Experimental study of atomization patterns produced by the oblique collision of two viscoelastic liquid jets

Experimental observations and analysis are presented for the formation and atomization of the fluid sheet created by obliquely colliding jets of viscoelastic fluids. Solutions of mono-disperse polystyrene (PS) in diethylphthalate and of poly-disperse polyethylene oxide (PEO) in glycerol/water mixtures were used to investigate the effects of fluid elasticity on the break-up patterns generated by the impact of two jets ejected from nozzles with an internal diameter of 0.85 mm. Various regimes of behaviour were identified which depend on the jet speed. The structures observed for these elastic fluids differ somewhat from those previously reported for Newtonian viscous fluids, and also show different behaviours depending on the degree of viscoelasticity. This study focuses on the periodic atomization, the so-called fishbone pattern, which occurs when the impinging jets form a liquid sheet which breaks up into a regular succession of ligaments and droplets. High-speed flash photography reveals that low concentrations of polymers significantly affect the evolution of the sheet and its fragmentation, the shapes of the ligaments, and the final drop sizes. The maximum fishbone angle is defined and shown to be a useful tool to describe the variation of the atomization pattern with polymer concentration. For the PS solutions the variation of maximum fishbone angle with reduced polymer concentration (c/c^*) follows a single master curve, but although the same is true for PEO with high molecular weights, the curves remain separate for low molecular weights. Observation of the fishbone patterns formed by the oblique impact of jets may provide a useful tool to observe and characterize inter-chain interaction in high speed extensional flow of polymer solutions.     

Deformation of liquid jets and drops injected into a gas stream

The process of deformation of liquid drops and jets is examined on a broad interval of two-phase flow parameters. The shape of a jet penetrating a gas stream directed at an angle to the jet-particle velocity vector is determined.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 3, pp. 82–88, May–June, 1971.In conclusion the authors thank A. K. Simonovskii for his useful comments.     

Comparison-speed liquid jets

The performance of a small high-speed liquid jet apparatus is described. Water jets with velocities from 200 to 700 m/s were obtained by firing a deformable lead slug from an air rifle into a stainless steel nozzle containing water sealed with a rubber diaphragm. Nozzle devices using the impact extrusion (IE) and cumulation (CU) methods were designed to generate the jets. The effect of the nozzle diameter and the downstream distance on the jet velocity is examined. The injection sequences are visualized using both shadowgraphy and schlieren photography. The difference between the IE and CU methods of jet generation is found.     

On the dynamical equations for liquid jets

Quasi-one-dimensional equations for the three-dimensional motion of thin liquid jets have been derived by Entov and the present author [1, 2] from the balance integral equations for the mass, momentum, and angular momentum written down for a jet section. Simplified equations of this kind make it possible, in particular, to investigate with comparative ease the motion of bending jets and also the loss of stability of jets moving in air associated with the development of kinks, etc. It is of interest to obtain quasi-one-dimensional equations of jet motion by direct integration over the section of a thin jet of the three-dimensional differential equations of hydrodynamics. In the present note, this approach is illustrated by the example of bending of a jet in a plane.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 1, pp. 161–163, January–February, 1983.     

Electroconvective jets in liquid dielectrics

The principal feature of electroconvective jets in liquid dielectrics developing under the influence of a high-voltage external field is the large value of the EHD interaction parameter. This leads to the coupling of the hydrodynamic and electric problems. As formulated in [1, 2] the situation is reversed: the EHD interaction parameter is small. In these problems the interest is usually confined to finding the electric characteristics of the jet for a given velocity field. In [3] flows from sharp electrodes in liquid dielectrics were analyzed under two principal assumptions: nonlinear ohmic conductivity and point EHD interaction. This paper deals with the calculation of submerged electroconvective jets with ionic conductivity on the basis of the boundary-value problem formulated in [4]. In this case point EHD interaction is not assumed. It should be noted that in this formulation the problem is of practical as well as theoretical interest, for example, in connection with the problem of designing throttle EHD converters [5].Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 6, pp. 13–19, November–December, 1984.     

Forced capillary breakup of liquid jets

The characteristics of the forced capillary breakup (FCB) of liquid jets have been investigated over a broad range of variation of the breakup parameters: jet orifice diameter (34–527 m), flow rate (10^–5–1 cm³/sec), and excitation amplitude and frequency. The theory is compared with experiment.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 2, pp. 53–61, March–April, 1988.The authors are grateful to E. V. Ametistov for his constant interest and assistance.     

Experiments with large diameter gravity driven impacting liquid jets

 The phenomenon of a liquid jet released under gravity and falling through or impacting onto another liquid before colliding with an obstructing solid surface has been studied experimentally under isothermal conditions. Usually the jet diameter was sufficiently large to ensure jet coherency until collision. Direct flow visualization was used to study jets released into water pools with no air head space and jets impacting onto water pools after falling through an air head space. It is shown that distances predicting the onset of buoyancy and the entrainment of air using derivations from continuous plunging jets, are not applicable for impacting jets. The morphology of jet debris after collision with the solid surfaces correlates with the wetting properties of the jet liquid on the surface. Received: 28 November 1997 / Accepted: 21 May 1998     

Hopf bifurcation in annular liquid jets with mass transfer

A numerical study of Hopf bifuractions in annular liquid jets with mass transfer is presented. The study is based on the asymptotic equations which govern the dynamics of inviscid, incompressible, thin, annular liquid jets and on equilibrium conditions for mass transfer at the jet's inner and outer interfaces. It is shown that the amplitude of the time-periodic motion that results from the Hopf bifurcation increases whereas its frequency decreases as the solubility ratio is increased.     

Thermal modulation and breakup of liquid jets

In this paper, we study the breakup behavior of Newtonian liquid and non‐Newtonian liquid jets with an arbitrary variation surface tension imposed along its length. The effect of duty cycle, fluid properties, and the various profiles of the surface tension is investigated. It is shown that the breakup behavior of a jet can be constructed by using the Fourier expansion of the surface tension profile. When the dimensionless wavenumber k is larger than 0.5, the jet breakup behavior is determined by the lowest frequency of the Fourier series expansion of the surface tension profile. As k decreases, higher frequency Fourier modes come to play. In general, for k between, 1∕(n+ 1) and 1∕n,n Fourier modes are needed to determine the jet breakup behavior. The current nonlinear model differs from the existing linear slender jet model in the literature in several ways. While the principle of superposition is valid for the linear model, it is not generally valid for the current nonlinear model. For the linear model, the jet will never break up when the wavenumber is larger than 1. The current model, however, shows clearly that the jet can indeed break up when the wavenumber is larger than 1. Furthermore, the current nonlinear model predicts a breakup time substantially higher than that from the linear model.Copyright © 2011 John Wiley & Sons, Ltd.     

Breakup of liquid jets from non-circular orifices

The purpose of this investigation is to study the effect of the orifice geometry on liquid breakup. In order to develop a better understanding of the liquid jet breakup, investigations were carried out in two steps—study of low-pressure liquid jet breakup and high-pressure fuel atomization. This paper presents the experimental investigations conducted to study the flow behavior of low-pressure water jets emanating from orifices with non-circular geometries, including rectangular, square, and triangular shapes and draws a comparison with the flow behavior of circular jets. The orifices had approximately same cross-sectional areas and were machined by electro-discharge machining process in stainless steel discs. The liquid jets were discharged in the vertical direction in atmospheric air at room temperature and pressure conditions. The analysis was carried out for gage pressures varying from 0 to 1,000 psi (absolute pressures from 0.10 to 6.99 MPa). The flow behavior was analyzed using high-speed visualization techniques. To draw a comparison between flow behavior from circular and non-circular orifices, jet breakup length and width were measured. The flow characteristics were analyzed from different directions, including looking at the flow from the straight edges of the orifices as well as their sharp corners. The non-circular geometric jets demonstrated enhanced instability as compared to the circular jets. This has been attributed to the axis-switching phenomenon exhibited by them. As a result, the non-circular jets yielded shorter breakup lengths as compared to the circular jets. In order to demonstrate the presence of axis-switching phenomenon in square and triangular jets, the jet widths were plotted along the axial direction. This technique clearly demonstrated the axis switching occurring in square and triangular jets, which was not clearly visible unlike the case of rectangular jets. To conclude, non-circular geometry induces greater instabilities in the liquid jets, thereby leading to faster disintegration. Thus, non-circular orifice geometries can provide a cheaper solution of improving liquid breakup and thus may enhance fuel atomization as compared to the precise manufacturing techniques of drilling smaller orifices or using costly elevated fuel injection pressure systems.     

Deformation boundaries of an axisymmetric cavity by gas jets

A method is proposed for calculating small deformations of the boundaries of an axisymmetric cavity with impinging gas jets. No constraints are imposed on the configuration and characteristics of the system of nozzles generating the jets. Numerical results are compared with data obtained by available semi-empirical methods and with experimental data. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 49, No. 5, pp. 80–86, September–October, 2008.