EXPERIMENTAL STUDY ON THE MACRO-AND MICRO- CHARACTERISTICS OF THE SPRAY FROM A PRESSURE SWIRL NOZZLE

The experimental study on the macro and micro characteristics of the spray from a pressure swirl nozzle embraces the growth of surface unstable wave,disintegration process,spray angle,breakup length and so on.The effects of injection pressure,nozzle geometry and liquid properties on these characteristics are also discussed.The results are helpful to understand the underlying physics of the pressure swirl nozzle and serve as the basis for the practical design,usage and improvement of the nozzle.

Supersonic swirling characteristics of natural gas in convergent-divergent nozzles

The supersonic nozzle is a new apparatus which can be used to condense and separate water and heavy hydrocarbons from natural gas.The swirling separation of natural gas in the convergent-divergent nozzle was numerically simulated based on a new design which incorporates a central body. Axial distribution of the main parameters of gas flow was investigated,while the basic parameters of gas flow were obtained as functions of radius at the nozzle exit.The effect of the nozzle geometry on the swirling separation was analyzed.The numerical results show that water and heavy hydrocarbons can be condensed and separated from natural gas under the combined effect of the low temperature（-80℃） and the centrifugal field（482,400g,g is the acceleration of gravity）.The gas dynamic parameters are uniformly distributed correspondingly in the radial central region of the channel,for example the distribution range of the static temperature and the centrifugal acceleration are from -80 to -55℃and 220,000g to 500,000g,respectively,which would create good conditions for the cyclone separation of the liquids.However,high gradients of gas dynamic parameters near the channel walls may impair the process of separation.The geometry of the nozzle has a great influence on the separation performance. Increasing the nozzle convergent angle can improve the separation efficiency.The swirling natural gas can be well separated when the divergent angle takes values from 4°to 12°in the convergent-divergent nozzle.

A swirling jet from a nozzle with tangential inlets and its characteristics in breaking-up rocks

In order to apply a swirling jet to a PDC drill bit, the nozzle performance influenced by nozzle inlet geometric parameters and rock breaking tests under submerged conditions were studied. Numerical simulation was used to study the influence of the nozzle structure on the swirling intensity and nozzle discharge coefficient. Simulation results indicate that spreading angle of the swirling jet is greater than that of＂ the non-swirling jet, and the swirling intensity of the jet is strongly influenced by the length of the nozzle body but weakly by the number of tangential inlets. Rock breaking tests were conducted to evaluate the performance of the swirling jet. It is found that the swirling jet shows a lower threshold pressure to break the rock samples and could break rock more efficiently compared with the non-swirling jet.

Prediction of atomization characteristics of pressure swirl nozzle with different structures

The structure of the pressure swirl nozzle is an important factor affecting its spray performance.This work aims to study pressure swirl nozzles with different structures by experiment and simulation.In the experiment,10 nozzles with different structures are designed to comprehensively cover various geometric factors.In terms of simulation,steady-state simulation with less computational complexity is used to study the flow inside the nozzle.The results show that the diameter of the inlet and outlet,the direction of the inlet,the diameter of the swirl chamber,and the height of the swirl chamber all affect the atomization performance,and the diameter of the inlet and outlet has a greater impact.It is found that under the same flow rate and pressure,the geometric differences do have a significant impact on the atomization characteristics,such as spray angle and SMD(Sauter mean diameter).Specific nozzle structures can be customized according to the actual needs.Data analysis shows that the spray angle is related to the swirl number,and the SMD is related to turbulent kinetic energy.Through data fitting,the equations for predicting the spray angle and the SMD are obtained.The error range of the fitting equation for the prediction of spray angle and SMD is within 15% and 10% respectively.The prediction is expected to be used in engineering to estimate the spray performance at the beginning of a real project.

Turbulent flow in converging nozzles,part one:boundary layer solution

The boundary layer integral method is used to investigate the development of the turbulent swirling flow at the entrance region of a conical nozzle. The governing equations in the spherical coordinate system are simplified with the boundary layer as- sumptions and integrated through the boundary layer. The resulting sets of differential equations are then solved by the fourth-order Adams predictor-corrector method. The free vortex and uniform velocity profiles are applied for the tangential and axial velocities at the inlet region, respectively. Due to the lack of experimental data for swirling flows in converging nozzles, the developed model is validated against the numerical simulations. The results of numerical simulations demonstrate the capability of the analytical model in predicting boundary layer parameters such as the boundary layer growth, the shear rate, the boundary layer thickness, and the swirl intensity decay rate for different cone angles. The proposed method introduces a simple and robust procedure to investigate the boundary layer parameters inside the converging geometries.

Numerical simulation on gas–liquid multiphase flow behavior under coupling effects of annular gas curtain and swirling flow at tundish upper nozzle

A three-dimensional mathematical model has been established for a novel metallurgy process coupling an annular gas curtain with swirling flow at tundish upper nozzle. The discrete phase model and volume of fluid model were applied to simulate the gas–liquid multiphase flow behavior in tundish and nozzle. The effect of argon flow rate on the migration behavior of bubbles and interface behavior between steel and slag was also investigated. The presented results indicate that the novel coupling process can significantly change the flow pattern in the stream zone of a tundish, prolong the average residence time of liquid steel, and reduce the dead fraction. A complete annular gas curtain is formed around the stopper rod of tundish. Under the action of drag force of liquid steel, a part of small bubbles enter the nozzle through the swirling grooves and gather toward the center of the nozzle by centripetal force. As the argon flow rate increases, the volume fraction of argon gas entering the nozzle increases, which enhances the swirl intensity and increases the concentration of bubbles in the nozzle. To avoid the formation of slag open eye in tundish, the argon flow rate should not exceed 8 L min−1.

离心喷嘴内部两相流动及液膜波动特性研究

应用界面跟踪方法,RNG(Renormalizationgroup)k-ε湍流模型,对离心喷嘴内部液膜波动特性进行了数值模拟研究.分析了不同的进口速度、燃油表面张力对液膜波动特性的影响.结果表明,离心喷嘴内部充液过程包括非稳态液膜形成过程和准稳态波动过程两个阶段,达到准稳态后,液膜(气核)存在明显的周期性波动特性.随着进口速度的增大,旋转所产生的离心力随之增大,气核尺寸也随之增大,液膜厚度变薄.不同表面张力下气核波动频率变化不大,但幅值不同,表面张力越小,波动振幅越大.

筒形五喷嘴燃烧室冷态时均流场特性实验研究

为深入研究五喷嘴燃烧室的流场特性,采用高频PIV测量方法对燃烧室中心截面的冷态流场开展实验研究,主要分析了燃烧室入口速度以及中心喷嘴旋流强度对五喷嘴燃烧室中心截面的时均流场特征的影响。实验结果表明:中心喷嘴和外侧喷嘴出口均存在主回流区,外侧喷嘴与燃烧室壁面间存在角回流区,相邻喷嘴射流相互干涉。喷嘴旋流强度相同时,入口速度由10 m/s增大到20 m/s,中心喷嘴和外侧喷嘴的回流区形态、主回流区长度、最大回流速度位置和气流合并点位置基本不变。入口速度为14.3 m/s时,中心喷嘴旋流强度由0.63增大到0.84,中心喷嘴回流区长度增大,外侧喷嘴回流区长度不变,主回流区最大回流速度显著增大,且更靠近喷嘴出口,气流合并点径向位置基本不变,轴向位置向喷嘴出口移动。

SCR系统压力旋流式喷嘴结构对近场喷雾特性的影响

选择性催化还原(SCR)系统是柴油机脱除尾气NO_(x)的核心,喷嘴的雾化性能直接影响NO_(x)转化率及尿素结晶,压力旋流式喷嘴比直流式喷嘴更有性能优势.以新设计的一款压力旋流式喷嘴为对象,结合试验数据,基于流体体积函数(VOF)法,耦合喷嘴内旋流与喷嘴外近场喷雾开展三维数值模拟,精准获取旋流液膜厚度、液膜锥角.基于喷孔内部流场与索特平均直径(SMD)的关系模型,实现喷嘴结构对喷雾雾化性能的直接耦合研究,进而获得了旋流室长度、旋流室直径、出口段长度和出口段孔径等压力旋流式喷嘴关键结构参数对喷雾性能的影响特性,结果表明:喷嘴几何参数调整需由气核生长情况判断;当气/液两相分界面呈多级阶梯型时,减小旋流室长径比、出口段长径比均可有效降低喷雾粒径,增强雾化效果.该新设计的压力旋流式喷嘴具备SMD小于30μm的潜力.

气体中心式气液同轴离心多喷嘴耦合喷雾特性研究

高温燃气流风洞的加热段喷注面板由数百个气液同轴离心喷嘴组成,各喷嘴间存在强烈的喷雾干涉现象,导致喷雾场相互耦合。为探究气体中心式气液同轴离心喷嘴喷雾的耦合对雾化特性及流场均匀性的影响,通过实验和仿真的方式研究了不同气液比对多喷嘴雾化特性的影响,以及喷嘴间距和喷嘴数目对喷雾流强分布的影响。设计安装多喷嘴的喷注器,搭建喷雾检测实验台,采用高速相机拍摄喷雾图像,采用马尔文激光粒度仪测量喷雾场中的液滴尺寸;并设计了流强测量系统,以测量喷雾场的流强分布。采用流体体积法(Volume of Fluid,VOF)和网格自适应技术(Adaptive Mesh Refinement,AMR)对多喷嘴的耦合喷雾场进行模拟。结果表明,仿真结果与实验测得的流量分布基本吻合;在液体流量较大的工况下,喷雾锥角基本稳定,粒径大小受液膜撞击破碎和液滴撞击聚合双重作用的影响;随着喷嘴间距的增加,喷雾分布的不均匀性增强;并且当存在3个及以上喷嘴时,喷雾场两两相互干涉,在喷雾耦合区域出现流强高峰。

超音速两相膨胀分离及制冷液化的研究进展

超音速膨胀降温并结合旋流分离技术是一种新型气体液化分离技术,近年来主要应用于分离多组分气体中的高凝点组分。介绍了超音速旋流分离器的2种典型结构;归纳了Laval喷管中凝结相变的理论发展、数值模拟、实验研究和分子模拟4个方面内容;对超音速旋流分离器中的激波问题、结构优化进行了分析总结;大量实验及现场应用证明了超音速旋流分离器具有节能环保、无运动部件、无需添加化学药剂等优势,在天然气净化处理等领域已得到广泛应用。下一步研究可从单组分、多组分气体凝结相变机理、提升液化效率等方面入手,促进超音速旋流分离技术在普冷温区、氢氦低温温区的液化及制冷技术应用。

密闭容器内旋流喷头除砂过程数值分析

为探究旋流喷头除砂过程容器内流场分布特性及流场对除砂能力的影响规律,采用RSM和DPM模型对密闭容器内部流场和颗粒运动轨迹进行了数值模拟。研究结果表明,压降从20 kPa增大到45 kPa时,容器内部旋流稳定性逐渐增强,容器中心颗粒质量分数不断增大,逃逸颗粒中大颗粒质量分数逐步增大;压降从45 kPa增大到100 kPa时,旋流稳定性减弱,逃逸颗粒中大颗粒质量分数小幅度下降,压降为45 kPa时旋流喷头能够以较低的能耗实现最佳的除砂效果。在旋流喷头中心管下端添加挡板可以有效减弱下游旋流切向速度,对旋流稳定性和轴向速度影响较小,有效提高了喷头对大颗粒的清除效率;挡板间隙h=15 mm时相比h=5 mm时整体旋流切向速度更小,对大颗粒的清除效果更高。喷头安装高度从100 mm下降到50 mm的过程中,喷头下方切向速度增大,喷头对大颗粒的清除能力减弱;安装高度为25 mm时喷头足够接近容器底部,中心轴向速度增大,喷头对大颗粒的清除能力激增。所得结论可为旋流喷头的操作参数、结构优化及安装位置确定提供数据参考。

Structural Optimization of Electromagnetic Swirling Flow in Nozzle of Slab Continuous Casting

During the slab continuous casting process, the flow field of molten steel in the mold plays a decisive role in the quality ofthe slab. In this paper, electromagnetic swirling flow in nozzle technology is proposed to control the flow field in mold.This technology can drive molten steel to rotate inside the submerged entry nozzle by electromagnetic force, therebycontrolling the flow field. This research shows that it can reduce the impact of molten steel on the bottom of nozzle andpartly reduce the negative pressure at the upper part of nozzle outlet which is even eliminated by optimizing the structureand angle of nozzle. The area of heat flux of the mold wall becomes larger, and the crest value of heat flux gets lower thanthat without swirling in nozzle and any nozzle optimization. The meniscus fluctuates smoothly, and the flow velocity at thetop surface is within a reasonable range. The temperature field distribution in the mold is uniform which was beneficial tothe growth of equiaxed crystal and decreased element segregation.

Effect of Nozzle Inlet Shape on Annular Swirling Flow with Non-Equilibrium Condensation

Recently,by combining a swirl flow with non-equilibrium condensation phenomena of condensate gas generated in a supersonic flow,a separating and extracting techniques of condensate gas have been developed.This technique can reduce the size of the device and don't use chemicals.In the present study,by using a non-equilibrium condensation phenomenon of moist air occurred in the supersonic flow in the annular nozzle composed of an inher body and an outer nozzle with a swirl,the possibility of separation of the condensable gas and the effect of shape of nozzle inlet on the flow field were examined numerically.

某电厂旋流燃烧器烧损原因分析及解决措施

本文主要介绍了某电厂旋流燃烧器喷口烧损事故的情况并针对旋流燃烧器出现的喷口烧损变形情况进行了原因分析,同时提出了解决措施,为同类型机组后续设计和运行提供了一定的借鉴经验。

基于Fluent的旋流喷嘴内流场速度数值模拟

目前我国针对井下粉尘的防治工作一般采用喷雾降尘方法,喷嘴作为喷雾的发生装置,其内部结构直接影响降尘效率。为了解喷嘴内部流场在流动过程中的变化情况,依据流体力学基本理论,结合Fluent流体分析软件对矿用五孔旋流喷嘴的单孔进行内部流场模拟仿真,分析了喷嘴流动过程中旋芯加速、旋流室强化、收缩段加速、出口段整流4个阶段。并在旋流室深度原有的基础上,分别加设1 mm、2 mm来探究对喷嘴出口速度的影响。结果表明:喷嘴出口速度分布随着旋流室深度增加呈现均匀趋势,最大出口速度呈现先增大后减小的趋势。

Effects of Variable Jet Nozzle Angles on Cross-Flow Suppression and Heat Transfer Enhancement of Swirl Chamber

This paper investigated the effects of variable jetting nozzle angles on the cross-flow suppression and heat transfer enhancement of swirl cooling in gas turbine leading edge. The swirl chamber with vertical jet nozzles was set as the baseline, and its flow fields and heat transfer characteristics were analyzed by 3D steady state Reynolds-averaged numerical methods to reveal the mechanism of cross-flow weakening the downstream jets and heat transfer. On this basis, the flow structure on different cross sections and heat transfer characteristics of swirl chamber with variable jetting nozzle angels were compared with the baseline swirl chamber. The results indicated that for the baseline swirl chamber the circumferential velocity gradually decreased and the axial velocity gradually increased, and the cross-flow gradually formed. The cross-flow deflected the downstream jets and drawn them to the center of the chamber, thus weakening the heat transfer. For swirl chamber with variable jetting nozzle angles, the air axial velocity is axial upstream, opposite to the mainstream, so that the impact effects of cross-flow on the jets were reduced, and the heat transfer was enhanced. Furthermore, with the increase of axial velocity along the swirl chamber, the jetting nozzle angle also gradually increased, as well as the effect of cross-flow suppression, which formed a relative balance. For all swirl chambers with variable jet nozzle angles, the thermal performance factors were all larger than 1, which indicated the heat transfer was enhanced with less friction increment.

Flow field, heat transfer and inclusion behavior in a round bloom mold under effect of a swirling flow submerged entry nozzle

Flow field,heat transfer and inclusion behavior in a 700 mm round bloom mold under the effect of a swirling flow submerged entry nozzle(SEN)were investigated with the aim to enhance the casting process.The results indicate that the impinging flow phenomenon,which is commonly observed in conventional single-port SEN casting,was completely suppressed by the swirling flow SEN coming from a novel swirling flow generator design in tundish.Steel from the SEN port moved towards the mold wall in 360 direction,leading to a uniform temperature distribution in the mold.Compared to a conventional single-port SEN casting,the steel super-heat was decreased by about 5 K at the mold center,and the temperature was increased by around 3.5 K near the meniscus.In addition,the removal ratio of inclusions to the mold top surface in the swirling flow SEN casting was found to be increased.Specifically,the removal ratio of spherical inclusions with diameters of 1,10,50 and 100μm was increased by 18.2%,18.5%,22.6% and 42.7%,respectively.Furthermore,the ratio was raised by 18.2%,20.8%,21.5% and 44.1%for non-spherical inclusions,respectively.

自激扫掠喷嘴气液两相流场特性研究

为研究自激扫掠喷嘴内、外流场结构,分析高频扫掠液柱的变形和破碎过程,首先采用高速阴影成像法,在0.1~4.0 MPa压降范围内,对喷嘴的扫掠频率及扫掠张角等基本工作特性进行了测量;其次,采用实验测量结果对气液两相数值模型进行了校核;最后,采用校核后的数值模型对喷嘴内、外气液两相流场结构开展了模拟研究。研究结果表明:喷嘴内部为单相流动,无气相介质的回流;液柱的高频扫掠使其在喷嘴出口形成了一个扇形液面;液柱的自旋增强了气相对液柱的剪切作用;在扇形液面两侧,液柱的反向偏转会导致其变形和破碎;在扇形液面中间,液柱的横向扫掠形成一个高速气相区,气相速度可达液相的3倍,提高了韦伯数,使得“液丝状”的液柱进一步破碎并扩散。

长旋流腔敞口型离心喷嘴注气雾化特性试验

以水和煤油模拟液作为液体工质,氮气和氦气作为注入气体,采用可视化试验技术和激光多普勒测速仪试验研究了不同气体流量作用下的长旋流腔敞口型离心喷嘴的雾化特性,包括喷注液膜破碎形态、气液两相混合建压与雾化粒径。研究结果表明:随着气液质量流量比升高,破碎模式逐步由轮缘型破碎、多孔型破碎过渡到爆裂型破碎。雾化过程中在喷嘴出口处伴随间歇性的中心气流冲击,冲击长度随气体流量升高而增大,但冲击频率随气体流量呈非线性变化,在气体流量较高或较低时的冲击频率反而升高。注气显著提高了喷注压降和雾化均匀性,相同气体流量的条件下,氦气相较于氮气具有更快的建压速度和更高的建压值,但氦气作用下的两相混合建压时混合室内的压力波动更为剧烈;氦气吹除的雾化粒径普遍小于氮气,但过高的氦气注气流量易引起气流冲击,引起冲击间隔时间内的雾化分布不均。