scholarly journals Rheology of dense granular suspensions

2018 ◽  
Vol 852 ◽  
Author(s):  
Élisabeth Guazzelli ◽  
Olivier Pouliquen
Keyword(s):  
Colloidal Particles ◽  
Volume Fraction ◽  
Phase System ◽  
Concentrated Suspensions ◽  
Two Phase ◽  
Transient Flows ◽  
Colloidal Spheres ◽  
Dense Suspensions ◽  
Granular Suspensions ◽  
Maximum Volume Fraction

Suspensions are composed of mixtures of particles and fluid and are omnipresent in natural phenomena and in industrial processes. The present paper addresses the rheology of concentrated suspensions of non-colloidal particles. While hydrodynamic interactions or lubrication forces between the particles are important in the dilute regime, they become of lesser significance when the concentration is increased, and direct particle contacts become dominant in the rheological response of concentrated suspensions, particularly those close to the maximum volume fraction where the suspension ceases to flow. The rheology of these dense suspensions can be approached via a diversity of approaches that the paper introduces successively. The mixture of particles and fluid can be seen as a fluid with effective rheological properties but also as a two-phase system wherein the fluid and particles can experience relative motion. Rheometry can be undertaken at an imposed volume fraction but also at imposed values of particle normal stress, which is particularly suited to yield examination of the rheology close to the jamming transition. The response of suspensions to unsteady or transient flows provides access to different features of the suspension rheology. Finally, beyond the problem of suspension of rigid, non-colloidal spheres in a Newtonian fluid, there are a great variety of complex mixtures of particles and fluid that remain relatively unexplored.

Transmission Electron Microscopy (TEM) Observations of Phase-Separations of Gamma-Prime Precipitates in Ni-Al-Fe and Ni-Si-Fe Ternary Alloys

2007 ◽  
Vol 26-28 ◽  
pp. 1311-1314 ◽  
Author(s):  
M. Senga ◽  
H. Kumagai ◽  
Tomokazu Moritani ◽  
Minoru Doi
Keyword(s):  
Phase Separation ◽  
Volume Fraction ◽  
Heating Temperature ◽  
Ternary Alloys ◽  
Phase System ◽  
Precipitate Phase ◽  
Two Phase ◽  
Gamma Prime ◽  
Transmission Electron ◽  
The Difference

In Ni-13.0at%Si-3.1at%Fe alloy, when γ/γ’ two-phase microstructure formed at 1123 K is isothermally heated at 923 K which is lower than the temperature where the initial γ/γ’ microstructure forms, the phase-separation of γ/γ’ precipitate phase occurs and γ particles newly appear in each cuboidal γ’ precipitate. While in Ni-10.2at%Al-10.8at%Fe alloy, when γ/γ’ two-phase microstructure formed at 1023 K is isothermally heated at 1123 K which is higher than the temperature where the initial γ/γ’ microstructure forms, the phase-separation of γ’ precipitate phase takes place and γ particles newly appear in each cuboidal γ’ precipitate. Such appearance of new γ particles in γ’ precipitates can be explained by the difference in the volume fraction of γ phase that should exist in the γ/γ’ two-phase system depending on the heating temperature.

Distribution of Cotton in Rectangular Pipeline for Horizontal Foreign Fiber Removed Device

2014 ◽  
Vol 951 ◽  
pp. 113-119
Author(s):  
Gai Li Gao ◽  
Guan Jun Wang ◽  
Peng Chuan Liu
Keyword(s):  
Cross Sections ◽  
Volume Fraction ◽  
Flow Direction ◽  
Simulation Method ◽  
Optimum Length ◽  
Two Phase ◽  
Maximum Volume Fraction ◽  
The Cross ◽  
Motion Characteristics ◽  
The One

A numerical simulation method using the model of the gas-cotton two-phase is used to analyze the distribution of the cotton in the rectangular pipeline for a horizontal foreign fiber removed device. According to the motion characteristics of the cotton, the optimum length of the rectangular pipeline is found and the distribution of the cotton in the pipeline is obtained. The simulation results show that the optimum length is for the cross-section pipeline. At the same time, in the range of the cotton mainly flows in the middle of the pipeline bottom and the maximum volume fraction of the cotton is 4.5%, at the both sides of the pipeline bottom the cotton is less and the average volume fraction of the cotton is 1%, and there is no the cotton in the middle and upper part of the pipeline; in the range of , the cotton increases rapidly in the middle and upper part of the pipeline and the volume fraction is about 2.7% at ; in the range of , the cotton flows steadily and the volume fractions of the cotton are the same in the middle and upper part of the pipeline, about 2.7% but 1.5% in the lower part of the one. In addition, for the level centers of the cross-sections perpendicular to the cotton flow direction, in the unsteady zone the volume fraction curves of the cotton are symmetrical like a saddle, and in the steady zone the cotton is evenly distributed and its volume fraction curves are horizontal lines.

Phase-Separation of B2 Precipitates in an Fe-Ni-Al Alloy

2010 ◽  
Vol 638-642 ◽  
pp. 2274-2278 ◽  
Author(s):  
Yasuhiro Kuno ◽  
Yasuo Nakane ◽  
Takao Kozakai ◽  
Minoru Doi ◽  
Junji Yamanaka ◽  
...  
Keyword(s):  
Free Energy ◽  
Phase Separation ◽  
Volume Fraction ◽  
Heating Temperature ◽  
Phase System ◽  
Al Alloy ◽  
Two Phase ◽  
Chemical Free Energy ◽  
The Difference ◽  
The Individual

When Fe-10.3mol%Ni-14.3mol%Al alloy is heated at 1173 K for 8.64104 s, a number of B2 precipitates are dispersed in the A2 matrix. When the two-phase microstructure of A2+B2 is aged at 973 K, the phase-separation of B2 precipitate particles takes place to form a new A2 phase in each B2 particle. In the course of further ageing at 973 K, the new A2 phase grows but decreases in number, and finally only one A2 particle is left in the individual B2 particles. The appearance of new A2 phase in each B2 precipitate is due to the difference in the volume fraction of A2 phase that should exist in A2+B2 two-phase system depending on the heating temperature: i.e., the phase-separation of B2 precipitates starts with the aid of chemical free energy.

Intersect distributions of a `dead leaves' model with spherical primary grains

2005 ◽  
Vol 38 (3) ◽  
pp. 520-527 ◽  
Author(s):  
Wilfried Gille
Keyword(s):  
Volume Fraction ◽  
Three Dimensional ◽  
Length Distribution ◽  
Hard Core ◽  
Spherical Particles ◽  
Characteristic Functions ◽  
Phase System ◽  
Two Phase ◽  
Linear Integration ◽  
Dead Leaves Model

This article analyses a tightly packed random two-phase system possessing spherical particles having the volume fraction of 1/8. For a three-dimensional hard-core `dead leaves' model of spheres of constant diameter, the chord length distribution density of typical chords m i of the connected phase (outside the hard particles) is investigated. The calculation starts from the second derivative of the small-angle scattering correlation function of the model and applies characteristic functions. The result fulfills Rosiwal's linear integration principle.

scholarly journals Rheology of concentrated suspensions of non-colloidal rigid fibres

2017 ◽  
Vol 827 ◽  
Author(s):  
Franco Tapia ◽  
Saif Shaikh ◽  
Jason E. Butler ◽  
Olivier Pouliquen ◽  
Élisabeth Guazzelli
Keyword(s):  
Friction Coefficient ◽  
Aspect Ratio ◽  
Volume Fraction ◽  
Normal Stresses ◽  
Maximum Volume ◽  
Concentrated Suspensions ◽  
Suspension Flows ◽  
Jamming Transition ◽  
Aspect Ratios ◽  
Maximum Volume Fraction

Pressure- and volume-imposed rheology is used to study suspensions of non-colloidal, rigid fibres in the concentrated regime for aspect ratios ranging from 3 to 15. The suspensions exhibit yield stresses. Subtracting these apparent yield stresses reveals a viscous scaling for both the shear and normal stresses. The variation in aspect ratio does not affect the friction coefficient (ratio of shear and normal stresses), but increasing the aspect ratio lowers the maximum volume fraction at which the suspension flows. Constitutive laws are proposed for the viscosities and the friction coefficient close to the jamming transition.

scholarly journals Dynamics of concentrated suspensions of non-colloidal particles in Couette flow

2010 ◽  
Vol 649 ◽  
pp. 205-231 ◽  
Author(s):  
KYONGMIN YEO ◽  
MARTIN R. MAXEY
Keyword(s):  
Couette Flow ◽  
Colloidal Particles ◽  
Volume Fraction ◽  
Three Dimensional ◽  
Channel Height ◽  
Wall Region ◽  
Concentrated Suspensions ◽  
Particle Layer ◽  
Shear Structure ◽  
Homogeneous Regions

Fully three-dimensional numerical simulations of concentrated suspensions of O(1000) particles in a Couette flow at zero Reynolds number are performed with the goal of determining the wall effects on concentrated suspensions of non-colloidal particles. The simulations, based on the force-coupling method, are performed for 0.2 ≤ φ ≤ 0.4 and 10 < Ly/a < 30, where φ denotes the volume fraction and Ly and a are, respectively, the channel height and the particle radius. It is shown that the suspensions can be divided into three regions depending on the microstructures; the wall region where a structured particle layering is dominant, the core region in which the suspension field is quasi-homogeneous, and the buffer region which shows the characteristics of both the particle layer and the shear structure. The width of the inhomogeneous region (wall and buffer) is a function of φ and not sensitive to Ly/a, once Ly/a is larger than a threshold. Rheological properties in the inhomogeneous and quasi-homogeneous regions are investigated. The particle stresses are compared with previous rheological models.

A two-phase thermomechanical theory for granular suspensions

2016 ◽  
Vol 808 ◽  
pp. 410-440 ◽  
Author(s):  
D. Monsorno ◽  
C. Varsakelis ◽  
M. V. Papalexandris
Keyword(s):  
Volume Fraction ◽  
Constant Density ◽  
Two Phase ◽  
Important Special Case ◽  
Carrier Fluid ◽  
Thermomechanical Theory ◽  
Rate Dependent ◽  
Granular Suspensions ◽  
Developed Pressure ◽  
Viscous Stresses

In this paper, a two-phase thermomechanical theory for granular suspensions is presented. Our approach is based on a mixture-theoretic formalism and is coupled with a nonlinear representation for the granular viscous stresses so as to capture the complex non-Newtonian behaviour of the suspensions of interest. This representation has a number of interesting properties: it is thermodynamically consistent, it is non-singular and vanishes at equilibrium and it predicts non-zero granular bulk viscosity and shear-rate-dependent normal viscous stresses. Another feature of the theory is that the resulting model incorporates a rate equation for the evolution of the volume fraction of the granular phase. As a result, the velocity fields of both the granular material and the carrier fluid are divergent even for constant-density flows. Further, in this article we present the incompressible limit of our model which is derived via low-Mach-number asymptotics. The reduced equations for the important special case of constant-density flows are also presented and discussed. Finally, we apply the proposed model to two test cases, namely, steady shear flow of a homogeneous suspension and fully developed pressure-driven channel flow, and compare its predictions with available experimental and numerical results.

Effects of porosity on the thermal properties of a 380-aluminum alloy

1999 ◽  
Vol 14 (10) ◽  
pp. 3901-3906 ◽  
Author(s):  
A. Manzano Ramírez ◽  
F. J. Espinoza Beltrán ◽  
J. M. Yáñez-Limón ◽  
Yuri V. Vorobiev ◽  
J. González-Hernández ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Aluminum Alloy ◽  
Thermal Diffusivity ◽  
Specific Heat ◽  
Volume Fraction ◽  
Maxwell Model ◽  
Phase System ◽  
Image Analyzer ◽  
Two Phase ◽  
Alloy Matrix

Effective values of the thermal diffusivity, specific heat, and thermal conductivity of a porous 380-aluminum alloy prepared by melting in a gas-fired furnace, were determined as a function of the volume fraction of porosity. For that, photoacoustic, differential calorimetric, density, and image analyzer measurements were done. Thermal conductivity and specific heat capacity decrease with the increase of porosity, whereas the thermal diffusivity shows less dependence. Among the effective models for analysis of the thermal conductivity of a two-phase system, the Maxwell model best fits the experimental data, implying a homogenous distribution of the pores in the aluminum-alloy matrix.

On the Problem of “Two-Phase” Activated Sludge

1991 ◽  
Vol 24 (7) ◽  
pp. 59-64 ◽  
Author(s):  
R. W. Szetela
Keyword(s):  
Activated Sludge ◽  
Single Phase ◽  
Phase System ◽  
Two Phase ◽  
Wastewater Treatment Process ◽  
Sludge Stabilization ◽  
Technological Advantage ◽  
In Series ◽  
State Models ◽  
Activated Sludge Systems

Steady-state models are presented to describe the wastewater treatment process in two activated sludge systems. One of these makes use of a single complete-mix reactor; the other one involves two complete-mix reactors arranged in series. The in-series system is equivalent to what is known as the “two-phase” activated sludge, a concept which is now being launched throughout Poland in conjunction with the PROMLECZ technology under implementation. Analysis of the mathematical models has revealed the following: (1) treatment efficiency, excess sludge production, energy consumption, and the degree of sludge stabilization are identical in the two systems; (2) there exists a technological equivalence of “two-phase” sludge with “single-phase” sludge; (3) the “two-phase” system has no technological advantage over the “single-phase” system.

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