Diffusion terminal velocity, effect

An evaluation of the retardation effects of surfactants on the steady velocity of a single drop (or bubble) under the influence of gravity has been made by Levich (L3) and extended recently by Newman (Nl). A further generalization to the domain of flow around an ensemble of many drops or bubbles in the presence of surfactants has been completed most recently by Waslo and Gal-Or (Wl). The terminal velocity of the ensemble is expressed in terms of the dispersed-phase holdup fraction and reduces to Levich s solution for a single particle when approaches zero. The basic theoretical principles governing these retardation effects will be demonstrated here for the case of a single drop or bubble. Thermodynamically, this is a case where coupling effects between the diffusion of surfactants (first-order tensorial transfer) and viscous flow (second-order tensorial transfer) takes place. Subject to the Curie principle, it demonstrates that this retardation effect occurs on a nonisotropic interface. Therefore, it is necessary to express the concentration of surfactants T, as it varies from point to point on the interface, in terms of the coordinates of the interface, i.e.,... 

Usually nozzles can be selected that give a certain average drop size. When this is known, the mass transfer rate can be calculated relatively easily. With eqs. (4.40) and (4.41) the terminal velocity can be calculated (assuming the drops are rigid spheres), so that the contact time can be estimated. The mass transfer within the drops can be described in terms of non-steady state diffusion. When contact times are relatively short, which they normally are, the effect of non-steady state diffusion can be expressed as a mass transfer coefficient, that is time dependent ... 

Support the anemometer sensor probe with a suitable stand so that optimum control of test positions can be maintained. Orient the probe perpendicular to the velocity flow vector being measured. Measure and record the velocity at the approximate center of each filter area of 0.37 m (4 ft ). The probe should be positioned at a distance of no more than 15 cm (6 in.) from the filter face. The effect of nonuniform velocity across the filter face can be minimized by taking more readings per unit area or by using a tube array sensor. Air flow volume test The supply air flow volume is measured by using a flow hood in a manner that includes all of the air issuing from each terminal filter or supply diffuser. The air flow volume test should be performed as follows ... 

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