scholarly journals Surface and subsurface contributions to the build-up of forces on bed particles

2018 ◽  
Vol 851 ◽  
pp. 558-572 ◽  
Author(s):  
Alessandro Leonardi ◽  
D. Pokrajac ◽  
F. Roman ◽  
F. Zanello ◽  
V. Armenio
Keyword(s):  
Mutual Influence ◽  
Subsurface Flow ◽  
Porous Wall ◽  
Industrial Applications ◽  
Solid Particles ◽  
Free Flow ◽  
Spherical Particles ◽  
Large Eddy ◽  
Lift Forces ◽  
Surface And Subsurface Flow

In nature and in many industrial applications, the boundary of a channel flow is made of solid particles which form a porous wall, so that there is a mutual influence between the free flow and the subsurface flow developing inside the pores. While the influence of the porous wall on the free flow has been well studied, less well characterized is the subsurface flow, due to the practical difficulties in gathering information in the small spaces given by the pores. It is also not clear whether the subsurface flow can host turbulent events able to contribute significantly to the build-up of forces on the particles, potentially leading to their dislodgement. Through large eddy simulations, we investigate the interface between a free flow and a bed composed of spherical particles in a cubic arrangement. The communication between surface and subsurface flow is in this case enhanced, with relatively strong turbulent events happening also inside the pores. After comparing the simulation results with a previous experimental work from a similar setting, the forces experienced by the boundary particles are analysed. While it remains true that the lift forces are largely dependent on the structure of the free flow, turbulence inside the pores can also give a significant contribution. Pressure inside the pores is weakly correlated to the pressure in the free flow, and strong peaks above and below a particle can happen independently. Ignoring the porous layer below the particle from the computations leads then in this case to an underestimation of the lift forces.

scholarly journals HYDRODYNAMIC FEATURES OF SUSPENSIONS AND EMULSIONS FLOWS.

2021 ◽  
Vol 2 (446) ◽  
pp. 99-104
Author(s):  
S.R. Rasulov ◽  
G.R. Mustafayeva
Keyword(s):  
Gas Flow ◽  
Fine Particles ◽  
Mutual Influence ◽  
Transport Coefficients ◽  
Spherical Particles ◽  
Scientific Article ◽  
Two Phase ◽  
Real Picture ◽  
Turbulent Gas Flow ◽  
Gas Pulsations

This scientific article is devoted to the problems associated with the flow of suspensions and emulsions and some simplifications of the real picture of the flow of a polydisperse medium are made. It is also stipulated that differential equations characterizing the motion of suspensions and emulsions should take into account the fundamental discontinuity of the medium and the physicochemical processes of heat and mass transfer occurring in it. Taking into account all these factors, a general equation for multiphase systems is proposed with certain simplifications that do not change. The behavior of particles in two-phase systems, their concentration, collision and coagulation are considered. As a result, it was concluded that there is a multifactorial interaction and mutual influence of both phases in a dispersed flow. A differential equation of motion of a single i-th spherical particle in suspension was proposed, and an equation describing the drag force of a solid spherical particles. Equations of conservation of mass and momentum are presented for one-dimensional laminar motion of two incompressible phases in a gravity field with the same pressure in the phases. Having studied the parameters of the flow of fine particles in a turbulent gas flow, some assumptions were made. It was found that the pulsating motion of particles, performed by them during one period of gas pulsations, can be represented as a change in the pulsating gas velocity in time. The parameter of entrainment of particles by a pulsating medium is an important characteristic in determining the transport coefficients in a turbulent flow. It is concluded that the presence of various kinds of particles in the liquid complicates the problem of solving hydromechanical problems in turbulent and laminar flow, and the assumptions given in the work facilitate the study of this problem.

Raman-Microsampling Technique Applying Optical Levitation by Radiation Pressure

1984 ◽  
Vol 38 (1) ◽  
pp. 78-83 ◽  
Author(s):  
R. Thurn ◽  
W. Kiefer
Keyword(s):  
Radiation Pressure ◽  
Optical Potential ◽  
Solid Particles ◽  
Spherical Particles ◽  
Exciting Light ◽  
Potential Wells ◽  
Ion Laser ◽  
Optical Levitation ◽  
Argon Ion ◽  
Microprobe Technique

We report on a new Raman microprobe technique where micron-sized solid particles are trapped in stable optical potential wells using only the force of radiation pressure from a continuous gas laser. We demonstrate this technique with Raman spectra from spherical and non-spherical particles of sizes ranging between 10–30 μm. The particles are stably supported by a vertical directed focused TEM00-mode cw argon ion laser of ∼500 mW. The latter simultaneously serves as the exciting light source. Several suggestions for improvements of this technique are made.

Experimental and Computational Investigation of an Air Core Inside a Milling Circuit Hydroclone

2017 ◽  
Author(s):  
J. R. Kadambi ◽  
C. Shingote ◽  
R. Ke ◽  
Z. Tian ◽  
J. Furlan ◽  
...  
Keyword(s):  
Flow Field ◽  
Flow System ◽  
Industrial Applications ◽  
Solid Particles ◽  
Test Fluid ◽  
Multiphase Model ◽  
Phase Flow ◽  
Computational Results ◽  
Number Range ◽  
Air Core

Hydrocyclone separators are widely used in various industrial applications in the oil and mining industries to sort, classify and separate solid particles or liquid droplets within liquid suspensions. Often, studies in the literature have investigated idealized and simplified geometries, which are also typically scaled down to very small sizes. In this study, the two phase flow system inside a transparent acyclic model with actual milling circuit cyclone hydraulics was investigated computationally and experimentally. The diameter and height of the hydrocyclone are 12.7 cm and 94 cm, respectively. In many industrial applications, a single phase flow system in a hydrocyclone is a rarity, since nearly all cyclones have an underflow which is open to atmosphere, and therefore an air core is present along the central axis. In this study, the flow field with an air core present has been investigated. The computational modelling was conducted using Star CCM+, a commercial Computational Fluid Dynamics (CFD) software package. Large Eddy Simulation (LES) and the Volume of Fluid multiphase model was used. Additionally, the computational studies also focused on the prediction of the dimensions of the air core, which were measured experimentally. The tests were conducted in the Reynolds number range of 20,000–150,000 and 9000–67,800 for the water and NaI solution respectively. The model hydrocyclone was made of optically transparent acrylic plastic with flat, smooth outer surfaces so that there were no reflections, distortions, or obstructions. Refractive index matching, to minimize refraction effects, between the test fluid and acrylic test piece was achieved using a test liquid of sodium iodide aqueous solution (63.3% NaI by weight). Images of the flow field with the air core were taken using a Canon DSLR camera. A comparison between the experimental data and the computational results were made in the r-z plane. The experimental results and the computational results will be discussed in this paper.

Turbulence Characteristics in a Rushton Stirring Vessel Measured via Time Resolved DPIV

2006 ◽  
Author(s):  
Michael R. Brady ◽  
Demetri P. Telionis ◽  
Pavlos P. Vlachos
Keyword(s):  
Experimental Studies ◽  
Turbulent Energy ◽  
Industrial Applications ◽  
Solid Particles ◽  
Analytical Models ◽  
Frequency Resolution ◽  
Time Resolved ◽  
Turbulence Characteristics ◽  
Stirred Vessels ◽  
Rushton Impeller

Stirred vessels are devices that find extensive industrial applications particularly in mineral and chemical industries. Interactions of solid particles and/or bubbles and particles depend on the characteristics of turbulent flow. In many analytical models, the rate of collision is a function of turbulence dissipation. It has been known that dissipation levels are much higher in the neighborhood of the agitating mechanism, in our case the Rushton impeller. In this paper we use time-resolved DPIV to measure the velocity field with a spatial resolution down to 100 μm, and a frequency resolution of 500 Hz. The range of Reynolds numbers investigated varied from 20,000 to 50,000, with the smallest Kolmogorov length scale of about 15 μm. The flow in the impeller stream of a Rushton impeller can be best summarized as a radial jet with a pair of convecting tip vortices. The turbulence quantities were found by removing the periodic component from the blade passing, which is the dominant part of the measured velocities. Dissipation was calculated from the velocity gradients, and assuming isotropy. We provide further evidence that larger dissipation values in the vicinity of the impeller are consistent with the dynamic motion generated by the blade passage. This is somewhat anti-intuitive, because energy is dissipated at the smallest eddy scales, and the immediate vicinity of the impeller contains large vortical structures and provides little space or time for such structures to break down. The maximum and mean normalized dissipation in the impeller stream showed decreasing trends with the Reynolds number. Other normalized turbulence quantities, namely Vrms and in plane vorticity are presented. Our experiments agree very well with other experimental studies. Estimates of turbulence characteristics and in particular distributions of turbulent energy dissipation determined in this study will be used in estimating rates of collisions of bubbles and particles in stirred vessels.

LES of Particle-Laden Flow With Inter-Particle Collisions

2003 ◽  
Author(s):  
Mikhael Gorokhovski ◽  
Anna Chtab
Keyword(s):  
Gas Flow ◽  
Particle Interaction ◽  
Solid Particles ◽  
Particle Interactions ◽  
Particle Collisions ◽  
Cpu Time ◽  
Eddy Simulation ◽  
Preferential Concentration ◽  
Large Eddy ◽  
Particle Laden Flow

By analogy with kinetic approach, the gas-solid turbulent flow was considered as an ensemble of interacting both stochastic liquid and solid particles. In this way, the motion equation for the solid particle along a smoothed trajectory has been derived. To close this equation, the statistical temperature of particles has been introduced and expressed by statistical properties of turbulence. The smoothed particles dynamics was then computed along with large-eddy simulation (LES) of turbulent channel gas flow with “two-way” coupling of momentum. The calculated results are compared with the experiment of Kulick et. al. (1994) and with computation of Yamomoto et. al. (2001), where the inter-particle interaction has been simulated by hard-sphere collisions with prescribed efficiency. It has been shown that our computation with smoothed motion of particle is relatively in agreement with experiment and computations of Yamomoto et. al. (2001). At the same time, the model presented in the paper has a following advantage: it, practically, does not require an additional CPU time to account for inter-particle interactions. The turbulence attenuation by particles and the preferential concentration of particles in the low-turbulence region have been shown.

Effect of Stress Wave Scattering at the Liquid-Particle Interface on Viscosity Calculation of Nanocolloidal Dispersions

2008 ◽  
Author(s):  
Tao Wang ◽  
Xinwei Wang ◽  
Haiping Hong ◽  
Zhongyang Luo ◽  
Kefa Cen
Keyword(s):  
Particle Size ◽  
Autocorrelation Function ◽  
Stress Wave ◽  
Wave Scattering ◽  
Volume Fraction ◽  
Solid Particles ◽  
Spherical Particles ◽  
Computational Domain ◽  
Liquid Particle ◽  
Pressure Tensor

In this work, extensive equilibrium molecular dynamics simulations are conducted to study the shear viscosity of nanocolloidal dispersion. Strong oscillation of the pressure tensor autocorrelation function is observed. The computational domain contains solvent of liquid argon at 143.4 K and spherical particles with volume fraction of 3%. By studying the effect of the particle size, particle density, and acoustic impedance, it is found for the first time that the stress wave scattering/reflecting at the liquid-particle interface due to acoustic mismatch plays a critical important role in the oscillation of pressure tensor autocorrelation function. The Brownian motion/vibration of solid particles is considered to have little effect on the oscillation of pressure tensor autocorrelation function curve except the frequency. And when the particle size is comparable with the wavelength of stress wave, the diffraction of stress wave happens at the interface that will also weaken the oscillation of pressure tensor autocorrelation function.

Sign in / Sign up

Export Citation Format

Share Document