Experimental study of the sedimentation of dilute and semi-dilute suspensions of fibres

1999 ◽  
Vol 384 ◽  
pp. 133-158 ◽  
Author(s):  
BENJAMIN HERZHAFT ◽  
ÉLISABETH GUAZZELLI
Keyword(s):  
Aspect Ratio ◽  
Volume Fraction ◽  
Particle Volume Fraction ◽  
Complex Function ◽  
Orientation Distribution ◽  
Particle Volume ◽  
Mean Velocity ◽  
Aspect Ratios ◽  
Dilute Suspensions ◽  
Orientation Distributions

Steady-state velocity and orientation distributions of sedimenting fibres were measured as a function of particle concentration and aspect ratio. Two different regimes of sedimentation were clearly identified. For dilute suspensions, the fibres tend to align in the direction of gravity with occasional flipping and clump together to form packets. In this regime, the vertical mean sedimentation speed is not hindered and can be larger than the Stokes' velocity of an isolated vertical fibre. Its scaling is a complex function of particle volume fraction and aspect ratio. As the concentration is increased, the fibres still tend to orient in the direction of gravity. The mean velocity becomes hindered and scales with particle volume fraction. The velocity fluctuations were found to be large and anisotropic. They were found to increase with increasing volume fraction. A similar substantial anisotropy of the orientation distribution was observed for all particle concentrations and aspect ratios studied.

Evaporating Meniscus of Ethanol and Ethanol-Based Nanofluids in Single Micro-Channels

2013 ◽  
Vol 390 ◽  
pp. 685-690
Author(s):  
Yuan Wang ◽  
Khellil Sefiane ◽  
Zhen Guo Wang
Keyword(s):  
Heat Flux ◽  
Aspect Ratio ◽  
Evaporation Rate ◽  
Volume Fraction ◽  
Particle Volume Fraction ◽  
Particle Volume ◽  
Cross Sectional ◽  
Stick Slip ◽  
Micro Channels ◽  
Sink Effect

Evaporating meniscus of ethanol and ethanol-based nanofluids (0.01vol.%) in micro-channels were experimentally studied. Visualisation and thermographic results of the stationary meniscus confined in high-aspect-ratio rectangular micro-channels (hydraulic diameters are 571 μm, 727 μm and 1454 μm, channel cross sectional aspect ratio is 20, 20, 10 respectively) were obtained. It was found that interface evaporation rate increases with heat flux. The meniscus interface becomes deformed when the evaporation rate increases. The use of nanofluids largely enhances the interface stability even though the particle volume fraction is at a very low level. Besides, a stick-slip and back-jump behaviour of the nanofluids meniscus was captured during the transition from stable to deformed interface. Moreover, sink effect at the liquid-vapour interface was discussed based on the IR results.

scholarly journals Apparent yield stress in rigid fibre suspensions: the role of attractive colloidal interactions

2016 ◽  
Vol 802 ◽  
pp. 611-633 ◽  
Author(s):  
S. Bounoua ◽  
E. Lemaire ◽  
J. Férec ◽  
G. Ausias ◽  
A. Zubarev ◽  
...  
Keyword(s):  
Yield Stress ◽  
Volume Fraction ◽  
Particle Volume Fraction ◽  
Van Der Waals ◽  
Simple Shear Flow ◽  
Average Particle ◽  
Particle Volume ◽  
Friction Forces ◽  
Aspect Ratios ◽  
Fibre Suspensions

This work is focused on the modelling of the shear and normal stresses in fibre suspensions that are subjected to a simple shear flow in the presence of short-range lubrication forces, van der Waals and electrostatic forces, as well as solid friction forces between fibres. All of these forces are weighed by the contact probability. The theory is developed for attractive fibres with van der Waals interaction dominating over electrostatic repulsion. The model predicts a simple Bingham law for both the shear stress and the first normal stress difference, with the apparent shear and normal yield stresses proportional to the second and the third power of the particle volume fraction respectively. The model is applied to the experimental data of Rakatekar et al. (Adv. Mater., vol. 21, 2009, pp. 874–878) and Natale et al. (AIChE J., vol. 60, 2014, pp. 1476–1487) on suspensions of carbon nanotubes dispersed in a Newtonian epoxy resin. It reproduces well the quadratic dependence of the apparent yield stress on the particle volume fraction $(\unicode[STIX]{x1D70E}_{Y}\propto \unicode[STIX]{x1D719}^{2})$ for average particle aspect ratios of $r=160$ and 1200, while it underpredicts the power-law exponent for $r=80$ (always predicting $\unicode[STIX]{x1D719}^{2}$ behaviour instead of $\unicode[STIX]{x1D719}^{3.2}$).

Rheology of a Suspension of 1000 Liquid Capsules in Channel Flow

2008 ◽  
Author(s):  
Prosenjit Bagchi ◽  
R. Murthy Kalluri ◽  
Sai K. Doddi
Keyword(s):  
Channel Flow ◽  
Volume Fraction ◽  
Particle Volume Fraction ◽  
Particle Surface ◽  
Constitutive Law ◽  
Particle Volume ◽  
Mean Velocity ◽  
Transform Method ◽  
Liquid Drops ◽  
Deformable Particles

Three-dimensional numerical simulations are presented on the motion of large ensembles of deformable particles (up to 1096 in number) in a channel flow at small inertia. Particles are modeled as capsules, that is, liquid drops surrounded by elastic membranes. Unlike liquid drops where the fluid-fluid interface is characterized by isotropic surface tension, that of a capsule is governed by more complex constitutive laws. Here we assume that the capsule membrane follows the neo-Hookean constitutive law. The particle volume fraction considered is up to 29%. The numerical methodology is based on a mixed finite-difference/Fourier transform method for the flow solver and a front-tracking method for fluid/membrane interaction. In the simulations, the flow field is resolved using up to 288×288×288 grid points, and each particle surface is resolved by 1280 triangular elements. The simulations are computation- and data-intensive, and the first of their kind in the context of deformable capsule suspension. The database generated from the simulations provides a wealth of information on the dynamics of semi-dense suspension of liquid capsules, in particular, and of deformable particles, in general. Preliminary results on flow visualization, particle trajectory, deformation, mean velocity and suspension viscosity are presented.

Hydrodynamic and boundary-layer dispersion in bidisperse porous media

1999 ◽  
Vol 385 ◽  
pp. 359-379 ◽  
Author(s):  
KONSTADINOS N. MOUTSOPOULOS ◽  
DONALD L. KOCH
Keyword(s):  
Boundary Layer ◽  
Porous Media ◽  
Volume Fraction ◽  
Particle Volume Fraction ◽  
Effective Diffusivity ◽  
Packed Bed ◽  
Present Calculation ◽  
Particle Volume ◽  
Mean Velocity ◽  
Molecular Diffusivity

The small grains in a bidisperse porous medium have the greater influence on the permeability, while the large grains are more effective in dispersing chemical tracers. We compute the dispersion induced by a dilute array of large spheres in a Brinkman medium whose permeability is determined by the radii and volume fraction of the small spheres. The effective diffusivity contains a purely hydrodynamic contribution proportional to Ua1ϕ1 and an O(Ua1ϕ1 ln (Ua1/D)) contribution from the mass transfer boundary layers near the spheres. Here, U is the mean velocity in the medium, a1 and ϕ1 are the radii and volume fraction of the large spheres and D is the molecular diffusivity. The boundary-layer dispersion is small when the Brinkman screening length κ (or square root of permeability) is much smaller than a1, but is important for κ[ges ]O(a1). Experimental results for the dispersion due to flow through a bidisperse packed bed are reported and compared with the theoretical predictions. In addition to its application to bidisperse porous media, the present calculation allows an extension of Koch & Brady's (1985) analysis of monodisperse fixed beds to include higher-order terms in the expansion for small particle volume fraction.

scholarly journals Performance improvement of double-tube gas cooler in CO2 refrigeration system using nanofluids

2015 ◽  
Vol 19 (1) ◽  
pp. 109-118 ◽  
Author(s):  
Jahar Sarkar
Keyword(s):  
Performance Improvement ◽  
Volume Fraction ◽  
Particle Volume Fraction ◽  
Cooling Capacity ◽  
Inlet Temperature ◽  
Refrigeration Cycle ◽  
Particle Volume ◽  
Transcritical Carbon Dioxide ◽  
The Given ◽  
Theoretical Analyses

The theoretical analyses of the double-tube gas cooler in transcritical carbon dioxide refrigeration cycle have been performed to study the performance improvement of gas cooler as well as CO2 cycle using Al2O3, TiO2, CuO and Cu nanofluids as coolants. Effects of various operating parameters (nanofluid inlet temperature and mass flow rate, CO2 pressure and particle volume fraction) are studied as well. Use of nanofluid as coolant in double-tube gas cooler of CO2 cycle improves the gas cooler effectiveness, cooling capacity and COP without penalty of pumping power. The CO2 cycle yields best performance using Al2O3-H2O as a coolant in double-tube gas cooler followed by TiO2-H2O, CuO-H2O and Cu-H2O. The maximum cooling COP improvement of transcritical CO2 cycle for Al2O3-H2O is 25.4%, whereas that for TiO2-H2O is 23.8%, for CuO-H2O is 20.2% and for Cu-H2O is 16.2% for the given ranges of study. Study shows that the nanofluid may effectively use as coolant in double-tube gas cooler to improve the performance of transcritical CO2 refrigeration cycle.

A simulation and experimental study on particle volume fraction of PMMA suspension in centrifugal fields

2021 ◽  
Author(s):  
Yosephus Ardean Kurnianto Prayitno ◽  
Tong Zhao ◽  
Yoshiyuki Iso ◽  
Masahiro Takei
Keyword(s):  
Experimental Study ◽  
Volume Fraction ◽  
Particle Volume Fraction ◽  
Particle Volume

Solidification Processing of Functionally Graded Materials by Sedimentation

1999 ◽  
Author(s):  
J. W. Gao ◽  
S. J. White ◽  
C. Y. Wang
Keyword(s):  
Functionally Graded Materials ◽  
Volume Fraction ◽  
Particle Volume Fraction ◽  
Computer Code ◽  
Functionally Graded ◽  
Particle Volume ◽  
Particle Sedimentation ◽  
Graded Materials ◽  
Free Zone ◽  
Free Region

Abstract A combined experimental and numerical investigation of the solidification process during gravity casting of functionally graded materials (FGMs) is conducted. Focus is placed on the interplay between the freezing front propagation and particle sedimentation. Experiments were performed in a rectangular ingot using pure substances as the matrix and glass beads as the particle phase. The time evolutions of local particle volume fractions were measured by bifurcated fiber optical probes working in the reflection mode. The effects of various processing parameters were explored. It is found that there exists a particle-free zone in the top portion of the solidified ingot, followed by a graded particle distribution region towards the bottom. Higher superheat results in slower solidification and hence a thicker particle-free zone and a higher particle concentration near the bottom. The higher initial particle volume fraction leads to a thinner particle-free region. Lower cooling temperatures suppress particle settling. A one-dimensional solidification model was also developed, and the model equations were solved numerically using a fixed-grid, finite-volume method. The model was then validated against the experimental results, and the validated computer code was used as a tool for efficient computational prototyping of an Al/SiC FGM.

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