FEDSM2006-98306 NUMERICAL SIMULATION OF A CONTAMINATED DROPLET BY FRONT-TRACKING METHOD TAKING THE EFFECT OF SURFACTANT TRANSPORT ON THE INTERFACE

ABSTRACT In this study, a front-tracking (FT) method combined with a solver of interfacial transport of surfactant was proposed in order to resolve interfacial flows affected by contamination. In the FT method, because the interfaces are presented explicitly, advection-diffusion equation on the interface can be easily treated and can be solved highly accurately. In this study, a scheme which conserves the total amount of surfactant completely was constructed. Numerical simulations of a water drop sinking in silicone oil were performed taking the Marangoni effect into account. The effects of three parameters, a damping coefficient of interfacial tension, a diffusion coefficient and a total amount of surfactant, were evaluated. Calculated results were compared with PTV measurement results and were in very good agreement with them on the points of stagnant cap size, flow separation point, peak of shear stress and so on. So, we can expect that our simulations can estimate the conditions of surfactant on the interfaces, which is very difficult to be measured

PTV Measurement at Close Region to Interface of a Water Drop in Oil

Velocity distributions adjacent to the interface between a water-drop and surrounding oil were measured using PTV. By analyzing the measured velocity data the physical properties such as surface slip conditions, circulating flow in a drop, distributions of contamination skin, are quantitatively obtained.Relating to the heat and mass transfer in multi-phase flows, information about microscopic phenomena occurred at the interface of fluids has been estimated so far from macroscopic measurements. Difficulties to directly measure the phenomena on the interface come from their special conditions of moving boundaries, transient, and spatially distributed phenomena. Most of those difficulties can be resolved by the PTV technique. Since it is the quantitative visualization method, only if some of those phenomena can visually captured, it is not difficult to obtain a part of the required information

Three-dimensional X-ray micro-velocimetry

Three-dimensional X-ray velocimetry with micrometer-level resolution is demonstrated

Binary Correlation Method for 2D・PTDand its Application to Two Cylinder Interaction Flow

This study deals with fluctuating interaction flows around two circular cylinders arrayed in tandem arrangement. After the flows are visualized by a hydrogen bubble tracer technique，the two-dimensional particle tracking velocimetry (2D-PTV) based on binary correlation method is applied to measure the flow velocities of the whole field. Using the results of instantaneous and time mean velocity vectors，vorticity contours, streamlines and root mean square values of the fluctuating velocities，the analysis and discussions on the flow fields are made

Gas-Liquid Mass Transfer in Simulated Turbulent Wake Flow

In materials engineering, gas injection processes are frequently adopted to remove impurities such as oxygen and carbon. There are two types of gas dispersion patterns formed above the nozzle; bubbling and jetting. The former is realized when the gas velocity at the nozzle exit vn, is lower than the speed of sound, c, while the latter is realized for vn≧c and a gas column is formed on the nozzle. This column disintegrates into many bubbles with different diameters above a certain distance from the nozzle exit. Many bubbles are therefore generated in the molten metal bath regardless of the bubbling and jetting. The removal of impurities is closely associated with the dissolving rate of the gas into the bath. However, under such a highly turbulent condition it is difficult to evaluate the mass transfer coefficient between the bubbles and molten metal because the precise evaluation of the interfacial area is actually impossible. As the gas flow rate increases, mass transfer at the gas-liquid interface increases. However, it is not clear whether the mass flux at the gas-liquid interface is attributed to the enhancement of the interfacial are A or to the enhancement of the mass transfer coefficient k. Accordingly, previous researchers introduced the volumetric mass transfer coefficient defined as kA/V, where V is the bath volume. In a series of studies on gas injection, the authors have tried to elucidate the contributions of the interfacial area and the mass transfer coefficient to the volumetric mass transfer coefficient. The mass transfer coefficient at a gas-liquid interface exposed to two types of liquid jets shown in Figs. 1(a) and 1(b) were measured. CO2 gas was supplied with a syringe into a top lance to form a gas-liquid interface at the exit of the top lance. Accordingly, the gas-liquid interfacial area can be measured with sufficient accuracy. The flow fields around the gas-liquid interface thus exposed to the two types of jets are models for the flow fields around the top and side of a bubble rising in ha highly turbulent flow field. In this study the gas-liquid interface was exposed to a turbulent wake flow, as shown in Fig. 1(c). This study therefore is intended to clarify the mass transfer coefficient at the rear part of a bubble