Particle entrainment by axisymmetric jets

The presence of particles can enhance or reduce the entrainment of an axisymmetric air jet. Measurements of particle entrainment in the 2 phase preheated jet were made by the Ricou and Spalding (1961) technique, and the results compared with theoretical estimates. Heating the jet stream improves the entrainment.     

Surface entrainment of air by high velocity water jets

A theory is given of the aeration produced by the impact of a high speed water jet on a water surface. Experimental verification agrees more than satisfactorily with the developed theory over a wide range. The boundary conditions for the theory have a physical meaning. The jet must be submitted to air friction forces (We > 10), and the accompanying air boundary layer must be laminar (Re_L < 5 × 10⁵). In the case of a turbulent boundary layer the same kind of analysis might be used, however at the moment no reliable solutions for a turbulent boundary layer are well established.     

Jet break-up and air entrainment by low velocity turbulent water jets

Correlating equations are developed for air entrainment by plunging water jets with velocities in the range between 2 and 5 m/sec. Energy considerations are shown to be a good basis for predictive equations. Two different situations are distinguished depending on whether or not the jet is near its break-up length; for jets produced by nozzles within which turbulence is fully developed the break length is correlated by

Beyond 90% of the total break length the air entrainment produced by vertical jets from 2·85 to 10 mm diameter is given by

For shorter jets which are vertical or inclined, there is a length dependence which leads to the relationship, accurate within 15%, of

     

Solid entrainment rate into gas and gas—solid,two-phase jets in a fluidized bed

A mathematical model for solid entrainment into a permanent flamelike jet in a fluidized bed was proposed. The model was supplemented by particle velocity data obtained by following movies frame by frame in a motion analyzer. The experiments were performed at three nominal jet velocities (35, 48, and 63 m/s) and with solid loadings ranging from 0 to 2.75. The particle entrainment velocity into the jet was found to increase with increases in distance from the jet nozzle, to increase with increases in jet velocity and to decrease with increases in solid loading in the gas—solid, two-phase jet.     

Influence of atomiser design and coaxial gas velocity on gas entrainment into sprays

To study the influence of atomiser design and coaxial air velocity on entrainment of coaxial and confined sprays, the sprays issuing from a number of different atomisers are investigated experimentally under various external flow conditions. Air and liquid velocity profiles in the spray are determined by phase-doppler-anemometry (PDA), liquid mass flux profiles are measured using a mechanical droplet collection device (patternator) with a high spatial resolution. Experiments are performed in a 300 mm diameter vertical wind tunnel at superficial air velocities up to 30 m s⁻¹ at liquid flow rates from 0.083 to 0.278 kg s⁻¹. Experimental results are compared with free spray data and a generalised free jet theory. Comparing the sprays from different atomisers displays high induced air flow rates for high velocity narrow sprays and high entrained air flow rates for wide sprays. The influence of coaxial air velocity depends largely on the width of the spray and may be predicted by a simple model that is developed to determine the entrainment of coaxial and confined sprays from free spray data.     

Influence of moisture on the entrainment of sand by wind

The theory of wet granular material is applied to the study of the influence of moisture on the entrainment of sand by wind in the first process of aeolian sand transport. The interparticle force due to water bridge is calculated using the toroidal approximation at first; and then the moment balance of a grain in the surface layer of sand bed is considered; finally, the change of threshold friction velocity with water content is obtained.     

Air entrainment rate and diffusion pattern of plunging liquid jets

In Section 1 of the paper the authors investigate the factors governing the rate of air entrainment by plunging jets by varying the jet velocity, jet dIn Section 2 the nature and extent of the biphasic diffusion region is investigated for both rough and smooth jets. These two types of jet produce very     

Gas entrainment rate and flow pattern of vertical plunging liquid jets

For a vertical plunging liquid jet system using various liquids, the effects of the operating conditions including the nozzle length-to-diameter ratio on the gas entrainment rate Q_g were evaluated experimentally. The differences in Q_g were related to the changes in the jet shape before plunging and the velocity of the plunging liquid jet at the point where the gas sheath breaks up. Empirical relationships were also presented to predict the maximum depth Z of bubbles entrained by the diffusing jet. The changes of Z were further discussed in terms of the downward liquid velocity distribution in the submerged two-phase region, which depends mainly on the size of entrained bubbles.     

Experimental investigation of flow regimes of axisymmetric and planar opposed jets

Dynamic behaviors of axisymmetric and planar opposed jets have been experimentally studied at 786 < Re < 6288. The flow patterns were investigated by a smoke‐wire technique, and the smoke‐wire photos were recorded by a high‐speed camera. Different flow regimes of axisymmetric and planar opposed jets have been identified. Axisymmetric opposed jets exhibit axial quasi‐periodic oscillations, stagnation point offsets, and steady states, while planar opposed jets exhibit both horizontal instabilities and deflecting oscillations. Effects of the nozzle separation and the exit Reynolds number on the dynamic characteristics of axisymmetric and planar opposed jets have been investigated and discussed. Maps of parameter spaces describing the flow regimes of axisymmetric and planar opposed jets at various nozzle separations and exit Reynolds numbers have been presented. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

Ablation of ice-solids and wax-solids mixtures in turbulent axisymmetric water jets

The ablation rate of frozen mixtures of water or wax with finely divided solids subjected to a turbulent axisymmetric water jet was investigated both experimentally and theoretically. The range of the water jet Reynolds number was 8700–29300 and the jet temperature varied between 22 and 60°C. The solids used were very fine kaolinite clay, titanium oxide and aluminium powder. The type of solids and their concentration were found to affect the ablation rate of ice-solids and wax-solids mixtures. This is mainly due to changes in the physical properties of the melt layer of the water-solids or wax-solids mixtures which forms between the impinging jet and the frozen mixtures.     

Physical modelling and similitude of air bubble entrainment at vertical circular plunging jets

When a plunging jet impinges into a pool of liquid, air bubble entrainment takes place if the inflow velocity exceeds a threshold velocity. This study investigates air entrainment and bubble dispersion in the developing flow region of vertical circular plunging jets. Three scale models were used and detailed air-water measurements (void fraction, bubble count rate, bubble sizes) were performed systematically for identical inflow Froude numbers. The results highlight that the modelling of plunging jet based upon a Froude similitude is affected by significant scale effects when the approach flow conditions satisfied We₁<1E+3, while some lesser scale effect was noticed for V₁/u_r<10 and We₁>1E+3. Bubble chord time measurements showed pseudo-chord sizes of entrained bubbles ranging from less than to more than with an average pseudo-chord size were between 4 and . However, bubble size data could not be scaled properly.     

平面气固撞击流周期振荡的模拟分析

由于喷嘴截面的高宽比远小于1,平面狭缝喷嘴撞击流可看作二维撞击流。采用欧拉双流体模型对二维气固撞击流进行数值模拟。模拟结果表明,当固相负载率m≤8.2,颗粒粒径为60 μm≤d_p≤175 μm时,大间距的平面气固撞击流也出现了周期振荡。通过分析射流轴线上不同位置的压力和速度的瞬时值和平均值,认为周期振荡是由于撞击面上压力释放和持续射流的共同作用导致。讨论了不同条件对振荡周期的影响:振荡周期随喷嘴间距或颗粒粒径的增加而增加;而随射流Reynolds数的增加或者固相负载率的增加而减小。     

Experimental study of parameters of structure loading by two-phase stream upon vessel fracture

We present the results of an experimental study of the interaction of a two-phase stream with structural elements and analyze the characteristics of loading by a dense two-phase medium after air shock wave passage. The experimental dependences of the impulse and duration of the compression phase on the particular impact conditions are presented.Military Space Engineering Academy, 197342 St. Petersburg. Translated from Fizika Goreniya i Vzryva, Vol. 30, No. 2, pp. 119–121, March–April, 1994.     

Turbulent gas jets and diesel-like sprays in a crossflow: A study on axis deflection and air entrainment

The interaction between a turbulent gas jet/diesel spray and a crossflow has been analysed. This phenomenon is a simplification of a more complex one that takes place in the combustion chamber of small direct injection diesel engines, and its study will help to better understand this more complex case. The two main aspects analysed here are axis deflection and air entrainment. It was found that both aspects are related to each other, and that the air/jet (or air/spray) momentum flux ratio is very relevant in the phenomenon. Scaling laws for the axis deflection of a jet/spray were obtained, and an original method to obtain fuel concentration along the axis of a jet/spray in a crossflow has been established. Gas jets and diesel sprays are found to be very similar even when they interact with a crossflow.     

Measurements of velocity and concentration for a two-phase turbulent jet

The velocity and concentration distributions for an axisymmetric air jet containing sand particles are determined in the fully developed region. Similarity of the profiles is seen beyond 40 nozzle radii downstream from the jet exit and entrainment is gradually suppressed with increase in the initial particle concentration.     

Theoretical aspects of critical flow and the velocity of sound in disperse two-phase flow

Analysis of the conservation equations of disperse two-phase flow reveals that the pressure gradient cannot reach infinity for critical flow conditions A new criterion of the critical flow conditions is suggested which agrees with experimental results. The critical velocity in disperse two-phase flow depends mainly on the density ratio of both phases and the particle concentration; the velocity of sound depends on the sound frequency in addition. Consequently, the velocity of sound can be higher or lower than the critical velocity.