Fluid Dispersion

As solvents, the amyl alcohols are intermediate between hydrocarbon and the more water-miscible lower alcohol and ketone solvents. Eor example, they are good solvents and diluents for lacquers, hydrolytic fluids, dispersing agents in textile printing inks, industrial cleaning compounds, natural oils such as linseed and castor, synthetic resins such as alkyds, phenoHcs, urea —formaldehyde maleics, and adipates, and naturally occurring gums, such as shellac, paraffin waxes, rosin, and manila. In solvent mixtures they dissolve cellulose acetate, nitrocellulose, and ceUulosic ethers. 

These humic acids are not dissolved because the pH of this slurry is in the range of 4 to 9. Small amounts of fulvic acids are formed, and these are soluble in the water of the slurry. The coal-derived humic acids find applications as drilling fluid dispersants and viscosity control agents, whereas the coal-derived fulvic acids may be used to produce plasticizers and petrochemicals. 

BASF encapsulates different paraffins with a special process and sells the micro capsules under the brand name Micronal as fluid dispersion or as dried powder (Figure 118). 

Figure 118. Micro encapsulation of paraffin produced by BASF/Germany as fluid dispersion...

Wakao, N. and Funazkri, T. Chem. Eng. Sci. 33 (1978) 1375. Effect of fluid dispersion coefficients on particle-fluid mass transfer coefficients in packed beds. 

Depending on the amount of amine used and on the milling time, the reaction mass either had a pastelike consistency or that of a fluid dispersion. The experiments were intended to establish some parameters (duration of mechanical processing, amount of diamine and complexing agent, etc.) and correlate them to characterize the polymers obtained, and to determine certain chemical and physical properties of the polymer. In all cases, the samples were purified by extraction in a Soxhlet apparatus with water or alcohol to remove unreacted ethylenediamine and metallic salts. The extractions were carried out until constant weight was obtained. Total removal of chloride was determined by silver nitrate. Purified samples were then washed with methanol, dried, and analyzed. 

The T distribution is the generalization of the Poisson one that is also in use [73]. A detailed demonstration of its usefulness for interpretation of the low-frequency magnetic spectra of magnetic fluids (dispersions of nanosize ferroparticles) was given in Ref. 74. 

Ruzicka and Hansen [359] characterized flow injection analysis (FIA) as ... information gathering from a concentration gradient formed from an injected, well-defined zone of a fluid, dispersed into a continuous unsegmented stream... 

No exact general criterion is available when it is necessary to include the relaxation terms in the equations of change however, relaxation terms are necessary for viscoelastic fluids, dispersed systems, rarefied gases, capillary porous mediums, and helium, in which the frequency of the fast variable transients may be comparable to the reciprocal of the longest relaxation time. 

The prospect of using enzymes as heterogeneous catalysts in scC02 media has created significant interest. Their low viscosity and high diffusion rates offer the possibility of increasing the rate of mass-transfer controlled reactions. Also, because enzymes are not soluble in supercritical fluids, dispersion of the free enzymes potentially allows simple separations without the need for immobilization. 

Because of the analogy between simulated and true counter-current flow, TMB models are also used to design SMB processes. As an example, the transport dispersive model for batch columns can be extended to a TM B model by adding an adsorbent volume flow Vad (Fig. 6.38), which results in a convection term in the mass balance with the velocity uads. Dispersion in the adsorbent phase is neglected because the goal here is to describe a fictitious process and transfer the results to SMB operation. For the same reason, the mass transfer coefficient feeff as well as the fluid dispersion Dax are set equal to values that are valid for fixed beds. 

K. B. Bischoff and O. Levenspiel, Fluid Dispersion—Generalization and Comparison of Mathematical Models, Chem. Eng. Sci., Yl 245 (1962). 

Chester AK (1991) The modelling of coalescence processes in fluid-fluid dispersions A review of current understanding. Trans IchemE 69(A) 259-270 Colella D, Vinci D, Bagatin R, Masi M, Bakr EA (1999) A study on coalescence and breakage mechanisms in three different bubble columns. Chem Eng Sci 54 (21) 4767-4777... 

As a rule, the fluid dispersions (emulsions, foams) are stabilized by adsorption layers of amphiphile molecules. These can be ionic and nonionic surfactants, lipids, proteins, etc. All have the property to lower the value of the surface (or interfacial) tension, o, in accordance with the Gibbs adsorption... 

The second factor to consider is the direction of the fluid flow, upward or downward. Upward flow will cause lift of the particle bed at some critical velocity that causes the bed to fluidize. This effect results in an increase in the fluid dispersion within the system and a decrease in performance. Downward flow could cause the particles to be crushed at some point. The allowable velocities for crushing are larger than those for lift, so downward flow is the normal operating condition. 

Note that the Casson model (the third model in Table 6.3) fairly well describes various varnishes, paints, blood, food compositions like cocoa mass, and some other fluid disperse systems [443]. 

In liquid/fluid disperse systems (emulsions, foams for example) the liquid interface is usually covered by an adsorption layer and often imder lateral movement. This movement causes lateral transport along the interface and brings the adsorption layer out of its equilibrium state so that an adsorption/desorption exchange of matter sets in. 

Appendix 3A Sound Propagation in Liquid/Fluid Disperse systems and Chemical Reaction... 

A simplified analysis of the complex viscous flow occurring during this coarsening process can be made by applying Tomotika s findings (25). He analyzed the breakup of an infinite cylindrical thread of one viscous, Newtonian fluid dispersed in a second viscous, Newtonian fluid by a linearized stability analysis. As indicated in Figure 12, breakup occurs by the exponential growth of certain infinitesimal transverse disturbances. Tomotika found that the dominant disturbance assumes a minimum value of,... 

The subject matter will frequently be concerned with situations where the fluid contains a dispersed phase that cannot be considered a component—for example, macromolecules, rigid particles, or droplets. In these cases the continuum approximation is assumed to hold within the suspending fluid and the dispersed phase. The concentration of the rigid or fluid dispersed phase will encompass both dilute and concentrated suspensions. 

Colloidal Crystalline Arrays Colloidal spheres of silica and of polymers can be made relatively monodisperse, with standard deviations of 4% of the mean diameter for silica and 1% for polymer latexes. The spheres pack as shown in Figure 11.22a from fluid dispersions into fee (sometimes hep or bcc) colloidal crystals (CC) by gravity, by membrane filtration, or by capillary forces at the surface of an evaporating dispersion (80-82). The crystalline order of the materials is strictly at the length scale of the packed colloidal particles the packing of the atoms and molecules within the silica and polymer particles is totally amorphous. The CCs diffract... 

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