Shear thickening and history-dependent rheology of monodisperse suspensions with finite inertia via an immersed boundary lattice Boltzmann method

This the pre-print of an article submitted to International Journal of Multiphase Flow,Volume 125, April 2020, 103205. The final published version is available at http://dx.doi.org/10.1016/j.ijmultiphaseflow.2019.103205Three-dimensional direct numerical simulations of dense suspensions of monodisperse spherical particles in simple shear flow have been performed at particle Reynolds numbers between 0.1 and 0.6. The particles translate and rotate under the influence of the applied shear. The lattice Boltzmann method was used to solve the flow of the interstitial Newtonian liquid, and an immersed boundary method was used to enforce the no-slip boundary condition at the surface of each particle. Short range spring forces were applied between colliding particles over sub-grid scale distances to prevent overlap. We computed the relative apparent viscosity for solids volume fractions up to 38% for several shear rates and particle concentrations and discuss the effects of these variables on particle rotation and cluster formations. The apparent viscosities increase with increasing particle Reynolds number (shear thickening) and solids fraction. As long as the particle Reynolds number is low (0.1), the computed viscosities are in good agreement with experimental measurements, as well as theoretical and empirical equations. For higher Reynolds numbers, we find much higher viscosities, which we relate to slower particle rotation and clustering. Simulations with a sudden change in shear rate also reveal a history (or hysteresis) effect due to the formation of clusters. We quantify the changes in particle rotation and clustering as a function of the Reynolds number and volume fraction

Inertial Rise in Short Capillaries

In this fluid dynamics video we show capillary rise experiments with diethyl ether in short tubes. The height of each short tube is less than the maximum height the liquid can achieve, and therefore the liquid reaches the top of the tube while still rising. Over a narrow range of heights, the ether bulges out from the top of the tube and spreads onto the external wall.Comment: Includes 2 videos for the Gallery of Fluid Motion in the 2013 American Physical Society Division of Fluid Dynamics Annual Meetin

Efficient mass-preserving finite volume approach for the rennet-induced coagulation equation

The coagulation of casein micelles caused by enzymes is a critical step in the dairy industry for cheese manufacture. During enzymatic coagulation of milk, three processes occur: enzymic proteolysis, coagulation, and gelation. This study presents the first numerical approach based on a finite volume scheme for describing the enzyme-induced coagulation of casein micelles. The finite volume scheme is mainly concerned with ensuring mass conservation and developed on the assumption that the particles are concentrated on the mean of each cell of the discretization. The key advantages of the new technique are its simple mathematical formulation and its robustness that allow it to be implemented on any type of grid and tailored to different coagulation kernels. The accuracy of the new approach is compared with newly derived analytical results for several gelling and non-gelling coagulation kernels. The comparison demonstrates that the new approach closely matches the exact results. In order to analyse the convergence behaviour of different order moments, various refined non-uniform grids have been taken into consideration.</p

Membraneless water filtration using CO2

Water purification technologies such as microfiltration/ultrafiltration and reverse osmosis utilize porous membranes to remove suspended particles and solutes. These membranes, however, cause many drawbacks such as a high pumping cost and a need for periodic replacement due to fouling. Here we show an alternative membraneless method for separating suspended particles by exposing the colloidal suspension to CO2. Dissolution of CO2 into the suspension creates solute gradients that drive phoretic motion of particles. Due to the large diffusion potential generated by the dissociation of carbonic acid, colloidal particles move either away from or towards the gas–liquid interface depending on their surface charge. Using the directed motion of particles induced by exposure to CO2, we demonstrate a scalable, continuous flow, membraneless particle filtration process that exhibits low energy consumption, three orders of magnitude lower than conventional microfiltration/ultrafiltration processes, and is essentially free from fouling

The effects of particle shape, orientation, and reynolds number on particle-wall collisions

Crystallisation is an important unit operation used in the production of Active Pharmaceutical Ingredients (APIs). Crystallisation is typically carried out using seed crystals in a process called secondary nucleation that allows for greater control of crystal quality attributes. The mechanism of secondary nucleation is still not well understood. Particle attrition is one proposed mechanism. This work examines the conditions under which particle-wall collisions occur. This is done through the simulation of free-moving particles in an impinging jet flow using an immersed-boundary lattice Boltzmann method (IB-LBM) CFD solver. Particle Reynolds numbers from 100 to 400 are examined. Particle shapes with aspect ratios from 1:1 to 8:1 are used to represent the crystal habits of APIs. Particles that start in their low-drag or high-drag orientation maintain this orientation on approach to the target surface. All other intermediate initial orientations examined cause particles to rotate toward and overshoot their high-drag form before adopting their high-drag form in proximity to the target surface. Particles in their low-drag form remain in their initial orientation due to the symmetry of the computational domain. In this orientation, a collision is most likely to occur, and the minimum critical Reynolds number at which a particle-wall collision will occur can be determined. This value is shown to increase with increasing particle frontal length. Pointed or rounded leading edges are shown to improve a particle’s ability to pierce the boundary layer adjacent to the target surface and reduce this value. In cases where a Reynolds number of 400 is insufficient to cause a particle-wall collision, the particles’ minimum distances from the target surface are reported. Using the minimum critical Reynolds number values obtained, the approach velocities required for particles to collide with a wall are shown to be larger than the impeller tip speeds typically used during crystallisation operations. This work provides for the first time the conditions under which particle-wall collisions occur for varying shape and orientation, their behaviour on approach, and the associated impact velocities.</p

The effect of electric double layers, zeta potential and pH on apparent viscosity of non-Brownian suspensions

We carried out 3D simulations of monodisperse particle suspensions subjected to a constant shear rate with the view to investigate the effect of electrical double layers around the particles on apparent suspension viscosities. To this end, expressions for Debye length, zeta potential, and ionic strength (pH) of the liquid were incorporated into our in-house lattice Boltzmann code that uses the immersed boundary method and includes subgrid lubrication models. We varied the solids concentration and particle radius, keeping the particle Reynolds number equal to 0.1. We report on results with respect to the effect of pH in the range 9 through 12 and of Debye length on apparent viscosity and spatial suspension structures, particularly at higher solids vol?ume fractions, and on the effect of flow reversals.</p

Inclusion of DLVO forces in simulations of non-Brownian solid suspensions: Rheology and structure

The understanding of the rheological behaviour of suspensions in aqueous electrolytes is necessary for the optimal design of hydraulic transport lines. In these applications, particle size is at least 10 micron, and the particle Reynolds number, Rep, is finite: O(10−1). Although there are some experimental and numerical data on the rheology of such suspensions, the number of detailed analyses is limited. Therefore, 3-D direct numerical simulations of dense suspensions in aqueous electrolytes are conducted to assess the dynamics of the relative apparent viscosity and particle structures. The solid–liquid interfaces are resolved, and the flow is simulated, employing an in-house immersed boundary-lattice Boltzmann method code. In addition to the hydrodynamics resolved in the computational grid, our simulations include unresolved sub-grid scale lubrication corrections and non-contact electric double layer (EDL) and Van der Waals forces for a wide range of particle volume fractions, ϕv, at a single Rep=0.1. Under these conditions, the contribution of the Van der Waals force was found to be weak. With an increase in ϕv, the effect of EDL forces decreased the relative apparent viscosity. Particle layering and structural arrangements were analysed for ϕv=43 and 52%. As the Debye length (i.e., the thickness of EDL) decreases, the particle layers near the walls weakened. The analyses reveal how at these high volume fractions, chain-like assemblies are transformed into hexagonal arrangements.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.ChemE/Transport Phenomen

The effect of electric double layers, zeta potential and pH on apparent viscosity of non-Brownian suspensions

We carried out 3D simulations of monodisperse particle suspensions subjected to a constant shear rate with the view to investigate the effect of electrical double layers around the particles on apparent suspension viscosities. To this end, expressions for Debye length, zeta potential, and ionic strength (pH) of the liquid were incorporated into our in-house lattice Boltzmann code that uses the immersed boundary method and includes subgrid lubrication models. We varied the solids concentration and particle radius, keeping the particle Reynolds number equal to 0.1. We report on results with respect to the effect of pH in the range 9 through 12 and of Debye length on apparent viscosity and spatial suspension structures, particularly at higher solids volume fractions, and on the effect of flow reversals.ChemE/Transport Phenomen