Behavior Of Spherical Particles Research Articles

Behavior of spherical particles in colloidal gel in shear flow

Behavior of spherical particles in colloidal gel in shear flow

Influence of flight shape on discharging profiles of granular material in rotary dryer

In this work, Discrete Element Method (DEM) is used in order to calculate the motion of granular material in rotating dryers. We are particularly interested in analysing the effect of flight shape on the behaviour of spherical particles in the cross section of the dryer. We will be using two segments flights and three different profiles : a straight flight (180° between both segments), an angled flight (with an angle of 120°) and a rightangled flight (90°). The results show that the profile of the flight affects significantly the motion of the particles in the cross section of the dryer. Changing the angle between the segment’s flight, changes the flight loading and thus the material hold-up which leads to different discharging profiles of the flight. For a right angled flight, the range of the discharge angle increases leading to a more uniformized cascade pattern in time and an enlarging of the area occupied by the curtains of particles. The specific durations (discharging time, falling time) are also determined and studied as a function of the flight shape.

Spherical particle dynamics at oscillations in tubes in the shock wave field

The behavior of spherical particles with various geometric and physical parameters is experimentally investigated at the stimulated longitudinal gas oscillations in closed and opened tubes as well as in the external wave field near subharmonic resonances. The temporal dependences of the oscillating particle coordinate are obtained for different tube lengths and excitement frequencies. It is shown that, inside the tube, a particle moves, performing the longitudinal oscillations, from the opened end to the piston. Outside the tube, a particle moves from the opened end to the external wave field, without oscillations and with nonlinear coordinate increase in time. Also investigated is the influence of the particle weight and diameter and of the gas excitement frequency on the oscillation amplitude of the particle and its average velocity. The nonmonotone character revealed the dependence of the average velocity of the spherical particle on the gaseous column oscillation frequency at passing through the subharmonic resonance frequencies.

Effect of Particle Shape on Colloid Retention and Release in Saturated Porous Media

Colloidal particles of environmental concern often have nonspherical shapes. However, theories and models such as the classical filtration theory have been developed based on the behavior of spherical particles. This study examined the effect of particle shape on colloid retention (e.g., attachment and straining) and release in saturated porous media. Two- and three-step transport experiments were conducted in water-saturated glass bead columns using colloids dispersed in deionized water and an electrolyte solution. The particles used in the experiments were carboxylate-modified latex colloids of spherical (500 nm diam.) and rod (aspect ratio, 7.0) shapes. The rod-like particles were prepared by stretching the spherical particles. Analysis of the colloid breakthrough curves indicates that particle shape affected transport behavior, but retention did not increase with increasing aspect ratio. Retention of the spherical particles occurred mainly in the secondary energy minimum, whereas retention of rod-like particles occurred in primary and secondary energy minima. There was less straining of rod-like particles compared with spherical ones, indicating that the minor axis was the critical dimension controlling the process. Release of spherical particles on elution was instantaneous, whereas release of rod-like particles was rate limited, giving rise to long tails, implying an orientation effect for rod-like colloids. The results suggest that the differences in electrostatic properties and shape contributed to the observed different retention and release behaviors of the two colloids.

The Wetting Behavior of Spherical Particles in Narrow Retaining Vessels

The capillarity-driven ascent of liquid through certain elementary assemblies of equal spherical particles held in a neutrally wetted container is considered and the conditions for liquid to flow are established. For flow through the assembly to be possible, critical contact angles of the liquid on the spheres must not be exceeded. These critical angles are considerably lower than the 90° which the Washburn equation predicts. Finally, the effect of sphere size disparity (or polydispersity) is considered in an Appendix. It is shown that wetting of the assembly may be controlled by manipulation of size distributions as well as by change in the contact angle. Experimental evidence in support of these ideas is presented for a two-dimensional array.

Fiber Classification and the Influence of Average Air Humidity

The use of man-made vitreous fibers (MMVFs) as a substitute for asbestos in industrial and residential applications has raised the concerns of the potential hazards associated with inhalable aerosolized fibers. The complex movement of fiber makes it difficult to predict the pattern of fiber deposition in human airways from the behavior of spherical particles. Difficulties in producing monodisperse length fibers has been an obstacle to study fibrous particle deposition in the human respiratory system. To address this problem, a narrow length distribution of fibers was generated using dielectrophoretic classification. Dielectrophoresis is the motion of neutral matter in a nonuniform electric field due to an induced dipole moment. It is sensitive to the conductivity of the matter in the field. A fiber classifier has been used to study the influence of atmospheric humidity on the behavior of glass fibers. Glass fibers, as insulators, can not be classified by the dielectrophoretic classifier. However, our study shows that a humidity higher than 15% RH can change the conductivity of the glass fibers so as to permit their effective classification.

Nematic-Wetted Colloids in the Isotropic Phase

We study the interaction and phase behavior of spherical particles immersed in the isotropic phase of a nematogenic liquid crystal. We find that colloidal stabilization can be achieved by a surface nematic wetting.

Settling and transport of spherical particles in power-law fluids at finite Reynolds number

This paper is concerned with the prediction of critical conditions for the behaviour of particles in simulated oil-drilling fluids. In practice, the rheology of many oil-drilling fluids can be represented adequately by a power-law model and the behaviour of spherical particles can give valuable information on the behaviour of less regularly shaped particles. In this paper, the flow of a power-law fluid past a single sphere located on the axis of a cylindrical pipe is simulated numerically. Two different regimes are considered. In the settling regime, the spherical particle moves through a quiescent fluid. For this regime, drag coefficients for a wide range of power-law indices and particle Reynolds numbers are computed. Power-law indices range from n = 0.4 to n = 1 and Reynolds numbers (based upon the radius of the sphere and the settling velocity) are in the range 0.2 ⩽ Re p ⩽ 100 for sphere/cylinder diameter ratios of 1 30 and 1 50 . An expression is proposed which determines the drag coefficient in power-law fluids as a function of power-law index n and particle Reynolds number Re p. Numerical results are compared with both experimental results and other published numerical results. In the transport regime, the fluid is in motion relative to the pipe and the sphere, so that the fluid in the cylinder is sheared. Drag coefficients in the mid-Reynolds-number range for the transport regime are compared with those obtained in the settling regime. Finally, the numerical results have been presented in the form of two graphs which can be used to predict velocities of particles settling in power-law fluids and also to predict the maximum-sized particle which can be transported upwards by the flow of a power-law fluid.

Angular dispersion of material lines in isotropic turbulence

The existing body of literature on particle transport by turbulent flow has concentrated on the behavior of spherical particles. However, the dispersed phase in several suspensions of industrial interest consists of nonspherical particles, in particular, flexible slender bodies or threads. The present work considers the problem of disorientation of initially aligned material lines in isotropic turbulence, an idealization which serves to test a general model for particle orientation effects in the transport of threads in turbulent flow. Results obtained from the model agree well with data.