Effect of cross flow on the spray characteristics of an industrial feed nozzle

The spray characteristics of a scaled-down version of an industrial feed nozzle are studied in the presence of a cross flow. Aerated liquid nitrogen is injected through the nozzle to generate the spray. The aeration rate is low and held constant, while two different liquid flow rates are used to produce the spray. A nonuniform wind profile is chosen to represent the cross flow condition. The droplet diameter and velocity measurements are acquired using a phase-Doppler particle analyzer. The results of the present study indicate that the spray momentum flux determines the extent of the jet bending. The droplets are accelerated significantly in the initial jet region as a result of flashing. However, further downstream of the nozzle, the vaporization of the droplets is considered to be negligible. The size-velocity correlation changes significantly for the case where the spray is shifted due to the cross flow.     

EFFECT OF CROSS FLOW ON THE SPRAY CHARACTERISTICS OF AN INDUSTRIAL FEED NOZZLE

The spray characteristics of a scaled-down version of an industrial feed nozzle are studied in the presence of a cross flow. Aerated liquid nitrogen is injected through the nozzle to generate the spray. The aeration rate is low and held constant, while two different liquid flow rates are used to produce the spray. A nonuniform wind profile is chosen to represent the cross flow condition. The droplet diameter and velocity measurements are acquired using a phase-Doppler particle analyzer. The results of the present study indicate that the spray momentum flux determines the extent of the jet bending. The droplets are accelerated significantly in the initial jet region as a result of flashing. However, further downstream of the nozzle, the vaporization of the droplets is considered to be negligible. The size-velocity correlation changes significantly for the case where the spray is shifted due to the cross flow.     

Spray droplet velocity characterization for convergent nozzles with three different diameters

The core of the present work consists of the phase-Doppler anemometry non-intrusive measurements performed at various points of diesel direct injection sprays in order to obtain the local speed of fuel droplets. The main objective was to perform extensive sets of measurements on convergent nozzles with various orifices diameters, observe and justify the differences and compare the experimental data with a theoretical approach derived by the authors in a previous work which takes into account the spray momentum flux. Experimental axial velocity profiles in different sections of the spray showed a radial distribution that was fitted with a high level of agreement to a Gaussian profile and so proving that this type of profile is a reasonable approach for the type of sprays within the scope of the present work. The experimental results showed that the velocity in the spray’s axis inversely depends on axial position and that for a given axial position; higher axial velocity has been measured for the nozzles with higher spray momentum.     

Airborne Dust Capture and Induced Airflow of Various Spray Nozzle Designs

Water spray characteristics, including droplet size and velocity, airborne dust capture potential, and induced airflow quantity for various spray nozzle designs were evaluated to provide basic information for improving spray applications. Water droplet size and velocity characteristics were initially measured by a Phase Doppler Particle Analyzer (PDPA) for hollow cone, full cone, flat fan, and air atomized spray nozzles at similar operating parameters. Airflow inducement and dust capture experiments were also conducted under the same operating parameters to examine any salient features of the spray nozzle type, droplet characteristics, induced airflow, and airborne dust capture.

Test results indicate that there are trade offs between airflow inducement and dust capture efficiency. A spray nozzle with a wider discharge angle was observed to induce more airflow, but at reduced dust capture efficiencies. Increasing spray nozzle fluid pressure(s) generally reduced water droplet sizes with concurrent increases in droplet velocity, airflow inducement, and airborne dust capture. Placing a three-sided barrier around the spray nozzles normally reduced spray air induction and increased dust capture efficiency. A direct relationship between airborne dust capture efficiency and spray input power normalized per unit of airflow induced was observed. This information can be utilized to improve the performance of water sprays for reducing airborne dust levels.     

Simulation and analysis of group-hole nozzle sprays using a gas jet superposition model

A gas jet superposition model has been recently developed for computing group-hole nozzle sprays in computational fluid dynamics (CFD) simulations. The objectives of this study are: (1) to perform a systematic validation of the comprehensive spray model for group-hole nozzles using a broad range of experimental data; (2) to analyze the dynamics and physical insight of group-hole nozzle sprays based on the simulation results; and (3) to further clarify the impact of included-angle on spray/mixture properties of group-hole nozzle sprays. An updated version of the KIVA-3V Release 2 code, which employs the Lagrangian-Drop Eulerian-Fluid (LDEF) methodology for numerical calculation of two-phase flows, was used in the simulations. Diverging group-hole nozzles with various included-angles were considered. The test conditions included non-evaporating and evaporating ambient conditions, free sprays and sprays impinging on a flat wall. Detailed comparisons were made between the experiments and computations in terms of spray/mixture characteristics. The results show that numerical parameter dependencies are significantly reduced with the new models, and good levels of agreement are obtained in terms of spray structure, liquid/vapor penetration, overall SMD and cumulative vaporized fuel mass. Both experimental measurements and simulations reveal the importance of included-angle in group-hole nozzle sprays. In particular, some important features of group-hole nozzle spray are captured in the computations by the present models: compared to the equivalent single-hole nozzle, smaller local droplet size can be achieved in the near nozzle field, indicating an enhanced fuel primary atomization; the ambient gas entrainment rate is increased during the injection period, implying the better mixing; the spray axis deflection is identified in the case of group-hole nozzles with smaller angles, which is caused by a negative relative pressure region that exists between the sprays; in addition, the asymmetric structure of wall-impinging group-hole nozzle spray is well predicted by the present models through applying the gas jet superposition model in the entire computational domain.     

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.     

An Experimental Investigation of Agglomeration with One and Two Nozzle Atomisation

Water-droplet size and velocity measurements were taken throughout two different sprays produced by a single nozzle and two nozzles pointed towards each other. The aim of this investigation was to understand the manner in which the motion of the droplets in a spray leads to agglomeration of these droplets. It appears that the inertia of the droplets plays an important role in the redistribution of droplets throughout a spray. Larger droplets tend to concentrate at the outer portions of the spray, because they are able to maintain their radial momentum farther downstream of a nozzle, while the smaller droplets follow the airflow more closely and thus collect in the core of the spray. Agglomeration can result from both turbulent collisions and collisions due to the relative velocities of the droplets. The difference between the agglomeration rates in the sprays from a single nozzle and two-nozzles pointed towards each other was difficult to resolve in these experiments, although the results suggest that th     

单双喷嘴雾化凝聚的实验研究

Water-droplet size and velocity measurements were taken throughout two different sprays produced by a single nozzle and two nozzles pointed towards each other. The aim of this investigation was to understand the manner in which the motion of the droplets in a spray leads to agglomeration of these droplets. It appears that the inertia of the droplets plays an important role in the redistribution of droplets throughout a spray. Larger droplets tend to concentrate at the outer portions of the spray, because they are able to maintain their radial momentum farther downstream of a nozzle, while the smaller droplets follow the airflow more closely and thus collect in the core of the spray. Agglomeration can result from both turbulent collisions and collisions due to the relative velocities of the droplets. The difference between the agglomeration rates in the sprays from a single nozzle and two-nozzles pointed towards each other was difficult to resolve in these experiments, although the results suggest that the outer portions of both sprays should be investigated more closely for evidence of agglomeration.     

Increase of electrospray throughput using multiplexed microfabricated sources for the scalable generation of monodisperse droplets

The development, fabrication, and testing of a compact multiplexed system of electrosprays are presented with the dual goal of increasing by orders of magnitude the liquid flow rate to be dispersed and of retaining the quasi-monodispersity of the generated droplets. The system was microfabricated as an array of nozzles etched in silicon, with a density of 250 sources/cm². Although the operation of a single electrospray is rather forgiving with respect to the electrode geometry, successful performance of the multiplexed system is critically dependent on a careful selection of the electrode configuration, which in the present work entails an extractor electrode mounted at a distance from the spray sources that is comparable to the distance between sources (on the order of 0.5 mm). The electrode has the dual function of limiting electric field cross-talk between neighboring sources and minimizing space charge feedback from the spray cloud. Measurements of current and droplet size as a function of flow rate and of droplet size distribution using ethanol demonstrated that the system may be optimized to produce uniform droplets simultaneously from all parallelized electrosprays, each one operating as an isolated spray in the quasi-monodisperse cone-jet mode. Ease of operation and uniformity in size from spray to spray require strategies to increase the pressure drop in the liquid flow path and/or to uniformize the electric field at the spray sources.     

INFLUENCE OF ELECTRIC FIELD PROFILE AND POLARITY ON THE MODE OF EHDA RELATED TO ELECTRIC DISCHARGE REGIMES

The paper deals with the production of charged droplets by electro-hydro dynamic atomization (EHDA). It brings three original features of EHDA of liquids in relation with electric field symmetry, polarity, intensity and divergence in the inter-electrode gap from the liquid surface to the ground electrode. We first describe the influence of the symmetry of the spraying electrodes system (axial or plane) on the cone and spray shape and on the droplet size produced in the cone-jet mode. The spray turns from a conical shape, with the axial symmetry nozzle/plane configuration, to an ellipsoid whose longer diameter is perpendicular to the tube with the planar symmetry tube/plane configuration. However, the initial droplet size in the production zone is the same whatever the symmetry is. EHDA in the cone-jet mode is then characterized under AC fields, as a succession of positive and negative cones on both sides of the pendant drop, leading to similar droplet diameter to that with DC polarity. Finally, electric and granulometric measurements are used to define the different modes of water sprays according to liquid properties and to experimental parameters (conductivity, flow rate and liquid voltage) related to electric discharge phenomena (continuous or impulse). We found that (i) a continuous corona discharge current (glow) allows the EHDA of water in, what we decided to call the “cone-jet-glow” mode, leading to the production of unimodal sprays, whereas (ii) a strong impulse discharge current (streamer) disturbs the continuous EHDA in the “cone-jet-glow” mode to, what we decided to call, the “electric-dripping” mode, because of the polymodal sprays induced by impulse electric discharges (streamer) development and by the resulting transient variation of the surface electric field. For stable EHDA of high surface tension liquid in a stable cone-jet glow mode, impulse discharges in the gas have to be prevented. In this respect, we have successfully increased the divergence of the field around the liquid (different nozzle diameters, and liquid flow rate) to promote the production mode of EHDA stabilized by a glow discharge, i.e. the cone-jet-glow mode.     

有限截面通道内喷雾顺流掺混动力学特征的实验研究

设计搭建了有限截面通道顺流喷雾掺混实验台,在横截面为70 mm×70 mm的透明方形掺混段内,将室温水经喷嘴雾化后顺流掺入不同流速的室温空气。实验中,喷水压力为0.1～1.5 MPa,风速为14.6～46.2 m?s^-1。分别采用高速摄影和马尔文粒度仪对该雾羽的速度场和初始粒径等动力学特征开展了实验研究。结果指出：掺混雾羽的径向速度及喷射轴线附近的轴向速度主要受制于喷水压力;而雾羽两翼处的轴向速度主要受风速影响。定义轴向平均速度为雾羽轴向特征速度,该平均速度随喷水压力或喷射距离的增大而增大;在喷水压力小时,风速的增大可使轴向平均速度随喷射距离增大的速率提高;在喷水压力高时则反之。掺混雾羽的初始粒径随喷水压力的减小或喷嘴出口处气液相对速度的增大而减小。最后,根据实验结果拟合了轴向平均速度和初始粒径的实验关联式,其计算值与实验值吻合良好。     

A study on the macroscopic spray behavior and atomization characteristics of biodiesel and dimethyl ether sprays under increased ambient pressure

The aim of this work is to investigate the spray behaviors of biodiesel and dimethyl ether (DME) fuels using image processing and atomization performance analysis of the two fuel sprays injected through a common-rail injection system under various ambient pressure conditions in a high pressure chamber. In order to observe the biodiesel and DME fuel spray behaviors under various ambient pressures, the spray images were analyzed at various times after the start of energization using a visualization system consisting of a high speed camera and two metal halide light sources. In addition, a high pressure chamber that can withstand a pressure of 4 MPa was used for adjusting the ambient pressure. From the spray images, spray characteristics such as the spray tip penetration, cone angle, area, and contour plot at various light intensity levels were analyzed using image conversion processing. Also, the local Sauter mean diameters (SMD) were measured at various axial/radial distances from the nozzle tip by a droplet measuring system to compare the atomization performances of the biodiesel and DME sprays.The results showed that the ambient pressure had a significant effect on the spray characteristics of the fuels at the various experimental conditions. The spray tip penetration and spray area decreased as the ambient pressure increased. The contour plot of the biodiesel and DME sprays showed a high light intensity level in the center regions of the sprays. In addition, it was revealed that the atomization performance of the biodiesel spray was inferior to that of the DME spray at the same injection and ambient conditions.     

APPLICATION OF LASER DIAGNOSTIC TECHNIQUES FOR THE EXAMINATION OF LIQUID FUEL SPRAY STRUCTURE

Results are presented on the spatial distribution of droplet mean size and number density obtained from a hollow-cone kerosene spray, introduced into nonswirling and swirling flow fields. An ensemble light scattering technique, based on measurement of the polarization ratio, has been employed to determine local droplet characteristics in both dense and dilute regions of the spray. The measurements are complemented with Lorenz-Mie calculations of the scattering characteristics for a polydispersion of droplets; the calculations were carried out for different mean sizes and refractive indices. The results reveal that the degree of swirl imparted to the surrounding air flow has a strong influence on spray structure. For all conditions examined the droplet mean size is found lo be larger on the spray boundary than towards the centerline. Droplet mean size is also found to increase with axial distance at all radial positions of the spray; this trend is attributed to the vaporization of smaller droplets and/or possible coalescence between the droplets.

In addition to the ensemble technique, measurements have also been obtained with the phase/Doppler interferometry and light intensity deconvolution techniques under identical experimental conditions. The droplet mean sizes obtained with the ensemble approach are in general smaller than those measured with the phase/Doppler technique; however, general features of the radial profiles obtained with both techniques are similar. The deconvolution technique also indicates the presence of smaller size droplets and supports the results obtained with the ensemble technique. The selective sensitivity of these sizing techniques to different ranges of droplet size and number density is discussed.     

基于图像法的环雾状流液滴参数测量与分析

环雾状流广泛存在于石油化工领域,其内部流场测量具有重要意义。本文结合光学图像法和高速摄影技术对撞针式喷嘴的雾化特性进行了测量分析,以此为基础对基于雾化混合的环雾状流中夹带液滴特性开展了实验研究。利用高速摄影技术对喷雾进行可视化,采用单帧单曝光法对液滴尺寸和速度信息进行提取。研究发现,液滴速度随轴向距离增大呈衰减趋势,且相同轴向距离（约在径向位置10mm处）条件下,速度达到峰值;液滴索泰尔平均直径（SMD）随喷嘴孔径d₀的增大而增大,并与液相质量流量m_l和喷嘴上下游压差?p均呈负相关;另外,在环雾状流环境中,相同气压条件下液滴SMD随气相体积流量Q_g增大而减小,而相同气相体积流量条件下SMD随气压p_g增大而增大。基于实验测量结果,以气相韦伯数We_g和液相雷诺数Re_l为主影响参数,引入相间滑移和压力系数建立了基于量纲分析的环雾状流液滴SMD预测模型,平均绝对百分比误差MAPE为11.4672%。     

An experimental and numerical study on sprays injected from two-hole nozzles for DISI engines

The objective of this study is to investigate the mixture formation process of sprays injected from two-hole nozzles for direct-injection spark-ignition (DISI) engines. Spray characteristics were examined for vapor and liquid mass distributions, spray tip penetration and spray angle using the laser absorption-scattering (LAS) technique and the computational fluid dynamics (CFD) simulation. Other characteristics including: the vapor phase concentration distribution, droplet spatial distribution and pressure distribution were acquired from the CFD simulation results. Comparison of measured and calculated results showed that as the hole-axis-angle (HAA) of the two-hole nozzle decreased, the droplet coalescence increased and vapor mass decreased. The spray with the HAA of 10° had the longest spray tip penetration and the spray with the HAA of 15° had the shortest one. The two jets of the two-hole nozzle spray had a tendency of offsetting to the central region of the spray. From 10 to 15 MPa, the increase in the injection pressure increased the vaporization rate and the spray tip penetration rate very much, but no such tendency was found when the injection pressure increased from 15 to 20 MPa.     

湿法脱硫雾化喷嘴特性实验研究

利用FAM激光颗粒测量仪,以水为工质对撞击流燃煤烟气湿法脱硫装置中采用的旋涡压力喷嘴的雾化特性进行了实验研究,测量了不同压力下液体雾化粒子的平均粒径和粒径分布,讨论了压力对雾化特性的影响,得出了压力和喷片结构尺寸对雾化特性的影响规律。     

An atomization model for splash plate nozzles

A model for the atomization and spray formation by splash plate nozzles is presented. This model is based on the liquid sheet formation theory due to an oblique impingement of a liquid jet on a solid surface. The continuous liquid sheet formed by the jet impingement is replaced with a set of dispersed droplets. The initial droplet sizes and velocities are determined based on theoretically predicted liquid sheet thickness and velocity. A Lagrangian spray code is used to model the spray dynamics and droplet size distribution further downstream of the nozzle. Results of this model are confirmed by the experimental data on the droplet size distribution across the spray. © 2009 American Institute of Chemical Engineers AIChE J, 2010     

Experimental investigation and model improvement on the atomization performance of single-hole Y-jet nozzle with high liquid flow rate

Y-jet nozzle, as an efficient multi-hole internal-mixing twin-fluid atomizer, has been widely used for liquid fuel spray in many industrial processes. However, single-hole Y-jet nozzle with high liquid flow rate is indispensable in some confined situations due to a small spray cone angle. In this paper, the atomization performance of single-hole Y-jet nozzles with high liquid mass flow rates ranging from 400 to 1500 kg/h for practical semidry flue gas desulfurization processes was investigated by the laser particle size analyzer, and the effects of spray water pressure, atomizing air pressure and air to liquid mass flow ratio on the liquid mass flow rate and the droplet size distribution were analyzed. Moreover, the secondary atomization model was modified on the basis of previous random atomization model of Y-jet nozzle. The predicted results agreed well with the experimental ones, and the improved atomization model of Y-jet nozzle was well validated to design the nozzle geometry and to predict the droplet size distributions for single-hole Y-jet nozzle with high liquid mass flow rate.     

Characterization of colloid thruster beams and plumes

Electrohydrodynamic atomization in the cone-jet mode can generate droplets with diameter as small as a few nanometers. The optimization of colloid thrusters, one of the important applications of this technology, requires a comprehensive understanding of the physics and structure of the associated beams and plumes. In this paper the electrospray beams and plumes emitted from a stable Taylor cone-jet are analyzed by means of a Lagrangian model using particle dynamics. The effect of droplets' charge involved with the electric field is identified as a Poisson problem and is solved through a PIC method. The model takes the electric forces and the droplet inertia into account with the colloid thruster operation in vacuum. Characteristics of the beam such as the size distribution of droplet diameter, the charge to mass ratio, the spray angle, the space distribution of droplets, the electric field and the velocity distribution along the axial and radial direction are presented in this paper. The relationship between droplet size and droplet charge in a spray was studied. The results of the model application are in good agreement with published experimental data and this proves that the electric interaction of charged droplets, the radial electric field and differences in inertia are the reasons for the size segregation effect in sprays.     

Spatially resolved characteristics of pharmaceutical sprays

Spatially resolved drop size, velocity, and volume flux data for five different spray coating guns were described in this study. Such spatially resolved measurements show how sprays respond to changes in operating conditions and gun design in ways that less complete measurements can not provide. Data for instance, allow us to recognize the unique drop size distribution of one of the sprays tested, which ultimately was an important factor in determining the dual roles of the shaping air flows: depending on drop size, viscosity, and the magnitude of the shaping air velocity, the shaping air can either pinch or induce secondary atomization to the sprays. When the former outweighs the latter, a dumbbell‐shaped spray develops; a more uniform spray results when the opposite occurs. Volume flux data from the different sprays also suggest that a more robust and consistent tablet coating process can likely be designed by utilizing multiple overlapping round sprays. © 2011 American Institute of Chemical Engineers AIChE J, 2012