This study addresses the effectiveness of constant and pulsed DC fields in promoting coalescence of dispersed water drops in an oil-continuous phase. For this purpose, a train of drops of relatively uniform size is injected into a stream of flowing sunflower oil. This stream is then admitted to a coalescing section, where an electric field is applied between a pair of ladder-shape bare electrodes. The capability of this device to enhance coalescence of droplets in a chain is investigated at different field intensities, frequencies and waveforms. The effect of the initial inter-droplet separation distance on the process performance is also addressed under constant DC fields. The dominant coalescence mechanism is found to be due to dipole-dipole interaction at low field strength, whereas electrophoresis becomes predominant at higher field strength. Experiments reveal the existence of an optimal frequency, where the average droplet size enlargement is maximized, especially at low field strengths. The droplet size at the outlet of the coalescer is also found to be dependent on the field waveform.
The complex mechanism by which homogeneous mixtures of two solids achieve fluidization is subjected to theoretical analysis, to elaborate relationships capable to provide their ''initial'' and ''final fluidization velocity'' u if and u ff , i.e., the limits that encompass the suspension process. The article shows how the equation that describes the force equilibrium of fluidization can be rewritten in forms that account for the distribution of the components of density-or size segregating mixtures during the transition to the fluidized state. This approach leads to the theoretical expression of u if and u ff of either type of system, whose differences of behavior are correctly reproduced by accounting for the voidage reduction typical of beds of particles of different size. The comparison with experimental results at varying mixture composition demonstrates that the equations give a coherent interpretation of the dependence of the fluidization velocity interval of two-solid mixtures on the principal variables of interest.
in Wiley Online Library (wileyonlinelibrary.com).Fluidization of binary beds of dissimilar solids has place along a fluidization velocity interval bounded by the ''initial'' and the ''final fluidization velocity'' of the mixture, with segregation phenomena that continuosly change the internal distribution of its components. Varying with the relative importance of size and density differences between components, the fluidization process may follow more than one mechanism, depending on whether the process of fluidization starts from bed top or bottom. It is shown how, irrespective of the fluidization pattern exhibited by the two-solid system, the limiting velocities of its fluidization interval can be calculated with good accuracy by the same relationships, derived from the analysis of the fluidization force equilibrium. The model proposed provides a unique theoretical frame for the analysis of the fluidization behavior of any twosolid system and encompasses as a particular case the behavior of simpler mixtures, whose components differ only in density or size.
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