Single Drop Formation Research Articles

Drop formation at submerged nozzles: Comparison of aqueous dispersed and organic dispersed cases for TBP-dodecane and nitric acid system

Abstract Understanding the phenomena of formation of single drops is necessary to understand the hydrodynamics in solvent extraction equipment which are used for separation of nuclear materials. In this work, the phenomena of aqueous phase and organic phase drop formation at submerged nozzles are compared by conducting experiments with 30%TBP (v/v) in dodecane as the organic phase and nitric acid as the aqueous phase. Two different nozzles and three different nitric acid concentrations are used. For each nozzle and nitric acid concentration, velocity of the dispersed phase is varied. Drops of aqueous phase formed at downward oriented nozzles submerged in organic phase are observed to be smaller than the drops of organic phase formed at upward oriented nozzles submerged in aqueous phase. Correlations to estimate drop diameter are proposed.

Mass transfer enhancement through Marangoni instabilities during single drop formation

The impact of Marangoni convection on the extraction efficiency during the drop formation stage is investigated in the system toluene/acetone/water for different initial solute concentrations and different drop diameters. Both mass transfer directions of the solute have been considered. Marangoni instabilities are supposed to increase the internal mixing and thus enhance mass transfer coefficients. Experimental results show a strong dependency on the mass transfer direction. The amount of solute extracted is between 19% and 55%. The total transferred mass M A increases with drop diameter and initial concentration. Present models from the literature which predict extraction efficiencies do not take into account interfacial effects like Marangoni convection. A correlation is proposed introducing an effective diffusivity which depends on the initial solute concentration. The diffusivity factor increases linearly with initial solute concentration and is more sensitive in the mass transfer direction c → d.

Observations on single drop formation from a capillary tube at low flow rates

The formation of organic drops from a capillary into a static water phase is studied experimentally at low flow rates (50–500 μl/min) using a high-speed video camera. Four different stages of the drop formation are identified and various geometric parameters, such as current contact angle (angle of the interface with the top capillary wall), drop height, neck length, mean drop growth velocity and drop wetted diameter on the top capillary wall are measured. It is found that the changes in current contact angle during the formation process follow different trends which coincide with different stages of drop formation. The attaching and detaching forces which act on the drop during formation are calculated based on the experimentally measured parameters. It is found that by using the current contact angle on the interfacial tension force calculation, the forces balance for most of the period of drop formation until the drop detachment stage.

Adsorption Kinetics of Oxyethylated Polyglycol Ethers at the Water−Nonane Interface

A special measuring cell modifies the maximum bubble pressure tensiometer MPT1 to a drop volume apparatus which allows us to analyze the stability of the formation of single drops and to detect instabilities as observed recently in the form of drop volume bifurcations. This modified apparatus was used to study the adsorption kinetics of different Tritons (X-45, X-100, X-165, and X-405) at the water−nonane interface. The results of the measured dynamic interfacial tensions for long adsorption times are fully in line with a diffusion-controlled adsorption model. The short adsorption time data show adsorption rates faster than expected from diffusion, which may be caused by reorientation processes of the Triton molecules at low interfacial coverage. The experiments performed under different conditions (Triton dissolved in water, in nonane, or in both phases, respectively) allow us to estimate the distribution coefficient of the Tritons between water and oil, which increases with a decrease in the number of EO groups.

Numerical analysis of a single drop formation process under pressure pulse condition

In order to obtain the detailed information on mechanism of the motion of a single droplet formation process in the pulsed sieve-plate column, the numerical analysis for transient behavior is carried out by using VOF (volume of fluid) method, and their results are compared with the experimental results. On the assumption that the essential shape of the pressure pulse added to the system can be described numerically by a simple sine wave, the numerical results agree approximately with the real drop formation process. The mechanism of the fluid flow inside and outside a drop can be clear from the obtained numerical results, and it is found that there is a circulation flow inside a drop. Furthermore, it is confirmed that VOF technique is useful and efficient as the method for tracking boundary interfaces and can predict numerically well the transient behavior of the drop with liquid-liquid interfaces.

HIGH-FREQUENCY SINGLE DROP FORMATION: PHENOMENOLOGY AND THE EFFECT OF SURFACTANTS

The phenomenology of high-frequency single drop formation from a capillary in air has been studied for single liquids and surfactant solutions. Attention has been given mostly to the region of high flow rates, close to the transition from single drops to a continuous jet. At these flow rates, periodicity and “chaotic” behavior have been elucidated in terms of the drop volume. A linear correlation between the transition flow rate and γD/ρ has been observed, where γ and ρ are the surface tension and density of the liquid, and D is the diameter of the capillary. This correlation may be useful for monitoring surface tension variations in continuous processes, and for estimating dynamic surface tensions of surfactant solutions, for surface ages of about 10-50 msec. An appreciable effect of the surfactant concentration on the transition flow rate has been noted within a certain concentration range. The CMC values of the surfactants fall in this range, an observation which suggests a new possible approach to the...

Formation of single charged drops in a non-uniform electric field.

Formation of single drops in a non-uniform electric field is studied for water drops in the atmosphere and in three kinds of dielectric liquids. Theoretical equations are derived for the volume and the electric charge of the formed drop and corresponding experiments were performed in a range of applied electric potential of 0-7.5 kV. It was clarified that measured drop volumes agree well with theoretical values for systems of liquid-gas and liquid-liquid. The experimental drop charges are not satisfactorily represented by theoretical analysis, but are well evaluated by a semi-empirical equation presented here.

Remarks on single drop formation

A brief discussion of available information on the description of single drop formation at a moderate formation rate as well as on the related determination of the volume of drops formed is presented. Experimental results obtained by authors of this paper were compared with most of earlier published relationships recommended for the calculation of drop volume. Some of the possible causes of discrepancies between experimental and calculated values are discussed.

Dispersion of Liquid from an Orifice. Noniterative Prediction of Exit Velocity at Transition from Single Drop Formation to Jet Injection

Dispersion of Liquid from an Orifice. Noniterative Prediction of Exit Velocity at Transition from Single Drop Formation to Jet Injection

Drop formation from liquid jet ejected from a rotating nozzle.

Stability theory is applied to the liquid jet ejected from a rotating nozzle, and the breakup length and the drop size are analyzed. By the ejection of water, methanol and aqueous glycerol solution from a nozzle rotating at 250-1450 rpm, the breakup length and drop size were measured. As the liquid velocity increases, the single drop formation, laminar, and turbulent jet are observed. The laminar breakup length increases with the increase of the liquid velocity and the rotating velocity. The diameter of drops formed from the laminar jet increases with the increase of the liquid velocity and decreases with the increase of the rotating velocity. Predictions show a good agreement with experimental data of breakup length and drop size.

A note on residual drop and single drop formation

Volume ratios of the residual and detached parts of drops, determined experimentally are compared with those predicted theoretically by Lohnstein.

Experimental study of mass transfer during single drop formation, release and fall

Mass transfer from a single drop during formation, release and fall has been measured using radiotracer technique. The transfer during release is of the order of magnitude of that during formation. Results indicate that drop circulation, present during the entire life of the drop, intensifies abruptly at a short distance from the nozzle.

Mass transfer during single drop formation

It is shown that five different mechanisms of mass transfer in forming drops and bubbles which have been proposed in the literature, for a sphere growing uniformly with time, can be described by the equation: ▪ where N A is the mass transferred from the drop or bubble in time t, and d f is the drop diameter at the end of the formation period t f . Depending on the particular mechanism the constant assumes different numerical values ranging from 6 7 to 24 7 . The validity of the different mechanisms has been tested by measuring mass transfer from drops formed at a nozzle tip at different rates. Sodium iodide (Na 131I) was extracted from single water drops into isobutyl alcohol and the mass transferred was measured by a radiotracer technique. Drop formation and withdrawal times were varied independently and mass transfer during the formation time was obtained by extrapolation. The results yielded a mean value of 1·32 ± 0·24 (95 per cent confidence level) for the constant which substantiates the value of 1·31 predicted by Ilcovic's mechanism.