Drop Hydrodynamics Behaviours In Liquid Liquid Dispersion Systems

The phenomenon of liquid-liquid contacting is often encountered in industrial processes such as energy, environmental protection, biology, papermaking, food, medicine, and cosmetics, etc. Taking absorption, distillation, flotation and extraction as examples, the liquid-liquid dispersion is achieved by dispersing the dispersion phase into the continuous phase in the form of drops, which is very important in equipment design.Previous researches on liquid-liquid dispersions were mostly focusing on the macro-kinetics of a large number of drops in the macroscopic reactors. However, the fluid mechanisms between a single or dual drops and the continuous phase were not fully understood. Deep understanding of single drop dynamic behaviors plays an important role in investigating the drop swarms and complex system in practical applications and designing the meso-scale multi-phase flow reactors. In order to obtain a universal applicability of single drop dynamics behaviors, as well as the critical conditions of the drops coalescence and breakage, the single and conjunct drops hydrodynamic behaviors, two drops interaction and a single drop breakup in the jet flow were investigated systematically by using high-speed camera and PIV measurement. The purpose is to provide the basic data and models for the further study of complex liquid-liquid reaction systems and the numerical simulation.In the section of the hydrodynamics and deformations of a single drop rising in Newtonian fluids, the diameters of single drops varied from 1.9 to 11.1 mm, the shape, terminal rising velocity, and trajectory oscillation of the oil drops were systematically investigated in seven continuous phases with different viscosity ratios. The terminal velocity of the drops with deformation is slightly different from those without deformation in the high viscosity system. Compared with the correlations reported in the literature, a semi-empirical approach developed by Grace et al. (1976) shows a good prediction for drops rising in the range of moderate Reynolds numbers (Re<80) when the drop diameter is smaller than 5.4 mm. Our results for drag coefficient are consistant with the study of Rodi et al. (2002) at Re<80, and the minimal value of the drag coefficient is found at Re of 360. By analyzing the rising trajectories of the drops, the maximal response frequency versus the drop diameter can be well expressed. We also obtain the spectra of deformation ratio (E). The maximal deformation frequency is naturally equal to the maximal oscillation frequency when the drop sizes are the same. The instantaneous 2D PIV measurements of the surrounding liquid flow field identify the regions of the vortex trail. It is found that the wake behind a drop is asymmetrical and unstable, implying that the characteristics of drop wake may impact on the oscillation of drops.In the research of hydrodynamic and motion of a single drop and conjunct drops rising in glycerol-water solutions, of which the viscosity of the continuous phase ranging from 0.132 to 1.11 Pa·s and the Morton number ranging from 0.009679 to 51.40, the effect of Bond Number (Bo) and the equivalent diameter ratio (λ) for dual drops collisions in six different concentrations glycerol-water solutions have been formulated, covering four possible situations, namely, coalescence, slip & separation, slip & conjunction and non-slip conjunction. The existence of the slip & conjunct drops was a kind of metastable state during the process of two drops interaction and the rising velocities obtained by experiments for both the single drop and conjunct drops with the same equivalent diameter are similar. The Rodriguez (2001) correlation (K=20) fits well with the drag coefficients of various drop sizes in terms of the single drop and conjunct drops. The transverse oscillation frequencies of the single drop and conjunct drops with the similar equivalent diameters have the same tendency. With the decreasing viscosity of the continuous phase, the average maximal response frequencies of two drops increase gradually. The instantaneous 2-D PIV measurements of the surrounding liquid flow field identify the regions of the vortex trail. The shapes of the wake behind the single drop and conjunct drops are different but the length are the same, and the wake velocity of the conjunct drops is slightly higher than that of the single drop.In the research of the interactions between two in-line drops rising in the pure glycerin, the velocity, shape, drag coefficient and the lateral oscillation between two in-line rising drops during their approaching process were systematically measured and analyzed. The geometric feature method and the energy change method were proposed to judge the starting and ending times of the approaching process between two drops. A conical wake model was applied to calculate the drag coefficient during the approaching process, where the drag coefficient of the leading drop decreases with the increase of time or Reynolds number. And the drag coefficient of the trailing drop will first decrease, then remain unchanged and finally increase due to the existence of an equilibrium distance. The transverse oscillation frequencies of two drops have the same trend during the approaching process.In the experiment of the single drop breakup in jet flow, the parameters of shape, deformation, rising velocity and acceleration of the drop were obtained by high-speed camera, and the flow fields of the jet flow were measured by PIV with fluorescent tracer particles. Results show that in order to describe the interaction between turbulent structures and the motion of the liquid-liquid interfaces directly, the deformations of drop are separated into three scales. Impacts of the flow shear rate on broken positions are discussed. The drop breakup often forms a lot of fragments, and the role of the flow characteristics in determining the numbers of daughter drops are considered.