Liquid Jet Stability in a Laminar Flow Field (original) (raw)
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Chemical Engineering Science, 2015
This work investigates the effects of multiple jet interactions and single jet instability on jet breakup and droplet size using experimental and computational techniques. In particular, the jet separation distance, jet breakup length and droplet diameter were measured as a function of initial nozzle separation distance and jet volumetric flow rate. It was found that the two jets moved closer to each other to reach an equilibrium separation distance that was approximately 70% of the spacing between the two nozzles. The distance at which the instabilities were first observed on the surface of the jet was also a function of the initial separation distance. However, it was weakly dependent on the jet velocity. The jet breakup length and resultant droplet diameter were both influenced by flow rate and nozzle separation distance. The jet breakup length was found to decrease with reduction in nozzle spacing at the high flow rates. Interestingly, a linear relationship between droplet diameter and breakup length was found that was largely independent of nozzle spacing and consist with conventional Rayleigh jet breakup theory. The implications of the experimental observations on the design of multi-jet systems are discussed. Furthermore, computational fluid dynamics simulations were also used to identify the mechanism and dynamics of jet instability in the single jet systems. The simulation results were analysed to study the effect of instability on various parameters such as jet breakup, droplet formation and size of emulsion droplets. It was found that at higher volumetric flow rates, the droplets size increased during the jet breakup due to an asymmetric instability. The asymmetric instability was caused by the pressure gradient in the continuous phase and was prevented in double jet systems.
On the separation of droplets from a liquid jet
Fluid Dynamics Research, 1996
The droplet separation from a liquid jet was investigated experimentally. Details of the shape of the thin liquid neck joining the droplet to its parent body were studied in terms of the fluid viscosity and the jet diameter. As the viscosity increased, the neck rapidly elongated creating a long thread. Its final diameter before rupture was approximately one micrometer and seems to be constant within wide range of parameters varied. One or multiple breakups of the micro-thread were observed, which produced micro-satellites, i.e. droplets in a micrometer range. The experimental results only partly confirmed the predictions of Eggers' (Phys. Rev. Lett. 71 (1993) 3458) similarity solution. The predicted shape of the pinch-off region well overlaps the long thread observed for very viscous liquids. However, the final jet diameter, retraction velocity of the thread and presence of multiple breakups differentiate the experimental evidence from the model expectations.
Behavior of Elongated Liquid Jets in Viscous Liquid-Liquid-Systems
Chemical Engineering & Technology, 2011
The stability of jets in elongational flow is exploited to obtain thin threads before breakup. Fine drops can be generated in suitable geometries with comparably large ducts. The examination deals with the stability of liquid threads simultaneously extended with the continuous phase in convergent flow. Breakup limits and regimes are discussed.
Breakup mode of an axisymmetric liquid jet injected into another immiscible liquid
Chemical Engineering Science, 2006
The breakup of an axisymmetric liquid jet, injected vertically upward from a nozzle into another immiscible liquid, into droplets is studied numerically. The unsteady motion of the interface separating two immiscible fluids is followed by solving the Navier-Stokes equations for incompressible and Newtonian fluids in axisymmetric cylindrical coordinates with a Front-Tracking method. The evolution of the interface and the specific surface area of the droplets are in good agreement with experimental results. Three breakup modes, dripping, jetting with uniform droplets, and jetting with non-uniform droplets, are identified. The different modes are shown on a Weber number-the viscosity ratio map. ᭧
Break-up dynamics and drop size distributions created from spiralling liquid jets
International Journal of Multiphase Flow, 2004
The dynamics of the break-up of spiralling jets of Newtonian liquids were visualised. The jets were created from orifices at the bottom of a 0.085-m-diameter can rotating about its vertical axis and imaged using a high-speed camera. The effects of liquid dynamic viscosity (0.001–0.09 Pa s), rotation rate (5–31 rad s−1) and orifice size (0.001 and 0.003 m) upon the jet break-up and drop size distributions produced in the Rayleigh regime were investigated. The ranges of dimensionless parameters were 1<Re<103, 0.2<Rb<4, 0.5<We<25 and 5×10−3<Oh<4×10−1. Four generic break-up modes identified were a strong function of dynamic viscosity and jet exit velocity. A flow pattern map of Ohnesorge number against Weber number enabled prediction of these modes. Increasing the can rotation rate increases jet exit velocity due to centrifugal forces and the trajectory of the jet becomes more curved. The break-up dynamics of the jets were non-linear, although some agreement between measured break-up lengths with the linear stability analysis developed previously was noted at low Reynolds numbers. A non-linear theoretical analysis is required to elucidate the important features.
Capillary instability of an annular liquid jet
Journal of Fluid Mechanics, 1987
An analytical investigation of the stability of a viscous, annular liquid jet moving in an inviscid medium is presented. This problem is a generalization of the well-known cases of a round cylindrical jet (obtained here when the ratio of internal to external radii tends to zero) and the flat thin liquid sheet (when the ratio above tends to unity).
Drop formation from cylindrical jets in immiscible liquid systems
AIChE Journal, 1969
A theoretical analysis is presented for predicting the size of drops formed from a laminar cylindrical jet when one Newtonian liquid is injected through a nozzle into a second immiscible Newtonian liquid. The analysis couples stability theory with the requirement that the disturbances travel at the same velocity as the jet interface. Comparison of the theory with experimental data for thirteen mutually saturated liquid-liquid systems covering a wide range of physical properties shows a mean error of 11.7% in prediction of the specific surface.
The non-linear breakup of an inviscid liquid jet
Fluid Dynamics Research, 1989
A liquid jet originating from a nozzle with radius * ro breaks up into droplets in consequence of disturbances of certain frequencies, depending on the fluid properties and the nozzle geometry. A theoretical model is developed to describe the growth of these disturbances at the jet surface. The model is based on the inviscid and irrotational flow governed by the Laplace equation together with the kinematicat and dynamical conditions at the free surface of the jet. A comparison is made between the model and experimental data from literature. The model predicts a dependence on the disturbance amplitude of the breakoff mode. Contrary to other experimental results, the model predicts satellites (i.e. smaller droplets between the main larger ones) at wavelengths exceeding a critical value of s x 2~rn*. The disturbances grow at wavelengths more than the theoretical bound of 2nr$. Discrepancies with experimental data are possible because of the neglect of the effect of viscosity in the theory. It is shown that the effect of viscosity on the jet can be neglected under certain conditions.
Hydrodynamics of a rectangular liquid JET in an immiscible liquid-liquid system
The Canadian Journal of Chemical Engineering, 2013
The formation of the droplets and the shape of liquid jet, injected vertically downward from a rectangular nozzle into another immiscible liquid, were studied using computational fluid dynamics (CFD). The unsteady motion of the interface separating two immiscible fluids is followed by solving the Navier-Stokes equations for incompressible and Newtonian fluids with a volume of fluid (VOF) and continuum surface force (CSF) method. Grid independent solution was attained for 2D and 3D models and the results were compared with experimental data. The 3D model was used to determine the effect of the flow rate and the shape of the nozzle on the resulting liquid jet diameters. The simulation results were in good agreement with experimental data. At a fixed flow-rate, the model indicated the presence of an optimal inlet aspect ratio in order to produce a smallest jet diameter. Consequently, droplet size can be optimized by manipulating the flow-rate and nozzle shape, when reducing the nozzle size is not desirable/ practical.
Instability of a liquid jet emerging from a droplet upon collision with a solid surface
Physics of Fluids, 2000
A linear perturbation theory is developed to investigate the interface instabilities of a radially-expanding, liquid jet in cylindrical geometries. The theory is applied to rapidly spreading droplets upon collision with solid surfaces as the fundamental mechanism behind splashing. The analysis is based on the observation that the instability of the liquid sheet, i.e., the formation of the fingers at the spreading front, develops in the extremely early stages of droplet impact. The shape evolution of the interface in the very early stages of spreading is numerically simulated based on the axisymmetric solutions obtained by a theoretical model. The effects that factors such as the transient profile of an interface radius, the perturbation onset time, and the Weber number have on the analysis results are examined. This study shows that a large impact inertia, associated with a high Weber number, promotes interface instability, and prefers high wave number for maximum instability. The numbers of fingers at the spreading front of droplets predicted by the model agree well with those experimentally observed.