Free jets spun from a prilling tower

A mathematical model of the dynamics of an inviscid liquid jet, subjected to both gravity and surface tension, which emerges from rotating drum is derived and analysed using asymptotic and computational methods. The trajectory and linear stability of this jet is determined. By use of the stability results, the break up length of the jet is calculated. Such jets arise in the manufacture of pellets (for example, of fertilizer or magnesium) using the prilling process. Here the drum would contain many thousands of holes, and the molten liquid would be pumped into the rotating drum. After the jet has broken up into droplets, these droplets solidify to form pellets. The jets in this prilling process are curved in space by both gravity and surface tension.     

Effect of gas stream swirls on the instability of viscous annular liquid jets

Summary. A linear temporal instability analysis has been carried out for a viscous annular liquid jet moving in two swirling gas streams of unequal velocities with the gas stream swirling motion represented by free-vortex rotation. It is found that two modes of unstable surface waves exist, the para-sinuous and para-varicose mode. The results of the two limiting flow situations, which are a cylindrical liquid jet in a swirling gas stream and a swirling gas jet in a liquid stream, indicate that their instabilities are associated with the para-varicose mode on the outer interface and para-sinuous mode on the inner interface of the annular liquid jet, respectively. It is shown that the centripetal force induced by the inner gas stream rotation is destabilizing and enhances the jet instability, while the centripetal force produced by the outer gas stream rotation is stabilizing and reduces the instability of annular liquid jets. It is interesting to find that for a para-varicose mode an increase in the outer gas rotation not only reduces the upper cut-off wave number, but also increases the lower cut-off wave number, leading to the significant reduction in the unstable wave number range. The stabilizing effect of the outer gas rotation is much more significant for para-varicose mode, and the destabilizing effect of the inner gas rotation is much more influential for para-sinuous mode. In general, the para-sinuous mode has a much larger growth rate and is predominant in the annular liquid jet breakup process. Therefore, increasing the inner gas stream rotation can significantly enhance the breakup of annular liquid jets for practical spray applications.     

液体射流扰动控制方程边界条件及稳定性分析

本文针对粘性气体中的粘性不可压缩液体射流的分裂与雾化过程边界条件,进行了扰动分析,并对其进行线性化及无量纲化,得到了射流扰动控制方程无量纲线化边界条件。最后对射流分裂与雾化过程的不稳定性做了数值分析,其结果与实际观测到的射流边界面变化规律一致。     

An experimental investigation of capillary breakup of a liquid metal jet

The limits of influence of oxidation on the capillary breakup of a liquid metal jet is investigated. It is shown that in a region of weak oxidation the disruption of the jet proceeds as is usual for a Newtonian fluid.Translated from Inzhenerno-fizicheskii Zhurnal, Vol. 60, No. 4, pp. 554–557, April, 1991.     

Sessile droplet formation in the laser-induced forward transfer of liquids: A time-resolved imaging study

The formation process of sessile droplets in the laser-induced forward transfer of aqueous solutions was analyzed through time-resolved imaging. At the irradiation conditions which lead to the deposition of well-defined droplets, a cavitation bubble is generated in the laser irradiated area. Such bubble evolves into a high-speed liquid jet which propagates towards the receptor solid substrate. Once the jet impinges on the receptor substrate, liquid gently starts accumulating on the impact position, and the growth of a sessile droplet initiates. In a first stage, which only lasts a few microseconds, the forming droplet suffers a fast spreading process. Then, the jet continues feeding the forming droplet for some hundreds of microseconds, but the droplet diameter remains constant, and thus the contact angle increases. Finally, liquid feeding stops due to jet breakup, and the sessile droplet initiates a slow relaxation process in which its contact angle diminishes and its diameter increases. This deposition process results in the deposition of a single sessile droplet up to donor film-receptor substrate distances of the order of the millimeter. At higher separations, satellite droplets appear, and at even higher separations only randomly distributed small droplets are deposited.     

Features of the breakup of jets of a low-viscosity liquid in a subsonic entraining flow of gas

The results of electrocontact measurements are used as a basis for examining the mechanisms (variants) of the breakup of a liquid jet and a dense atomizing jet. The deformational scheme of breakup in an entraining subsonic gas flow is generalized.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 60, No. 1, pp. 24–32, January, 1991.     

Characterization of initial disturbances in a liquid jet by rainbow sizing

The development of initial disturbances is relevant to the understanding of atomization processes in which droplets are generated by the breakup of a liquid jet. We theoretically and experimentally demonstrate that such disturbances can be characterized by rainbow sizing. More specifically, for a liquid jet with a diameter of 600 mum, disturbances in the range from 10 nm to 0.2 mum are accessible.     

Two-dimensional modeling of viscous liquid jet breakup

A two-dimensional computational model has been developed to study the evolution and breakup of a viscous laminar liquid jet, using a boundary-fitted curvilinear coordinate system. A system of elliptic partial differential equations for coordinate transformations has been developed to map the moving boundaries’ physical domain of the jet to a simple rectilinear computational domain. The equations developed for the model comprise the transformed two-dimensional unsteady Navier–Stokes equations for the liquid jet, grid velocity equations, kinematic boundary conditions, and the Geometric Conservation Law. The resulting systems of equations are solved using an implicit finite difference scheme. Effects of inflow oscillation magnitude, wave number, Weber number, and Reynolds number on the breakup process of jets have been studied. The model predicts the instantaneous shape of the jet surface, formation of the main and satellite drops, and the breakup length and time. These results are compared with available experimental data. The comparisons show a good agreement between measured and computed values of drop sizes and breakup lengths for different Reynolds and Weber numbers. However, at a relatively high Reynolds number of 1,254, the model slightly overpredicts the main drop sizes and underpredicts the satellite drop sizes at a wave number of 0.4. At a low Reynolds number of 587, the model overpredicts the main drop sizes at a lower wave number of 0.3. Moreover, the model underpredicts the satellite drop sizes at a lower wave number of about 0.4 and overpredicts the satellite drop sizes at a wave number of 0.8.     

Instability of an annular viscous liquid jet

Summary A linear analysis has been carried out for the temporal instability of an annular viscous liquid jet moving in an inviscid gas medium, which includes three limiting cases of a round liquid jet, a gas jet and a plane liquid sheet. It is found that there exist two independent unstable modes, which become the well-known sinuous and varicose modes for plane liquid sheets as annular jet radii approach to infinity. Hence, they are named as para-sinuous and para-varicose. It is shown that an ambient gas medium always enhances the annular jet instability. The curvature effects in general increase the disturbance growth rate, and may not be neglected for the breakup process of an annular or conical liquid sheet. An annular jet with a sufficiently small thickness tends to break up much faster than the corresponding plane liquid sheet, in accordance with existing experimental observations. Liquid viscosity has complicated dual effects on the instability. It is also found that there exists a critical Weber number below which surface tension is the source of instability. Whereas above it, instability is suppressed by surface tension effect and it promoted by aerodynamic interaction between the liquid and gas phase. For the practical importance of large Weber numbers such as related to liquid atomization, the para-sinuous mode is always predominant.     

Nonlinear viscous liquid jets from a rotating orifice

A liquid jet follows a curved trajectory when the orifice from which the jet emerges is rotating. Surface-tension-driven instabilities cause the jet to lose coherence and break to form droplets. The sizes of the drops formed from such jets are in general not uniform, ranging from drops with diameters of the order of the jet diameter to droplets with diameters which are several orders of magnitude smaller. This presentation details a theoretical investigation of the effects of changing operating parameters on the break-up of curved liquid jets in stagnant air at room temperature and pressure. The Navier–Stokes equations are solved in this system with the usual viscous free-surface boundary conditions, using an asymptotic method based upon a slender-jet assumption, which is clearly appropriate from experimental observations of the jet. Nonlinear temporal simulations of the break-up of the liquid jets using slender theory are also presented. These simulations based upon both a steady-trajectory assumption, and the more general equations which allow for an unsteady trajectory, show all the break-up modes viewed in experiments. Satellite-droplet formation is also considered. A. C. King deceased.     

Breakup of brittle deposits by supersonic air jet: The effects of varying jet and deposit characteristics

The breakup by supersonic air jet of cylindrical brittle gypsum deposits formed on tube surfaces was studied using high-speed imaging. The breakup of symmetric deposits was visualized from the front and back simultaneously, and the effects of deposit asymmetry, jet/deposit attack angle, and jet duration and frequency, were investigated. Three jet types were considered: short and long duration single pulses, and a pulsating jet. For each experiment, the time to breakup, the breakup duration, and the breakup length were measured. Results indicate that the breakup of asymmetric deposits depends on orientation, and that attack angle affects the probability of breakup and breakup length. Results also indicate that soft deposits can be broken by any jet type, while harder deposits, especially those farther from the nozzle exit, require a longer exposure time to be broken. Pulsating jets do not improve breakup effectiveness. This work has relevance to cleaning of fireside deposits formed on heat exchanger tubes in boilers.     

Experimental investigation on the effect of liquid injection by multiple orifices in the formation of droplets in a Venturi scrubber

Venturi scrubbers are widely utilized in gas cleaning. The cleansing elements in these scrubbers are droplets formed from the atomization of a liquid into a dust-laden gas. In industrial scrubbers, this liquid is injected through several orifices so that the cloud of droplets can be evenly distributed throughout the duct. The interaction between droplets when injected through many orifices, where opposite clouds of atomized liquid can reach each other, is to be expected. This work presents experimental measurements of droplet size measured in situ and the evidence of cloud interaction within a Venturi scrubber operating with multi-orifice jet injection. The influence of gas velocity, liquid flow rate and droplet size variation in the axial position after the point of the injection of the liquid were also evaluated for the different injection configurations. The experimental results showed that an increase in the liquid flow rate generated greater interaction between jets. The number of orifices had a significant influence on droplet size. In general, the increase in the velocity of the liquid jet and in the gas velocity favored the atomization process by reducing the size of the droplets.     

Monodisperse breakup of liquid jets

The monodisperse breakup of liquid jets with various physical properties is investigated experimentally and theoretically over a wide range of jet breakup parameters.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 55, No. 3, pp. 413–418, September, 1988.     

Jet formation upon ultrafast laser induced breakdown in the vicinity of liquid-gas interface

We have studied the phenomenon of breakdown in liquids under the action of ultrashort (160 fs) laser pulses focused in the vicinity of a flat or curved liquid-gas interface. It is established that a slightly divergent jet containing micron-sized bubbles is formed in the liquid, which originates from the laser-induced breakdown zone and propagates inward the liquid along the normal drawn to the interface from the point of laser beam focusing. The jet length depends on the distance from this focal point to the interface, as well as on the energy, and the repetition rate of laser pulses and can reach several centimeters.     

Performance estimation of a Venturi scrubber using a computational model for capturing dust particles with liquid spray

A Venturi scrubber has dispersed three-phase flow of gas, dust, and liquid. Atomization of a liquid jet and interaction between the phases has a large effect on the performance of Venturi scrubbers. In this study, a computational model for the interactive three-phase flow in a Venturi scrubber has been developed to estimate pressure drop and collection efficiency. The Eulerian-Lagrangian method is used to solve the model numerically. Gas flow is solved using the Eulerian approach by using the Navier-Stokes equations, and the motion of dust and liquid droplets, described by the Basset-Boussinesq-Oseen (B-B-O) equation, is solved using the Lagrangian approach. This model includes interaction between gas and droplets, atomization of a liquid jet, droplet deformation, breakup and collision of droplets, and capture of dust by droplets. A circular Pease-Anthony Venturi scrubber was simulated numerically with this new model. The numerical results were compared with earlier experimental data for pressure drop and collection efficiency, and gave good agreements.     

不同界面约束对爆炸作用下液体抛撒影响分析

采用高速摄影仪拍摄了不同界面约束条件液体抛撒的高速撮影图片,通过对这些图片的分析,得出了不同界面约束条件液体抛撒的最大速度、作用时间、半径、速度衰减系数以及液体抛撒的不对称性。依据不可压缩柱面流体界面运动、变化规律,在分析了爆炸作用下液体抛撒初期界面初始扰动运动、变化的基础上,探讨了不同界面约束对扰动放大因子及界面稳定的影响。根据液体二次破碎理论,分析了不同界面约束条件对液体二次破碎的影响;结合实验结果讨论了不同界面约束对液体抛撒的作用时间、半径以及速度衰减系数的影响。     

Features of the capillary breakup of jets of dielectric viscous liquids with surface charges

An investigation is reported of the forced capillary breakup of a jet of charged viscous liquid in a corona discharge field.Translated from Inzhenerno-fizicheskii Zhurnal, Vol. 60, No. 4, pp. 576–582, April, 1991.     

Investigation of the evolution of the spectrum of oscillations of the surface of a jet of liquid with forced capillary breakup

The results of an experimental study of the spectral composition of the surface oscillations of a jet of liquid at different distances from the point of efflux from the head of the apparatus which produces forced capillary breakup of fluid jets are presented.Translated from Inzhenerno-fizicheskii Zhurnal, Vol. 60, No. 4, pp. 550–553, April, 1991.     

Spraying mode effect on droplet formation and ion chemistry in electrosprays

Depending on the spraying conditions and fluid properties, a variety of electrospray regimes exists. Here we explore the changes in ion production that accompany the transitions among the three axial spraying modes, the burst mode, the pulsating Taylor cone mode, and the cone-jet mode. Spray current oscillation and phase Doppler anemometry measurements, fast imaging of the electrified meniscus, and mass spectrometry are utilized to study the formation, size, velocity, and chemical composition of droplets produced in the three modes. High-speed images indicate that the primary droplets are produced by varicose waves and lateral kink instabilities on the liquid jet emerging from the Taylor cone, whereas secondary droplets are formed by fission. Dramatic changes in the droplet size distributions result from the various production and breakup mechanisms observed at different emitter voltages and liquid flow rates. We demonstrate that droplet fission can be facilitated by space charge effects along the liquid jet and in the plume. Compared to the other two regimes, a significantly enhanced signal-to-noise ratio, a lower degree of analyte oxidation, and milder fragmentation are observed for the cone-jet mode.     

Nonlinear breakup of thin liquid sheets

Summary The breakup of thin planar liquid sheets due to the nonlinear growth of disturbances is determined. Conservation equations are derived using a control volume method and solved using MacCormack's predictor-corrector scheme. It is found that the size and geometry of ligaments, formed during breakup, vary with the weber number. Antisymmetric waves, which spontaneously intensify at higher values of the Weber number, give rise to thin ligaments. At lower values of the Weber number antisymmetric waves formed initially get transformed into symmetric interfaces giving larger ligaments. The magnitude of the initial amplitude of the disturbances is shown to strongly influence the disintegration. The results are compared with experimental results obtained for thin water sheets and good agreement is demonstrated.