Dispersion viscosity bubbles

For a given geometry of the set-up, the relevance list for this problem contains the power consumption, P, as the target quantity, the stirrer diameter, d, as the characteristic length and a number of physical properties of the liquid and the gas (the latter are marked with an apostrophe) Densities, p and p, kinematic viscosities, v and v, surface tension, a, and an unknown number of still unknown physical properties, S, which describe the coalescence behaviour of finely dispersed gas bubbles and by this, indirectly, their hold-up in the liquid. The process parameters are the stirrer speed, n, and the gas throughput, q, which can be adjusted independently, as... 

As a result, this equation is usually the only one needed for liquid or solid aerosols. Figure 6.18 shows several sets of experimental data compared with the Einstein equation. In practice once cp reaches between 0.1 and 0.5, dispersion viscosity increases significantly and can also become non-Newtonian (due to particle/droplet/bubble crowding or structural viscosity). The maximum volume fraction possible for an internal phase made up of uniform, incompressible spheres is 0.74, although emulsions and foams with an internal volume fraction of over 0.99 can exist as a consequence of droplet/bubble distortion. Figure 6.18 and Equation 6.33 illustrate why volume fraction is such a theoretically and experimentally favoured concentration unit in rheology. In the simplest case, a colloidal system can be considered Einsteinian, but in most cases the viscosity dependence is more complicated. 

If the liquid phase viscosity is too high (greater than approximately 50 cp, for example), the dispersed foam bubbles may not respond well to the applied centrifugal field within the cyclone. Likewise, if the bubbles are too small or form a micro-dispersion , the separation will be ineffective. 

Unlike the liquid/liquid emulsions, dispersions of bubbles cannot be treated as incompressible. The viscosity of a dispersion of bubbles can be written as [6] ... 

Properties of Component Phases As discussed in the preceding subsection, dispersions of gases in liquids are affected by the viscosity of the hquid, the density of the liquid and of the gas, and the interfacial tension between the two phases. They also may be affected directly by the composition of the hquid phase. Both the formation of bubbles and their behavior during their lifetime are influenced by these quantities as weh as by the me(manical aspects of their environment. 

Although it is entirely possible for erosion-corrosion to occur in the absence of entrained particulate, it is common to find erosion-corrosion accelerated by a dilute dispersion of fine particulate matter (sand, silt, gas bubbles) entrained in the fluid. The character of the particulate, and even the fluid itself, substantially influences the effect. Eight major characteristics are influential particle shape, particle size, particle density, particle hardness, particle size distribution, angle of impact, impact velocity, and fluid viscosity. 

Silicones exhibit an apparently low solubility in different oils. In fact, there is actually a slow rate of dissolution that depends on the viscosity of the oil and the concentration of the dispersed drops. The mechanisms of the critical bubble size and the reason a significantly faster coalescence occurs at a lower concentration of silicone can be explained in terms of the higher interfacial mobility, as can be measured by the bubble rise velocities. 

The influence of dispersed-phase viscosity was found to be negligible by Hayworth and Treybal (H5), but found to be significant (K2) when a greater range of dispered-phase viscosity was investigated. From the graph of Hayworth and Treybal, the influence of interfacial tension appears, as in the case of bubbles, to be more at low flow rates than at high flow rates. 

Skeggs innovative step, the introduction of air bubbles into the flowing stream, attempted to minimize the time taken for a steady-state condition to be reached in the detector. The definitive description of dispersion in segmented streams (Snyder [37]) showed a complex relationship between internal diameter, liquid flow rate, segmentation frequency, residence time in the flow system, viscosity of the hquid and surface tension. 

As is known, if one blows air bubbles in pure water, no foam is formed. On the other hand, if a detergent or protein (amphiphile) is present in the system, adsorbed surfactant molecules at the interface produce foam or soap bubble. Foam can be characterized as a coarse dispersion of a gas in a liquid, where the gas is the major phase volume. The foam, or the lamina of liquid, will tend to contract due to its surface tension, and a low surface tension would thus be expected to be a necessary requirement for good foam-forming property. Furthermore, in order to be able to stabilize the lamina, it should be able to maintain slight differences of tension in its different regions. Therefore, it is also clear that a pure liquid, which has constant surface tension, cannot meet this requirement. The stability of such foams or bubbles has been related to monomolecular film structures and stability. For instance, foam stability has been shown to be related to surface elasticity or surface viscosity, qs, besides other interfacial forces. 

A horizontal interface between two fluids such that the lower fluid is the less dense tends to deform by the process known as Rayleigh-Taylor instability (see Section UFA). Spikes of the denser fluid penetrate downwards, until the interface is broken up and one fluid is dispersed into the other. This is observed, for example, in formation of drops from a wet ceiling, and of bubbles in film boiling. For low-viscosity fluids, the equivalent diameter of the particle formed is of order Ja/gAp. 

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