Numerical Method for Heat and Mass Transfer in Air Washer——3.Two-phase Flow in Eliminator

Numerical simulation method is applied in the study oftwo - phase flow dynamics in the eliminator of air wash-er. The carrier phase (air) is treated in Eulerian frame,the water droplets are tracked in the Lagrangian frame.A three - dimensional unsteady two - phase flow model isdeveloped. With the help of FLUENT software, air-stream velocity field and water droplets trajectories havebeen illustrated when their mixture passing through tra-ditional folded eliminator. The result of the simulationcan be used to investigate the mechanism of

Experimental and numerical simulation of air-water two-phase flow in the rod bundle with grid spacer

Experimental and numerical simulation were carried out on vertically upward air-water two-phase flow in the rod bundle with grid spacer. The related numerical simulation has been performed by using the Computational Fluid Dynamics code-CFX4.2, in which lateral interfacial effects based on a two-fluid model are accounted for. This model has been used to evaluate the velocity fields of gas and liquid phases, as well as phase distribution between elements in rod bundle by simulating 1/4 zone of experimental model, and mixing vanes of spacer in this area. Fur- thermore, this model has been used to predict the effects of spacer on flow and pressure drop along the rod bundle. The calculation results show that the mixing vane has significant influence on axial and lateral velocity. In order to obtain some experimental data to verify the numerical solutions, a series of tests, using a specially designed 3×3 rod bundle test section with AFA-2G structure spacer have been performed. An optical probe was used to measure local void fractions. At the same time, the pressure loss has been measured. A comparison between the calculated void pro- file and pressure loss and the measured results shows that the predicted void profiles are consistent at low gas appar- ent velocity. This research shows that the code CFX4.2 can be used to describe the 3-D air-water two-phase flow in the rod bundle channel with grid spacer.

Air flow patterns and noise analysis inside high speed angular contact ball bearings

The vortex formed around the rolling ball and the high pressure region formed around the ball-raceway contact zone are the principle factors that barricades the lubricant entering the bearing cavity, and further causes improper lubrication. The investigation of the air phase flow inside the bearing cavity is essential for the optimization of the oil-air two-phase lubrication method. With the revolutionary reference frame describing the bearing motion, a highly precise air phase flow model inside the angular contact ball bearing cavity was build up. Comprehensive factors such as bearing revolution, ball rotation, and cage structure were considered to investigate the influences on the air phase flow and heat transfer efficiency. The aerodynamic noise was also analyzed. The result shows that the ball spinning leads to the pressure rise and uneven pressure distribution. The air phase velocity, pressure and cage heat transfer efficiency increase as the revolving speed increases. The operating noise is largely due to the impact of the high speed external flow on the bearing. When the center of the oil-air outlet fixes near the inner ring, the aerodynamic noise is reduced. The position near the inner ring on the bigger axial side is the ideal position to fix the lubricating device for the angular contact ball bearing.

Analysis on Link Between the Macroscopic and Microscopic Air–Water Properties in Self-Aerated Flows

Self-aeration in high-speed free surface flows occurs commonly and is of interest to ocean engineering, hydraulic engineering, and environmental engineering. For two-phase air–water flows, macroscopic air–water flow properties develop gradually, accompanied by the change of microscopic air–water structures. In this article, representational experimental studies on macroscopic and microscopic characteristics of self-aerated open-channel flows are summarized and compared. The isolated effect of the flow Reynolds number and air quantity on the differences in air count rate and chord size are analyzed and discussed. The results show that the characterized flow depth y, affected by the turbulence transfer, is a specific criterion to distinguish the interior air–water structure development. Two distinct linear trends of self-aeration are found, depending on the y/yvariation with a breaking point at Cmean =0.50. The air count rate and size scale in self-aerated flows are affected by the air quantity of self-aerated flows, even with identical flow Reynolds numbers. Thus, a specific parameter is proposed to assess the air–water structures and a series of self-similarity relationships in self-aeration properties are obtained. The link between macroscopic and microscopic air–water properties results in significant scale effect on air–water structures in self-aerated flows.

Introduction to investigations of the negative corona and EHD flow in gaseous two-phase fluids

Research interests have recently been directed towards electrical discharges in multi-phase environments.Natural electrical discharges,such as lightning and coronas,occur in the Earth＇s atmosphere,which is actually a mixture of gaseous phase（air） and suspended solid and liquid particulate matters（PMs）.An example of an anthropogenic gaseous multi-phase environment is the flow of flue gas through electrostatic precipitators（ESPs）,which are generally regarded as a mixture of a post-combustion gas with solid PM and microdroplets suspended in it.Electrical discharges in multi-phase environments,the knowledge of which is scarce,are becoming an attractive research subject,offering a wide variety of possible discharges and multi-phase environments to be studied.This paper is an introduction to electrical discharges in multi-phase environments.It is focused on DC negative coronas and accompanying electrohydrodynamic（EHD） flows in a gaseous two-phase fluid formed by air（a gaseous phase） and solid PM（a solid phase）,run under laboratory conditions.The introduction is based on a review of the relevant literature.Two cases will be considered：the first case is of a gaseous two-phase fluid,initially motionless in a closed chamber before being subjected to a negative corona（with the needle-toplate electrode arrangement）,which afterwards induces an EHD flow in the chamber,and the second,of a gaseous two-phase fluid flowing transversely with respect to the needle-to-plate electrode axis along a chamber with a corona discharge running between the electrodes.This review-based introductory paper should be of interest to theoretical researchers and modellers in the field of negative corona discharges in single-or two-phase fluids,and for engineers who work on designing EHD devices（such as ESPs,EHD pumps,and smoke detectors）.

Numerical Investigation on Flow Pattern of Air-Oil with Different Viscosities Lubrication

In the present work, the performance of oil-air two-phase flow under different lubricant oils was investigated. The simulation method was applied to study the influence of the oil viscosity on the flow pattern, velocity distribution and Re number in oil-air lubrication by FLUENT software with VOF model to acquire the working performance of oil-air lubrication for high-speed ball bearing. This method was used to obtain the optimum lubrication conditions of high-speed ball bearing. The optimum operating conditions that produce the optimum flow pattern were provided. The optimum annular flow was obtained by PAO6 oil with the low viscosity. Reynolds number influences the fluid shape and distribution of oil and air in pipe. The annular flow can be formed when Reynolds number is an appropriate value. The velocity distribution of oil-air two-phase flow at outlet was also discussed by different oil viscosities. The simulating results show that due to the effect of the oil viscosity and flow pattern the velocity decreased and expanded gradually close to the pipe wall, and the velocity increased close to the central pipe. The simulation results provide the proposal for the design and operation of oil-air two-phase flow lubrication experiments in the present work. This work provides a useful method in designing oil-air lubrication with the optimum flow pattern and the optimum operating conditions.

快掘面风流动态调控参数与压抽比对粉尘运移的影响及降尘分析

随着矿山快掘设备的逐渐引进,快掘面粉尘污染问题愈加严重。为有效减少快掘面生产过程中的粉尘污染,设计出风流动态调控降尘净化系统,通过调节风流的状态并设计了不同工况下的风流调控方案,以降低司机处粉尘浓度与粉尘的扩散距离。以陕西某矿快掘面为例,建立了风流—粉尘耦合场有限元模型,并对模型进行了井下验证;分析了风流动态调控降尘净化系统中出风口偏角、出风口缩放口径、出风口距端头距离及风量压抽比4个参数对风流与粉尘场的影响规律;设计正交试验分析了各参数与司机处粉尘浓度与粉尘扩散距离之间的关联性,确定了最佳调控净化方案。结果表明:各参数对司机处粉尘浓度与粉尘扩散距离影响程度的显著性排序由大到小依次为风量压抽比、出风口偏角、出风口距端头距离、出风口缩放口径。确定的最佳调控净化方案为出风口距离端头10 m、出风口偏角20°、出风口缩放口径1.0 m及风量压抽比1。设计搭建试验平台进行了准确性及净化效果测试验证,模拟值与试验值的平均误差小于8.91%,净化后司机处粉尘浓度由327.22 mg/m^(3)降低至156.47 mg/m^(3),降低了52.18%,粉尘扩散距离由39.74 m缩短至25.91 m,缩短了34.80%,有效改善了快掘面的空气环境。

角接触球轴承内圈织构设计及对油气润滑两相流的影响

针对角接触球轴承油气润滑中内圈润滑油含量少和保持性差的问题,提出在轴承内圈滚道设计圆凹坑形表面织构的润滑增效方法。基于气液两相流模型和多重参考系方法,建立内圈织构化角接触球轴承腔内油气两相流数值分析模型,分析内圈织构对轴承油气两相流动及润滑增效的影响。结果表明:织构化轴承可以显著提高润滑油在内圈的保持量,同时改善轴承腔内润滑油分布不均的状况;在微织构附近油气两相流动更不规则,所产生的压力梯度和速度梯度有利于提高气液两相膜的承载力;随着轴承转速的升高,内圈织构润滑增效效果相对减弱;随着供油量的增加,内圈织构润滑增效效果更加显著。

不同倾斜度下管道充水特性分析

针对管道充放水周期较长的问题,在对比模拟结果与试验数据吻合度的基础上,建立5种不同倾斜角度的管道三维模型,仿真不同倾斜角度下管道充水过程,分析其内部流速、压力和气液两相分布变化情况。结果表明,管道倾斜度小于30°时,水流流态稳定,流线均匀,管内水位均匀上升,平均充水流速1.3 m/s;随着倾斜度增加,流速越来越快,气液两相混合流动现象越来越明显,当倾斜角度为60°时,存在气体拥塞管道现象。综合对比,建议管道在倾斜度小于30°时可以适当增加充水速度,缩短充水周期。

喷嘴位置对轴承腔内油气润滑两相流的影响

基于气液两相流理论,采用多重坐标系法构建角接触球轴承数值计算模型,分析不同喷嘴位置和转速下轴承腔内油相体积分数、保持架表面及轴承内外圈的油气分布特性。结果表明:在轴承低转速下,正面供油时轴承腔内油相体积分数及其周向分布的波动大于背面供油;正面供油时保持架下表面会产生润滑油的积聚,造成润滑油无法及时通过出口排出,而背面供油时润滑油在保持架表面的油相分布更均匀;正面供油时内圈左面油相体积分数较高,外圈油相分布变化较大,而背面供油时内圈右面、中间面及外圈中间面油相体积分数较高。不同转速下喷嘴位置对腔内油相分布的影响也不同,低转速下正面供油时腔内油相体积分数更高,高转速下喷嘴位置对轴承腔内油相分布的影响较小,润滑油在轴承腔内分布较为均匀,保持架下侧未见明显的润滑油积聚。

孔隙率对多孔介质模型内水-气两相驱替规律的影响

多孔介质的孔隙率是影响水气两相驱替模式和注液饱和度的重要因素,饱和度是决定离子型稀土矿浸出率的关键指标。开展四种孔隙率的多孔介质中水气两相驱替微流体模型试验,确定了水气两相驱替模式,分析了气体团簇的形成机理及其分布特征,研究了孔隙率对模型内注液饱和度的影响。结果表明:水气两相驱替为毛细管指进模式,孔隙率高的多孔介质中指进现象更显著;随着毛细管数的增大,渗流模式逐渐趋于稳定。毛细管指进过程容易在多孔介质孔隙中形成气体团簇,低孔隙率模型中的气体团簇小而多;高孔隙率模型内的气体团簇大而少。模型内的注液饱和度随着孔隙率的增大而减小,随着注液强度的增大而增大。

基于水气两相流的海拔高程对某电站溢洪道泄洪雾化的影响分析

海拔高程增加所引起的气象条件的改变会对泄洪水舌的运动产生影响,进而影响泄洪雾化风场及雨场的时空分布。为此,基于水气两相流理论,考虑不同海拔高度的环境压强、温度、粘滞性及空气密度等参数的变化,采用数值模拟的方法研究了海拔高程对泄洪雾化的影响。结果表明,相同泄洪条件下,泄洪稳定后的压强值随海拔升高无明显增加趋势,然而海拔越高,水舌空中运动所受空气阻力越小,相同条件下落水点压强增幅越大;温度降低带来的水的粘滞性增加对水雾运动影响较小,海拔高程越高,雾化风速到达最大值的时间越早,所能达到的最大值也越大;泄洪稳定时近地表雾化降雨强度随海拔高程的增加而增大,与海拔高程呈近似线性关系,此外强降雨范围随海拔的升高而逐渐扩大。

波浪对水平板冲击作用水气二相流数值模拟研究

冲击波压力是水工结构物的主要致灾动力之一.针对波浪裹挟气体作用于结构物的波浪冲击问题,考虑气体的可压缩性对准确计算结构物所承受的冲击波压力具有重要影响.基于简化的水-气二相流通用控制方程,结合动量源项造波法,采用加权本质无振荡(WENO)格式求解对流项,同时使用以加权线性界面计算法改进的多维双曲线切线法的界面捕捉法(THINC/WLIC)追踪水气界面,建立了不可压缩-可压缩水-气二相流的数值波浪模型.首先,通过将数值模型生成的行进波和驻波结果与其解析解进行比较,验证了本数值波浪模型在波浪生成和传播模拟方面具有较高的精度.据此,本研究将模型应用于模拟规则波对水平板的冲击过程,将冲击压强的模拟结果与实测数据以及未考虑空气压缩性的模型结果进行了对比,本数值模型能有效再现空气可压缩性对波浪冲击过程中冲击压强的影响,能够给出较高精度的冲击压强定性和定量结果.同时对水平板底部的流场结构进行了分析,结果显示,波浪冲击过程中不同的空腔形态会影响流速分布,从而对冲击压强产生影响.

取向硅钢常化冷却段空气雾化喷嘴内流场数值模拟

为改善取向硅钢常化过程带钢的冷却效果,对空气雾化喷嘴内气液两相流动过程进行三维数值模拟研究,分析空气压力和水流量对喷嘴内流场速度和液相体积分数的影响。数值计算值与实验测试值吻合良好且最大误差小于10%。结果表明:当水流量一定时,随着空气压力的逐渐增大,喷嘴内速度增大、液相体积分数减小,喷嘴出口处速度分布均匀性变差,液相体积分数分布更均匀;当空气压力一定时,随着水流量的逐渐增大,喷嘴内速度逐渐减小、液相体积分数增大,喷嘴出口处速度分布更均匀,液相体积分数分布均匀性变差;喷嘴气水压力比为1.1时冷却均匀性较好,冷却均匀性最佳的工况为空气压力0.2 MPa、水流量180 L/h。

侧深施肥装置三通管气固两相流仿真与试验

为探究气吹式侧深施肥装置三通管不同结构特征对气流和肥料颗粒运动的影响,通过理论分析,设计气流入口与出口轴线垂直的a型三通管、气流入口与出口轴线呈45°夹角的b型三通管、气流入口与出口同轴的c型三通管。在三通管内径为28 mm、通入气流速度为16.4 m/s、肥料颗粒流量为20 g/s的条件下,采用CFD-EDM耦合方式对不同管道内气流、压力、颗粒运动状态进行仿真分析。结果表明:气流经a、b、c三种类型三通管产生不同的流动效果,进而影响肥料颗粒运动特性,颗粒最大运动速度分别为1.99 m/s、2.94 m/s、2.07 m/s,期间颗粒产生最大碰撞力分别为0.05 N、0.13 N、0.34 N。通过验证试验对比表明,采用b型管侧深施肥装置排肥稳定性变异系数为0.81,肥料破损率为0.72%,施肥过程中无肥料堵塞。

基于电容传感器的液体管内含气率测量系统的研究

电容传感器具有非侵入式、低成本、结构简单等特点,被广泛应用于液体管内含气率的测量。基于电容传感器,设计了含气率测量系统,对外径25mm、内径21mm液体管内含气率进行测量。为了验证含气率测量系统的准确性,搭建了可视化验证平台。对管内气液两相进行图像采集,对管道截面处的含气率进行计算;分析了视窗左右截面的含气率偏差,研究了采集位置偏差对验证方法有效性的影响。研究表明:通过传感器系统测量的含气率与图像处理得到的含气率吻合;视窗左右截面的平均含气率的偏差不超过3.097%。本研究设计的含气率测量系统的准确性较好,所提出的可视化验证方法能够有效地对含气率测量系统的准确性进行验证。

基于CFD-DPM模拟的中速磨煤机风粉分配特性

中速磨煤机是燃煤电厂制粉系统的重要部件,承担原煤的研磨、干燥、运输等,磨煤机出粉管的风粉分配性能直接关系燃煤电厂的安全稳定高效运行。基于CFD-DPM方法,在全结构、足尺度、考虑实际运行中转动部件条件下,开展磨煤机内部气固两相流动研究。在网格无关性验证和模型验证的基础上,研究中速磨煤机粉管出口风粉分配特性,揭示煤粉分配不均匀的成因,进而提出在分离器折向门处于同一高度的筒壁上布置导流块体结构,改善粉管中粉量分配均匀性。结果表明,风环区域对磨煤机阻力贡献最大,分离器区域和粉管区域阻力较为接近,模拟条件下二者之和占磨煤机阻力的份额为28.3%~29.4%;各粉管之间风速差异很小,但粉量差异显著,其原因是风粉混合物受到磨辊的阻碍作用,被分为3股,从而进入分离器内锥体的风粉混合物呈现不均匀状态;在分离器折向门处于同一高度的筒壁上布置导流块体结构,可使各粉管风粉分配均匀性得到显著改善。

气冷冷凝相变脱白法系统计算研究

根据气冷冷凝相变脱白系统设计的需要,开发了排放气体温度、湿度的计算程序,在此基础上研究了冷空气温度、湿度和风量对脱白效果的影响,结果显示:气冷冷凝相变脱白法除雾存在临界风量线,这条线由冷空气温度、湿度和风量共同决定;冷凝相变脱白法比混风脱白法和混合冷凝脱白法效果好。

环形自激振气举泵提升性能试验研究

为提高气举泵的提升效率,设计了一种带有振荡腔结构的新型气举泵,通过振荡腔对混合流的激励作用,增强气液混合物在提升管内的输运能力。计算了提升管内气液两相流流型随气相速度的变化规律,并通过试验对比分析振荡腔结构与无振荡腔结构在不同浸没率下,排水量、峰值点位置、提升效率随着进气量增加的变化规律。结果表明:受提升管内流型变化的影响,排水量随着进气量增大存在先升后降的趋势;进气量<75 m^(3)/h时,有振荡腔结构提升效率高于无振荡腔结构,进气量>75 m^(3)/h时,提升效率低于无振荡腔结构,最佳进气量范围在50~75 m^(3)/h之间;新型结构气举泵提升性能受进气量、浸没率影响,存在最佳工况,且在最佳工况范围内,相较于传统结构效率提高10%~20%。研究结果可为气举泵的优化设计提供参考。

不同环境参数对300 MW压缩空气储能系统运行的影响

压缩空气储能系统是提高电力系统稳定性的有效手段,为研究环境温度和湿度对压缩空气储能系统性能的影响,基于MSP平台建立300 MW压缩空气储能系统热力学模型,研究环境温度和湿度对压缩过程性能的影响规律。结果表明,随空气温度增大,压缩机总功率增大,压缩过程时间增大;随空气湿度增大,压缩机总功率增大,压缩过程时间增大且变化幅度极小。研究结论对压缩空气储能系统的实际运行具有一定的参考意义。