Rheology of a Dilute Suspension of Aggregates in Shear-Thinning Fluids

D’Avino, Gaetano

doi:10.3390/mi11040443

Cited by 4 publications

(6 citation statements)

References 36 publications

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“…This would need, at each time step, the calculation of the particle angular velocity from the solution of the set of equations presented in the previous section (as discussed above, the translational dynamics is irrelevant). Instead of directly solving the governing equations to compute the orbit, we can greatly speed-up the calculations by precomputing a database of particle translational and angular velocities for different orientations of the aggregate [35,36]. The velocities needed at the right-hand side of Equations (10) and (11) are, then, obtained by interpolating the data of the database.…”

Section: Methodsmentioning

confidence: 99%

“…Finally, the aggregate orbit can be reconstructed by transforming the force from the body to the lab reference frame, i.e., by rotating the aggregate according to the rotation matrix that, at every instant, transform f in F = (F, 0, 0) (that is the applied force in the lab frame). The procedure summarized in Algorithm 1 has been adopted to simulate the rheology of a dilute suspension of fractal aggregates in shear-thinning fluids and validated by reproducing the dynamics of spheroids in shear flow [36].…”

Section: Methodsmentioning

confidence: 99%

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Sedimentation of Fractal Aggregates in Shear-Thinning Fluids

D’Avino

2020

Applied Sciences

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Solid–liquid separation is a key unit operation in the wastewater treatment, generally consisting of coagulation and flocculation steps to promote aggregation and increase the particle size, followed by sedimentation, where the particles settle due to the effect of gravity. The sedimentation efficiency is related to the hydrodynamic behavior of the suspended particles that, in turn, depends on the aggregate morphology. In addition, the non-Newtonian rheology of sludges strongly affects the drag coefficient of the suspended particles, leading to deviations from the known settling behavior in Newtonian fluids. In this work, we use direct numerical simulations to study the hydrodynamic drag of fractal-shaped particles suspended in a shear-thinning fluid modeled by the power-law constitutive equation. The fluid dynamics governing equations are solved for an applied force with different orientations uniformly distributed over the unit sphere. The resulting particle velocities are interpolated to compute the aggregate dynamics and the drag correction coefficient. A remarkable effect of the detailed microstructure of the aggregate on the sedimentation process is observed. The orientational dynamics shows a rich behavior characterized by steady-state, bistable, and periodic regimes. In qualitative agreement with spherical particles, shear-thinning increases the drag correction coefficient. Elongated aggregates sediment more slowly than sphere-like particles, with a lower terminal velocity as the aspect ratio increases.

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Sedimentation of Fractal Aggregates in Shear-Thinning Fluids

D’Avino

2020

Applied Sciences

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“…Regarding the effect of the non-Newtonian properties of the solvent on the viscosity of the suspension, Trofa and D'Avino 6 showed that power-law index affected intrinsic viscosity using fractal-shape aggregates in shear flow. Tanaka et al 7 found that the non-Newtonian properties of the solvent affected the relative and intrinsic viscosity of the suspension in a flow field in which the particles are homogeneously distributed.…”

Section: Introductionmentioning

confidence: 99%

Numerical simulation of the effects of non-Newtonian property of the solvent on particle suspension rheology

Masuyama,

Fukui

2023

Advances in Mechanical Engineering

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To investigate the effects of the non-Newtonian properties of solvents on particle suspension rheology (non-Newtonian property and viscosity), we analyzed suspension flows with different solvent characteristics. We used the power-law model to express the non-Newtonian properties of solvents. The power-law index of the suspension was denoted as nsus. and that of the solvent as [Formula: see text] to distinguish between their non-Newtonian properties. Besides, to evaluate the non-Newtonian property of the particle suspension, we estimated its power-law index [Formula: see text] by comparing its particle velocity with the velocity profile of a power-law fluid. As a result, regardless of the different area fraction, the power-law index of the particle suspension was lower than that of the solvent for [Formula: see text], 0.8, and 1.0. On the other hand, for [Formula: see text] and [Formula: see text], the power-law index of the particle suspension was higher than that of the solvent. Regarding the particle position, particles for [Formula: see text] were more concentrated on the wall side than those of the suspensions with [Formula: see text], 0.8, and 1.0. Thus, this study confirms that a change in the non-Newtonian property of a suspension due to interactions between particles and power-law fluids is an essential factor when discussing the rheology of suspensions.

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“…5 In these processes, aggregates are exposed to shear, which directly affects their size and structure, 6−8 thus affecting the overall suspension properties, such as its rheology. 9 When an aggregate is introduced in shear flow, it restructures so that particle contacts within the aggregate balance the external action of the flow. The aggregate breaks when force equilibrium cannot be achieved.…”

Section: ■ Introductionmentioning

confidence: 99%

“…Consequently, aggregate properties, such as size and structure, govern the efficiency of many industrial processes, including polymer manufacturing, wastewater treatment, , mineral processing, and liquid metal treatments . In these processes, aggregates are exposed to shear, which directly affects their size and structure, − thus affecting the overall suspension properties, such as its rheology . When an aggregate is introduced in shear flow, it restructures so that particle contacts within the aggregate balance the external action of the flow.…”

Section: Introductionmentioning

confidence: 99%

Role of Flow Inertia in Aggregate Restructuring and Breakage at Finite Reynolds Numbers

2023

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Forces acting on aggregates depend on their properties, such as size and structure. Breakage rate, stable size, and structure of fractal aggregates in multiphase flows are strongly related to the imposed hydrodynamic forces. While these forces are prevalently viscous for finite Reynolds number conditions, flow inertia cannot be ignored, thereby requiring one to fully resolve the Navier−Stokes equations. To highlight the effect of flow inertia on aggregate evolution, numerical investigation of aggregate evolution in simple shear flow at the finite Reynolds number is conducted. The evolution of aggregates exposed to shear flow is tracked over time. Particle coupling with the flow is resolved with an immersed boundary method, and flow dynamics are solved using a lattice Boltzmann method. Particle dynamics are tracked by a discrete element method, accounting for interactions between primary particles composing the aggregates. Over the range of aggregate-scale Reynolds numbers tested, the breakage rate appears to be governed by the combined effect of momentum diffusion and the ratio of particle interaction forces to the hydrodynamic forces. For higher shear stresses, even when no stable size exists, breakage is not instantaneous because of momentum diffusion kinetics. Simulations with particle interaction forces scaled with the viscous drag, to isolate the effect of finite Reynolds hydrodynamics on aggregate evolution, show that flow inertia at such moderate aggregate Reynolds numbers has no impact on the morphology of nonbreaking aggregates but significantly favors breakage probability. This is a first-of-its-kind study that establishes the role of flow inertia in aggregate evolution. The findings present a novel perspective into breakage kinetics for systems in low but finite Reynolds number conditions.

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Rheology of a Dilute Suspension of Aggregates in Shear-Thinning Fluids

Cited by 4 publications

References 36 publications

Sedimentation of Fractal Aggregates in Shear-Thinning Fluids

Sedimentation of Fractal Aggregates in Shear-Thinning Fluids

Numerical simulation of the effects of non-Newtonian property of the solvent on particle suspension rheology

Role of Flow Inertia in Aggregate Restructuring and Breakage at Finite Reynolds Numbers

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