Solids particle arrangement

Students will construct models of four basic crystalline structures, noting the different possibilities for crystalline-solid particle arrangement. 

Solid particles. Let us consider stationary diffusion to two axisymmetric solid particles arranged one after the other on the axis of a translational Stokes flow. We assume that the solid particles are symmetric with respect to some plane z = const (see Figure 4.8) and each of them has only two stagnation points on the surface, which lie on the flow axis (closed streamlines are absent). The surfaces of solid particles completely absorb the solute. 

The following limit relation for the total diffusion fluxes on the surface of two identical solid particles arranged on the axis of a translational Stokes flow (Figure 4.8) was derived in [169] ... 

Filtration. In filtration, suspended solid particles in a liquid or gas are removed by passing the mixture through a porous medium that retains the particles and passes the fluid. The solid can be retained on the surface of the filter medium, which is cake, filtration, or captured within the filter medium, which is depth filtration. The filter medium can be arranged in many ways. 

The unit shown in Figure 4-49 has been used in many process applications with a variety of modifications [18,19,20]. It is effective in liquid entrainment separation, but is not recommended for solid particles due to the arrangement of the bottom and outlet. The flat bottom plate serves as a protection to the developing liquid surface below. This prevents re-entrainment. In place of the plate a vortex breaker type using vertical cross plates of 4-inch to 12-inch depth also is used, (Also see Reference [58].) The inlet gas connection is placed above the outlet dip pipe by maintaining dimension of only a few inches at point 4. In this type unit some liquid will creep up the walls as the inlet velocity increases. 

When separating low-density solid particles or oil droplets from water, the most common method used is dissolved-air flotation. A typical arrangement is shown in Figure 8.12b. This shows some of the effluent water from the unit being recycled, and air being dissolved in the recycle under pressure. The pressure of the recycle is then reduced, releasing the air from solution as a mist of fine bubbles. This is then mixed with the incoming feed that enters the cell. Low-density material floats to the surface with the assistance of the air bubbles and is removed. 

In Figure 21.1, the first division is with respect to flow arrangement. Traditionally, most fixed-bed reactors are operated with axial flow of fluid down the bed of solid particles. A more recent trend is to use radial flow, either outward, as depicted in Figure 21.1, or inward. In the case of styrene monomer production (reaction (D) in Section 21.1), the purpose is to reduce the pressure drop (-AP) by increasing the flow area for a given bed volume. We restrict attention to axial flow in this chapter. 

A semicontinuous reactor for a fluid-solid reaction involves the axial flow of fluid downward through a fixed bed of solid particles, the same arrangement as for a fixed-bed catalytic reactor (see Figure 15.1(b)). The process is thus continuous with respect to the fluid and batch with respect to the solid (Section 12.4). 

In Volume 1, the behaviour of fluids, both liquids and gases is considered, with particular reference to their flow properties and their heat and mass transfer characteristics. Once the composition, temperature and pressure of a fluid have been specified, then its relevant physical properties, such as density, viscosity, thermal conductivity and molecular diffu-sivity, are defined. In the early chapters of this volume consideration is given to the properties and behaviour of systems containing solid particles. Such systems are generally more complicated, not only because of the complex geometrical arrangements which are possible, but also because of the basic problem of defining completely the physical state of the material. 

Amorphous Solid solids with a random particle arrangement... 

These measure turbidity, usually by sensing light scattered at 90° to the direction of the incident light beam. This type of turbidimeter is frequently termed a nephelo-meter or nephelometric turbidimeter. A typical arrangement is shown in Fig. 6.46. The nephelometer is commonly used for detecting solid particles present in water (e.g. waste water) or in air (e.g. smoke). The instrument requires periodic cleaning due to fouling of the optical system. 

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