气泡雾化喷头流量特性实验研究

设计了一种气泡雾化喷头,利用喷头雾化性能综合实验平台,对喷头的流量特性进行实验研究。考察了压降、气液比、压力比对流量特性的影响,通过实验测量与拟合得到了气泡雾化喷头气液比与液体流量系数的经验公式。实验研究结果表明,压降与气液比、液气压力比与气液比、气液比与液体流量系数均成反比关系。压力比、气液比对于喷头的最终雾化效果具有很大的影响,气压为0.1 MPa时,当液气压力比低于1.045,此时气液比大于0.1,液体流量系数小于0.13。     

Atomization of fuel mixtures

The combustion process of a coal/oil slurry begins by atomization of the slurry. This project is a presentation of experimental system and results on atomization of coal/oil(COM) and coal/methanol mixtures with a twin-fluid and a wheel atomizer. The slurries are consisted of coal/methanol and coal/oil mixtures with two different concentrations and two coal particile sizes. The volume median diameters of the coal particles were 45 and 130 microns. The oil was No. 2 diesel oil. The droplet size was determined by photographing the spray and the photographs were analyzed to determine droplet size and distribution. The results show that the inclusion of particles in the liquid(both methanol and diesel oil) does not appreciably affect the atomized droplet size. The tendency is for the slurry droplets to be somewhat smaller than the droplets atomized with the pure liquid.     

The effect of spray characteristics on the etching of invar alloy with FeCl3 solution

The objective of this study was to investigate the significant characteristics in the sprays of industrial etching nozzles for the sake of process design. The experiment was carried out with different spray pressures and industrial nozzles in the spray etching. Characteristics of the spray, such as the axial velocity and the Sauter mean diameter (SMD), were obtained through the Phase-Doppler Anemometer (PDA). The impact force was calculated through the spray characteristics. It was found that liquid with higher spray pressure resulted in a smaller SMD, higher droplet velocity, and greater impact force. The depth of etching was increased in the case of higher spray pressure. When the spray angle oscillated between 20° and −20°, the effect of etching remained constant. The relationships between the spray characteristics and the etching characteristics were analyzed. The depth of etching had significant, positive correlations with the axial velocity and the impact force. Four liquids of different kinematic viscosities were used to reveal the effects of the kinematic viscosity on the spray characteristics. The results indicated that a lower viscosity of the spray yielded a higher etching rate than a higher viscosity of the liquid. The results clearly show that the characteristics of the spray etching are strongly related to the spray characteristics with the spray conditions.     

基于Ｆｌｕｅｎｔ的雾化器雾滴粒径的研究

对雾化器的喷嘴结构进行研究,通过分析实验结果,得出影响液滴粒径的因素。以不同尺寸的液相通道为实验对象,通过改变轴向中心截面距、气液比、液相压力和气相压力的大小,分析以上实验参数对雾化发生器雾化后液滴颗粒大小的影响。由实验结果可知:在气液比、液相压力和气相压力的逐渐增加的过程中,液滴粒径呈现变小的趋向;在轴向中心截面距逐渐增加的过程中,液滴粒径呈现增大趋向。     

An investigation of design parameter and atomization mechanism for air shrouded injectors

With increasing requirements for the less harmful exhaust emissions and the better fuel economy, the conventional injectors in gasoline engines can be replaced by the air shrouded injector in order to provide improved combustion in engine operations. To find out the optimal shape of air shrouded atomizer attached to the conventional injector nozzle, the critical design parameters such as droplet size, fuel and air inlet angles, and injection angles were investigated based on experimental analyses. To explain the characteristics of fuel atomization, these experimental approaches were carried out using a Phase Doppler Particle Analyzer (PDPA) system. The droplet sizes of injected air fuel mixture were obtained by using the beam diffraction phenomenon. In order to improve the atomization effect, the various atomizers were investigated. The Sauter Mean Diameter (SMD) measured at the predetermined locations outside the atomizer represented the performance of fuel atomization. The experimental results show that the design factors and atomization mechanism needed for developing air shrouded injectors. The suggested design parameters in this paper can be a useful reference in the early design stage.     

高压细水雾灭火喷嘴的雾化特性研究

高压细水雾灭火系统是采用纯水液压技术的新型灭火装置,具有无环境污染、灭火迅速、用水量少和水渍损失极小等优点,是目前国际上推祟的哈龙替代系统。运用轴对称射流边界层动量积分法,对系统关键执行元件—直射式雾化喷嘴的内部流动进行分析,对边界层厚度δ和加速因子K这两个内部流动参数进行考查;同时对一些与灭火效果有关的外部雾化特性参数如出口速度和雾滴平均粒径SMD等进行分析,得出压力是影响外部雾化特性参数的最关键因素。认为8~9 Mpa是所设计喷嘴的最低稳定雾化工作压力区域。同时,喷嘴结构参数收缩角α、收缩段长度l/d对内部流动参数、外部雾化特性参数均有影响,但不明显。试验验证了上述分析结果,优选出了适合的喷嘴内部结构。     

两相脉冲爆震发动机的燃油喷射、混合及其雾化研究

两相爆震燃烧近来得到了广泛的重视和关注,但在它走向应用之前仍有很多问题需要解决。燃油的喷射、混合和雾化对两相爆震燃烧的影响就是其中之一。本文利用激光喷雾测量仪分别就直射喷嘴与气动喷嘴研究了汽油的喷射雾化与混合雾化,得到了汽油的雾化粒度与供油量、供气量间的关系。利用CFD程序对混合室中油、气的混合特性进行了模拟,结果与试验结果非常吻合。结合脉冲爆震发动机模型机多循环爆震试验,发现汽油的粒度大小对脉冲爆震模型机的油气当量比、燃油填充比有显著的影响。     

Spray characteristics on the electrostatic rotating bell applicator

The current trend in automotive finishing industry is to use more electrostatic rotating bell (ESRB) need space to their higher transfer efficiency. The flow physics related with the transfer efficiency is strongly influenced by operating parameters. In order to improve their high transfer efficiency without compromising the coating quality, a better understanding is necessary to the ESRB application of metallic basecoat painting for the automobile exterior. This paper presents the results from experimental investigation of the ESRB spray to apply water-borne painting. The visualization, the droplet size, and velocity measurements of the spray flow were conducted under the operating conditions such as liquid flow rate, shaping airflow rate, bell rotational speed, and electrostatic voltage setting. The optical techniques used in here were a microscopic and light sheet visualization by a copper vapor laser, and a phase Doppler particle analyzer (PDPA) system. Water was used as paint surrogate for simplicity. The results show that the bell rotating speed is the most important influencing parameter for atomization processes. Liquid flow rate and shaping airflow rate significantly influence the spray structure. Based on the microscopic visualization, the atomization process occurs in ligament breakup mode, which is one of three atomization modes in rotating atomizer. In the spray transport zone, droplets tend to distribute according to size with the larger drops on the outer periphery of spray. In addition, the results of present study provide detailed information on the paint spray structure and transfer processes.     

Investigation of droplet size distribution in two-phase flows using a combined method for recording droplet fluorescence and diffraction scattering of light

A prototype of a combined measurement system (MS) based on the fluorescent and small-angle methods of determining the parameters of a fuel-air spray using a pulsed laser as a light source and a color digital video camera to record spray sections was designed and tested. The tests of the MS showed that it has good performance and is suitable for determining the characteristics of advanced atomizers in a pressure chamber. Spatial concentration distributions of aerosols generated by a centrifugal atomizer were studied. Distributions of time-averaged Sauter diameters of droplets, their concentration, and the circumferential inhomogeneity of droplet concentration in the spray cross section were obtained. A study of fuel atomization from a plate was performed showing the possibility of using this device in power plants to improve the atomization performance compared to the atomization of a free jet in crossflow.     

圆管式压电喷头的液体分配

针对用于喷墨打印的圆管式压电喷头建立了计算模型,并且根据它的驱动特点选择了合适的边界条件。介绍了仿真软件针对自由表面流动问题的计算原理。然后,以乙二醇水溶液为例,计算了压电喷头分配该溶液的分配过程;利用液滴成像系统获取了不同时刻的液滴图像,验证了建立的模型和数值算法的正确性。最后,计算了压电喷头在不同输入位移、不同黏度以及不同表面张力下的液体分配过程。仿真结果显示:液体分配性能与激励位移密切相关,在72.5mN/m的表面张力作用下,10nm的输入位移很难分配黏度为4.0mPa·s的液体,而15nm的输入位移在分配黏度为4.0mPa·s液体时却能够产生卫星液滴。因此,对于某种液体寻找一个合适的激励条件非常重要,过小的激励产生不了液滴,过大的激励则会产生较大甚至多个卫星液滴;增大黏度会延缓或阻滞液滴形成过程,增大表面张力却能加快液滴形成过程。本文的计算方法对于研制新式喷头或者研究喷头的喷射能力均具有指导意义。     

High flow-rate ultrasonic seeder

Application of optical techniques to gaseous flows usually requires seeding the fluid with tracers sufficiently small to follow the flow, added in suitable concentrations. This work describes the design and manufacture of a seeder based on ultrasonic atomization of aqueous solutions or other fluids of similar viscosity, capable of operating in a continuous way with high atomization rates. It includes a dozen piezoceramic disks that oscillate at 1.65 MHz, generating droplets with Sauter mean diameter in the range of 4–5 μm and rates over 0.6 g/s when working with water. To test its performance, the device has been used to seed a simple free air jet issuing from a 3.5 cm diameter pipe. Initially the seeding density is very satisfactory, but if only water is nebulized the droplets evaporate in a short time and the concentration becomes too low when moving downstream. The situation can be greatly improved mixing the water with a less volatile liquid. Here, a small percentage of glycerol (5% in volume) has been added to the water to extend the droplet lifetime, although in general, atomization rate strongly decreases when increasing the liquid viscosity. The seeded flow has been visualized, and the 3D velocity field has been successfully measured using stereoscopic particle image velocimetry.     

Experimental analysis and numerical modeling using lisa-ddb hybrid breakup model of direct injected gasoline spray

This paper presents the effect of injection pressure on the atomization characteristics of high-pressure injector in a direct injection gasoline engine both experimentally and numerically. The atomization characteristics such as mean droplet size, mean velocity, and velocity distribution were measured by phase Doppler particle analyzer. The spray development, spray penetration, and global spray structure were visualized using a laser sheet method. In order to investigate the atomization process in more detail, the calculations with the LISA-DDB hybrid model were performed. The results provide the effect of injection pressure on the macroscopic and microscopic behaviors such as spray development, spray penetration, mean droplet size, and mean velocity distribution. It is revealed that the accuracy of prediction is promoted by using the LISA-DDB hybrid breakup model, comparing to the original LISA model or TAB model alone. And the characteristics of the primary and secondary breakups have been investigated by numerical approach.     

An investigation on effect of geometrical parameters on spray cone angle and droplet size distribution of a two-fluid atomizer

A visual study is conducted to determine the effect of geometrical parameters of a two-fluid atomizer on its spray cone angle. The liquid (water) jets exit from six peripheral inclined orifices and are introduced to a high speed gas (air) stream in the gravitational direction. Using a high speed imaging system, the spray cone angle has been determined in constant operational conditions, i.e., Reynolds and Weber numbers for different nozzle geometries. Also, the droplet sizes (Sauter mean diameter) and their distributions have been determined using Malvern Master Sizer x. The investigated geometrical parameters are the liquid jet diameter, liquid port angle and the length of the gas-liquid mixing chamber. The results show that among these parameters, the liquid jet diameter has a significant effect on spray cone angle. In addition, an empirical correlation has been obtained to predict the spray cone angle of the present two-fluid atomizer in terms of nozzle geometries.     

Effects of ALR and configuration ratio on turbulent structures in swirling flows

To assess the significant physics associated with the increase of ALR and configuration ratio of the nozzle tip in pneumatic swirling flows, comprehensive observations using a 3-D PDPA system were experimentally carried out. Profiles of mean velocities, turbulence intensities, SMD variations, and correlations between droplet size and turbulence components were quantitatively acquired. As discussed in a previous literature, axisymmetric swirl angle of 30° is selected for this investigation because of its strong turbulence levels in the flowfield and finer droplet disintegrations. Various ALRs (Air-to-Liquid Mass Ratio) as well as the length-to-diameter ratios of nozzle tip as parameters were chosen. Due to the complex interactions in swirling flows under these variables, this experimental observation will be of fundamental importance to the understanding of turbulence structures. From the observations, it indicated that increasing the ALR causes the spray development to be positively fluctuated on the atomization in both axial and tangential RMS velocities. Also, it can be concluded that the SMD decreases continuously with increase of ALR, substantiating the fact that the fluctuations are inversely proportional to the SMD variation. Meanwhile, the spray behavior is characteristic with a reduction of length-to-diameter ratio; smaller the configuration ratio, the higher the turbulence intensities and smaller SMD variations in the flowfield.     

车灯清洗器喷嘴内流体流动的CFD分析

在建立了某车灯清洗器喷嘴内部流动的三维CFD计算模型之后,对该喷嘴内部的三维流动进行了数值模拟分析,分析了喷嘴旋芯结构参数对喷嘴的压力、出口速度等的影响。分析结果为喷嘴结构的设计提供了重要的参考依据,从而可以减少大量的实验操作。     

气动式微滴喷射中液滴稳定生成的动力学特性研究

微滴喷射增材制造技术作为制造领域的新兴前沿技术有着广泛的应用前景,微滴生成特性对增材制造中微滴在基板铺展、搭接、凝固等过程影响较大,研究微滴生成特性对于提高液滴生成尺寸、频率和稳定性有重要意义。通过试验研究气动按需喷射作用下的微滴喷射行为,探究喷嘴尺寸、黏度和供给压力等因素对射流断裂过程及液滴生成稳定性的影响关系,并进一步研究形成角的变化对液桥断裂顺序及卫星液滴产生的影响关系。研究结果表明,随着喷嘴直径减少,韦伯数（We）显著减少,当喷嘴直径减少到100 μm时,We变为0.33,液滴尺寸与喷嘴直径的比值急剧增大;随着黏度的增加,射流颈缩段的液桥显著增长,液滴尺寸明显增大。在保证生成单个液滴的压力条件下,当供给压力较小时,液桥两端先后断裂形成卫星滴,并最终与半月面融合;随着压力的增大,液桥只发生一次断裂,剩余射流回缩到喷嘴内。在气动式喷射方式中由于上形成角始终大于下形成角,所以液桥总是在靠近液滴端首先断裂,该研究结果有助于提高气动式微滴喷射装置的液滴生成质量。     

液滴撞击多孔表面动力学特性研究进展

液滴与多孔表面碰撞时，多孔表面的孔隙所引起的毛细力作用将对液滴的动力学行为产生一定的影响。研究液滴撞击多孔表面后的铺展、渗透、蒸发、传热等问题对调控多孔表面液滴的铺展以满足不同领域的应用需求具有重要的意义。总结归纳了液滴撞击多孔表面的理论、数值和实验方面的研究方法，对液滴撞击速度、液滴直径、孔隙率、孔径、韦伯数、黏度和表面张力等主要因素对液滴撞击动力学特性的影响规律进行综述，提出液滴在多孔表面的研究可从更加符合液滴撞击多孔介质的理论模型建立，新型多孔介质内部液滴特性及热物理参数测试技术等方面进行。     

Theoretical calculations and experimental verification for the pumping effect caused by the dynamic micro-tapered angle

The atomizer with micro cone apertures has advantages of ultra-fine atomized droplets, low power consumption and low temperature rise. The current research of this kind of atomizer mainly focuses on the performance and its application while there is less research of the principle of the atomization. Under the analysis of the dispenser and its micro-tapered aperture’s deformation, the volume changes during the deformation and vibration of the micro-tapered aperture on the dispenser are calculated by coordinate transformation. Based on the characters of the flow resistance in a cone aperture, it is found that the dynamic cone angle results from periodical changes of the volume of the micro-tapered aperture of the atomizer and this change drives one-way flows. Besides, an experimental atomization platform is established to measure the atomization rates with different resonance frequencies of the cone aperture atomizer. The atomization performances of cone aperture and straight aperture atomizers are also measured. The experimental results show the existence of the pumping effect of the dynamic tapered angle. This effect is usually observed in industries that require low dispersion and micro- and nanoscale grain sizes, such as during production of high-pressure nozzles and inhalation therapy. Strategies to minimize the pumping effect of the dynamic cone angle or improve future designs are important concerns. This research proposes that dynamic micro-tapered angle is an important cause of atomization of the atomizer with micro cone apertures.     

Atomization characteristics and prediction accuracy of LISA-DDB model for gasoline direct injection spray

In this paper, the spray atomization characteristics of a gasoline direct-injection injector were investigated experimentally and numerically. To visualize the developing spray process, a laser sheet method with a Nd :YAG laser was utilized. The microscopic atomization characteristics such as the droplet size and velocity distribution were also obtained by using a phase Doppler particle analyzer system at the 5 MPa of injection pressure. With the experiments, the calculations of spray atomization were conducted by using the KIVA code with the LISA-DDB breakup model. Based on the agreement with the experimental results, the prediction accuracy of LISA-DDB breakup model was investigated in terms of the spray shapes, spray tip penetration, SMD distribution, and axial mean velocity. The results of this study provides the macroscopic and microscopic characteristics of the spray atomization, and prediction accuracy of the LISA-DDB model.     

MODELING OF A SOLID CONE PRESSURE-SWIRL ATOMIZER

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