气液交叉流阵列PM2.5热泳和扩散泳拟传质模型

基于气溶胶中PM2.5微细颗粒物拟流体特性,对气液交叉流阵列中PM2.5在气溶胶流体传热传质边界层内热泳和扩散泳运动进行拟传质机理分析,与跟随气体的对流传质相叠加,建立了气液交叉流阵列PM2.5热泳和扩散泳拟传质模型,并进行了实验检验。实验在固定对流条件下,考察了不同气液相温度差导致的热泳、不同气相湿度差导致的扩散泳和颗粒粒径等因素对气液交叉流阵列PM2.5拟传质系数的影响。实验数据统计值与模型表达趋势一致,在初始温差40℃、初始湿度0.118 kg/kg条件下,100排气液交叉流阵列PM2.5拟传质系数模型预测值为3.33×10~(-3)m/s、实验值为3.75×10~(-3)m/s。     

气液交叉流阵列PM2.5热泳和扩散泳拟传质模型

基于气溶胶中PM2.5微细颗粒物拟流体特性，对气液交叉流阵列中PM2.5在气溶胶流体传热传质边界层内热泳和扩散泳运动进行拟传质机理分析，与跟随气体的对流传质相叠加，建立了气液交叉流阵列PM2.5热泳和扩散泳拟传质模型，并进行了实验检验。实验在固定对流条件下，考察了不同气液相温度差导致的热泳、不同气相湿度差导致的扩散泳和颗粒粒径等因素对气液交叉流阵列PM2.5拟传质系数的影响。实验数据统计值与模型表达趋势一致，在初始温差40℃、初始湿度0.118 kg/kg条件下，100排气液交叉流阵列PM2.5拟传质系数模型预测值为3.33×10^-3 m/s、实验值为3.75×10^-3 m/s。     

多喷嘴对置式气化炉内气固两相流动与炉壁的颗粒捕捉特性

对多喷嘴对置式气化炉内复杂的气固两相流动与炉壁的颗粒捕捉特性进行三维数值模拟。应用Euler-Lagrange模型模拟气固两相流动,采用Realizable k-ε湍流模型计算炉内气相湍流流场,颗粒轨迹跟踪采用随机轨道模型。模拟结果与冷模测试数据吻合,且流场与热模实验现象一致,壁面捕捉颗粒平均粒径与热态水煤浆气化实验数据吻合。工业规模模拟结果表明,壁面捕捉的颗粒平均粒径呈现一定的规律性,存在两个极大值位置,分别在喷嘴平面下方0.2 m及上方2.8 m处,在喷嘴平面上方,壁面捕捉颗粒粒径随颗粒密度的增大而减小;颗粒沉积能基本覆盖整个炉膛内壁,颗粒在撞击流股作用下在喷嘴平面上方1.8 m及下方1.9 m处沉积量最大;缩短喷嘴上方直段高度将影响炉内流场,拱顶对撞击流股产生一定的限制作用,使其变短变宽,并且使拱顶捕捉颗粒粒径增加,颗粒沉积速率增加。     

带绕流板的湍流管道内细颗粒物沉积实验

微细颗粒物在管内的沉积现象发生于各类颗粒输运、通风系统、烟气管道积尘过程。实际过程中有各类复杂的管道情况,然而现有研究多针对的是光滑管道。对带有扰流挡板的管道内微细颗粒物沉积进行实验探究。搭建了带有系列扰流挡板的湍流管道系统,研究粉煤灰和碳酸钙颗粒在各类条件下的沉积情况。实验获得带扰流挡板的管道的沉积效率,发现其数量级高于光管,与文献中的模型研究结果一致。实验进一步在挡板涂抹油脂,发现其抑制颗粒物在壁面上的反弹,使得沉积效率得以少量提高;同时也说明,限制微细颗粒沉积的主要瓶颈在于其流场跟随性强从而无法有效到达挡板壁面,而不是其在壁面上的反弹。实验结果证明管道中的挡板结构对颗粒物沉积产生重要影响,挡板壁面属性为次要因素,结论可为相关积尘、除尘工业管道设计提供重要参考。     

带绕流板的湍流管道内细颗粒物沉积实验

微细颗粒物在管内的沉积现象发生于各类颗粒输运、通风系统、烟气管道积尘过程。实际过程中有各类复杂的管道情况,然而现有研究多针对的是光滑管道。对带有扰流挡板的管道内微细颗粒物沉积进行实验探究。搭建了带有系列扰流挡板的湍流管道系统,研究粉煤灰和碳酸钙颗粒在各类条件下的沉积情况。实验获得带扰流挡板的管道的沉积效率,发现其数量级高于光管,与文献中的模型研究结果一致。实验进一步在挡板涂抹油脂,发现其抑制颗粒物在壁面上的反弹,使得沉积效率得以少量提高;同时也说明,限制微细颗粒沉积的主要瓶颈在于其流场跟随性强从而无法有效到达挡板壁面,而不是其在壁面上的反弹。实验结果证明管道中的挡板结构对颗粒物沉积产生重要影响,挡板壁面属性为次要因素,结论可为相关积尘、除尘工业管道设计提供重要参考。     

多场耦合作用脱除PM2.5的数值模拟与实验研究

气液间传热传质推动力是PM2.5脱除的关键因素。基于欧拉-拉格朗日模型,考虑热泳力、扩散泳力影响,对流场、温度场和浓度场耦合作用下液膜捕集颗粒过程进行模拟。模拟结果表明:水蒸气浓度差对PM2.5脱除作用明显,当颗粒粒径d_p=1μm时,在水温20℃,气体入口温度60℃,气体入口相对湿度由0.575提高到0.757时,20排液膜柱阵列颗粒脱除总效率提高了35.1%。最后通过含尘气体横掠液膜柱阵列除尘实验验证了模拟结果的准确性。     

含K成分形成初始沉积层的数学模型及烟气条件影响分析

针对积灰初始沉积层形成的两种主要机理即凝结和热泳机理,建立了含K成分形成初始沉积层的数学模型,采用文献中的实验结果检验了模型,表明考虑沉积层厚度、表面温度随位置和时间的变化对模型预测有合理的改善。应用该模型研究含K气体成分和气溶胶颗粒在受热面上的沉积过程,并考察烟气中含K成分组成、烟温和烟速等因素的影响。研究表明,由于烟气中含K气体成分和气溶胶颗粒相对浓度的差异,凝结和热泳在沉积过程开始时都可能对初始沉积层的形成起主要作用,而在沉积过程后期热泳沉积则占据主导地位;烟温和烟速对含K成分沉积过程的影响相似,即较高的烟气温度和速度,其初期沉积速率高,而后期沉积速率相对低,形成的沉积层厚度较低。     

含K成分形成初始沉积层的数学模型及烟气条件影响分析

针对积灰初始沉积层形成的两种主要机理即凝结和热泳机理,建立了含K成分形成初始沉积层的数学模型,采用文献中的实验结果检验了模型,表明考虑沉积层厚度、表面温度随位置和时间的变化对模型预测有合理的改善。应用该模型研究含K气体成分和气溶胶颗粒在受热面上的沉积过程,并考察烟气中含K成分组成、烟温和烟速等因素的影响。研究表明,由于烟气中含K气体成分和气溶胶颗粒相对浓度的差异,凝结和热泳在沉积过程开始时都可能对初始沉积层的形成起主要作用,而在沉积过程后期热泳沉积则占据主导地位;烟温和烟速对含K成分沉积过程的影响相似,即较高的烟气温度和速度,其初期沉积速率高,而后期沉积速率相对低,形成的沉积层厚度较低。     

低温省煤器飞灰沉积阻塞机理分析及结构优化

针对热电厂低温省煤器发生飞灰沉积阻塞炉管间隙的情况,本文采用剪切力传递（SST）k-ω湍流模型和离散粒子模型（DPM）分析飞灰颗粒沉积行为,预测省煤器中支撑梁附近的沉积动态,进而对支撑梁上方翅片布置结构进行优化和流场分析。结果表明：省煤器中由于支撑梁和上方翅片的存在,飞灰颗粒会在支撑梁上表面进行沉积。在脱硝条件下,硫酸氢铵增加了飞灰间的黏结力,加剧了黏附沉积,进而积灰不断地向上累积增长并造成堵塞。通过改变支撑梁上方的翅片布置结构,可改变支撑板附近的烟气流动规律。对于烟气中的绝大部分飞灰颗粒（d_p>40μm）,其所受到的惯性作用占据主导地位,与壁面有着较大的撞击率。通过改变炉管上翅片的布置方式,增加飞灰颗粒横向移动的能力,对支撑梁上的沉积堵塞有着较好的改善作用。     

Rushton涡轮搅拌槽内流场特性及颗粒运动行为数值模拟

基于计算流体动力学（CFD）方法,采用大涡模拟（LES）和拉格朗日颗粒追踪技术计算了Rushton涡轮搅拌槽内流场特性及三种St颗粒的运动行为。平均流场（切向速度、轴向速度和径向速度）、颗粒速度及浓度分布方面与实验值的吻合度较好,验证了数值模拟的可靠性。结果表明,搅拌流场及颗粒运动均呈现循环流特性,当转速N=313r/min不变时,St=0.24的小颗粒几乎实现了均匀分布;而St=37.3的大颗粒与流体的跟随性较差,底部沉积率较高,容器顶部会出现一定的颗粒空白区。叶轮附近产生一系列的湍流涡结构,并且由于剧烈的颗粒-壁面碰撞,该位置颗粒拟温度最高;小颗粒（St=0.24）的运移主要受叶片后方尾涡的控制,均匀分布在低涡量区;而大颗粒（St=37.3）由于具有较大的惯性,运动不再由涡主导,很快被叶轮甩向边壁,穿过了尾涡所形成的高涡量区,故而叶轮对附近大颗粒的搅拌效果较差。     

可吸入颗粒物在管内湍流流动时的动力学特性及热泳沉积

The kinematical characteristics and thermophoretic deposition of inhalable particles with the diameters of 0-2.5μm （hereafter referred to as PM2.5） suspended in turbulent air flow in a rectangular duct with temperature distribution were experimentally studied. Particle dynamics analyzer （PDA） was used for the on-line measurement of particle motion and particle concentration distribution in the cross-sections of the duct. The influences of the parameters such as the ratio of the bulk air temperature to the cold wall temperature and the air flow rate in the duct on the kinematical characteristics and the deposition efficiencies of PM2.5 were investigated. The experimental re- sults show that the deposition efficiencies of PM2.5 mainly depend on the temperature difference between the air and the cold wail, wffile the air flow rate and the particlecon~centration almost affect hardly tile clep0si-tion-effi ciency. The radial force thermophoresis to push PM2.5 to the cold wail is found the key factor for PM2.5 deposition.Based on the experimental results, an empirical modified Romay correlation for the calculation of thermophoretic deposition efficiency of PM2.5 is presenlext. The empirical correlation agrees reasonably well with the experimental data.     

Experimental and numerical study of the airflow distribution in mixed-flow grain dryers

The aim of this study was to investigate the airflow distribution in a mixed-flow dryer (MFD) and to study the effect of different bed materials and air duct arrangements. The results were used to validate the numerical model developed in a previous work based on Computational Fluid Dynamics (CFD). A series of experiments have been conducted at a semi-technical MFD test dryer with horizontal and diagonal air duct arrangement. Wheat and rapeseed were used as bed materials. The experiments were performed under isothermal conditions. Two experimental methods were selected and adapted to the measuring problem—the measurement of the isobar distribution within the grain bed and the residence time analysis using the tracer gas pulse method. As could be shown, the isobar distributions measured for wheat and rapeseed agreed well with the model predictions. The numerical model could calculate the influence of the bed material with its different particle characteristics (e.g., particle shape, particle size, bed porosity). The results obtained from the residence time analysis confirmed the known quartering of the air stream flowing from one inlet air duct to the four surrounding outlet air ducts for the horizontal air duct arrangement; in the diagonal air duct arrangement, the air stream from one inlet air duct was nearly halved flowing to the two adjacent diagonal outlet air ducts. These results were confirmed by investigations of the air velocity distribution within the grain bulk. Further experiments are necessary to refine the model. The residence time and isobar measurements will be extended to study the influence of different air properties under real drying conditions, the effect of structural elements, and dryer designs.     

Direct Numerical Simulation of Kinematics and Thermophoretic Deposition of Inhalable Particles in Turbulent Duct Flows

Three-dimensional, incompressible turbulent air-particle flows in a channel with a temperature gradient are simulated by direct numerical simulations (DNS). The calculations used the fractional projection method to directly solve the Navier-Stokes equations. For obtaining more accurate results, the Oberbeck-Boussinesq model was used for considering the convective heat transfer and applied two-way coupling between the particles and the air phase to accurately simulate flow field state. The particles motions including mutual collisions were calculated with the direct simulation Monte-Carlo method (DSMC). The particles agglomeration and deposition in the turbulent channel flow with a temperature gradient were simulated by the Dahneke model. The research focused on the effects of the Reynolds number, the temperature gradient and particle concentration which simultaneity affect particle kinematics, impacts, agglomerations, and deposition characteristics. The numerical results show that the thermophoresis dominates the particle deposition, which agrees well with the experimental data, the particle concentration determines the particle collision and agglomeration rate, the Reynolds number determines the particle distribution in the duct and the 2.5 μm particles do not obviously affect the air phase motion under comparatively low concentration referred in this research.     

Effects of air temperature and humidity on particle deposition

Particle deposition in a fully developed turbulent duct flow was studied. The random walk model of Lagrangian approach was used to predict the trajectories of 3000 particles with a density of 900 kg/m³. The effects of thermophoretic force and air humidity were also considered. The results were compared with the previous studies with a particle size range of 0.01–50 μm and air flow velocity of 5 m/s. The profile of dimensionless deposition velocity with relaxation time presents a V-shaped curve and the results are in good agreement with the previous studies.The effects of air temperature and humidity on particle deposition with a particle size of 1 μm were also investigated. The results show that thermophoretic force accelerates particle deposition onto the duct walls with increasing temperature difference between air flow and the duct wall surface. Meanwhile, it was found that particle deposition velocity increases with air humidity.     

径向流吸附器流体流动特性及其结构参数优化

径向流吸附器通常存在流体沿轴向床层分布不均匀,从而导致吸附剂利用率下降和空分系统运行安全性问题。通过对表征Z型径向流吸附器流动特性的微分控制方程中包含的结构参数进行量纲1化,系统地研究了各结构参数对吸附器内流体分布的影响。同时针对实验室已有的一台Z型径向流吸附器,采用理论求解和实验数据对照的方法验证了模型的可靠性。结果表明,减小吸附床层轴向高度和吸附剂颗粒直径能显著提高Z型径向流吸附器内流体分布的均匀性;当空气的运动黏度和其他结构参数不变时,吸附器的空气处理量在一定范围内变化对吸附床层内流体的均匀性影响不大。     

Experiments Measuring Particle Deposition from Fully Developed Turbulent Flow in Ventilation Ducts

Particle deposition in ventilation ducts influences particle exposures of building occupants and may lead to a variety of indoor air quality concerns. Experiments have been performed in a laboratory to study the effects of particle size and air speed on deposition rates of particles from turbulent air flows in galvanized steel and internally insulated ducts with hydraulic diameters of 15.2 cm. The duct systems were constructed of materials typically found in commercial heating, ventilating, and air conditioning (HVAC) systems. In the steel duct system, experiments with nominal particle sizes of 1, 3, 5, 9, and 16 μm were conducted at each of three nominal air speeds: 2.2, 5.3, and 9.0 m/s. In the insulated duct system, deposition rates of particles with nominal sizes of 1, 3, 5, 8, and 13 μm were measured at nominal air speeds of 2.2, 5.3, and 8.8 m/s. Fluorescent techniques were used to directly measure the deposition velocities of monodisperse fluorescent particles to duct surfaces (floor, wall, and ceiling) at two straight duct sections where the turbulent flow profile was fully developed.

In steel ducts, deposition rates were higher to the duct floor than to the wall, which in turn were greater than to the ceiling. In insulated ducts, deposition was nearly the same to the duct floor, wall, and ceiling for a given particle size and air speed. Deposition to duct walls and ceilings was greatly enhanced in insulated ducts compared to steel ducts. Deposition velocities to each of the three duct surface orientations in both systems were found to increase with increasing particle size or air velocity over the ranges studies. Deposition rates measured in the current experiments were in general agreement with the limited observations of similar systems by previous researchers.     

Investigation of Particle and Air Flows in a Mixed-Flow Dryer

Even though the mixed-flow dryer is well established on the commercial market for the drying of grain, maize, and rice, there further potential as well as a need to optimize the dryer apparatus and to improve product quality. Unfavorable designs can cause uneven mass flow and air flow distributions, resulting in locally different drying conditions and, hence, uneven grain drying. The aim of the present article is to evaluate traditional designs of mixed-flow dryers by numerical and experimental investigation of particle and air flows and to discover design deficits. For this purpose, the dryer geometry and different air duct arrangements (horizontal and diagonal) were studied using the discrete element method (DEM) and computational fluid dynamics (CFD). Drying experiments were performed to evaluate the grain moisture and temperature distributions. With regard to particle flow, a typical core flow was detected as in silos with a retarded particle flow at the dryer walls and a fast flow region in the center of the dryer. This was caused by the wall friction effect and the half air ducts fixed at the side walls. With regard to the air flow, dead zones were discovered for the diagonal air duct arrangement. Based on the design deficits identified for the traditional geometry, a new geometry for the mixed-flow dryer that is still under development is discussed.     

RESIDENCE TIME DISTRIBUTION AND DRYING CHARACTERISTICS OF A CONTINOUS VIBRO-FLUIDIZED BED

An experimental study of the residence tine distribution and drying characteristics of a continous pilot-plant vibrated fluidized bed dryer(the air distributor plate is 1.50 m in length and 0.24 m in width) is presented and discussed. Operating variables in the study included: vibration intensity, mass flow rate of air, granules feed rate, inlet air temperature and particle size. It was inferred from the experimental results that the flow of particles in the continous VFB could be considered as plug flow. Among the variables considered, vibration intensity was identified as the most significant factor to affect particle mean residence time, particle diffusivity and constant drying rate for the bed of wheat particulates and instant pharmaceutical BYN granules.     

旋风预热器连接风管的分析

运用Yong分析方法，从旋风预热器系统连接风管的传热与流动的特点出发，推导出管道内气体与管道壁间换热量的能级表达式，结果表明，管道内最佳气体速度与气壁温度差密切相关，结合工厂实际生产数据，分析了各连接风管的设计。     

HANDLING AIR1

The following points are brought out in this paper: (1) composition of air, (2) laws governing flow of air, (3) laws governing expansion of air due to temperature and pressure, (4) methods of proportioning ducts and fans as equipment for moving air (cen- trifugal and disk), (6) coijrdination of fan and duct characteristics, (7) selecting proper type of fan, and (8) use of the disk fan.