CFD Studies of Indoor Airflow and Contaminant Particle Transportation

This article presents a numerical study of indoor airflows and contaminant particle transportation in three ventilated rooms. The realizable k - ε model is employed to model the air-phase turbulence, while the Lagrangian particle tracking model is utilized for the particle-phase simulation. The predicted air-phase velocities and contaminant particle concentrations are validated against the experimental data obtained from the literature. In the first case, the realizable k - ε model successfully captures the flow trend and reasonably predicts the airflow velocity. The realizable k - ε model under-predicts the vertical air velocities along the vertical inlet jet axis by 11% at x = 0.219 m, which is slightly better than the standard k - ε model error of 17%. In a two-zone room case, the realizable k - ε model, combined with a Lagrangian particle tracking model, predicts the particle concentration decay with the highest normalized difference being 24%. In the third case, the influence of particle size, location of particle resource, and particle-wall collision on the particle concentrations is investigated by the realizable k - ε model and the Lagrangian model. It is found that for relatively small particles (diameter ≤ 10 μm), the particle concentration may be insensitive to the particle diameter. In addition it has been observed that the particle-collision model may have considerable effect on the particle concentration prediction.     

室内气流模拟过程中计算流体力学(CFD)的紊流模型评价和选择

论述了采用计算流体力学技术模拟室内空气的优越性,介绍几种紊流模型的性能以及各种模型在模拟室内空气流动时的适用性.     

基于Airpak的室内空气品质分析

随着人们生活水平的提高,人们对室内空气品质的要求越来越高,室内空气品质的好坏与人们的健康、工作效率息息相关。用Airpak软件模拟计算了某空调办公室在开门和不开门时的气流组织,通过对计算结果的分析,可以看出不同的气流组织对空气品质的影响,为合理改善和提高室内空气品质提供了参考。     

基于CFD技术的气流温度传感器数值校准虚拟风洞初探

在气流温度传感器风洞校准试验中,由于试验成本高、校准试验环境与实际使用环境差距大等原因,有必要构建气流温度传感器数值校准虚拟风洞,实现极限非常规校准工况的气流温度传感器误差修正及虚拟校准,并通过气流温度传感器的虚拟校准数值风洞获取仿真结果,尽可能地减少实物校准的工况数量,同时也从理论层面为气流温度传感器的设计与校准提供...     

污染气流扩散三维场景的实时模拟

在环境污染应急系统中,实时模拟污染气流扩散场景是制定污染事故应急措施的关键.为兼顾模拟的实时性和逼真性,利用离散化的思想,提出了一种基于粒子系统的简单快捷的数学建模方法,实现了对污染气体排放现象的建模,并在此基础上设计了一个污染气流的生成算法.最后给出了污染气流扩散的动态模拟效果图.     

上海地铁A型车车厢体空调气流组织的模拟研究

利用计算流体力学软件对地铁A型车厢空调系统在不同工况下的温度场和速度值进行了数值模拟,就其所涉及的风口尺寸、位置、型式以及气流组织等方面定性地进行了比较分析,提出了一个优化方案,为车厢内气流分布的优化设计提供参考。     

基于卡尔曼滤波和粒子滤波融合的UWB室内定位算法

基于超宽带(ultra-wideband, UWB)室内定位技术得到了广泛的发展,然而,在LOS(line-of-sight)和NLOS(non-line-of-sight)环境下的UWB的测距信息均存在不同程度的误差,因此,提出了一种改进的卡尔曼滤波算法对UWB原始数据进行平滑处理;之后提出卡尔曼滤波(Kalman filters and particle filters, KPF)和粒子滤波融合的算法。通过卡尔曼滤波得到的状态量和误差协方差进行粒子采样,克服了传统粒子滤波进行粒子采样时的运动学模型与实际运动不相符的缺点,大幅减少了粒子退化的现象。经过实验,该算法在LOS和NLOS环境中的定位精度分别提升了20.6%和15.6%。     

客房空调气流组织的实验研究及优化

利用CFD技术与实验相结合的方式对客房空调气流的温度场和速度场进行了分析。根据客房的实际情况提出了优化方案，并给予模拟和分析。     

Applications of high‐resolution schemes based on normalized variable formulation for 3D indoor airflow simulations

Computational fluid dynamics (CFD) has been used in a routine manner for the design of indoor environments. The quality of these CFD studies varies from poor to excellent, and only in year 2003 Sørensen and Nielsen recommend a detailed guideline on imposing quality control in the CFD‐related works for indoor airflow simulations. One of these recommendations is to use monotone high‐resolution (HR) schemes that apply flux limiters to ensure solution boundedness while preserving the high‐order accuracy of the differencing schemes. In this paper, based on the γ‐formulations derived from the normalized variable formulation, four recently developed HR schemes, GAMMA, CUBISTA, AVLSMART and HOAB, are applied to several indoor airflow problems such as (1) Smith–Hutton problem (dead‐end channel); (2) forced convection problem (horizontal/oblique inflow) in a parallelepiped room; (3) mixing ventilation problem focusing on the prediction of local mean age of air; (4) flow in a two‐room chamber with internal partition and (5) displacement ventilation in a mockup office. Based on the flow results, the aspects of accuracy and robustness of these HR schemes are addressed for appropriate selection of an ‘ideal’ differencing scheme to improve the quality of 3D indoor CFD calculations. Copyright © 2007 John Wiley & Sons, Ltd.     

教学机房室内空气品质现状调查及改善措施

教学机房是学生学习的重要场所,也是集中授课的重要场所之一.机房内人员多,电子设备多,室内照明要求高,因此室内负荷大.目前许多教学机房是对教室或其他场所改造而成的,原来室内无空调通风措施.改造后的机房多数是在室内安装空调器试图降低室内温度,但是受空调器安装位置限制,室内温度场分布不均匀.同时为减少耗电量,房间门窗一般关闭,只设置排气扇进行通风换气,室内空气品质较差.本文通过对某典型教学机房室内空气品质中部分主要指标进行现场测试及问卷调查,发现机房内空气品质较差,分析了原因,并提出了改善措施.     

CFD simulation and performance optimization of a new horizontal turbo air classifier

A new horizontal turbo air classifier equipped with two inclined air inlets has been introduced. The flow field and classification performance of the classifier have been investigated using CFD method and response surface methodology (RSM). Simulation results show that the flow field is composed of the primary swirling flow and the secondary upward washing air, and the uniformly distributed swirling flow occupies the classifying chamber. The tangential gas velocity reaches the maximum value on the outer surface of the rotor cage, generating strong centrifugal force for the particle classification. The discrete phase model (DPM) can predict the cut sizes, but cannot present the fish-hook phenomenon. The desirable experimental condition by targeting the cut size of 20 μm and minimizing the classifying accuracy index is, rotor speed of 1373.6 rpm, primary air volume flow rate of 261.8 m³/h and secondary air volume flow rate of 42.4 m³/h. The corresponding fine and coarse fraction loss are less than 1.42% and 7.24%, respectively. This study provides a new strategy to design the horizontal turbo air classifier.     

Validation of CFD model of multiphase flow through pipeline and annular geometries

Accuracy of prediction of pressure losses plays a vital role in the design of multiphase flow systems. The present study focused on the development of a computational fluid dynamics model to predict these parameters conveniently and accurately. The main objective was to validate the developed model through comparison of its simulation results with existing experimental data and empirical correlations. Both pipeline and annular geometries were considered for validation. Several data sets that involved a significant variation in process conditions were used for the validation. All three phases—liquid (water), gas (air), and solid (sand)—were taken into account. The simulations were conducted using the workbench platform of ANSYS Fluent 16.2. The Eulerian model of multiphase flow and the Reynolds stress model of turbulence closure available in Fluent were used for the present study. The average velocities and volumetric concentrations of involved phases were specified as the inlet boundary conditions. The stationary surfaces of the flow channels were hydrodynamically considered as either smooth or rough walls, and the outlets were regarded as being open to the atmosphere. The simulation results of pressure loss showed a good agreement with the corresponding measured values as well as with the predictions of well-established correlations.     

CFD modeling of erosion wear in pipe bend for the flow of bottom ash suspension

In the present study, erosion wear behavior of slurry pipeline due to solid–liquid suspension in the pipeline has been investigated using commercial computational fluid dynamics (CFD) code FLUENT. A multiphase Euler–Lagrange model was adopted to predict the solid particle erosion wear in a 90° pipe bend for the flow of bottom ash–water suspension. A standard k–ε turbulence modeling scheme was used to simulate the flow through the pipeline. Water and bottom ash were taken as liquid and as a dispersed phase of solid–liquid mixture, respectively. A simulation study for erosion wear in a pipe bend was carried out to investigate the influence of various parameters including velocity, solid concentration, and particle size. The velocity of the bottom ash–water suspension varied from 0.5 to 2.5?m/s for solid concentrations with a range of 2.5 to 10.0% (by volume). The particle diameters of the bottom ash were 162 and 300?µm. The simulation results agree with the results of previous studies.     

CFD simulations of droplet and particle agglomeration in an industrial counter-current spray dryer

In this study, CFD simulations of particle and droplet agglomeration in an industrial counter-current spray dryer are presented. For this purpose, a modified form of the stochastic collision agglomeration model is proposed. This model takes into account droplet–droplet collision as well as wet and dry particle interaction. These events are coupled with heat, mass and momentum transfer. A comprehensive moisture evaporation model based on the concept of characteristic drying curve (CDC) was applied to predict the drying kinetics of the detergent slurry. Due to high instability in air flow inside the drying chamber, simulations were carried out under transient condition. A comparison between time-averaged simulation results and measurements, which were performed on an industrial spray drying installation, shows a good agreement. This finding proves the correctness of the developed agglomeration and drying models. The presented methodology of CFD simulations of agglomeration can be used to design or optimise spray-drying installations and to predict the final particle size distribution of the product.     

Predictive CFD modeling of whey protein denaturation in skim milk spray drying powder production

A new model of whey protein thermal inactivation has been combined with a CFD model developed for skim milk spray drying. Extensive evaporation and particle formation models were used to calculate particle moisture contents, temperatures and residence times. Calculated parameters were then used as input data for an experimentally developed quality model based on Williams-Landel-Ferry (WLF) equations for inactivation kinetics. The developed quality model was implemented into the CFD code and calculated in parallel to simulations of skim milk droplets evaporation based on the characteristic drying curve approach. The quality model and the simulation procedure were validated by comparison of protein activity levels obtained from the CFD with data obtained from differential scanning calorimetry (DSC) of milk powder samples collected during skim milk spray drying experiments. The simulations for different feed rates fit well with measurement results and show that the loss of whey protein activity is lower at higher feed rates, due to lower temperature fields in this case.     

Experimental and Simulation Studies of Dilute Horizontal Pneumatic Conveying

Dilute horizontal pneumatic conveying has been the subject of this experimental and numerical study. Experiments were performed utilising a 6.5 m long, 0.075 m diameter horizontal pipe in conjunction with a laser-Doppler anemometry (LDA) system. Spherical glass beads with three different sizes 0.8–1 mm, 1.5 mm, and 2 mm were used. Simulations were carried out using the commercial discrete element method (DEM) software, EDEM, coupled with the computational fluid dynamics (CFD) package, FLUENT. Experimental results illustrated that, for mass solid loading ratios (SLRs) ranging from 2.3 to 3.5, the higher the particle diameter and solid loading ratio, the lower the particle velocity. From the simulation investigations it was concluded that the inclusion of the Magnus lift force had a crucial influence, with observed particle distributions in the upper part of the conveying line reproducible in the simulation only by implementing the Magnus lift force terms in the model equations.     

粉煤灰粒度分布及其活性的灰系统研究

用激光粒度仪测定不同细度粉煤灰的粒度分布,以灰色关联方法分析了粉煤灰粒度分布与其胶砂性能之间的相关性,并建立了粉煤灰粒度分布与其活性指数的灰系统模型。结果表明:粉煤灰粒度分布明显影响胶砂性能;19.953～45.709μm颗粒含量与胶砂需水量的正关联度最大;5.012～19.953μm颗粒含量与粉煤灰活性的正关联度最大;根据抗压强度活性指数的灰色模型可以预测粉煤灰活性大小。     

颗粒碰撞环形调谐质量阻尼器的设计与实验

石化企业中缓冲罐、管道、压力容器及换热器等圆筒形设备普遍存在振动。采用低元化模型和等效质量辨识法,对调谐质量阻尼器在此类连续系统中的振动控制机理进行研究,设计一种便于安装的新型颗粒碰撞环形调谐质量阻尼器。理论推导阻尼器环向对称布置弹簧的综合刚度,测量颗粒碰撞阻尼系数,得到了最优调谐参数的阻尼器。运用MATLAB对不同阻尼比的阻尼器减振特性进行仿真,并设计悬臂钢结构圆筒模型作为振动控制对象。对结构1阶模态频率附近的振动控制情况进行实验,对比有无颗粒阻尼下的减振效果差异。结果表明,设计的颗粒碰撞阻尼器能够有效抑制圆筒设备各方向振动,且减振频带大幅度拓宽。这种环形设计思想和颗粒碰撞阻尼可以对调谐质量阻尼器提供更大的应用空间。     

Influence of Particle Size and Heating Rate on Decomposition of BC Dry Chemical Fire Extinguishing Powders

Pyrolysis of BC dry chemical fire extinguishing powders which are useful for Class “B” and Class “C” fires was conducted on a thermogravimetric analyzer with sample loading of 10–25 mg under dynamic air atmosphere. The effect of particle sizes (medium value 48.99, 27.24, 4.93 µm) and heating rates (10, 15, and 20°C min^?1) were examined. The pyrolysis kinetics of the samples was analyzed using a distribution activation energy model. It was found that the decomposition temperature decreased and the pyrolysis rate increased after the samples were milled. The agglomeration of particles during production did not have an appreciable influence on the pyrolysis process of the samples in our experimental conditions. The activation energy value was 77.13?219.78 kJ · mol^?1, 58.18?288.67 kJ · mol^?1, and 44.59?209.17 kJ · mol^?1 for the powder of particle size 48.99, 27.24, 4.93 µm. We should use micro powder in fire extinguishing.