Magnitude Of Particle Velocity Research Articles

V-blender segregation patterns for free-flowing materials: effects of blender capacity and fill level

Stable segregation patterns are shown to form in V-blenders over a wide range of vessel capacities, fill levels, and rotation rates. Slight changes in either rotation rate or fill level induce changes in pattern formation. Trajectory segregation in two regions of the flow, accumulating over many flow periods, drives segregation pattern formation. Scaling criteria derived to relate particle velocities to vessel size and rotation rate in rotating cylinders successfully predict the rotation rate for the transition between patterns across V-blenders of 0.8–26.5 quart total capacity. This agreement suggests that pattern formation is governed by the magnitude of particle velocities. Regardless of vessel size, when particle velocities at specific regions of the blender are below a certain value, one particular pattern appears, and when they increase beyond that speed (i.e. by changing the rotation rate or the vessel size), a different pattern emerges. A scaling relation between segregation pattern formation and blender fill level was not identified because the complex flow patterns in the V-blender (the length of the flowing layer and the mixture center of mass relative to the blender are constantly oscillating) preclude the determination of a relationship between blender fill level and particle velocities.

The influence of convection during solidification on fragmentation of the mushy zone of a model alloy

Experiments have been conducted to observe fragmentation events in a model alloy (succinonitrile and acetone) solidifying in the presence of forced convection in the superheated melt. Measurements of fragmentation rates have been made, and an attempt was made to relate the results to the controllable parameters of the system. A microscope-video system recorded the mushy zone-melt interface, and the fragmentation process and fragmentation rates could be determined from a frame-by-frame analysis of the video images. Experiments were conducted for varying cooling rates, overall temperature differences, melt flow rates, and for two different concentrations of acetone (1.3 and 6.1 wt pct). Significant dendritic fragmentation occurred for all runs. In addition, the influence of buoyancy forces is clearly evident from particle motion near the mushy zone-melt interface. Fragmentation rates appear to correlate well with the magnitude of particle velocities near the interface, with increasing fragmentation being associated with higher particle velocity magnitude (either in the same or the opposite direction to the mean flow) for the 1.3 wt pct acetone mixture. However, the correlation is quite different for the higher concentration. The relationship between these results and the possible mechanisms for fragmentation are discussed. Although it appears that either constitutional remelting or capillary pinching are likely of importance, hydrodynamic shear forces or some other mechanism as yet undiscovered cannot be completely discounted, although circumstantial evidence suggests that mechanical shearing is inconsistent with observations made both here and already in published literature. The results provide a step in the development of solidification models that incorporate fragmentation processes in the mushy zone as an important mechanism of grain refinement and a potential source of macrosegregation in ingots and large castings.

Electron-ion collisions in intensely illuminated plasmas

In the presence of a high-frequency intense uniform electric field, the collisions of electrons with ions can be made more frequent or less frequent, depending on the polarization of the hf field, the direction and magnitude of particle velocity, and the ratio of the plasma Debye length to the size of the electron oscillation in the hf field. The stimulated bremsstrahlung emission is calculated for both circularly and linearly polarized fields.

Gravity flow of granular materials round obstacles—I: Investigation of the effects of inserts on flow patterns inside a silo

Triangular and square inserts were placed at different heights within a tall observation bunker of rectangular cross-section. The flow patterns produced by the materials were photographed through the float glass front wall of the bunker. The photographs taken at different exposure times were used to determine particle streamlines, vertical velocity contours and the boundaries of the so-called stagnant zones formed inside the bunkers.Velocity contours within the converging flow zones were compared with the predictions based on the kinematic flow model proposed earlier by the authors. The results presented seem to indicate a dependence of the observed flow fields on the magnitude of particle velocities within the bunker.