双通道气流式喷嘴雾化特性实验研究

以清水和空气为实验介质,对同轴双通道气流式喷嘴雾化特性进行了实验研究,分析了喷淋量对雾化角及径向流通量分布的影响,分别考察了气速和喷嘴轴向位置对液滴索特平均直径(SMD)的影响。研究结果表明,喷嘴径向流通量分布随着雾化气量的升高而趋于集中,当气体流量高于1500 L/min时,雾化角随着气量升高而降低;喷口处气速与喷嘴轴向位置均是影响液滴SMD与粒径分布的重要因素,液滴SMD随着气速增大逐渐减小,当气速超过150 m/s时其下降趋势变缓,粒径分布均匀度显著提高;随着喷嘴轴向距离增大液滴SMD逐渐减小,当距离大于300 mm时其变化不再显著,但粒径分布均匀度显著提高。     

空气助力改善气化炉激冷室喷嘴特性的实验研究

设计了4种不同结构的用于气化炉激冷室内喷雾激冷的压力雾化喷嘴,采用马尔文激光粒度分析仪和数码单反照相机分别测量了不同压差、不同水流量等工况参数下的液滴粒径(SMD)D32分布和雾化角变化规律,并对4种喷嘴进行了优化选型。研究结果表明:雾滴粒径随压力的增加而减小,随水流量的减小而减小,空气助力可以明显改善液滴的雾化质量;雾化角随压差的增大先增大后趋于平缓;当压差增大到0.4 MPa时,雾滴粒径、雾化角等参数的变化渐趋平缓。通过比较气化炉激冷室中4种压力式雾化喷嘴的测量结果,1-2号内混式空气雾化喷嘴在4组喷嘴中具有最好的雾化效果,当气压为0.8 MPa,水流量为20 L/h时,SMD极小值为16,因此优选出喷嘴1-2作为气化炉激冷室冷模实验的定型喷嘴。     

旋流压力式喷嘴低压喷淋液滴粒径的实验研究

以自来水为喷淋介质,对旋流压力式喷嘴低压喷淋液滴粒径进行了测试,分析了压力、喷孔直径和喷嘴流量对液滴索特平均直径(d_(SMD))的影响规律,研究了旋流压力式喷嘴液滴尺寸的分布规律。采用跨径(K)和均匀度指数(N)来揭示喷嘴低压喷淋质量。实验结果表明,d_(SMD)较大,超过250μm；d_(SMD)随喷孔直径增大而增大,随压力和喷嘴流量增大而减小；喷淋液滴尺寸分布均匀性较好,K小于0．65,N大于4。实验结果可以为旋流压力式喷嘴设计和改进提供重要的实验依据。     

喷嘴雾化参数轨迹图像法测量实验研究

针对喷嘴雾化多参数同步测量问题,提出了基于图像处理的喷嘴雾化角、雾化细度、液滴运动速度及分布参数测量方法,利用背光阴影成像技术搭建了喷嘴雾化参数测量系统,建立了基于轨迹图像法原理的喷嘴雾化参数图像处理流程与算法,利用标准颗粒测量验证了该方法对颗粒粒径测量的精度,并开展了不同孔径与压力下扇形喷嘴雾化参数同步测量实验研究。结果表明:当雾化压力不变,扇形喷嘴孔径从0.66 mm变为1.10 mm时,雾化细度与液滴平均运动速度分别增加26.82%、10.42%,而雾化角随扇形喷嘴孔径增大而减小16.66%;当扇形喷嘴孔径不变,雾化压力从0.1 MPa增加到0.4 MPa时,雾化角与液滴平均运动速度分别增加47.71%、95.10%,而雾化细度随雾化压力增加而减小44.23%。这为雾化液滴特性研究与喷嘴性能评估提供了有效手段。     

喷淋塔液滴粒径分布及比表面积的实验研究

以水和空气为实验介质,通过拍照法获得喷淋塔内液滴粒径分布,考察了不同喷淋量及空塔气速对塔内不同高度处液滴Sauter平均直径(SMD)的影响,并对液滴粒径分布进行了理论分析.结果表明,喷淋塔顶部液滴分布密集,底部稀疏,液滴群在下落过程中,平均粒径减小且趋于均匀化;塔顶处液滴SMD随喷淋量的增加而增大,处在塔中下部的液滴SMD则随喷淋量增大而减小,提高空塔气速,可减小平均粒径;理论分析认为,液滴粒径减小主要是由于发生了碰撞破碎的缘故,而塔内液滴大小不一是碰撞的主要原因;通过量纲1化拟合得到喷淋塔内液滴SMD经验关联式,其计算结果与实验值吻合较好;考虑液滴破碎的喷淋塔比表面积比不考虑破碎的比表面积大70%左右.     

同轴四通道喷嘴气流式雾化特性影响因素研究

提出一种新型同轴四通道喷嘴——由内到外采用气-液-气-液设置,最外环液体可以将合成气和氧气隔离,大幅降低喷嘴出口温度,可望延长气化炉中喷嘴使用寿命。为研究喷嘴雾化效果的影响因素,以水和空气为介质,利用马尔文激光粒度分析仪对同轴四通道喷嘴的气流式雾化液滴索特平均直径进行实验研究。发现对雾化效果影响程度从大到小依次为通道三、通道四、通道二和通道一;增大通道二、四液量分配比可以降低雾化粒径;增大外环液膜厚度会增大雾化粒径;通道一、三气量分配比对雾化颗粒的影响是非单调性的,雾化粒径先增大后减小。基于实验结果进行数值分析,拟合获得了同轴四通道喷嘴雾化液滴粒径关系式。     

多喷嘴脱硫废水烟道蒸发特性模拟分析

火力发电厂湿法脱硫产生的脱硫废水处理难度大,脱硫废水烟道蒸发技术能够有效降低脱硫废水排放量,甚至实现脱硫废水零排放,进而降低电厂运行成本。为研究多喷嘴脱硫废水雾化液滴在锅炉尾部烟道中的蒸发规律,建立了脱硫废水雾化液滴在烟气内的传热传质模型。以某330 MW锅炉尾部烟道为研究对象,利用Ansys Fluent模拟研究了不同喷嘴数量时,烟气和雾化液滴性质对废水运动蒸发过程的影响。结果表明,当脱硫废水流量一定时,随喷嘴数量增多,单个喷嘴废水流量逐渐减少,使废水液滴在烟道内的分布更均匀,喷嘴上方的低温区域面积沿流动方向逐渐增大,平均温度和最低温度升高。在不同烟气和液滴性质条件下,随喷嘴数量增多,液滴的蒸发速度均增大,蒸发时间和运动距离缩短,但降幅逐渐变小,且液滴蒸发距离与蒸发时间正相关。此外,液滴运动速度几乎不受喷嘴数量变化的影响,液滴运动速度主要受烟气速度的影响。不同喷嘴数量时,随烟气温度升高、烟气含水量降低、液滴粒径减少、液滴初始速度初始温度增加,废水液滴的蒸发时间降低,蒸发距离缩短;烟气流速的增加降低了蒸发时间,单喷嘴时,蒸发距离先减小后增大,当烟气流速为10 m/s时,蒸发距离最短为9...     

空气雾化喷嘴的液滴雾化性能实验研究

采用LSA-Ⅲ型激光粒度仪对一种常用的小流量空气雾化喷嘴的液滴雾化性能进行实验研究。实验主要测定了不同气液比、气相压力和液相压力情况下沿喷雾轴向不同位置处的液滴粒径分布。测定结果表明气液比和气相压力对雾化液滴粒径影响均较大,其中气相压力影响最大,气液比其次,液相压力影响最小。在本实验测定条件下,经过喷嘴雾化后在轴向100、200、300、400和500 mm位置处液滴的表面积平均直径（SMD）和体积平均直径（D43）出现波动性变化。通过对实验测得液滴粒径分布数据的分析,可以得到Rosin-Rammler分布函数中的特征参数和n,为定量计算液滴粒径提供理论基础。     

压力雾化喷嘴在受限空间气流中喷雾特性的实验研究

对出口直径为0.21、0.28、0.38、0.46mm的4种压力雾化喷嘴及其组合在150mm×150mm×1 000mm的矩形通道中的喷雾流场进行了实验研究,矩形通道中的空气流速为10m/s。研究了喷嘴布置和组合方式对雾化流场的影响。实验结果表明:喷雾不碰壁距离随入射角的增大而增大;顺流喷雾比无气流时液滴的平均D32减小10%,粒径范围略有扩大;逆流喷雾比无气流时液滴的平均D32增大约70μm,粒径范围扩大了3⁴倍;出口直径小的喷嘴可通过逆流布置和顺流布置的组合,获得液滴粒径分布范围更宽的气液两相流场。双喷嘴在有限空间内的雾化效果与流场中气液流量比有关。所得研究结论对天然气加湿技术的开发有一定参考价值。     

压力式喷嘴雾化特性研究

用一操作简单的实验装置,以一定质量分数的甘油水溶液为工质,研究了压力式喷嘴雾化角、雾滴Sauter直径(SMD)与喷嘴孔径、雾化压力和粘度的关系。研究表明:雾化压力是雾化的有利因素,物料粘度是不利因素;实验条件下,压力式喷嘴雾化角随压力增大而减小,随喷嘴孔径增大而增大;在其他条件相同时,雾滴SMD随雾化压力增大而减小,随喷嘴孔径增大而增大,随物料粘度增大而增大。     

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.     

喷动床脱硫压力旋流喷嘴的雾化性能

雾化喷嘴是半干式喷动床的关键部件之一,其雾化性能直接影响脱硫效率。为了得到喷嘴雾化的详细信息,用激光粒度测试仪对空心锥压力旋流式喷嘴和实心锥压力旋流式喷嘴雾化性能进行了实验研究,得出不同类型、不同孔径的喷嘴的流量,索太尔直径DSM,雾滴粒径分布DSP等与压力的关系。实验表明:流量与压力平方根成正比关系;DSM与压力为e函数的单调减函数关系;实心锥喷嘴出口直径越大,雾滴粒径平均分布(■)越小,粒径分布范围越窄,雾化性能越好,空心锥喷嘴则变化不明显;压力增大,实心锥喷嘴的DSP变大,雾滴粒径在压力低时分布比较均匀。     

Characterization of the surface area of overflow droplets generated by a gas-lift pump under reduced pressure

Water-modelling experiments were carried out to characterize the surface area of overflow droplets generated by a gas-lift pump under reduced pressure as a function of various operating parameters, namely, top pressure, gas flow rate, nozzle submergence, lift ratio and riser diameter. The liquid phase mass transfer coefficient was obtained by applying the penetration theory (Treybal, 1980; Bird et al., 1960) to the overflow generated from the riser. Under reduced pressure, churn-turbulent flow, consisting of distorted bullet-shaped bubbles, was predominant in the flow regime. The increase of liquid circulation rate and flight time and the decrease of droplet size increased the refining rate. Because of the large droplet size, the refining rate of molten metals was smaller than that of water.     

Mean Droplet Size and Local Velocity in Horizontal Isothermal Free Jets of Air and Water,respectively, Viscous Liquid in Quiescent Ambient Air

Measurements using two‐dimensional Phase Doppler Anemometry as well as high speed cinematography in free jets at several nozzle exit pressures and mass flow rates, show that the Sauter mean droplet diameter decreases with increasing air and liquid‐phase mass flow ratio due to the increase of the air stream impact on the liquid phase. This leads to substantial liquid fragmentation, respectively primary droplet breakup, and hence, satellite droplet formation with small sizes. This trend is also significant in the case of a liquid viscosity higher than that of water. The increased liquid viscosity stabilizes the droplet formation and breakup by reducing the rate of surface perturbations and consequently droplet distortions, ultimately also leading, in total, to the formation of smaller droplets. The droplet velocity decreases with the nozzle downstream distance, basically due to the continual air entrainment and due to the collisions between the droplets. The droplet collisions may induce further liquid fragmentation and, hence, formation of a number of relatively smaller droplets respectively secondary breakup, or may induce agglomeration to comparatively larger liquid fragments that may rain out of the free jet.     

Water spray cooling of polymers

The cooling process in conventional rotomolding is relatively long due to poor thermal conductivity of plastics. The lack of internal cooling is a major limitation although rapid external cooling is possible. Various internal cooling methodologies have been studied to reduce the cycle time. These include the use of compressed air, cryogenic liquid nitrogen, chilled water coils, and cryogenic liquid carbon dioxide, all of which have limitations. However, this article demonstrates the use of water spray cooling of polymers as a viable and effective method for internal cooling in rotomolding. To this end, hydraulic, pneumatic, and ultrasonic nozzles were applied and evaluated using a specially constructed test rig to assess their efficiency. The effects of nozzle type and different parametric settings on water droplet size, velocity, and mass flow rate were analyzed and their influence on cooling rate, surface quality, and morphology of polymer exposed to spray cooling were characterized. The pneumatic nozzle provided highest average cooling rate while the hydraulic nozzle gave lowest average cooling rate. The ultrasonic nozzle with medium droplet size traveling at low velocity produced satisfactory surface finish. Water spray cooling produced smaller spherulites compared to ambient cooling whilst increasing the cooling rate decreases the percentage crystallinity. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers     

Assessment of fire protection performance of water mist applied in exhaust ducts for semiconductor fabrication process

Fume exhaust pipes used in semiconductor facilities underwent a series of fire tests to evaluate the performance of a water mist system. The parameters considered were the amount of water that the mist nozzles used, the air flow velocity, the fire intensity and the water mist system operating pressure. In order to make a performance comparison, tests were also performed with a standard sprinkler system. The base case served as a reference and applied a single water mist nozzle (100 bar operating pressure, 7.3 l/min water volume flux and 200 µm mean droplet size) installed in the pipe (60 cm in diameter) subjected to a 350°C air flow with an average velocity of 2 m/s. In such a case, the temperature in the hot flow dropped sharply as the water mist nozzle was activated and reached a 60°C saturation point. Under the same operating conditions, four mist nozzles were applied, and made no further contribution to reducing the fire temperature compared with the case using only a single nozzle. Similar fire protection performances to that in the base case were still retained when the exhaust flow velocity increased to 3 m/s and the inlet air temperature was increased to 500°C due to a stronger input fire scenario, respectively. Changing to a water mist system produced a better performance than a standard sprinkler. With regard to the effect of operating pressure of water mist system, a higher operating pressure can have a better performance. The results above indicate that the droplet size in a water‐related fire protection system plays a critical role. Copyright © 2005 John Wiley & Sons, Ltd.     

Robust generation of monodisperse droplets using a microfluidic step emulsification device with triangular nozzle

In this work, the droplet generation process in the microfluidic step emulsification chip with a triangular nozzle (SE-T) was investigated in the combination of visualization experiment and numerical simulation, through a comparison with a rectangular nozzle (SE-R). The flow regimes, including dripping, dripping-jetting transition, and jetting, were observed in the SE-T, among which the dripping is the preferred flow regime to generate monodispersed droplet with corresponding C.V. (coefficient of variation) of the droplet size smaller than 1.9%. Compared with the SE-R, the larger space and expanding structure of the triangular nozzle in the SE-T enhance the wall wetting effects, which induces earlier appearance and accelerates shrinking of the neck. As a result, the SE-T exhibits more robust droplet performance under the dripping regime, which produces the droplets with nearly unchanged size and higher monodispersity, especially little related to the variations of surfactant concentrations and dispersed phase flow rates.     

Influence of Atomizing Parameters on Droplet Properties in a Pulse Combustion Spray Dryer

A pulse combustor employed in a spray-drying system offers a new approach for liquid atomization that yields high-quality powders at low cost. Using a pulse combustion atomizer, there is no need for any form of nozzle dispersion and its atomization mechanism differs from those of conventional atomizers, such as rotary atomizers and pressure and pneumatic nozzles. In this work, based on the analysis of atomization mechanism, experiments of unsteady pulsating atomization were carried out in an experimental system of a Helmholtz-type pulse combustor. An optical analyzer was used for measuring the mean diameter of atomized droplet and droplet distribution. The effects of liquid feed rate, air flow oscillatory frequency, and liquid viscosity on atomized droplet size and size distribution were investigated and analyzed. The results indicate that the uniform droplet size distribution can be obtained under the conditions of a low feed rate, high-frequency pulsating flow, and moderate viscosity. The range of the droplets' Sauter mean diameter (SMD) is between 50 and 80 µm. The pulsating air flow from the pulse combustor can be used to atomize liquid or slurry without a nozzle and the atomizing quality can meet the requirements of spray drying.     

空心喷嘴喷淋特性实验研究

为使大型水平管降膜多效蒸发海水淡化装置的横管降膜蒸发器均匀布液,自主设计并搭建了一套离心喷嘴喷淋特性实验台及径向喷淋密度测量装置,通过高速摄影仪拍摄的喷淋照片对喷淋外缘进行标注测量,得到喷嘴各喷淋锥角,对旋流式空心喷嘴的流量、喷淋锥角和径向喷淋密度等喷淋参数随入口压力、喷淋高度的变化规律进行实验探究分析。结果表明,流量随入口压力增加而增加,但入口压力越大,流量增长速度越缓慢;正常工况下,喷淋锥角由喷嘴出口扩张段角度决定,与喷嘴扩张角保持一致,在重力作用下出现向内的收缩圆弧液膜边;喷淋形状为规则的环形喷淋,入口压力增加使有效喷淋区域整体向中心压缩,喷淋密度峰值变大,两波峰的对称性得到改善,压力为349 kPa时,喷淋密度基本完全对称,增加喷淋高度则情况相反。根据此喷淋密度分布特点,在设计横管蒸发布液器时合理控制工况压强,根据峰谷叠加原理可有效消除无效喷淋区域。