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Liquid-Liquid Extraction
Published in John J. McKetta, Unit Operations Handbook, 2018
The conclusions drawn from studies of single-droplet behavior cannot necessarily be directly applied to a population of droplets as exists in a practical liquid-liquid contactor.The flow field of each droplet is affected by the fields of adjacent droplets, and also mass transfer may promote coalescence between droplets, thereby changing the hold-up and drop size distribution. Concentration profileswithin the column can be severely affected by the entrainment of one phase in the main flow of the other. Furthermore, the Reynolds numbercannot be relied on as the sole criterion fordetermining the circulation conditions in a droplet. Heavy contamination with surfactants may reduce internal circulation, forexample, whereas mild interaction of the droplets with each other or packing elements will improve mixing. These and otherconsiderationsclearIy point to the need forspecific Iaboratorydata with real solutions.
General Considerations
Published in Arthur H. Lefebvre, Vincent G. McDonell, Atomization and Sprays, 2017
Arthur H. Lefebvre, Vincent G. McDonell
A typical spray includes a wide range of drop sizes. Some knowledge of drop size distribution is helpful in evaluating process applications in sprays, especially in calculations of heat or mass transfer between the dispersed liquid and the surrounding gas. Unfortunately, no complete theory has yet been developed to describe the hydrodynamic and aerodynamic processes involved when jet and sheet disintegration occurs under normal atomizing conditions, so that only empirical correlations are available for predicting mean drop sizes and drop size distributions. Comparison of the distribution parameters in common use reveals that all of them have deficiencies of one kind or another. In one the maximum drop diameter is unlimited; in others the minimum possible diameter is zero or even negative. So far, no single parameter has emerged that has clear advantages over the others. For any given application the best distribution function is one that is easy to manipulate and provides the best fit to the experimental data.
Molecular Description of Heterophase Polymerization
Published in Hugo Hernandez, Klaus Tauer, Heterophase Polymerization, 2021
Drops of different sizes have different chemical potentials. Thus, there are two ways to increase the stability of an emulsion. First, in order to reach thermodynamical stability, the drop size distribution of an emulsion must be monodisperse. Second, the amount of hydrophobe per drop must be adjusted according to the drop size. However, both ways are practically impossible to realize. Miniemulsion polymerization is also favored when the monomers have a very low solubility in the aqueous phase. This way, polymerization is expected to occur mainly inside the original monomer droplets, without the formation of new particles in the continuous phase.
Investigation of airflow onto uncooled and cooled perpendicular substrates for bioaerosol sampling
Published in Aerosol Science and Technology, 2023
Zhixiong Song, Hassan Ali Abid, Eric Shen Lin, Jian Wern Ong, Md. Hemayet Uddin, Kenneth Margo, Oi Wah Liew, Tuck Wah Ng
A pertinent situation to consider is the behavior of DWC when the substrate temperature is lowered. In theory, DWC is expected to occur on cooled surfaces as well. Since this is generally demarcated by the drops assuming relatively uniform sizes as they form and grow, determining the size distributions of the drops will provide better insights. Experimentally, analysis of drop size distribution was performed by measuring the overhead area of a specific drop located closest to the center of the plate. This measurement is then repeated on 69 other drops that are located closest to the original drop. Figure 11 presents histograms of the size distributions found when the plate was kept at 25 and 4 °C and at 5- and 10-min timepoints after the flow of humid air onto the substrate was initiated. In the analysis of drops collected in the region along one edge of the plate, one drop located next to the edge was first selected and its overhead area determined. This measurement was then repeated on 69 other drops that are located closest to the original drop. Figure 12 similarly presents histograms of the size distributions uncovered under the same plate temperature conditions and air flow timepoints.
Computational Fluid Dynamics Modelling to Predict Axial Dispersion in Pulsatile Liquid-liquid Two-phase Flow in Pulsed Sieve Plate Columns
Published in Solvent Extraction and Ion Exchange, 2021
Nirvik Sen, K.K. Singh, A. W. Patwardhan, K.T. Shenoy
Turbulence has been modelled by using the mixture k-ε model in which the turbulence equations are solved for the mixture as a whole. This approach reduces the number of equations to be solved, as turbulence equations are not solved for each phase. One major limitation of most of the previous studies on CFD simulations of PSPCs is the assumption of monodispersed drops. With this assumption, the information on coalescence and redispersion of droplets, which are continuously taking place inside the column, is lost. Thus, the local drop dynamics is not captured with the assumption of monodispersed droplets. In our recent work, we had addressed this issue and coupled population balance equations (PBE) along with flow and turbulence equations to do away with the assumption of monodispersed droplets.[39] Local drop size distribution in a liquid–liquid dispersion depends on local velocity, breakage and coalescence rates of droplets. Breakage and coalescence rates, in turn, depend on physical properties of the phase system considered, local turbulent energy dissipation rate and dispersed phase holdup. This physics is captured by the population balance equations. A method of classes has been used and one drop number density conservation equation has been solved for each class of drops (class diameter L) in a computational cell. The pulsing action is introduced into the computational model using an user-defined function. The relevant governing equations are summarized in Table 1 .
Impact of mixed surfactant composition on emulsion stability in saline environment: anionic and nonionic surfactants
Published in Journal of Dispersion Science and Technology, 2023
Yue Zheng, Eduard A. Caicedo-Casso, Cole R. Davis, John A. Howarter, Kendra A. Erk, Carlos J. Martinez
The emulsion stability against coalescence and coarsening was evaluated by visualization and measuring oil drop size distributions over 20 days. Emulsions containing 500 ppm surfactant and 5 wt.% of mineral oil (surfactant to oil ratio (SOR): 0.01) were stable against coalescence and coarsening for more than 20 days regardless of surfactant ratios. As shown in Figure 5a and 5b, the drop size distribution curves did not change significantly, suggesting strong emulsion stability. Macroscale photographs (Figure S3) of the creaming layers were taken to ensure there was no large oil droplet uncaptured by laser diffraction measurements. There was no obvious coalescence or formation of large oil droplet.