Immiscible Jets Research Articles

On the near-field interfaces of homogeneous and immiscible round turbulent jets

Quantifying accidental opaque discharges is a challenging task, since probing beyond their visible interfaces may be difficult or impossible. In this case, we show that the visible interface features near the jet exit can be used to gauge the flow. This work examines the interface in the near-field features of submerged homogeneous and immiscible turbulent jets. Experiments were carried out with water jets and immiscible silicone oil jets of two viscosities in a water tank. The jet Reynolds numbers are in the range of $Re\sim 4500{-}50\,000$ for homogeneous water jets and $Re\sim 3500{-}27\,000$ for silicone oil jets in water. The jet fluids are made visible by doping with fluorescent dye and excitation with directional illumination. The jet interfaces are continuous and convoluted for water jets, while convoluted and discontinuous with droplets and ligaments for oil jets. Direct flow visualization, schlieren photography, shadowgraph photography and particle image velocimetry are employed as appropriate. Interface length scales are characterized using various image processing techniques. Droplet sizes are quantified using Hough transformation. Interface length scales decrease with Reynolds number and increase gradually with distance from the exit plane for a given Reynolds number. These scales are isotropic for the homogeneous water jets and exhibit a streamwise-to-cross-stream ratio of approximately 1.3 for the oil jets. Interfacial tension, hence the Weber number, determines the average droplet size in the immiscible jets.

Collisions of drops with an immiscible liquid jet

The collisions of a drop stream with an immiscible jet are experimentally studied revealing the formation of several complex structures classified in four main regimes. When neither the drops nor the jet fragment,``drops in jet'' are observed that could be hardened to produce advanced fibers.

Refractive index matched visualization and particle image velocimetry measurements of initial breakup of turbulent oil jet

Subsurface oil well blowouts create buoyant, immiscible jets and plumes. Turbulent breaks jets into oil droplets with sizes ranging from several millimeters to sub-microns. The fate of oil droplets largely depends on their sizes. The physics of single thread of fluid breaks into several smaller droplets in low Reynolds number and Ohnesorge number can be well explained by Plateau-Rayleigh instability. However, when Reynolds number and Ohnesorge number are high, namely the atomization regime, the physics of high-speed jet fragments into a wide range of droplets is not well understood. Because of the opaque nature of crude oil, it is difficult to visualize and optically quantify the process of initial jet breakup and droplet generation within the zone of flow establishment (less than 10 nozzle diameters downstream). In order to overcome this issue, in this experimental study, two immiscible fluids (silicone oil, 64% v/v sugar water solution) with a matching index of refraction of nD=1.4015 are used as surrogates of crude oil and seawater. High speed visualization and particle image velocimetry (PIV) are implemented to study vertical turbulent oil jets of varying Reynolds and Ohnesorge numbers, all falling in the atomization range. The refractive index match enables light to pass through the test sample region with little refraction, thus providing undistorted images for flow visualization and quantitative measurements. The kinematic viscosity ratio voil/vaq = 5.64, density ratio ρoil/ρaq = 0.83, and interfacial tension σ = 28.8 mN/m between silicone oil and sugar water solution are closely matched with those of crude oil and seawater. Entrainment of the aqueous phase by the high speed oil jet can be clearly shown by PIV. Using fluorescent dye in the oil phase, jet fragmentation morphology can be captured simultaneously with PIV images.

Effect of viscosity ratio on the self-sustained instabilities in planar immiscible jets

Previous studies have shown that intermediate surface tension has a counterintuitive destabilizing effect on 2-phase planar jets. Here, the transition process in confined 2D jets of two fluids with varying viscosity ratio is investigated using DNS. Neutral curves for persistent oscillations are found by recording the norm of the velocity residuals in DNS for over 1000 nondimensional time units, or until the signal has reached a constant level in a logarithmic scale - either a converged steady state, or a "statistically steady" oscillatory state. Oscillatory final states are found for all viscosity ratios (0.1-10). For uniform viscosity (m=1), the first bifurcation is through a surface tension-driven global instability. For low viscosity of the outer fluid, there is a mode competition between a steady asymmetric Coanda-type attachment mode and the surface tension-induced mode. At moderate surface tension, the Coanda-type attachment dominates and eventually triggers time-dependent convective bursts. At high surface tension, the surface tension-dominated mode dominates. For high viscosity of the outer fluid, persistent oscillations appear due to a strong convective instability. Finally, the m=1 jet remains unstable far from the inlet when the shear profile is nearly constant. Comparing this to a parallel Couette flow (without inflection points), we show that in both flows, a hidden interfacial mode brought out by surface tension becomes temporally and absolutely unstable in an intermediate Weber and Reynolds regime. An energy analysis of the Couette setup shows that surface tension, although dissipative, induces a velocity field near the interface which extracts energy from the flow through a viscous mechanism. This study highlights the rich dynamics of immiscible planar uniform-density jets, where several self-sustained and convective mechanisms compete depending on the exact parameters.

Extraction in thin liquid films generated by impinging streams

AbstractA new device for liquid–liquid extraction was developed, tested, and modeled, based on two immiscible thin films, flowing one on the top of the other while exchanging mass. The films are formed by impinging streams: collision of two immiscible jets flowing one toward the other on the same axis. Thus, the flow of the films is in a direction perpendicular to the initial flow of the jets. Two liquid systems (diluent–solute–solvent) were tested: water–iodine–kerosene and aqueous solution of HCl–pure water. In the latter case, HCl is transferred from its initial solution comprising one film to the other film of pure water flowing on the top of it. The experiment determined geometrical parameters of the thin film, mass‐transfer coefficients of the solute between the films, as well as power input. For a relatively identical power input, the measured mass‐transfer coefficients were higher by a factor of 10–200 compared to conventional devices. In addition, the mean residence time in the new device is shorter than in conventional devices due to minimal dispersion of the phases during the extraction stage, making the settling stage relatively simple and short.