Numerical simulation of airflow distribution in mine tunnels

Based on 3D modelling of typical tunnels in mines, the airflow distribution in a three-center arch-section tunnel is investigated and the influence of air velocity and cross section on airflow distribution in tunnels is studied. The average velocity points were analyzed quantitatively. The results show that the airflow pattern is similar for the three-center arch section under different ventilation velocities and cross sectional areas. The shape of the tunnel cross section and wall are the critical factors influencing the airflow pattern. The average velocity points are mainly close to the tunnel wall. Characteristic equations are developed to describe the average velocity distribution, and provide a theoretical basis for accurately measuring the average velocity in mine tunnels.

Multi-factor influence of cross-sectional airflow distribution in roadway with rough roof

The wall surface roughness renders a significant impact on ventilation of roadways and cross-sectional wind speed distribution.Herein,the wall roughness(Ra)in the roadway has been defined theoretically.Moreover,three-center arched roadway models for different situations are established based on the normal distribution of roof roughness.The influence of inlet velocity,roof roughness and roadway height on wind speed distribution is systematically studied by using Fluent software.At Ra=0.1 m,the simulation results reveal that the wind speed is negatively related to the distance from the wall to the point where 80%of the central wind speed is reached(DA).Also,the wind speed distribution is significantly influenced by increasing the roof roughness.However,the wind speed distribution becomes asymmetric at Ra=0.2 m and 0.3 m.Furthermore,the low-speed area(v≤1 m/s)started to concentrate on the roof with the increase of roadway height.Overall,an Ra value of<0.1 m can reduce the influence of wall roughness on wind speed distribution of the roadway,which is suggested in practical applications.

Airflow Distribution Measurements around the Human Body Using a Thermal Manikin by Particle Image Velocimetry

The human body is a heat source in a room. As the human body has a complex shape, it is difficult to accurately measure the airflow distribution around the human body using a conventional anemometer. This study measured the airflow distribution around a thermal manikin acting as a human body by visualization and particle image velocimetry (PIV). The thermal manikin was 1700 mm in height, and its surface temperature was set to 30oC. The experiments were performed in the conditions when the manikin was seated on a chair. The ambient air temperature and wind velocity were experimental variables. The airflow distribution around the manikin was reported by considering the relationships between convection and ambient wind velocity. There were no differences in the airflow distribution around the manikin due to the ambient air temperature when the wind velocity in the chamber was set as 1.0 m/s. Hence, it was assumed that the ambient wind velocity was dominant in this condition. Various airflow distributions were formed around the manikin due to the difference between the body surface temperature and the ambient air temperature in the case where the wind velocity in the chamber was set to approximately equal to 0.0 m/s.

Distribution properties of airflow in the full envelope type maize stalk chopping chamber

Chopped and spread maize stalks improve soil structure and fertility. However, because of the absence of research on airflow distribution in the chopping chamber, improvement of the spreading uniformity of chopped stalks has been limited. Therefore, in this study, computational fluid dynamics (CFD) technology was applied to analyze the influence of structural and operational parameters of the chopping and spreading machine on the velocity, pressure, and turbulent kinetic energy distribution of airflow in the chopping chamber. The experimental factors considered were the relative position angle (RPA) between the collecting-chopping shaft and the sliding-supporting shaft, working velocity (WV) of the chopping chamber, and rotational velocity of the collecting-chopping blade (RVCCB). The results revealed that RPA and RVCCB had a significant influence on the maximum negative pressure in the inlet (MNPI), the proportion of negative pressure area at inlet (PNPAI), and the maximum pressure drop at inlet and outlet (MPDIO). Additionally, RVCCB had a strong influence on the maximum velocity, average velocity, and velocity variation coefficient of airflow at the outlet. Moreover, maximum turbulence (MT) and maximum turbulent kinetic energy dissipation rate (MTKEDR) showed a positive relationship with RVCCB. To determine the values of RPA, RVCCB, and WV, a multivariate parameters optimization regression model was constructed, which yielded the optimal values of 15°, 1800 r/min, and 0.50 m/s, respectively. Subsequently, a hyperbolic spiral-type guiding shell with an arc length of 90° was designed to enhance the uniform distribution of airflow in the chopping chamber. Finally, a validation experiment of airflow distribution was conducted. The results showed that the velocity difference between the simulation and the validation experiment was less than 15%, indicating the accuracy of CFD simulation, and the spreading uniformities of the chopped stalks were better than national standards. These findings can serve as technical and theoretical support for the design and optimization of chopping and spreading machines.

CFD modeling of methane distribution at a continuous miner face with various curtain setback distances

Knowledge of the airflow patterns and methane distributions at a continuous miner face under different ventilation conditions can minimize the risks of explosion and injury to miners by accurately forecasting potentially hazardous face methane levels. This study focused on validating a series of computational fluid dynamics(CFD) models using full-scale ventilation gallery data that assessed how curtain setback distance impacted airflow patterns and methane distributions at an empty mining face(no continuous miner present). Three CFD models of face ventilation with 4.6, 7.6 and 10.7 m(15, 25, and 35 ft) blowing curtain setback distances were constructed and validated with experimental data collected in a full-scale ventilation test facility. Good agreement was obtained between the CFD simulation results and this data.Detailed airflow and methane distribution information are provided. Elevated methane zones at the working faces were identified with the three curtain setback distances. Visualization of the setback distance impact on the face methane distribution was performed by utilizing the post-processing capability of the CFD software.

洁净手术室气流组织效果的影响因素综述

我国医院建设规模庞大、分布广泛,就医人数居世界第一,医疗洁净手术室空气洁净技术发展迅速。手术室的气流组织是其空气洁净技术的重要方面,与手术部位感染的关系一直存在争议。本文对手术室中的气流组织形式进行了综述。研究表明,层流通风和温控气流通风在去除携带细菌的颗粒方面具有优势,且层流通风对飞沫的控制能力更强。本文梳理了手术室内人员数量和位置、手术人员的动作和流动、医用设备的数量和发热量、人员着装和手术台次等因素对气流组织效果的影响。发现手术人员的动作和流动是相关研究的热点,气流组织与手术人员、患者热舒适的关联仍有待深入。未来研究方向包括手术室内局部气流组织与手术微环境空气质量的定量关系、新型气流组织形式和末端、个性化通风与手术人员热舒适等。

数据中心主机房的能效评价方法及提升路径

本研究主要根据数据中心主机房的气流组织和UPS应用的实测结果,分析低负载率工况下气流组织存在的问题和UPS电源质量和运行效率,提出相应的机房能效提升路径,从而降低数据中心PUE值。

综掘工作面风幕阻尘效果影响因素研究

目前综掘工作面粉尘污染的研究多集中于单一因素对综掘工作面风幕阻尘效果的影响,而未充分考虑各因素间的交互作用,使得压风分流技术的工程应用效果欠佳。为明确附壁风筒径向出风距离、径向出风比及轴向出风距离对风幕阻尘效果的影响,以潘三矿810西翼机巷综掘工作面为研究对象,运用Fluent软件对径向出风距离为10~25 m、径向出风比为0.6~0.9及轴向出风距离为6~12 m条件下的风流分布和粉尘扩散情况进行数值模拟。结果表明:(1)随着径向出风距离增大,径向涡流风幕在巷道内的转变更充分,综掘机司机前端的风流分布越均匀,更有利于形成风速方向均指向工作面的轴向阻尘风幕。当径向出风距离为10 m时,距工作面7 m断面内涡流特性明显,风速方向紊乱;当径向出风距离为25 m时,距工作面7 m断面内,风流分布趋于均匀,风速方向均指向工作面,形成了能够覆盖全断面的轴向阻尘风幕。(2)随着径向出风比增大,整流风筒轴向风流风量减小,轴向风流风速和射流强度降低,轴向风流对综掘工作面前端气流的扰动减弱;径向出风比越大,越有利于形成风流方向指向工作面且能覆盖全断面的轴向阻尘流场,即轴向阻尘风幕。(3)径向涡流风幕的阻尘能力随径向出风比的增大先增强后减弱,轴向阻尘风幕的阻尘能力随径向出风比的增大而不断增强。(4)在采取压风分流风幕阻尘技术后,当压风总量为300 m^(3)/min,吸风量为400 m^(3)/min,附壁风筒径向出风距离为20 m,径向出风比为0.9,整流风筒轴向出风距离为8~10 m时,能很好地将粉尘聚集在吸尘口附近,达到高效控尘除尘的目的。在810西翼机巷综掘工作面进行现场测试,测点风速和粉尘质量浓度实测值与模拟值基本一致,高浓度粉尘被有效阻控于工作面前端,隔尘效果较为明显,验证了数值模拟的有效性。

5XZ-10型比重式种子分选机气流孔板布置优化

种子的好坏,直接影响粮食产量,优良种子的筛选对于国家粮食安全问题具有重大意义。针对5XZ-10型比重式种子分选机筛面气流分布不均的问题进行单因素试验。利用Fluent软件,采用数值模拟与试验相结合的方法对比重式分选机气室流场进行了求解。为了简化计算量,引入多孔介质模型代替气流孔板。利用数值拟合求解了多孔介质模型参数,建立气室几何模型并验证了模型的可行性。将气流孔板布置高度比例系数α作为单因素变量,得到分选机空气流场及空气动力场的分布特点。为获得合理的筛面气流,讨论了不同的气流孔板高度对气室出口界面气流稳定性、均匀性的影响,发现当α=0.84时,气室出口界面气流稳定性、均匀性较好。确定气流孔板合理的安装高度530 mm,为比重式种子分选机优化设计提供了试验数据及理论依据。

Downwash airflow field distribution characteristics and their effect on the spray field distribution of the DJI T30 six-rotor plant protection UAV

Spray characteristics are the fundamental factors that affect droplet transportation downward,deposition,and drift.The downwash airflow field of the Unmanned Aviation Vehicle(UAV)primarily influences droplet deposition and drift by changing the spray characteristics.This study focused mainly on the effect of the downwash airflow field of the UAV and nozzle position on the droplet spatial distribution and velocity distribution,which are two factors of spray characteristics.To study the abovementioned characteristics,computational fluid dynamics based on the lattice Boltzmann method(LBM)was used to simulate the downwash airflow field of the DJI T30 six-rotor plant protection UAV at different rotor rotational speeds(1000-1800 r/min).A particle image velocimetry system(PIV)was utilized to record the spray field with the downwash airflow field at different rotational speeds of rotors(0-1800 r/min)or different nozzle positions(0,0.20 m,0.35 m,and 0.50 m from the motor).The simulation and experimental results showed that the rotor downwash airflow field exhibited the‘dispersion-shrinkage-redispersion’development rule.In the initial dispersion stage of rotor airflow,there were obvious high-vorticity and low-vorticity regions in the rotor downwash airflow field.Moreover,the low-vorticity region was primarily concentrated below the motor,and the high-vorticity region was mainly focused in the middle area of the rotors.Additionally,the Y-direction airflow velocity fluctuated at 0.4-1.2 m under the rotor.When the rotor airflow developed to 3.2 m below the rotor,the Y-direction airflow velocity showed a slight decrease.Above 3.2 m from the rotor,the Y-direction airflow velocity started to drastically decrease.Therefore,it is recommended that the DJI T30 plant protection UAV should not exceed 3.2 m in flight height during field spraying operations.The rotor downwash airflow field caused the nozzle atomization angle,droplet concentration,and spray field width to decrease while increasing the vortex scale in the spray field when the rotor system was activated.Moreover,the increase in rotor rotational speed promoted the abovementioned trend.When the nozzle was installed in various radial locations below the rotor,the droplet spatial distribution and velocity distribution were completely different.When the nozzle was installed directly below the motor,the droplet spatial distribution and velocity distribution were relatively symmetrical.When the nozzle was installed at 0.20 m and 0.35 m from the motor,the droplets clearly moved toward the right under the induction of stronger rotor vortices.This resulted in a higher droplet concentration in the right-half spray field.However,the droplet moved toward the left when the nozzle was installed in the rotor tip.For four nozzle positions,when the nozzle was installed at 0 or 0.20 m from the motor,the droplet average velocity was much higher.However,the droplet average velocity was slower when the nozzle was installed in the other two positions.Therefore,it is recommended that the nozzle is installed at 0 or 0.20 m from the motor.The research results could increase the understanding of the downwash airflow field distribution characteristics of the UAV and its influence on the droplet spatial distribution and velocity distribution characteristics.Meanwhile,the research results could provide some theoretical guidance for the choice of nozzle position below the rotor.

风流速度与喷雾角度对雾滴场分布特征的影响

雾滴分布特征是决定喷雾系统降尘效果的关键因素之一。为研究不同工况下雾滴分布特征,利用CFD模拟技术分析了风速及喷雾角度对雾滴分布特征的影响机制;并探究了采煤机附近布置喷雾喷嘴后的雾滴分布特征。研究结果表明:不同风速和喷雾角度主要是通过增大雾滴的横向动量,造成喷雾带纵向高度和横向长度的增加;风速的增大,造成不同空间位置的雾滴间动量屏蔽效应更加突出,进一步增大了雾滴间所受横向动量的差异,增强了雾滴间集聚效应,使喷雾带周围形成大粒径雾滴层;喷雾角度的增大主要改变了出口动量在横向和纵向2个方向的分配比例,空间内所有雾滴所受动量更为均匀,进而对喷雾粒径分布特征无明显影响。

垂直单向流洁净室下夹层空气流速与孔板排布规律研究

提出了基于高架地板下夹层空气流速的量纲一速度参数K_(1),利用ANSYS Fluent软件对不同洁净室结构形式、风机过滤单元布置率和出口风速等条件下的空态洁净室高架地板布置方式与下夹层空气流速的匹配关系进行了研究。结果表明:当K_(1)<5时,洁净室内宜使用相同规格开孔率的孔板均匀布置;当5≤K_(1)<9时,应优先使用具有一定压力梯度变化的孔板非均匀布置,其次使用低开孔率的孔板均匀布置;当K_(1)≥9时,应使用具有较大压力梯度的孔板非均匀布置,且K_(1)值越大,靠近回风道位置孔板开孔率越小,孔板压力梯度变化越大。

严寒地区车库采用散热器地沟敷设供暖研究

在严寒、寒冷地区地面具有高大空间特点的停车库供暖问题上,提出了一种不受外墙敷设空间影响的地沟散热器安装供暖方案,并利用Airpak气流组织模拟手段,对供暖方案的供暖效果进行计算。通过计算结果可知,采用散热器地沟安装供暖方案,散热器表面能够产生稳定的上升气流,空气流动最大风速达到0.47m/s,车库内部整体温度能够达到采暖设计温度;考虑外窗、外门及外墙内壁温度较低,对于车库内部安装的宜结冻管道、设备应适当保持一定距离。

综掘工作面气幕控尘参数对粉尘污染的影响

气幕控尘效果受压抽风及径向分风多要素影响,而现有研究多局限于某单一要素对气幕控尘的影响规律。为掌握气幕控尘参数对综掘工作面粉尘污染的影响,对不同径向分风流量和负压控尘流量条件下的风流场演变和粉尘场扩散开展了数值模拟研究。结果表明:①径向分风流量主要影响轴向射流场的卷吸效应,负压控尘流量主要影响工作面的抽风负压作用,当径向分风流量与压风总流量比值≥0.8、压风总流量与负压控尘流量比值<1.0时,气幕运移至射流区域时转变为轴向运移,形成厚度≥1.4m的轴向控尘流场。②径向分风流量及负压控尘流量越大,巷道压抽风侧风流流量及风速分布越均匀,粉尘扩散距离越小,掘进机司机处粉尘质量浓度越低。在此基础上,确定了综掘工作面气幕控尘优化参数:径向分风流量为288m/min(径向分风流量与压风总流量比值为0.9),负压控尘流量为426m^(3)/min(压风总流量与负压控尘流量比值为0.75)。经现场实测,应用气幕控尘优化参数后,掘进机司机处降尘率达93.5%,人员作业环境得到明显改善。

催化裂化工业再生器底部气流分布及优化分析

为了不断提升催化裂化工业再生器底部气体流向分布的均匀性,文章通过实验形式对催化裂化工业再生器底部气流分布进行研究,经实验研究结果发现,对再生器主风入口倒锥结构进行改变对底部气流分布均匀性没有显著影响,而增大气体分布器孔径以及改变分布器上端区域气体出口速度对再生器底部气流分布的均匀性具有显著改善,并且改善效果良好。此次研究有助于提升工业再生器的应用效率,对石油炼制行业的可持续发展具有重要意义。

通信基站与汇聚机房制冷优化潜力浅析

随着通信网络的不断发展,通信基站与汇聚机房的制冷系统在产品硬件、系统能效及调控策略等方面暴露出诸多问题。为打造更加绿色、高效、可靠的通信网络,本文从安全、节能与智能化的角度展开深入研究。首先对现阶段通信基站与汇聚机房制冷系统的送风方式、供电方式及调控策略进行分析,在此基础上,提出多制式供电、优化气流组织与智能化群控策略相结合的优化思路。该方案可提升制冷系统节能率至30%以上,为通信行业的可持续发展提供有力支持,也为相关领域的研究和实践提供参考和借鉴。

轨道交通车辆孔板送风数值模拟简化方法研究

城市轨道车辆车体内气流组织分布是评价车乘人员热舒适的关键指标之一。孔板送风具有送风均匀、局部温差小等优点,被诸多车辆采用为主要的送风方式。然而,这种送风方式的物理模型极其复杂,在采用CFD仿真模拟其气流分布时计算量大、对硬件要求高且耗时间长。因此,本文提出了一种条缝模型,并以某城市轨道车辆为例进行了验证。结果表明所提出的条缝模型在简化孔板圆孔模型的基础上较好地复现孔板圆孔模型的气流分布。

复杂建筑环境中冷却塔风环境数值模拟及散热优化

采用CFD技术数值模拟分析了复杂建筑环境中不同冷却塔布置方案的气流分布和气流温度分布,比较了不同工况下冷却塔的热工特性,提出了改善冷却塔有效运行的技术措施。算例结果表明,CFD模拟是解决此类问题的有效手段;为其他类似冷却塔散热设计提供了一定的参考。

数据中心气流组织研究进展及展望

随着数据中心规模的不断扩大和业务应用的增加,热环境问题越来越突出。优化气流组织作为改善热环境的重要手段,已经成为了数据中心建设和运营中关注的热点领域。通过对国内外改善气流组织研究现状的分析,对气流组织优化方法进行了分类,总结了现有研究各自的优缺点,并分析了气流组织技术发展的趋势。提出了优化气流组织的建议:一是加装、改造挡板类导流装置,可以分离热空气和冷空气,阻止它们混合并提高冷却效率;二是针对地板和静压箱提升深度和高度,达到改善气流路径的效果;三是优化穿孔地板结构,也能达到改善气流路径的效果;四是控制优化风扇调控,改善气流路径,达到气流组织改善、提高机柜热性能。并对未来数据中心热环境研究进行了展望。

地上列车活塞风对站台环境的影响——以松江大学城站地上站台为例

以上海9号线松江大学城站地上站台为研究对象,利用重叠网格技术模拟列车运动,研究半高安全门下列车活塞风对站台的影响,对单辆列车进站、停站、出站过程中的速度场、压力场进行数值模拟,分析了3种工况下列车活塞风对站台内气流分布和空气质量的影响。结果表明,活塞效应会增加站台的颗粒物浓度,应避免乘客因站台内颗粒物浓度过高而影响健康。