Breakup mode of an axisymmetric liquid jet injected into another immiscible liquid (original) (raw)

BREAKUP OF MULTIPLE JETS IN IMMISCIBLE LIQUID-LIQUID SYSTEMS: A COMPUTATIONAL FLUID DYNAMICS STUDY

2011

Hydrodynamic behavior of immiscible liquid-liquid systems has great importance in many industrial operations such as mining, food, cosmetics and pharmaceuticals industries. This behavior governs jet formation and breakup, droplet formation and coalescence in emulsification. For successful emulsion applications, it is very important to generate small and uniform droplets to ensure product stability. In addition, the breakup of the jet increases the interfacial area and hence enhances efficiency of processes such as heat transfer, mass transfer and sometimes chemical reactions. In this study, the formation of droplets from multiple circular nozzles into an immiscible liquid was 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) method. Most significantly, the interaction between neighboring jets was modelled for micro-jet condition.

1706 Computations of Formation and Breakup of a Compound Liquid Jet in a Co-flowing Immiscible Fluid

The Proceedings of The Computational Mechanics Conference, 2011

In this paper, we numerically study the formation and breakup of an axisymmetric immiscible, viscous and taminar compoundjet flowing in a coflowing immiscible outer fluid. We use a front-trackinglfinite difference method to track the evolution and breakup of the compound jet, which is govemed by the incompressible Navier-Stoke equations for Newtonian fluids, The method is modified to account for three-fluid flows. The density and viscosity jumps at interfaces are distributed to the nearby grid points by using area weighting and solving Poisson equations. Thereby, we investigate the effects of interfacial tensions, in terms of the Weber number TVIe and interfacial tension ratio ai],on the various modes ofthe compoundjet breakup: inner drippingouter dripping, inner drippingouter jetting, and innerjettingouter jetting. Numerical results show that the transition frorn dripping to jetting is affected not only by the Weber number but also by interfacial tensien ratio since the compound jet possesses two different interfaces, i.e., either decreasing TM! or increasing thJi promotes the dripping regime. In addition, the orifice ratio also affects the transitional values of PVla and qt, i,e,, as it increases the transition Ife decreases and the transition aiL increases. The transition from dripping to jetting is mapped in the P}i?oj] parameter space. However, the variations of PPle and qi do not affect the aspect ratio ofthe compound drops,

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.

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.

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.

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.

Breakup modeling of a liquid jet in cross flow

International Journal of Automotive Technology, 2011

We propose a novel breakup model to simulate the catastrophic breakup regime in a supersonic cross flow. A developed model has been extended from an existing Kelvin-Helmholtz/Rayleigh-Taylor (K-H/R-T) hybrid model. A new mass reduction rate equation, which has critical effects on overall spray structure, is successfully adopted, and the breakup length, which is an important parameter in existing model, is replaced by the breakup initiation time. Measured data from the supersonic wind tunnel with a dimension of 762×152×127 mm was employed to validate the newly developed breakup model. A nonaerated injector with an orifice diameter of 0.5 mm is used to inject water into a supersonic flow prescribed by the momentum flux ratio of the liquid jet to free stream air, q 0. The conservation-element and solution-element (CE/SE) method, a novel numerical framework for the general conservation law, is applied to simulate the supersonic compressible flow. The spray penetration height and average droplet size along with a spray penetration axis are quantitatively compared with data. The shock train flow structures induced by the presence of a liquid jet are further discussed.

Breakup of Turbulent and Non-Turbulent Liquid jets in Gaseous Crossflows

44th AIAA Aerospace Sciences Meeting and Exhibit, 2006

An experimental and computational investigation of the primary breakup of nonturbulent and turbulent round liquid jets in gas crossflow is described. Pulsed shadowgraph and holograph observations of jet primary breakup regimes, conditions for the onset of breakup, properties of waves observed along the liquid surface, drop size and velocity properties resulting from breakup and conditions required for the breakup of the liquid column as a whole, were obtained for air crossflows at normal temperature and pressure. The test range included crossflow Weber numbers of 0-2000, liquid/gas momentum ratios of 100-8000, liquid/gas density ratios of 683-1021, Ohnesorge numbers of 0.003-0.12, jet Reynolds numbers of 300-300,000. The results suggest qualitative similarities between the primary breakup of nonturbulent round liquid jets in crossflows and the secondary breakup of drops subjected to shock wave disturbances with relatively little effect of the liquid/gas momentum ratio on breakup properties over the present test range. The breakup of turbulent liquid jets was influenced by a new dimensionless number in terms of liquid/gas momentum ratio and the jet Weber number. Effects of liquid viscosity were small for present observations where Ohnesorge numbers were less than 0.4. Phenomenological analyses were successful for helping to interpret and correlate the measurements. Nomenclature d i = streamwise jet diameter at onset of drop formation d j = liquid jet diameter at jet exit d li = diameter of ligaments at liquid jet surface d p = diameter of drops formed by primary breakup Oh = Ohnesorge number, µ L /(ρ L d j σ) 1/2 q = flow momentum ratio, ρ L v j 2 /(ρ G u ∞ 2 ) Re = Cross stream Reynolds number, ρ G u ∞ d j /µ G Re Ld = liquid jet Reynolds number, ρ L V

Effect of liquid entry conditions Liquid jet in crossflow – Effect of liquid entry conditions

The focus of the present article is to study the effect of liquid jet injection velocity profile on the structure of liquid jet in crossflow (JICF). The experiments are conducted over a range of liquid-to-air momentum ratios (Q ~ 3-100) and aerodynamic Weber numbers (We = 17 -89). Control over the velocity profile of the injected liquid is achieved through the usage of different L/D ratios of the nozzle of the plain-orifice atomizer. The geometrical parameter L/D is varied between 10 and 100 in order to obtain fully-developed laminar flow, transition and turbulent flow. High-speed imaging and Shadowgraphy are used to study the trajectory, dropsizing and transient behavior of the resultant spray. It is observed that the dependence of trajectory of the spray is not just limited to the momentum ratio, Q, but also requires correction factors with respect to the injection velocity profiles, which are in turn related to L/D. The trajectory for the turbulent jet is found to be lower at all times when compared to that of a laminar jet for the corresponding conditions. This behavior may be attributed to the inherent instabilities present in a turbulent jet as opposed to a perfectly laminar jet. Further, we also investigate the transient phenomena of the liquid jet breakup at different conditions with the aid of Proper Orthogonal Decomposition (POD) analysis. Distinct modes of breakup are captured for the laminar and turbulent cases.

Axis-switching and breakup of low-speed elliptic liquid jets

International Journal of Multiphase Flow, 2012

Theoretical and experimental investigations are conducted to analyze the instability of a low-speed liquid jet emerging from an elliptic nozzle. The complexity of viscous free surface flow analysis for an asymmetric geometry is simplified using an approach based on the Cosserat theory (also called director theory) which reduces the exact three-dimensional equations to a system depending only on time and on a single spatial variable. This work is mainly focused on the spatial instability analysis to examine the key characteristics of an elliptic jet such as jet profile, axis-switching and breakup length. In the experimental part, both natural (free) and excited (forced) breakup behaviors are studied. In the natural breakup, the effects of nozzle's ellipticity and length to diameter ratio are examined. In the forced breakup case, disturbances are applied to the jet, by modulating the jet exit velocity using a piezoelectric actuator with given sinusoidal perturbations. The spatial evolution of the jet shape is captured with a high speed camera. Liquid jet instability is studied for various nozzle geometries over a specific range of jet velocities and excitation frequencies. Results are compared with conventional circular nozzles which can be considered as a special case of an elliptic jet.