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We perform Eulerian-Lagrangian simulations of solid-liquid flow in a mixing tank. The simulations are three-dimensional and time dependent and in the transitional flow regime. The lattice-Boltzmann method is used to solve the volume-averaged Navier-Stokes equations. The overall solids volume fraction is of the order of 10%. Situations with the solids only partly suspended are compared to those with fully suspended solids. The emphasis is on the effect of the particle size distribution (PSD) on the suspension behavior. Four PSD’s all having the same d 32 were investigated. It is harder to fully suspend particles with wider size distribution as compared to narrow distributions. [ABSTRACT FROM AUTHOR]

Abstract: Numerical simulations were used to study mobilization and mixing of a bottom layer of Bingham liquid by agitating a Newtonian liquid above the Bingham layer. The agitation is done by a pitched-blade impeller at a Reynolds number of 6000. The Bingham liquid and the Newtonian liquid are miscible. The parameter space of the simulations has a yield stress number and a Richardson number as dimensionless variables. The yield stress number quantifies the importance of the yield stress relative to inertial stresses, the Richardson number the role of the density difference between the two liquids. The simulation procedure is based on the lattice-Boltzmann method for the flow dynamics, and a finite volume scheme to solve for the local and time dependent composition of the liquid mixture. Flow dynamics and liquid composition are intimately coupled. The moderate Reynolds number tentatively allows us to directly simulate the transitional flow, without a need for a turbulence closure model. The results quantify the increase of mixing time with increasing yield stress and (to a weaker extent) density difference. [Copyright &y& Elsevier]

Simulations of solid-liquid flow in an agitated tank have been performed. The simulations fully resolve the mildly turbulent liquid flow (Re ≈ 2000) in the tank, and the spherical solid particles suspended in the liquid. Full resolution of the particles sets the grid spacing and thereby limits the tank size and the number of particles (up to 3600 in this article) that are computationally affordable. The solids volume fraction is some 8%. The lattice-Boltzmann method has been used to solve the flow dynamics; the particles move under the influence of resolved hydrodynamic forces, unresolved lubrication forces, net gravity, and collisions (with other particles, the tank wall, and the impeller). We show the start-up of the suspension process, demonstrate its dependency on a Shields number (that we interpret in terms of the Zwietering correlation) and show the impact of polydispersity on the suspension process. © 2012 American Institute of Chemical Engineers AIChE J, 58: 3266-3278, 2012 [ABSTRACT FROM AUTHOR]

Abstract: A direct simulation methodology for solid spheres moving through viscoelastic (FENE-CR) fluids has been developed. It is based on a lattice-Boltzmann scheme coupled with a finite volume solver for the transport equation of the conformation tensor, which directly relates to the elastic stress tensor. An immersed boundary method imposes no-slip conditions on the spheres moving over the fixed grid. The proposed method has been verified by comparison with computational data from the literature on the viscoelastic flow past a stationary cylinder. Elastic effects manifest themselves in terms of drag reduction and for-aft asymmetry around the cylinder. Single sphere sedimentation in viscoelastic fluids shows velocity overshoots and subsequent damping before a steady settling state is reached. In multi-sphere simulations, the interaction between spheres depends strongly on the (elastic) properties of the liquid. Simulations of sedimentation of multiple spheres illustrate the potential of the method for application in dense solid–liquid suspensions. The sedimentation simulations have Reynolds numbers of order 0.1 and Deborah numbers ranging from 0 to 1.0. [Copyright &y& Elsevier]

Abstract: Detailed simulations of aerated stirred tanks with shear-thinning power law liquids are presented. The lattice-Boltzmann scheme was used to discretize the filtered conservation equations of the liquid phase. The motion of bubbles was tracked based on the Euler–Lagrange approach with a bubble cluster concept. The collision, breakup and coalescence of bubbles were modeled as stochastic events. The predicted flow field of a single-phase stirred tank with shear-thinning power law liquid shows reasonable agreement with experimental data. For aerated systems, qualitatively similar gas holdup distribution was achieved when comparing the predicted result with experiments. Using the proposed modeling approach, it was found that a change in rheology alters the number mean diameter, Sauter diameter and the shape of bubble size distribution. [Copyright &y& Elsevier]

Abstract: Turbulent fluid flow and related solid particle behaviour in the direct vicinity of the heat exchanging (HE) surface of a scraped heat exchanger crystallizer was studied. The liquid flow is visualized by dye injection and the particles are monitored directly for two types of commonly used scraper geometries. In conjunction with this experimental work, we performed direct numerical simulations of the two-phase (solid–liquid) flow system. Our main goal is the design of scraper geometries that enhance heat transfer by perturbing the thermal boundary layer, and effectively scrape off particles that nucleate, grow and adhere onto the HE surface. Also the turbulent flow generated by the moving scrapers should direct the particles into the bulk of the tank. The experiments and simulations show good qualitative resemblance which enables the design of scrapers based primarily on numerical predictions. [Copyright &y& Elsevier]

Highlights: [•] We simulate gas–liquid mass transfer for bubble train flow. [•] The bubble shapes are obtained numerically without analytical simplifications. [•] The lattice Boltzmann method was used for mass transfer and flow simulations. [•] One unit cell simulations are enough to obtain the correct mass transfer coefficient. [Copyright &y& Elsevier]