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Fluidized beds are commonly used for industrial drying applications due to their excellent heat and mass transfer characteristics. These features are desired since solids drying is very energy-intensive. Computer models such as Computational Fluid Dynamics - Discrete Element Method (CFD-DEM) can be employed to facilitate the fundamental understanding of solids drying and as a tool to improve process design. A crucial step is model validation with experimental data. In this study, the CFD-DEM drying simulations are validated using a detailed one-to-one comparison with the experimental results of De Munck et al. (2022). The pressure drop over the bed, the solids volume fluxes, the particle temperatures, and the particle densities are presented and discussed. Reasonable agreement between the experiments and simulations is observed. Furthermore, a connection between the local bed hydrodynamics and the local solids density distribution is found. • Fluidized bed solids drying is numerically studied. • Detailed one-to-one validation with experimental results of De Munck et al. (2022). • The influence of solids drying on the bed hydrodynamics is characterized. • The local particle density distribution has a clear impact on the local solids volume fluxes. [ABSTRACT FROM AUTHOR]

• Fully resolved simulations of fluid-particle systems. • Surface reaction with significant heat effects. • Temperature-dependent reaction rates determined by the Arrhenius equation. • Simulation parameters adopted from realistic POX reaction. In this paper, an efficient ghost-cell based immersed boundary method (IBM) is used to perform direct numerical simulation (DNS) of reactive fluid-particle systems. With an exothermic first order reaction proceeding at the exterior particle surface, the solid temperature rises and consequently increases the reaction rate via an Arrhenius temperature dependence. In other words, the heat and mass transport is dependently coupled through the particle thermal energy equation and the Arrhenius equation, and they offer dynamic boundary conditions for the fluid phase thermal energy equation and species equation respectively. The fluid-solid coupling is enforced at the exact position of the particle surface by implicit incorporation of the boundary conditions into the discretized momentum, species and thermal energy conservation equations of the fluid phase. Different fluid-particle systems are studied with increasing complexity: a single sphere, three spheres and a dense array consisting of hundreds of randomly generated particles. In these systems the mutual impacts between heat and mass transport processes are investigated. [ABSTRACT FROM AUTHOR]

In this work, a detailed three dimensional model is employed for the quantitative description of flow and coupled heat and mass transfer in a gas channel coated with porous adsorbent layer. The flow field of the gas stream is obtained by solving the Navier-Stokes equation. The highly coupled mass and heat transfer in both the gas channel and the adsorbent layer are locally described, and the accompanying adsorption/desorption dynamics in the adsorbent layer are modelled as well. A parametric study has been carried out, in which the influences of thermal conductivity of the adsorbent layer, specific heat, porosity, tortuosity, layer thickness and geometrical shape on the performance of moisture adsorption processes are investigated in an exhaustive way. The heat and mass transfer mechanisms in the investigated cases are thoroughly analysed taking advantage of the rigorous 3D model, which deepens our understanding on the intricately coupled transport processes. The results reported in this work are useful for rational design and optimization of adsorption processes in adsorbent coated gas channels. [ABSTRACT FROM AUTHOR]

In this paper, a detailed three dimensional mathematical formulation and a simplified one dimensional model for the numerical simulation of the flow and coupled heat and mass transport in a gas channel coated with adsorbing material are presented. In the three dimensional model, the velocity distribution of the gas flow is obtained by solving the momentum equation. The coupled heat and mass transport phenomena are locally described in both the gas channel and the adsorbent layer, and the concomitant adsorbate adsorption and desorption processes are taken into account. In the one dimensional model, the gas flow is assumed as a plug flow, and the heat and mass transfer across the solid-fluid interface is estimated by empirical transfer coefficients. A comparative study between the detailed three dimensional model and a simplified one dimensional model is carried out. Both model predictions are compared with experimental data available from literature. The heat and adsorbate concentration gradients observed in both radial and circumferential directions indicate that the detailed three dimensional model is desired. The time-dependent variations of temperature and heat flux distributions at the interface between the gas channel and the adsorbent layer justify the use of the more detailed three dimensional model. Three dimensional modelling is essential to obtain accurate predictions for cases where the solid side transport resistances are dominating. [ABSTRACT FROM AUTHOR]

[Display omitted] • Fluidized bed particle drying is experimentally studied. • Particle image velocimetry and infra-red thermography techniques are applied. • Full field solids fluxes and temperatures are measured. • Gas-particle heat and mass transfer is characterized. • Drying influences the solids hydrodynamics by changes in particle density. Fluidized bed drying is an unsteady process where particle and gas properties evolve in time. The bed hydrodynamics and its interplay with mass and heat transfer changes in time. In this study, experiments in a pseudo-2D fluidized bed setup are performed to obtain insight in this complex behavior. A coupled particle image velocimetry infrared thermography technique provides solids velocity and temperature fields in the bed. Significant hydrodynamic changes due to the evaporation of water from the porous γ - Al 2 O 3 material for three superficial velocities were observed. The 1.25 u mf case resulted in an fixed bed state, but after drying for 580 s a bed inversion took place. The 1.50 and 1.75 u mf experiments showed an increase in bed expansion over time. Furthermore, clear asymmetrical solids volume fluxes were observed for the wet material that became more symmetrical over time when the material dried. [ABSTRACT FROM AUTHOR]

Abstract: This paper describes the separation of vaporous alcohol–water mixtures using the FricDiff separation technology. This separation process is based on a difference in interspecies friction between the components of a feed mixture and a sweep gas. A comparison is made between the performances of tubular and plate FricDiff-modules for several dimensions of the module using the finite element program COMSOL [Comsol, 2006. COMSOL Multiphysics User''s Guide, version 3.3]. It is shown that these configurations give different results when the fluxes through the porous barrier (which separates the feed mixture compartment from the compartment where the sweep gas is flowing) increase. These differences can be attributed to the resistances to mass transfer located in flow channels adjacent to the porous barrier. These resistances are different for the two configurations and when they become dominant, the tubular and plate FricDiff-modules behave differently. Sherwood correlations are derived to describe the resistances to mass transfer in the flow channels. Both the developing and fully developed boundary layer regimes are taken into account. In the developing regime, the derivation is based on that of a pseudo-binary system, consisting of one of the feed components and the sweep gas. In the fully developed regime the true multi-component behavior of the system is taken into account. It is shown that these Sherwood correlations give a very accurate description of the separation process in a FricDiff-module. [Copyright &y& Elsevier]

Highlights • Axial Dispersion in open-cell foams scales non-linearly with the Péclet Number. • Phenomenon equivalent to Taylor dispersion is observed for Darcy flow. • Non-mechanical dispersion is induced by the appearance of stagnant zones. • Hydrodynamic dispersion is governed by chaotic advection at high velocities. • Dispersion coefficients have an inverse dependency on the particle diameter. Abstract Fully resolved simulations of flow and mass transfer in a unit cell of structured open-cell foam catalysts are presented. Numerical studies are conducted on a uniform three-dimensional Cartesian grid where the fluid-solid interface coupling is enforced via a sharp interface Immersed Boundary technique. Several validation cases for the numerical method are presented followed by extensive calculations to quantify hydrodynamic dispersion in open-cell foams. In our study five different porosities of the idealized foam structure, represented by the spatially periodic Kelvin's unit cell, were considered. Dimensionless dispersion coefficients were calculated for varying Péclet numbers and flow directions using volume-averaging theory. Our numerical studies indicate that Taylor dispersion is the dominant mechanism for structured porous media in the Darcy-Brinkman flow regime. [ABSTRACT FROM AUTHOR]

Mass transfer plays an important role in chemical engineering applications involving multiphase systems. Several techniques have been developed in the field to measure the global mass concentration in multiphase chemical reactors. However, because of the complexity of multiphase processes, only few techniques are able to provide local and quantitative information. In this study a dual-emission Laser Induced Fluorescent technique (LIF) has been developed to locally measure the mass transfer of a rising CO 2 bubble in a quiescent fluid. Details of the pH field with an overall precision of ± 0.04 pH units, dissolved CO 2 concentration, and the mass transfer evolution in the bubble wake can now be measured quantitatively. It is capable to provide quantitative comparison with simulation results and as such experimental validation of multiphase CFD models. [ABSTRACT FROM AUTHOR]

In this paper, an efficient ghost-cell based immersed boundary method is introduced to perform direct numerical simulation (DNS) of mass transfer problems in particulate flows. The fluid-solid coupling is achieved by implicit incorporation of the boundary conditions into the discretized momentum and species conservation equations of the fluid phase. Taking the advantage of a second order quadratic interpolation scheme utilized in the reconstruction procedures, the unique feature of this ghost-cell based immersed boundary method is its capability to handle mixed boundary conditions at the exact position of the particle surface as encountered in systems with interplay between surface reactions and diffusion. A fixed Eulerian grid is used to solve the conservation equations for the entire computational domain. Following a detailed verification of the method in the limiting case of unsteady molecular diffusion without convection, we apply our method to study fluid-particle mass transfer for flow around a single sphere and a dense stationary array consisting of hundreds of spheres over a range of Damköhler numbers. [ABSTRACT FROM AUTHOR]

Fluidized bed drying is an evolving process: The bed hydrodynamics, including the segregation and mixing tendencies, and its interplay with mass and heat transfer change in time. In this study, pseudo-2D fluidized bed experiments are performed using binary (50/50%) and ternary (33.3/33.3/33.3%) solids mixtures. A coupled particle image velocimetry infrared thermography technique provides local solids velocity and temperature fields. Furthermore, a machine learning algorithm is applied to characterize the bed segregation and mixing dynamics. Significant hydrodynamic changes and various segregation and mixing tendencies due to the evaporation of water from the porous γ - Al 2 O 3 material were observed. A competition between size and density-based segregation and mixing dynamics resulted in changing bed configurations, which are correlated to the local solids drying behavior. Besides, it showed that drying of wider size distributions could lead to more complex efficient process operation. • Fluidized bed particle drying is experimentally studied. • Particle image velocimetry and infrared thermography are applied. • Size-segregation is determined by a machine learning algorithm. • Drying shows a strong connection with the bed hydrodynamics and the segregation and mixing dynamics. [ABSTRACT FROM AUTHOR]

• Extended the Adaptive Mesh Refinement (AMR) methodology for deformable interfaces. • Extended the AMR for moving interfaces. • Validation in 2D and 3D simulations. • Simulation of single bubble mass transfer using high Schmidt numbers. Gas–liquid systems involving dispersed bubbly flows are often encountered in industry due to their favourable heat and mass transport characteristics. A key element of such systems involving interfacial mass transfer are the thin mass boundary layers prevailing at the phase boundaries. Resolving these thin boundary layers in numerical simulations is very challenging because of the need for very fine grids. Such grids often over-resolve the hydrodynamics which accounts for most of the CPU time. In this paper, we propose a multiple resolution approach that resolves the momentum boundary layers on a coarse (fixed) Cartesian grid and the mass boundary layers on a finer (adaptive) grid. The methodology proposed in Panda et al. (2019) for static rigid particles is extended to deformable moving interfaces and applied to single rising bubbles where the computed Sherwood number is compared with empirical correlations and numerical simulations available in literature. [ABSTRACT FROM AUTHOR]

• Systematic analysis of the mass transfer limitation in wash-coated open-cell foams. • CFD simulations on Kelvin's cell by DNS. • Mass transfer correlation for low Reynolds number. • Practical criteria in terms of dimensionless numbers for rate limiting regimes. In this work, the analysis of the mass transfer phenomena in catalytic open-cell foams is carried out through the combination of computational fluid dynamics (CFD) simulations and experiments, using the CO oxidation on Pt(1%)/γ-Al 2 O 3 /foam as a model reaction. The influence of the local hydrodynamic effects on the diffusion-reaction phenomena occurring at the gas-solid interface of the open-cell solid foams are investigated by Direct Numerical Simulations assuming an infinitely fast reaction. A correlation for the Sherwood number as function of Reynolds -for low Re- is proposed. To validate this experimentally, aluminum foams coated with Pt(1%)/γ-Al 2 O 3 are tested at different reaction conditions for the CO oxidation. The obtained reaction rates and apparent activation energy show the presence of external mass transfer limitations. An analysis of the diffusion-reaction phenomena taking place in the wash-coated layer is presented in terms of dimensionless numbers. A practical criterion is developed in terms of the Thiele modulus (ϕ w) and the Biot number (Bi m) for the identification of the reaction regimes: kinetic control ( ϕ w 2 / B i m < 0.1) , internal and/or external mass transfer limitations (0.1 < ϕ w 2 / B i m < 10) , and full mass transfer control ( ϕ w 2 / B i m > 10). [ABSTRACT FROM AUTHOR]