. The new generalized multirate transfer model (GMRT) has the advantage of providing a direct method for calculating the model coefficients for immobile regions of arbitrary shapes, through the solution of appropriate microscale cell problems. An important finding is that a simple rescaling or reparametrization of the transfer rate coefficient (and thus, the memory function) is not sufficient to account for the flow field in the mobile region and the resulting nonuniformity of the concentration at the interfaces between mobile and immobile regions

Highly efficient spatial data filtering in parallel using the opensource library CPPPO

This program has been imported from the CPC Program Library held at Queen's University Belfast (1969-2018) Abstract CPPPO is a compilation of parallel data processing routines developed with the aim to create a library for “scale bridging” (i.e. connecting different scales by mean of closure models) in a multi-scale approach. CPPPO features a number of parallel filtering algorithms designed for use with structured and unstructured Eulerian meshes, as well as Lagrangian data sets. In addition, data can be processed on the fly, allowing the collection of relevant statistics without saving individual snapshot... Title of program: CPPPO Catalogue Id: AFAQ_v1_0 Nature of problem Development of closure models for momentum, species transport and heat transfer in fluid and fluid-particle systems using purely Eulerian or Euler-Lagrange simulators. Versions of this program held in the CPC repository in Mendeley Data AFAQ_v1_0; CPPPO; 10.1016/j.cpc.2016.05.02