Particles In Viscous Medium Research Articles

Propagation of longitudinal waves in a linear viscoelastic medium

The article is devoted to the study of longitudinal wave propagation in a viscoelastic medium. A mathematical model of the problem of a linear viscoelastic medium was developed. The solution to the considered problems is reduced to the solution of a system of differential equations solved by the method of characteristics with the appropriate boundary conditions. The results are compared with known results obtained by other authors; a comparison shows the adequacy of the task posed. It was determined that the maximum values of stress, strain, and velocity of particles in viscous media vary according to a non-linear law. In the initial section of the medium and near it, first, the stress reaches its maximum, and then the strain and velocity of particles reach their maximum values.

Anomalous Viscosity Reduction and Hydrodynamic Interactions of Polymeric Nanocolloids in Polymers

One of the central dogmas of fluid physics is the no-slip boundary condition, whose validity has come under scrutiny, especially in the fields of micro and nanofluidics. Although various studies show the violation of the no-slip condition its effect on flow of colloidal particles in viscous media has been rarely explored. Here we report unusually large reduction of effective viscosity experienced by polymeric nano colloids moving through a highly viscous and confined polymer, well above its glass transition temperature. The extent of reduction in effective interface viscosity increases with decreasing temperature and polymer film thickness. Concomitant with the reduction in effective viscosity we also observe apparent divergence of the wave vector dependent hydrodynamic interaction function of these colloids with an anomalous power law exponent of similar to 2 at the lowest temperatures and film thickness studied. Such strong hydrodynamic interactions are not expected for polymeric colloidal motion in polymer melts. We suggest hydrodynamics, especially slip present at the colloid-polymer interface which determines the observed reduction in interface viscosity and presence of strong hydrodynamic interactions.

A Model To Predict the Concentration of Submicrometer Solid Particles in Viscous Media Confined inside Horizontal Cylindrical Channels

As light oil reserves dwindle, the extraction and processing of heavy crude oils are becoming increasingly important. The use of ultradispersed catalysts (nanometric catalytic particles dispersed in the oil) is considered to be a promising way to upgrade these materials. To simulate such processes, mass transfer of the ultradispersed particles must be estimated. However, an adequate mathematical expression to describe the motion of these particles through viscous media in a horizontal cylindrical channel is still missing. In this paper, we developed and solved a time-dependent, two-dimensional convective−dispersive model, which simulates the transient deposition and suspension of ultradispersed particles immersed in a viscous medium, inside the cross section of a horizontal cylindrical channel in a stagnant situation. The results of the modeling are compared with a series of experiments that permit knowledge of the concentration of the ultradispersed particles inside a horizontal cylinder. These experiments were performed using particles in the submicrometer range (average sizes of 198 nm) and fluid media with diverse densities and viscosities. The effect of the fluid medium properties and the initial particle concentration in the calculation of the dispersion coefficient was also studied. The conditions needed to maintain the solid particles suspended in the liquid medium, contained in a vessel with cylindrical geometry, are also unveiled by the presented model.

Structures on interfaces of mingled magmas, Stewart Island, New Zealand

Strain analysis of magmatic rocks has been attempted using the shapes of enclaves of contrasting magmas and analysis of mineral fabrics. In composite plutonic rocks of the Anglem Complex, Stewart Island, New Zealand, interfaces between different magma types are deformed into fold-like patterns which have the potential to provide new data on strain in magmatic processes. The fold-forms have shorter wavelength and higher amplitude on interfaces at a high angle to layering whereas fold-forms are either absent or of low amplitude on interfaces parallel to layering. The fold-forms may be amplified/de-amplified irregularities or buckle folds, and in either case they indicate shortening perpendicular to rock layering. Whole-rock fabrics of the plagioclase–hornblende–biotite rocks, analysed by shape preferred orientation and centre-to-centre methods, record less intense alignment and strain than predicted by free rotation of particles in viscous media. The inhibition of crystal rotation at high crystal concentrations and the growth of late poorly aligned crystals present difficulties for calibrating whole-rock fabrics with the strain incurred by magmatic flow.

Wall effects on free-settling velocity of non-spherical particles in viscous media in cylindrical tubes

This work sets out to investigate the effect of confining walls on the settling velocity of variously shaped rigid particles in stationary Newtonian liquids. Cubes, parallelepipeds, cylinders, needles, thin plates and circular discs of different sizes and made of different materials (1200–7800 kg/m 3) have been sedimented in scores of liquids in cyclindrical tubes of different inside diameters (20–100 mm). The retardation effect due to the presence of bounding walls has been quantified in terms of a wall factor which is a function only of particle size and shape, and tube diameter in the low Reynolds number region ( <7). Simple expressions are presented that not only correlate well the present results but also describe satisfactorily the scant literature data.

The dispersion patterns of acicular particles in viscous medium

A lattice model of ferrofluid with time dependent viscosity has been developed to simulate the dispersion patterns of interacting fine ferromagnetic particles during the manufacturing process of magnetic recording medium. Closure and chaining of the magnetic particles in uniform magnetic field have been obtained. The length of the chain is dependent on the packing factor. For magnetic particles possessing electric charge, the agglomeration of particles will reduce. The hysteresis corresponding to different patterns are calculated using quasi-dynamic vectorial model.

Three-Dimensional Presentation of Electrostatic Fields by Trajectories

The three-dimensional presentation of electrostatic fields by trajectories of charged slender particles in viscous medium is considered. Some Laplacian fields are presented with charged cotton fibers in air.