scholarly journals Tunable fall velocity of a dense ball in oscillatory cross-sheared concentrated suspensions

2014 ◽  
Vol 746 ◽  
Author(s):  
Frédéric Blanc ◽  
Elisabeth Lemaire ◽  
François Peters
Keyword(s):  
Strain Amplitude ◽  
Volume Fraction ◽  
Particle Volume Fraction ◽  
Small Strain ◽  
Concentrated Suspensions ◽  
Particle Volume ◽  
Fall Velocity ◽  
Brownian Particles ◽  
Ball Velocity ◽  
Neutrally Buoyant

AbstractThe fall velocity of a dense large ball in a suspension of neutrally buoyant non-Brownian particles subjected to horizontal oscillatory shear is studied. As the strain amplitude is increased, the velocity increases up to a maximum value before decreasing to the value that it would have in a resting suspension. The higher the frequency is, the stronger the effect is. The falling ball velocity can be largely increased in the presence of the oscillatory cross-shear flow. For instance, for a particle volume fraction of $\varPhi =0.47$ it reaches four times the value it has in the unsheared suspension. At small strain amplitudes, it turns out that the velocity of the falling ball is determined by a balance between the steady drag flow, which drives the apparent suspension viscosity toward a high value, and the oscillatory cross-shear, which lessens it. A simple model is proposed to explain the experimental observations at small strain amplitude. The velocity decrease observed at larger amplitude is not completely understood yet.

The motion of Brownian particles and sediment on an inclined plate

1997 ◽  
Vol 337 ◽  
pp. 25-47 ◽  
Author(s):  
A. A. DAHLKILD
Keyword(s):  
Volume Fraction ◽  
Particle Density ◽  
Particle Volume Fraction ◽  
Present Theory ◽  
Brownian Diffusion ◽  
Inclined Plate ◽  
Particle Volume ◽  
Hindered Settling ◽  
Brownian Particles ◽  
And Migration

The gravitational settling of a homogeneous suspension of Brownian particles on an inclined plate is considered. The hindered settling towards the wall and the viscous, buoyancy-driven bulk motion of the sediment are considered assuming steady conditions and accounting for the effects of Brownian diffusion, shear-induced diffusion and migration of particles due to a gradient in shear stress. Generally, the results show the development of a sediment boundary layer where the settling towards the wall is balanced by Brownian diffusion at the beginning of the plate and by shear-induced diffusion further downstream. Compared to previous results in the literature, the present theory allows steady-state solutions for extended values of the plate inclination and particle volume fraction above the sediment; upon reconsidering the case with non-Brownian particles, a new similarity solution, with a stable shock in particle density, is developed.

Spreading of the interface at the top of a slightly polydisperse sedimenting suspension

1988 ◽  
Vol 196 ◽  
pp. 107-134 ◽  
Author(s):  
Robert H. Davis ◽  
Mark A. Hassen
Keyword(s):  
Volume Fraction ◽  
Particle System ◽  
Particle Volume Fraction ◽  
Thin Sheet ◽  
Small Degree ◽  
The Self ◽  
Light Extinction ◽  
Concentrated Suspensions ◽  
Particle Volume ◽  
Hindered Settling

The interface at the top of a dilute sedimenting suspension of small particles which are not identical does not remain sharp but instead becomes increasingly diffuse as the sedimentation proceeds. For more concentrated suspensions, the self-sharpening effect of hindered settling leads to a considerable reduction in the observed spreading of the sedimenting interface. In order to quantify this spreading, a light extinction technique was used to measure the concentration profile in the interface of a suspension of particles with a small spread of sizes as it fell past a thin sheet of light. A particle volume-fraction range of 0.002 ≤ Φ0 ≤ 0.15 was examined, and each fluid-particle system had a particle Reynolds number less than 10−3 and a Péclet number greater than 107 so that inertia and colloidal effects were negligible. Calculations of the spreading arising from the small degree of polydispersity in particle sizes and the self-sharpening effect are presented. Surprisingly, the measured vertical thickness of the interface was found to be several times that predicted from this theory.It is proposed that the observed spreading may be attributed to hydrodynamic interactions between particles that lead to fluctuations in particle settling velocities about the mean. An analysis of the data shows that the measured interface thickness, after subtracting off that predicted from polydispersity and self-sharpening, increases approximately with the square root of the settling distance and may therefore be described as a diffusion process, termed ‘self-induced hydrodynamic diffusion’. By sealing the hydrodynamic diffusivity as $D = au_{\frac{1}{2}}\hat{D}(\Phi_0)$, where u½ is the median hindered settling velocity, a is the median particle radius, and Φ0 is the volume fraction of particles well below the interface, an approximate analysis of the data was used to infer that the dimensionless scaled diffusion coefficient, $\hat{D}$, is between 1 and 2 for the smaller particle volume fractions examined, increases very rapidly with increasing concentration to a value between 10 and 15 for particle concentrations of a few percent by volume, and then levels off or declines slightly as the particle concentration is increased further.

scholarly journals Finite-sized rigid spheres in turbulent Taylor–Couette flow: effect on the overall drag

2018 ◽  
Vol 850 ◽  
pp. 246-261 ◽  
Author(s):  
Dennis Bakhuis ◽  
Ruben A. Verschoof ◽  
Varghese Mathai ◽  
Sander G. Huisman ◽  
Detlef Lohse ◽  
...  
Keyword(s):  
Volume Fraction ◽  
Laser Doppler Anemometry ◽  
Particle Volume Fraction ◽  
Marginal Effect ◽  
Particle Volume ◽  
Rigid Spheres ◽  
Velocity Fluctuations ◽  
Torque Measurements ◽  
Taylor Couette ◽  
Neutrally Buoyant

We report on the modification of drag by neutrally buoyant spherical finite-sized particles in highly turbulent Taylor–Couette (TC) flow. These particles are used to disentangle the effects of size, deformability and volume fraction on the drag, and are contrasted to the drag in bubbly TC flow. From global torque measurements, we find that rigid spheres hardly decrease or increase the torque needed to drive the system. The size of the particles under investigation has a marginal effect on the drag, with smaller diameter particles showing only slightly lower drag. Increase of the particle volume fraction shows a net drag increase. However, this increase is much smaller than can be explained by the increase in apparent viscosity due to the particles. The increase in drag for increasing particle volume fraction is corroborated by performing laser Doppler anemometry, where we find that the turbulent velocity fluctuations also increase with increasing volume fraction. In contrast to rigid spheres, for bubbles, the effective drag reduction also increases with increasing Reynolds number. Bubbles are also much more effective in reducing the overall drag.

Simulation study of particle clouds in oscillating shear flow

2018 ◽  
Vol 852 ◽  
pp. 484-506
Author(s):  
Amanda A. Howard ◽  
Martin R. Maxey
Keyword(s):  
Strain Amplitude ◽  
Volume Fraction ◽  
Normal Direction ◽  
Streamwise Direction ◽  
Large Role ◽  
Single Body ◽  
Brownian Particles ◽  
Force Coupling ◽  
Induced Flow ◽  
Neutrally Buoyant

Simulations of cylindrical clouds of concentrated, neutrally buoyant, suspended particles are used to investigate the dispersion of the particles in an oscillating Couette flow. In experiments by Metzger & Butler (Phys. Fluids, vol. 24 (2), 2012, 021703) with spherical clouds of non-Brownian particles, the clouds are shown to elongate at volume fraction $\unicode[STIX]{x1D719}=0.4$ but form ‘galaxies’ where the cloud rotates as a single body with extended arms when $\unicode[STIX]{x1D719}>0.4$ and the ratio of the cloud radius to particle radius, $R/a$, is sufficiently large. The simulations, which use the force coupling method, are completed for $\unicode[STIX]{x1D719}=0.4$ and $\unicode[STIX]{x1D719}=0.55$, with $R/a$ between $5$ and $20$. The cloud shape for $\unicode[STIX]{x1D719}=0.4$ is shown to be reversible at low strain amplitude, and extend in the streamwise direction along the centre of the cloud at moderate strain amplitude. For higher strain amplitude the clouds extend near the channel walls to form a parallelogram. The results demonstrate that the particle contact force determines the transition between these states and plays a large role in the irreversibility of the parallelograms. Rotating galaxies form at $\unicode[STIX]{x1D719}=0.55$ with $R/a\geqslant 15$, and are characterized by a particle-induced flow in the wall-normal direction.

scholarly journals Pinch-off of a viscous suspension thread

2018 ◽  
Vol 852 ◽  
pp. 178-198 ◽  
Author(s):  
Joris Château ◽  
Élisabeth Guazzelli ◽  
Henri Lhuissier
Keyword(s):  
Viscous Fluid ◽  
Interstitial Fluid ◽  
Volume Fraction ◽  
Particle Volume Fraction ◽  
Spherical Particles ◽  
Ohnesorge Number ◽  
Particle Volume ◽  
Neutrally Buoyant ◽  
Neck Diameter ◽  
Thinning Rate

The pinch-off of a capillary thread is studied at large Ohnesorge number for non-Brownian, neutrally buoyant, mono-disperse, rigid, spherical particles suspended in a Newtonian liquid with viscosity $\unicode[STIX]{x1D702}_{0}$ and surface tension $\unicode[STIX]{x1D70E}$. Reproducible pinch-off dynamics is obtained by letting a drop coalesce with a bath. The bridge shape and time evolution of the neck diameter, $h_{\mathit{min}}$, are studied for varied particle size $d$, volume fraction $\unicode[STIX]{x1D719}$ and liquid contact angle $\unicode[STIX]{x1D703}$. Two successive regimes are identified: (i) a first effective-viscous-fluid regime which only depends upon $\unicode[STIX]{x1D719}$ and (ii) a subsequent discrete regime, depending both on $d$ and $\unicode[STIX]{x1D719}$, in which the thinning localises at the neck and accelerates continuously. In the first regime, the suspension behaves as an effective viscous fluid and the dynamics is solely characterised by the effective viscosity of the suspension, $\unicode[STIX]{x1D702}_{e}\sim -\unicode[STIX]{x1D70E}/{\dot{h}}_{\mathit{min}}$, which agrees closely with the steady shear viscosity measured in a conventional rheometer and diverges as $(\unicode[STIX]{x1D719}_{c}-\unicode[STIX]{x1D719})^{-2}$ at the same critical particle volume fraction, $\unicode[STIX]{x1D719}_{c}$. For $\unicode[STIX]{x1D719}\gtrsim 35\,\%$, the thinning rate is found to increase by a factor of order one when the flow becomes purely extensional, suggesting non-Newtonian effects. The discrete regime is observed from a transition neck diameter, $h_{\mathit{min}}\equiv h^{\ast }\sim d\,(\unicode[STIX]{x1D719}_{c}-\unicode[STIX]{x1D719})^{-1/3}$, down to $h_{\mathit{min}}\approx d$, where the thinning rate recovers the value obtained for the pure interstitial fluid, $\unicode[STIX]{x1D70E}/\unicode[STIX]{x1D702}_{0}$, and lasts $t^{\ast }\sim \unicode[STIX]{x1D702}_{e}h^{\ast }/\unicode[STIX]{x1D70E}$.

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.

Sign in / Sign up

Export Citation Format

Share Document