Experimental Study on the Flow Characteristics of a Plate with a Mechanically Choked Orifice

The mechanically choked orifice plate (MCOP) is a new type of device for flow control by which choking conditionsfor incompressible fluids can be obtained with relatively small pressure losses. Given the lack of relevant results anddata in the literature, in the present study, we concentrate on the experimental determination of the flow coefficientfor the annular orifice, the pressure distribution in the MCOP, and the characteristics of the choked flow itself. Asconfirmed by the experimental results, the Reynolds number, the orifice plate thickness, the plug taper, and theeccentricity have an obvious influence on the aforementioned flow coefficient. The pressure drop in the MCOPis mainly generated near the orifice plate, and the pressure upstream of the orifice plate is slightly reduced in theflow direction, while the pressure downstream of the orifice plate displays a recovery trend. The choked flow rateof the MCOP can be adjusted by replacing the spring with a maximum flow control deviation of 4.91%.

Experimental study on prediction model of wet gas pressure drop across single-orifice plate in horizontal pipes in the low gas phase Froude number region

The pressure drop prediction of wet gas across single-orifice plate in horizontal pipes had been solved satisfactorily under an annular-mist flow in the upstream of orifice plates.However,this pressure drop prediction is still not clearly determined when the upstream is in an intermittent flow or stratified flow,which is corresponding to a region of low FrG(gas phase Froude number)in the flow pattern map of wet gases.In this study,the wet gas pressure drop across a single-orifice plate was experimentally investigated in the low FrG region.By the experiment,the flow pattern transition in the downstream of single-orifice plates,as well as the effects of FrG and FrL(liquid phase Froude number)on UG(gas phase multiplier),were determined and compared when the upstream is in the flow pattern transition and the stratified flow region,respectively.Prediction performances were examined on the available pressure drop models.It was found that no model could be capable of jointly predicting the wet gas pressure drop in the low FrG region with an acceptable accuracy.With a new method of correlating FrG and FrL simultaneously,new correlations were proposed for the low FrG region.Among which the modified Chisholm model shows the best prediction accuracies,with the prediction deviations of UG being within 7%and 3%when the upstream is in flow pattern transition and stratified flow region,respectively.

Design and Range of Application of Slot Bushings with Volumetric Orifice Fields

A design of a slot bushing with a volumetric field has been developed, which allows to produce continuous fibers from melts with difficult processing characteristics in order to produce fibers with better operating characteristics. The operability of the design was confirmed when solving two problems of special technological complexity. 1. 400 and 800 orifice bushings for production of continuous fibers from the basalt melt have been developed and recommended for manufacture. 2. The process of production of continuous fibers from standard glass using 2400 orifice bushing with perforated plates instead of orifice tips without air cooling, has been realized for the first time.

Flow field characteristics,mixing and emissions performance of a lab-scale rich-quench-lean trapped-vortex combustor utilizing a quench orifice plate combined with a bluff-body

In this study,the low emission combustion technology of Rich-Quench-Lean(RQL)has been applied in Trapped-Vortex Combustor(TVC),and the combinative RQL-TVC shows a promising low emissions performance.By utilizing a quench orifice plate combined with a bluffbody,a lab-scale RQL-TVC was designed.The flow fields of RQL-TVC were measured by 2-D PIV and predicted by 3-D numerical simulation.Flow structures,radial profiles of normalized mean axial velocity,turbulence intensity and mixing level of the quench zone were analyzed.Results reveal that the dual-vortex and the single-vortex flow patterns both exist in cavities and quench zone of RQL-TVC,and the turbulence intensity is strong in the quench zone with some reverse flows.The spiral vortex was discussed by 3-D streamlines and the detail flow structures of the quench zone were analyzed based on the numerical results.The mixing level of the quench zone was determined,and results show that the quench device enhances the mixing level compared with TVC.Combustion efficiency and emissions performance were investigated experimentally,and results demon-strate that RQL-TVC has relatively higher combustion efficiency and lower emission index of CO,UHC and NO_xthan the same size lab-scale TVC in present work.

Vortex Simulation of Axisymmetrical Flows in Cylindrical Geometries．PartII：Application to Pipes Incorporating an Orifice Plate

The Random Vortex Method extended to an azisymmetrical flow is used in the study of the flow field inside pipes incorporating an orifice plate with different contraction ratios and different inlet velocity profiles. Three test-cases, each having experimental measurements available in the literature, are studied. In particular, instantaneous and average velocity fields along with the turbulent statistics for high Reynolds number flows are computed and compared to the corresponding experimental results.These comparisons show the ability and the citations of the method. The results of the numerical simulations are used in the physical analysis of the flow fields and thus allow for a better understanding of the dynamics of the flow in pipes incorporating an orifice plate.

含孔板微通道内随流气泡运动的两相格子Boltzmann模拟

带有气泡的两相流系统存在于各种工业过程中,涉及复杂的相界面变化,但气泡在管道中伴随液相流动时,通过孔板的运动过程尚未有充分的研究结果.相场格子Boltzmann模型在模拟复杂界面方面具有优势,适合研究气泡两相流在含孔板微通道内的运动,分析We数、气泡相对大小和孔板表面润湿性等因素对气泡动力学特性的影响.数值计算结果显示,随着We数增加,气泡表面张力减小,导致其穿过孔板结构时更易被撕裂,峰值速度降低.在研究的参数范围内存在两个临界直径比,这两个临界值将气泡通过孔板的运动分成三种形态,而且临界直径比会随We数的增加而减小.另外,随着接触角的增大,孔板表面对气体的吸附能力加强,气泡与孔板表面的接触面积增加,引起穿过孔板气泡的质量减少和气泡通过的速度增加.

多孔孔板空化流动特性实验研究

多孔孔板常作为节流元件安装在管道中,但孔板下游的空化流动容易导致管道振动,对系统产生不利影响,本文通过实验测量不同孔隙率孔板在不同空化阶段产生的振动及对应的压差和流量。结果表明,随着空化程度的不断加剧,全频段振动加速度级显著增大,峰值逐渐也增大,振动加速度呈现宽频特性。通过空化振动曲线中拟合曲线的斜率不同,可以区分出不同空化阶段以及临界空化数,孔隙率小于1.8的孔板临界空化数随孔隙率的增大迅速减小,当孔隙率大于1.8,初生及持续空化数随孔隙率增速变缓,阻塞空化数基本不变,即适当增大孔隙率有利于延缓空化的发生。根据空化流阻曲线,未发生空化时孔板流阻系数基本不变,空化初生时流阻系数略有减小,而后随着空化不断加剧,流阻系数迅速增大,孔隙率越大,流阻越大,流阻受空化数的影响越大。综合考虑孔板的振动和流阻特性,建议孔板孔隙率应保持在1.8~2.0之间。

基于孔板的圆柱绕流减阻降载研究

流体绕过海洋立管后,会在其下游产生交替脱落的漩涡。因此海洋立管将周期性地承受平行来流方向的阻力和垂直来流方向的升力。这种疲劳载荷会对海洋立管及其支撑系统造成结构损伤或增大结构成本。本文在海洋立管表面附加基于孔板的结构物,以减缓漩涡脱落及其导致的疲劳载荷。使用基于SST k-ω湍流模型的计算流体力学方法对基于孔板的表面附加结构物的圆柱绕流进行数值模拟。通过分析一系列阻力系数、升力系数、流场压强分布和涡量分布,研究在雷诺数为2×10^(4)时,基于孔板的表面附加结构物对圆柱绕流特性的影响。结果发现这种基于孔板的表面附加结构物,能够明显减小漩涡脱落对海洋立管产生的作用,从而减小阻力、减弱升力波动,显著起到对海洋立管减阻降载的效果。

平衡流量计在蒸汽计量中的应用及节能效果评价

优化流量仪表配置,合理选用节能型计量仪表,正成为企业节能增效的重要措施之一。针对标准孔板流量计在实际应用中压力损失大的局限性,介绍了平衡流量计的优化测量原理和性能优势,结合A+K平衡流量计在常减压装置蒸汽计量中的实际应用,对比分析了改造前后流量计能耗及运行成本,分析评价了采用A+K平衡流量计后的节能效果,认为在蒸汽流量测量中采用A+K平衡流量计优化流量仪表配置,在提高蒸汽计量精度的同时,可以降低仪表运行成本,减少蒸汽管网损耗,具有很好的节能效果。

适用于冷水机组的节流孔板计算新方法

当孔板作为冷水机组节流部件时,制冷剂在其下游会发生空化并形成阻塞流,目前尚无合适的公式计算孔板在这种状态下的流量。在离心式冷水机组上测试不同工况下的节流孔板,分析了压差、质量流量和流出系数的关系。根据试验工况模拟计算了节流孔板的流量特性,模拟与试验结果误差不超过5%。分别模拟得到了不同孔板在不同边界条件下的质量流量,结果发现,过冷度以及等效直径比的增加均会使流出系数增大。根据阻塞流形成时的压差重新定义流出系数的计算方法,并与模拟及测试结果对比,结果表明,该方法可准确预测不同制冷剂流经孔板的质量流量,可为其优化设计提供依据。

应用改型三通实现气液两相流的等干度分配

针对冲击型三通进行气液两相分配时,两支路之间出现干度不相等的现象,提出了一种有效的改进措施——在三通的支路中加装孔板。首先,通过分析冲击型三通的相分配特点,解释了其不能实现等干度分配的原因。然后,又进一步阐述了改型三通的分配原理,并且在空气-水回路上对该分配装置进行了实验研究。实验结果表明,该分配装置能显著改善气液两相流的分配特性,降低两支路之间的干度差,在孔板尺寸选取合适的情况下,基本上实现了等干度分配。最后根据理论模型和实验数据,给出了影响该分配装置等干度分配的因素和最佳孔径比的计算式。

蒸汽发生器传热管一、二次侧耦合换热及管外过冷沸腾数值研究

采用两流体欧拉数学模型,结合气相和液相之间的界面传热、传质和动量交换封闭模型以及RPI壁面沸腾模型,利用ANSYS CFX 12.0对蒸汽发生器局部传热管束二次侧的过冷沸腾进行数值研究。数值研究结果与单管内过冷沸腾实验数据对比验证符合良好。结果表明,采用壁面沸腾模型能准确预测沸腾起始点的位置,同时梅花孔板的存在对二次侧流动换热特性影响显著。

水平管内多孔板后的气液两相流型可视化实验

多孔板后是否形成均匀分散的泡状流流型是影响多孔板废气吸收装置吸收效果的关键因素。以空气和水作为两相介质,对气液两相混合物在水平管内流经多孔板后形成的流型进行实验。通过孔径分别为2、3、4、5 mm的4只多孔板在内径98.5 mm水平有机玻璃管内的可视化流动及高速摄像,研究了孔径大小、气相流量变化及液相流量变化对多孔板后流型的影响规律。实验结果表明:水平管内插入多孔板后,分层/塞状流转变边界向液相流量增大方向推移,塞状/泡状流转变边界向液相流量减小方向推移;随气相流量减小或液相流量增大,多孔板后流型趋于形成泡状流;孔径大小对多孔板后流型具有重要影响,减小孔径使塞状/泡状流转变边界移向更大气相流量和更小液相流量,即形成泡状流的两相流量范围增大;随孔径减小,孔板后流型趋于由分层流直接过渡至泡状流,塞状流趋于消失。为保证多孔板吸收装置的良好流型和吸收效果,建议多孔板孔径不大于3 mm。

液体火箭发动机氧腔流动分析及均流板设计研究

采用Navier-Stokes方程数值模拟了某型火箭发动机推力室氧腔流动,计算分析了节流板表面的总、静压分布及其畸变指数。依据压力畸变提出了氧腔均流孔板改进方法,并通过多次分析-设计循环得到了新的均流板。最后对所设计的均流板进行了详细地计算分析和实验验证。分析和验证表明新设计的均流板使氧腔出口节流板表面压力畸变降低了30.4%,显著提高了氧腔压力均匀性,进而可以大大提高燃烧效率。

孔板流场的二维激光测速试验研究

本文通过二维激光测速试验分析了孔板流场特性，并深入研究了孔板内缘型式对流场影响规律，采用圆形管道和模拟孔板断面的矩形管道两种模型试验对比分析，研究了孔板环内分离流发展过程与孔板内缘型式的关系，从而揭示了内缘型式对消能系数影响的内部机理。

新型气液两相流量计设计与试验

采用双节流元件组合的方式,建立了基于Murdock系数的流量测量的数学模型,在此基础上研制开发了一种新型的基于双槽式孔板节流元件的流量计,并用流量计样机对空气和水组成的两相流进行了测试试验。结果表明,气相流量测量的相对误差绝对值平均在10%以内,液相流量测量的相对误差平均在30%以内,验证了该流量计可以在一定范围内对气液两相流进行在线计量。

一种槽式孔板流动特性的研究

基于计算流体力学理论,应用计算流体力学软件Gambit和Fluent6.0,对流体流经槽式孔板前后的流动状态进行了仿真研究,得到了流体流经槽式孔板前后的动压、静压、速度剖面及压力和速度分布曲线。通过槽式孔板和标准孔板流动特性的比较得出了槽式孔板优于标准孔板的一系列结论。实验结果表明槽式孔板测量误差小于5%,研究结果对槽式孔板流量计的开发具有一定借鉴意义。

单孔孔板水力空化特性的可视化与数值模拟

在自行搭建的单孔孔板空化反应试验台上,采用高速数码摄影和长工作距离显微成像技术,对单孔孔板中心孔内和孔板下游进行空化特性试验研究,分析了背压、空化数等参数对孔板水力空化的影响.试验结果显示:当背压一定,逐渐改变喷射压力时,会出现"空化初生迟滞"现象,在空化两相流区,较高的背压对应着较小的流动损失;孔板内和孔板下游都有空化区存在,且孔内空化对下游空化区影响较大.数值模拟结果显示,孔内空化与试验相符合,且下游空化区的产生是由孔内空化云脱落至下游漩涡区引起的.

应用动态法进行气液两相流的双参数测量

发展了一种新的气液两相流的流量和气相质量含量的双参数测量方法。只需应用一个孔板即可完成上述两参数的在线测量。测量误差对气相质量含量为≤±4.5％,对流量为≤±5.5％。

孔数与孔厚对多孔板压损系数的影响机理

多孔板作为管道内节流降压或流量测量元件,在减小管道振动、流动噪声及流动压损等方面较之传统的单孔板具有明显优势。影响多孔板压损系数的结构因素主要有开孔等效直径比、孔数及孔板厚度,其中等效直径比的影响规律已为人熟知,而孔数与孔板厚度的影响机理仍不清晰。本文以均匀布孔的多孔板为研究对象,通过数值模拟方法研究了孔数与孔板厚度对多孔板稳定区压损系数的影响机理。结果表明:在相同的孔板厚度下,压损系数随孔数增多而先快速减小后趋于不变,使压损系数达到稳定的临界孔数随管径减小而减少,但临界孔数对应的孔板相对厚度均接近0.5;在相同的孔数下,随孔板相对厚度增大压损系数先快速降低后趋于不变,使压损系数达到稳定的临界相对厚度为0.5~1.0,临界相对厚度随孔数增多而减小;在相同的相对厚度下,压损系数在薄孔板中随孔数增多先减小后增大,而在厚孔板中随孔数增多而单调增大。这说明除等效直径比外,孔数与孔厚均对多孔板压损系数有影响,应在压损系数关联式模型中予以考虑。