Auxiliary ventilation in mining roadways driven with roadheaders: Validated CFD modelling of dust behaviour

The production of dust when driving mining roadways can affect workers health. In addition, there is a decrease in productivity since Mine Safety regulations establish a reduction in the working time depending on the quartz content and dust concentration in the atmosphere.One of the gate roadways of the longwall named E4-S, belonging to the underground coal mine Carbonar SA located in Northern Spain, is being driven by an AM50 roadheader machine. The mined coal has a high coal dust content.This paper presents a study of dust behaviour in two auxiliary ventilation systems by Computational Fluid Dynamics (CFD) models, taking into account the influence of time. The accuracy of these CFD models was assessed by airflow velocity and respirable dust concentration measurements taken in six points of six roadway cross-sections of the mentioned operating coal mine.It is concluded that these models predicted the airflow and dust behaviour at the working face, where the dust source is located, and in different roadways cross-sections behind the working face.As a result, CFD models allow optimization of the auxiliary ventilation system used, avoiding the important deficiencies when it is calculated by conventional methods.     

Air flow and particle control with different ventilation systems in a classroom

Most ventilation and air conditioning systems are designed without much concern about how settling particles behave in ventilation air flows. For displacement ventilation systems, designers normally assume that all pollutants follow the buoyant air flow into an upper zone, where they are evacuated. This is, however, not always true. Previous studies show that high concentrations of settling respirable particles can be found in the breathing zone, and that the exposure rates can be a health hazard to occupants. The emphasis here is on how ventilation systems should be designed to minimize respirable airborne particles in the breathing zone. The supply and exhaust conditions of the ventilation air flow are shown to play an important role in the control of air quality. Computer simulation programs of computational fluid dynamics (CFD) type are used. Particle concentrations, thermal conditions and modified ventilation system solutions are reported.     

Numerical simulation of ventilation and dust suppression system for open-type TBM tunneling work area

In order to study the characteristics of the ventilation and dust suppression system for open-type TBM tunneling work area in a Ø8.53 diversion project, the numerical simulation method is adopted, and a three-dimensional steady airflow model, a dust flow model as well as other related flow characteristic equation models are established by considering the dust production mechanism of TBM construction. Besides, corresponding simulation models validated by experiment are established using CFD software, and the impacts of the main vent location, the air baffle length in the main beam and the exhausting air flow quantity on flow field distribution and dust flow behavior in open-type TBM tunneling work area are investigated. The results show: when the main vent is located 70–80 m away from the working face, the ventilation in TBM tunneling work area is optimal; when the air baffle is as long as the main beam, the dust collection efficiency is the highest, reaching 89.4%; under the condition that the exhausting air flow quantity is less than half of the ventilation air flow quantity required by energy consumption and the minimum backflow velocity, the best dust suppression effect can be achieved when the exhausting air flow quantity is 40% of the ventilation air flow quantity.     

综掘面抽出风筒吸风口直径对风流场影响分析:以煤矿矿井为例

矿井综掘工作面良好的通风环境是保障煤矿安全生产的前提。文章以某煤矿综掘巷道为研究对象,采用Fluent软件模拟长压短抽通风系统中抽出风筒吸风口直径变化对风流场的影响。由模拟结果可知:吸风口直径的大小直接影响巷道内风流分布,吸风口直径的改变会对压入射流形成干扰,对距掘进端头0~10 m范围内的风速影响最大;同时对巷道内涡流有明显的影响,吸风口直径从0.5 m增加到0.6 m时,涡流区域减小,直径从0.6 m增加到1.0 m时,涡流区域逐渐扩大,吸风口直径0.6 m时能实现最佳通风效果。     

Experimental and Numerical Study of the Interaction Between Water Mist and Fire in an Intermediate Test Tunnel

The paper deals with interaction between water mist and hot gases in a longitudinally ventilated tunnel. The work aims at understanding the interaction of mist, smoke and ventilation.The study is based on one intermediate tunnel test and an extensive use of the computational code Fire Dynamics Simulator (FDS, NIST). The approach consists first of reconstructing the test with the CFD code by defining the relevant numerical parameters to accurately model the involved water mist system. Then, it consists of handling from the local data the complicated flows generated by the water mist flooding on the one hand and by fire and ventilation on the other hand. The last stage consists in quantifying each mechanism involved in interaction between water mist and hot gases. There are three main results in this study. Firstly, the CFD code prediction is also evaluated in this configuration, with and without water mist. Before the mist system activation, the agreement is satisfactory for gas temperatures and heat flux. After the activation time, the CFD code predicts well the thermal environment and in particular its stratification. Secondly, water mist plays a strong thermal role since in the test studied, roughly half of the heat released by fire is absorbed by water droplets. Thirdly, heat transfer from gaseous phase to droplets is the main mechanism involved (73%). The remaining heat absorbed by droplets results from tunnel surface cooling which represents (9%) and radiative attenuation (18%).     

超细水雾抑制甲烷-煤尘复合爆炸的实验研究

为掌握瓦斯-煤尘复合爆炸机理,通过可视化爆炸装置进行了密闭空间的超细水雾抑制甲烷-煤尘复合爆炸实验,探究了不同浓度的超细水雾对爆炸超压、压力上升速率、火焰传播速度的影响;研究了超细水雾作用下的火焰传播特征和爆炸不同阶段的抑爆机理。测定了不同煤尘粒径、浓度下的临界抑爆浓度。结果表明：超细水雾使爆炸超压延迟上升;爆炸火焰经历了点火焰、局部强发展火焰、连续不光滑火焰以及稳定分层火焰4 个发展阶段,抑制局部强发展火焰的出现是抑制爆炸的关键;随着超细水雾浓度的增加,压力的二次加速上升现象逐渐消失,放热速率与火焰锋面的燃烧速率的相关性增强;水雾的临界抑爆浓度随煤尘浓度的增加先增后降,随煤尘粒径的增加而降低。     

Influence of ventilation systems and related energy consumption on inhalable and respirable dust concentrations in fattening pigs confinement buildings

In this paper are presented the results of experimental analysis of the influence of ventilation systems and related energy consumption on inhalable and respirable dust concentrations in fattening pigs confinement buildings. The application of different under pressure ventilation systems in reducing and controlling dust concentrations was analyzed. Optimal ventilation systems designs and the ranges of airflow velocities were defined and discussed.Airflow velocities in the finishing room, under floor, roof and both ventilations, ranged from: 0.01 to 0.10, 0.01 to 0.10 and 0.02 to 0.10 m/s, respectively.The average inhalable dust concentrations during the reference regime (no ventilation), as well as second (floor-), third (roof-) and fourth (both ventilations) regime were: 20, 20, 25 and 17 particles/cm³, respectively. The average respirable dust concentrations during the reference regime, as well as second, third and fourth regime were: 18, 19, 23 and 16 particles/cm³, respectively.Significant decrements of inhalable (F = 44.35, P ≪ 0.01) and respirable (F = 43.82, P ≪ 0.01) dust concentration, in the finishing fattening pig house, were achieved only with the fourth regime (both ventilations).     

Distribution of brominated flame retardants in different dust fractions in air from an electronics recycling facility

Twelve air samples were collected from an electronic recycling facility in Sweden representing three different dust fractions; respirable, total and inhalable dust. Four samples were collected from each fraction. The highest concentration of polybrominated diphenyl ether (PBDE) #209 (ten bromine atoms) was found in the samples from the inhalable dust fraction (ID), which was 10 times higher than for the "total dust" fraction (TD). The concentration ranges were 157.6-208.6; 13.9-16.7; and 2.8-3.3 ng/m3 for inhalable, total and respirable fractions, respectively. The second most abundant PBDE congener was PBDE #183 (seven bromine atoms), followed by the second most abundant substance 1,2-bis(2,4,6-tribromophenoxy)ethane (BTBPE) in all samples. In addition, decabromodiphenyl ethane (DeBDethane) was tentatively identified in five of the samples. Because of the large differences in air concentrations between the three fractions in ID, TD and RD, it is suggested that the inhalable instead of "total dust" fraction should be used to assess air concentrations, in particular for the larger and higher brominated flame retardants (BFRs).     

Fractional Aerosol Filtration Efficiency of In-Duct Ventilation Air Cleaners

The filtration efficiency of ventilation air cleaners is highly particle-size dependent over the 0.01 to 3 μm diameter size range. Current standardized test methods, which determine only overall efficiencies for ambient aerosol or other test aerosols, provide data of limited utility. Because particles in this range are respirable and can remain airborne for prolonged time periods, measurement of air cleaner fractional efficiency is required for application to indoor air quality issues. The objectives of this work have been to 1) develop a test apparatus and procedure to quantify the fractional filtration efficiency of air cleaners over the 0.01 to 3 μm diameter size range and 2) quantify the fractional efficiency of several induct air cleaners typical of those used in residential and office ventilation systems. Results show that efficiency is highly dependent on particle size, flow rate, and dust load present on the air cleaner. A minimum in efficiency was often observed in the 0.1 to 0.5 μm diameter size range. The presence of a dust load frequently increased an air cleaner's efficiency; however, some air cleaners showed little change or a decrease in efficiency with dust loading. The common furnace filter had fractional efficiency values of less than 10% over much of the measurement size range.     

Visualization of Three Dimensional Failure in Sand Due to Water Inflow and Soil Drainage from Defective Underground Pipe Using X-ray CT

The roadway surface locally subsides due to material aging or settlement of a base course in particular, resulting in failure of the ground with a plenty of water inflow. In most cases of roadway subsidence, underground pipes exist underneath the subsidence. In order to understand significant factors leading to local subsidence at a ground surface, a series of model tests using sandy soil were performed with the concerned defect configuration of the underground pipe and hydraulic condition. An industrial X-ray computed tomography (CT) scanner was used to investigate the behaviour of the model ground at each step of monotonic water inflow, monotonic soil drainage and the cyclic water inflow—soil drainage. Then, the behaviour density change of the model ground was visualized as a density change in two-dimensions and three-dimension. This paper concludes that the cyclic condition of water inflow—soil drainage caused fatal ground failure as the water inflow process created a water path disturbing the soil. Subsequently, the soil drained and the soil particles were interlocked due to the drainage. The movement of soil particles were restricted with the arching effect; and, the factors causing the cavity in the ground were not only the existing defect in the underground pipe but also the water flow towards the defective part after the loss of capillary force.     

A study of physicochemical characteristics of respirable dust in an Indian coal mine

The respirable coal dust samples were collected from the mine atmosphere during drilling of coal seams using ‘Hexlet’ apparatus. Sixteen dust samples were collected from each three different seams for investigations. After destruction of the organic matter by wet oxidation and filtering off the clay and silica, Fe, Ca, Mg, Na, K, Mn, Zn, Cu, Cd and Ni were determined directly in the resulting solution by atomic absorption spectrophotometric methods. The x-ray diffraction studies have shown the presence of kaolinite, quartz, pirrsonite, and beidellite clay minerals in the coal dust.The mass-size distribution of the coal dust has been studied by using micron photosizer. The results showed that the distribution are unimodal, asymmetric, and positively skew. Although the assumption of log-normality was useful in interpreting the results, closer observations indicated that the relationship between the size and weight of the particles can be represented by a second degree parabolic equation W = a + bS + cS², where W and S are weight and size of the particles and a, b and c are constants. This equation helps us to characterise the mass of the respirable particles if the size is known.The studies throw light on the nature and mode of trace elements found in Indian Coal as well as on the causes of respiratory disease, pneumoconiosis, affecting the workers in the mine environmental condition.     

The Use of CFD Calculations to Evaluate Fire-Fighting Tactics in a Possible Backdraft Situation

This paper is an attempt to integrate theoretical Computational Fluid Dynamics (CFD) calculations with practical fire-fighting tactics commonly used when arriving at the scene of an underventilated fire. The paper shows that CFD has a great potential in improving understanding and creating better effectiveness in the estimation of fire-fighting tactics. If burning has occurred in a lack of oxygen for a long time, excessive pyrolysis products may have accumulated in the fire compartment. If air is suddenly introduced in the compartment a backdraft may occur. The CFD code used for the simulations is fire dynamics simulator (FDS). In this paper, we focus on the conditions that can lead to backdraft, and not the deflagration or rapid combustion in itself. Therefore, the simulations focus on the gravity current and the mixing process between cold fresh air and hot smoke gases by considering a uniform temperature inside the building as initial condition. The different tactics studied include natural ventilation, positive pressure ventilation (PPV) and dilution by water mist. Their effectiveness is observed comparing them with a reference scenario, where no action is taken. The main objective of natural ventilation is to find the fire source, and the venting is more effective with several openings. Tactics involving PPV are very effective in evacuating the unburnt gases, but increases the mixing, and consequently the probability of backdraft during the early stage of operation. On the other hand, the addition of water mist can reduce the danger of backdraft by reducing the concentration of unreacted combustible gases below the critical fuel volume fraction (CFVF), where ignition cannot occur. If the dilution level is insufficient the danger of backdraft is increased, mainly because the process of gases evacuation is longer due to cooling, which reduces the density difference between hot and cold gases. During a fire-fighting operation, the choice of tactic depends mainly on whether there are people left in the building or not, but also on the fire-fighters’ knowledge of the building’s geometry and the fire conditions. If the situation shows signs of strongly underventilated conditions, the danger of backdraft has to be considered and the most appropriate mitigation tactics must be applied.     

The effects of intervention with local electrostatic air cleaners on airborne dust and the health of office employees

The aim of this intervention study was to identify any health improvements in the upper and lower airways of office workers after the installation of local electrostatic air cleaners. Eighty persons with airways symptoms were recruited and randomly assigned to an intervention or control group. Half of the air cleaners had a non-functioning electrostatic unit. Both participants and field researchers were blinded to the group status. Subjective symptoms were recorded using a questionnaire, and indexes calculated for general, irritation and skin symptoms. Objective respiratory health indicators were recorded, with acoustic rhinometry and peak expiratory flow (PEF) meters. In the intervention group there was a decrease in mean dust concentration from 65 to 35 microg/m(3), and a reduction from 57 to 47 microg/m(3) in the control group (P < 0.05 for difference in decline). The reduction was observed for all particles sizes. The irritation and general symptom indices decreased in both groups, but there was no improvement in the intervention group, compared with the control group. Median PEF increased 3 ml/s in the intervention group, and decreased 4 ml/s in the control group. The adjusted odds ratio for an increase above the 70th percentile was 5.7 (95% CI 1.0-32). PRACTICAL IMPLICATIONS: Electrostatic air cleaners can reduce the dust concentration effectively in the office environment. Small, medium and large sized particles can be reduced by approximately 50%, relatively most effectively for the respirable particles. However, the air cleaners tested in this study produced an annoying fan noise. Cleaning efficiency and noise data should be given consideration before installation. This experimental field study suggests that office workers with airways symptoms may benefit from installation of local electrostatic air cleaners.     

Indoor and outdoor PM2.5 and PM10 concentrations in the air during a dust storm

Asian dust storms (ADS) originating from the arid deserts of Mongolia and China are a well-known springtime meteorological phenomenon throughout East Asia. The ventilation systems in office utilize air from outside and therefore it is necessary to understand how these dust storms affect the concentrations of PM_2.5 and PM₁₀ in both the indoor and outdoor air. We measured dust storm pollution particles in an office building using a direct-reading instrument (PC-2 Quartz Crystal Microbalance, QCM) that measured particle size and concentration every 10 min for 1 h, three times a day. A three-fold increase in the concentrations of PM_2.5 and PM₁₀ in the indoor and outdoor air was recorded during the dust storms. After adjusting for other covariates, autoregression models indicated that PM_2.5 and PM₁₀ in the indoor air increased significantly (21.7 μg/m³ and 23.0 μg/m³ respectively) during dust storms. The ventilation systems in high-rise buildings utilize air from outside and therefore the indoor concentrations of fine and coarse particles in the air inside the buildings are significantly affected by outside air pollutants, especially during dust storms.     

Numerical simulation of air ventilation in super-large underground developments

Recent advancements in engineering technology have enabled the construction of super-large underground engineering projects in China. Currently, the ventilation requirements and standards of normal-size underground spaces are used for super-large underground excavating engineering projects in China. For example, the minimum air velocity of 0.15 m/s is the standard velocity for normal-size underground spaces; however, this value is also used as the required air velocity for diluting underground contaminants in super-large underground developments. This paper aims to examine the minimum ventilation requirements for super-large underground developments (S > 100 m²). A three-dimensional computational domain representing a full-scale underground space has been developed. The pertinent parameters such as dust concentration, smoke density, oxygen concentration and air temperature have been simulated. The results show that at some specific underground conditions, the ventilation air velocity of 0.15 m/s is sufficient to control the dust level, provide required oxygen concentration and maintain the air temperature at acceptable levels during development; however, it is not sufficient to bring the CO concentration below an acceptable safe limit. This must be considered by the ventilation system designers of super-large underground developments.     

地下风机房与风道交叉口段四连拱隧道施工技术

介绍了虹梯关隧道辅助通风巷道的地下风机房系统施工情况,具体阐述了风机房与风道交叉口连接段四连拱隧道的设计要点、施工开挖顺序以及施工方法,保证了该工程安全高效的完工。     

地下景观防结露系统设计及其气流组织模拟

为了解决某地下景观观赏玻璃内表面的结露问题,本文设计了1个通风除湿系统,由风机引入环境空气,并及时排除内部的湿负荷,防止玻璃内表面产生结露现象.应用CFD软件对该通风除湿设计进行了气流组织模拟,结果表明在设计工况下,通风30 min后,玻璃下方空气的相对湿度明显降低;通风2 h后,内部湿度场接近稳定状态,整个空间内湿度均比较低,内部空气的露点温度比玻璃内表面温度低4℃,说明该通风设计可以很好地防止结露现象的产生.     

天津西站地下出租车蓄车区通风系统模拟分析

本文以天津西站交通枢纽的地下出租车蓄车区为研究对象,建立了通风系统的数学模型,并用Airpak软件对其在不同换气次数工况下的污染物及温度分布进行了模拟分析。模拟结果表明:综合考虑空气品质、舒适性以及节能运行,得到最佳换气次数为10次/h;排风口位置对空气中污染物浓度没有显著影响,受热气流影响,将排风口设置在车辆集中区域上方的排风效果更好;由于污染源种类比较单一且空气流速较大,CO和CO2的浓度分布相似。本文结论对天津西站地下出租车蓄车区通风系统设计具有一定指导意义,也可为同类型建筑的通风系统设计提供参考。     

Cfd analysis and airflow measurements to approach large industrial halls energy efficiency: A case study of a cardboard mill hall

This paper deals with numerical methods for predicting air flow patterns in large industrial halls. Some major findings of the investigation of the airflow patterns in paper machine hall of Umka Cardboard Mill are presented in the paper. The main reason for the interest in this problem is to find optimal locations for extract air intake connections of the ventilation system connected to the exhausted air waste heat utilization. Previous studies have shown that the amount of heat released from the cardboard machine to the surrounding air in the hall and extracted by the series of ceiling mount axial fans was almost 30% of the total waste heat from the paper machine's drying section. These results have indicated the need for the waste heat utilization, but also for the optimization of the ventilation system. CFD simulation for predicting of air flow patterns was applied. The accuracy of the simulation was evaluated by comparing its results with the results of field measurements. Simulation results served well for qualitative analysis, gave better insight in general air movements inside the hall and indicated the extract air intake locations. By utilizing the waste heat from proposed optimal locations, fuel savings of 5% and reduction of 1140 t/year in CO₂ emissions can be achieved.     

不同压力下细水雾雾场特征参量模拟研究

为研究细水雾雾场特性,定量分析压力对细水雾雾场特征参数的影响,利用计算流体动力学软件 Fluent 对不同压力下细水雾雾场的粒径分布、速度分布、浓度分布等进行数值分析,利用高速摄像技术和激光粒度分析技术对细水雾雾场特征参数的模拟研究进行实验验证。结果表明：流体从喷嘴喷射到连续相空气中后,喷雾形态均保持为圆锥形。细水雾外部流场速度在截面中心处最大,向边缘处逐渐减小。喷头正下方粒子数量最多,随着距喷头水平距离的增加,粒子数量逐渐减小。