Coalescence, effect

The prediction of drop sizes in liquid-liquid systems is difficult. Most of the studies have used very pure fluids as two of the immiscible liquids, and in industrial practice there almost always are other chemicals that are surface-active to some degree and make the pre-dic tion of absolute drop sizes veiy difficult. In addition, techniques to measure drop sizes in experimental studies have all types of experimental and interpretation variations and difficulties so that many of the equations and correlations in the literature give contradictoiy results under similar conditions. Experimental difficulties include dispersion and coalescence effects, difficulty of measuring ac tual drop size, the effect of visual or photographic studies on where in the tank you can make these obseiwations, and the difficulty of using probes that measure bubble size or bubble area by hght or other sample transmission techniques which are veiy sensitive to the concentration of the dispersed phase and often are used in veiy dilute solutions. 

Cross Flow Interceptors employ sloping corrugated plates to provide some coalescing effect and to reduce the effective separtion path. They olso provide effective separation of solids which accumulate at the bottom of the plate pock and can be removed by periodic blow-down. They con ochieve very high separation efficiencies but only when designed for known droplet sizes. 

The second generation model comprised more refined flow analysis, two mechanisms of dispersion (the fibrillation mechanism and a drop splitting mechanism for low supercritical capillary numbers, with the choice of break-up mechanism based on locally computed microrheological criteria), as well as coalescence effects [Huneault et al., 1995a]. The latter effects were taken into account by determining the coalescence constant in Equation 7.117 from the plot shown in Figure 7.18. Thus, the developed model was self-consistent, fully predictive, without any adjustable parameters. 

The particle sizes and size distributions found experimentally are much less favorable than the expected values, probably due to strong coalescence effects during expansion. 

If the modifying agent is in the form of the elemental metal or the metal oxide, hydrous oxide, hydroxide, or other insoluble compound, no problem of coagulation of the silica particles will ordinarily be encountered when it is added to the sol. However, if the metal modifier is in the form of a soluble salt, it it usually desirable to introduce it into the silica sol immediately before the drying step so that the extent to which it can promote coalescence of the silica is minimized. Since the proportion of metal compound is generally quite small the coalescence effect in any event is not very pronounced. 

Prediction of the gas-phase mean and rms velocity fields and the distribution of the liquid axial mass fluxes as predicted by the simulation are in good agreement with the experimental data. Details of these comparisons are provided by Apte et al. [36]. The breakup model does not include coalescence effects. In addition, the effect of injecting different size distributions near the injection must be investigated to address sensitivity of the model parameters to flow conditions. Specifically, size distributions further away from the injector (in the intermediate and dilute regimes) may be influenced by these inlet conditions. 

Pore nucleation density (Nq) is defined as the number of nuclei per cubic centimeter of the precursor (unfoamed) material. In samples in which the coalescence effect can be neglected, this value can be calculated using Eq. (9.5) ... 

Bubble size is expressed in terms of volume rather than diameter. Though the behavior of a single bubble (e.g., terminal rise velocity, drag, shape) is correlated by equivalent diameter, coalescence effects are best treated with volume. Volumes are added in coalescence, regardless of bubble shape, which is seldom spherical in parameter ranges of interest. If necessary, of course, equivalent diameter can be computed from the volume whenever required, but volume remains the primary measure. 

Microrheology considers only individual drops in an infinite sea of the matrix fluid. At concentrations with < )> 0.005, the coalescence effects must be taken into account. Coalescence can be driven either by the thermodynamics (i.e. minimization of the interfacial energy), or by flow (shear coalescence). During compounding the latter type dominates. It has been shown that the dynamic coalescence increases with and thus at equilibrium between dispersion and coalescence the drop diameter can be expressed as [7] ... 

Lamella separators or plate separators where the oil is collected directly by the lower surface of oblique plates and then brought up to the surface. The plates have a dual function. They define very short routes for die droplets and they have a coalescence effect. Both of these functions are due to the close interlamella spacing. 

The coalescence effects have been taken into account. This was accomplished by determining the coalescence kinetic constant in an internal mixer and incorporating its numerical value into the model computations. 

Coalescence rates depend on both dispersed phase concentration and physicochemical factors. Except for strongly coalescing systems, coalescence effects are minimal at concentrations less than 5%. 

When a mixture of materials with different properties, such as oil and water, passes through fine pores, the mixed state becomes unstable and particle size increases by association. This phenomenon is known as the capillary coalescence effect. If the coalesced oil adheres, liquid flow is... 

Coalescence is also affected by the viscosity of the blended polymers a decrease in the matrix viscosity being favorable to coalescence. Several models are now available that predict the final particle size. Among them, the equation proposed by Fortelny et al. is particularly interesting, since it takes into account both the classical theory of phase breakup (first term in the equation) and the coalescence effect (second term in this equation) [62]. 

Fig. 12.13 High-resolution TEM images resulting from phase contrast (with increasing exposure time), showing the Au nanoparticle mobility and coalescence effects induced by the energy of the incident beam in the material. Acquiring the first image for the third (from left to right), the elapsed time was 1 min (Pyrz Butlrey Langmuir. 2008 24 11350-60 (Adapted with permission) [27]...

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