Impact of Air Velocity on the Detection of Fires in Conveyor Belt Haulageways

A series of large-scale experiments were conducted in an above-ground fire gallery using three different types of fire-resistant conveyor belts and four air velocities for each belt. The goal of the experiments was to understand and quantify the effects of air velocity on the detection of fires in underground conveyor belt haulageways and to determine the rates of generation of toxic gases and smoke as a fire progresses through the stages of smoldering coal, flaming coal, and finally a flaming conveyor belt. In the experiments, electrical strip heaters, imbedded approximately 5 cm below the top surface of a large mass of coal rubble, were used to ignite the coal, producing an open flame. The flaming coal mass subsequently ignited 1.83-m-wide conveyor belts located approximately 0.30 m above the coal surface. Gas samples were drawn through an averaging probe for continuous measurement of CO, CO₂, and O₂ as the fire progressed. Approximately 20 m from the fire origin and 0.5 m below the roof of the gallery, two commercially available smoke detectors, a light obscuration meter, and a sampling probe for measurement of total mass concentration of smoke particles were placed. Two video cameras were located upstream of the fire origin and along the gallery at about 14 m and 5 m in order to detect both smoke and flames from the fire. This paper discusses the impact of ventilation airflow on alarm times of the smoke detectors and video cameras, CO levels, smoke optical densities and smoke obscuration, total smoke mass concentrations, and fire heat release rates, examining how these various parameters depend upon air velocity and air quantity, the product of air velocity, and entry cross-section.     

基于缓冲区分析的云南省文山州森林火灾分布研究

为研究文山州森林火灾分布特征,选取2012-2019年文山州森林火灾数据,采用ArcGIS的缓冲区分析与叠加分析方法探究居民点、道路、水系、GDP与森林火灾的关系,绘制火点分布图,建立居民点缓冲区Ⅰ、Ⅱ、Ⅲ区,道路缓冲区Ⅰ、Ⅱ、Ⅲ区,水系缓冲区Ⅰ、Ⅱ、Ⅲ、Ⅳ区,和4个GDP缓冲区,剖析云南省文山州森林火灾分布特征。结果表明：文山州道路缓冲区Ⅱ区、居民点缓冲区Ⅱ区、水系缓冲区Ⅲ区、GDP缓冲区Ⅰ区发生森林火灾的次数最多,火灾风险等级最高;2012-2015年和2016-2019年森林火灾次数在居民点、道路和水系缓冲区内均服从正态分布,道路、居民缓冲区Ⅱ区森林火灾次数分别占60.28%、62.30%,53.73%、59.01%,缓冲区Ⅰ、Ⅲ区均在28%以下;水系缓冲区Ⅲ区分别占37.85%、39.34%,其他区域呈阶梯式下降,2012-2015年文山州水系缓冲区林火次数Ⅱ区>Ⅳ区>Ⅰ区,2016-2019年Ⅳ区>Ⅱ区>Ⅰ区。2012-2019年平均火灾下降率排序为GDP缓冲区>水系缓冲区>居民点缓冲区>道路缓冲区。GDP缓冲区Ⅱ区、居民点缓冲区Ⅲ区、水系缓冲区Ⅰ区森林火灾数量下降率最高,分别是89.74%、83.67%、80%。因此,森林火灾防控管理优先级为道路缓冲区>居民点缓冲区>水系缓冲区>GDP缓冲区;可优先考虑道路缓冲区Ⅱ区、居民点缓冲区Ⅱ区、水系缓冲区Ⅲ区、GDP缓冲区Ⅰ区的森林火灾防控。研究可为文山州及云南省森林火灾防范提供技术支持。     

液氮及排烟共同作用扑灭电缆火灾有效性研究

城市地下综合管廊电缆火灾危险性极大。运用FDS软件模拟液氮和机械排烟共同作用、仅有机械排烟以及无液氮和机械排烟3 种工况下,综合管廊内部电缆火灾蔓延情况。分析火灾发生后综合管廊内部烟气蔓延及温度分布,发现液氮和机械排烟的共同作用能迅速扑灭火灾从而减小由于发生火灾造成严重后果的危险程度。分析不同的注氮速度和机械排烟速度对扑灭综合 管廊电缆火灾的影响,发现适当增加注氮速度和排烟速度有利于扑灭电缆火灾。     

Assessment of rock mass characteristics and the excavation disturbed zone in the Lingxin Coal Mine beneath the Xitian river, China

Safe production and induced hazard prevention in coal mines mainly concern problems in the excavation disturbed zone (EDZ), but coal mining can also make a significant impact on the environment. Comprehensive techniques using a borehole TV viewer system, electrical logging, and monitoring of drilling fluid leakage offer the ability to identify changing geological conditions and the location of any nearby abandoned mining workings. The inner collapsed zone and the expanding height of the crack zone transmitting water plus their spatial distribution after excavating the superincumbent coal seam stratum are determined at no. L3414 workings, Lingxin Coal Mine beneath the Xitian river, China. An integrated system of GIS-based on a stochastic model, which has been developed for the prediction of dynamic subsidence coupling the time function and probabilistic integral method, is verified through practice at the Lingxin Coal Mine. This development has greatly expanded the ability of the mine operator to characterize previously inaccessible areas of the mine, providing a reliable basis for safe mining and prevention of induced-hazards to ensure high production mining underneath the river bed.     

Spontaneous combustion coal parameters for the Crossing-Point Temperature (CPT) method in a Temperature–Programmed System (TPS)

Coal fires originate from coal spontaneous combustion caused by oxidation starting even at low temperatures. In order to evaluate the heating and oxidation of coal placed inside a container, a Temperature-Programmed System (TPS) is used under various flow and oxidation conditions for temperatures ranging from 40 to 250 °C. As the coal samples are heated in the container within the TPS, the concentration histories of the gaseous products are measured as well as the temperature history at the center of the container. The Crossing-point Temperature (CPT) is the temperature (temperature and corresponding time) at which the increasing coal temperature is equal to the increasing oven temperature within the TPS. We have developed energy and oxygen mass conservation equations for the coal pile in a container inside the TPS oven assuming uniform conditions for temperature and oxygen concentrations, both assumptions partially justified because the heating rate in the oven is very low (1 °C/min). By subtracting the convective heat from the thermal inertia of the coal pile in the energy equation, we have obtained from the experimental data the heat owing to oxygen reaction or moisture evaporation. From the oxygen conservation and measurements, we have determined apparent activation energy and pre-exponential factor for oxidation assuming that oxidation is proportional to oxygen concentration. This information is useful for the mathematical modeling of oxidation and heating in the present experiments. Subsequently, the energy and mass conservation equations were solved after being transformed to non-dimensional form, which shows that four dimensionless parameters control the heating of coal in the present experiments. Only three of these parameters are examined in detail, namely a dimensionless flow time, a heat release parameter B, and a Damkohler number Da whereas a moisture parameter is discussed qualitatively. Based on the present analysis and data, four stages are identified: (I) initial heating with essentially no reaction or evaporation, (II) evaporation period with essentially no reaction, (III) an unsteady accelerated oxidation period during which crossover may occur and (IV) a heating late period where all the oxygen reacts inside the container.     

Impact of a desalination plant on the physical and chemical properties of seawater, Bahrain

The impact of effluent from the Sitra power and desalination plant (SPDP), Bahrain, on the physical and chemical properties of the receiving water was investigated. Two distinguished zones of the receiving water were recognized. These zones resulted from the presence of the jetty. The length of the first zone is about the same length as the jetty, 70 m. The length of the second zone extends to about 150 m. Seventy five case stations were selected on the receiving water. On the intake side, fifteen stations were considered as control stations. The SPDP effluent significantly changed the temperature and salinity of the receiving water of the first zone. The dissolved oxygen levels vary slightly from the control stations. The jetty was found to restrict the water circulation of the first zone. This restriction caused a delay in the temperature, salinity and dissolved oxygen dispersion. Beyond the first zone, this restriction is removed and the dispersion processes affected the control stations.     

Determination of optimum thickness of double-glazed windows for the climatic regions of Turkey

In this study, the optimum air layer thickness of double-glazed windows is determined using the degree-days method. Calculations are obtained for ?skenderun, Kocaeli, Ankara and Ardahan which are in different climate zones of Turkey. Heating cost of the objective function is calculated for natural gas, coal, fuel-oil, electricity and LPG. The optimum air layer thickness is obtained for three different base temperatures which are 18, 20 and 22 °C. The results show that the optimum air layer thickness varies between about 12 and 15 mm depending on the climate zone, fuel type and base temperature. The effect of the fuel type and the base temperature on the optimum air layer thickness diminishes in cold zones. It is shown that with a well-optimized glazed window, up to 60% energy saving can be achieved.     

Ventilation by displacement in a three-dimensional room— A numerical study

Displacement flow systems are becoming popular, especially in Scandinavia, for comfort ventilation. In these systems air is supplied near the floor at low velocity; the temperature of the supply air is a few degrees below that of the air in the room. The supply air is heated by persons and/or machinery in the room. Turbulent plumes are formed above these heat sources. Apart from the plumes, the flow in the room is divided into two zones: a lower zone (the occupied zone) to which clean cool air continuously is supplied, and an upper zone (above the occupied zone) where contaminated warm air is recirculating.

In the present study, the flow in displacement flow systems (a water box model) has been calculated using finite difference methods; the results have been compared with experimental data, and the agreement is reasonably good.     

Simulation of tunnel fires using a zone model

The use of a fire zone model for simulating tunnel fires is reported in this paper. The zone model CFAST version 2.0 was selected as the fire simulator. Numerical experiments were performed in an arbitrary tunnel by considering it as a single compartment, a two-room structure and a three-room structure. Five fires that would have a high likelihood of occurring in a tunnel were considered. They were caused by burning wood cribs, a passenger train, a subway coach, a truck, and a school bus. Results are also compared with another zone model, CCFM.VENTS, and those predicted from a self-developed fire field model for studying the aerodynamic and smoke movement in a tunnel. Further, experimental data collected in a smaller tunnel from an abandoned copper mine in Norway was used to justify the prediction.     

基于多因素的城市燃气管道泄漏警戒区域模拟研究

以城市燃气管道泄漏应急救援警戒范围为研究对象,建立区域典型场景,设置管道压强、泄漏时长、风速、气温、日照辐射强度等5组单变量场景组合,模拟管道破损、可燃气体泄漏扩散行为。提出将影响范围"稳态到达时间"与影响范围大小一并作为特征指标,分析不同变量对特征指标的影响。结果表明,在各单变量场景组内,吸入毒性范围值最小;易燃范围值最大,各级易燃范围略大于爆炸破坏范围。横向对比各单变量场景组,在连续泄漏时,泄漏时长与吸入毒性、易燃、爆炸破坏等3个危险影响范围值和稳态到达时间不相关,仅对影响范围的维持时长有影响;管道压强、风速、环境气温、日照辐射强度等参数对2个特征指标的影响程度为:管道压强>风速>日照辐射强度>环境气温;在单变量对比条件下,各危险影响范围值和稳态到达时间随管道压强、环境气温增大而增大,随风速或日照辐射强度的增大而普遍减小;得出各变量不同取值对2个特征指标的量化影响和变化规律;对比得出连续泄漏、瞬时泄漏2种气体泄漏形式事故场景的不同规律。同时有针对性分析提出消防救援队伍处置城市燃气管道泄漏事故应注意的重点。     

CFD analysis of heat collection in a glazed gallery

A glazed gallery in most old buildings is a space located on the first floor (and/or higher floors), facing south and almost fully glazed. As a result of the large glazed area and the orientation of the gallery, its temperature is warmer than the exterior and, in cold weather, it is used both as a space to insulate the adjacent rooms and as a leisure area, among other applications. In the framework of the ARFRISOL project (Bioclimatic Architecture and Solar Cooling), a demonstration container has been constructed in northern Spain (Asturias) which includes, among other bioclimatic elements, a glazed gallery. This gallery is considered as an element of Bioclimatic Architecture that enables solar radiation to be collected and the energy obtained to be used to support the building's air conditioning system. It consists of a south-facing glazed exterior wall, an intermediate space or passage and a partially glazed interior wall. Dampers located in the floor and ceiling of the intermediate space and connected to the air ducts enable the air circulating inside the gallery to be heated or cooled, depending on the season of the year, before it is further conditioned and conveyed to the rooms. This paper focuses on the three-dimensional numerical simulation of the airflow inside the gallery. The aim is to obtain a model to evaluate the thermal energy obtained in this architectural feature, integrating the effect of certain variables, such as the incident solar irradiation, the outdoor temperature and the air flow rate circulating in the gallery.     

Modeling of gas flow and temperature fields in underground coal fires

A two-dimensional model to simulate the flow and temperature fields in underground coal fires has been studied. The model is based on the theory of natural convection in porous media. A numerical solution procedure is used. Its predictions are compared with the limited field temperature data available. It is found from the model predictions that fractures or higher permeability are necessary to enhance natural convection. The air penetrates in the area behind the fire where many fractures of higher permeability occur due to subsidence. Air flows out from the hot area or cold area in front of the fire. In a shallow depth fire convection plays an important role, whereas in a deep fire convection velocities are smaller. Moreover, secondary combustion of volatiles produced from coal seam in the fracture or crack can markedly increase the convection.     

关键区温度重设定的自适应按需新风控制

针对多区域变风量空调系统,提出一种关键区温度重设定的自适应按需新风控制策略,以最少的能耗满足各区的室内空气质量要求。该策略实时检测各区人员负荷,识别关键区,充分考虑关键区的新风需求,在进行新风设定时充分考虑循环空气中没有使用完的新风。关键区的温度重设定可以加大输送到关键区的送风量从而加大关键区的新风量,新风比减小,从而达到节能目的。利用多区域变风量空调系统的动态仿真平台对该控制策略进行了测试,对其动态控制性能、能耗特性及空气质量特性进行了评估,同时将该控制策略与其他按需新风控制策略进行了比较。     

综放开采“原位”沿空掘巷探讨

 在分析综放开采工艺特点的基础上, 首次提出了综放“原位”沿空掘巷的概念, 即在上区段原废弃巷道位置开挖为下区段工作面服务的巷道。并从理论和技术上对其可行性进行了初步探讨; 认为“原位”沿空掘巷可以最大限度地减少综放工作面“两巷”煤损, 其位置处于悬臂平衡岩梁保护之下的免压区内, 掘进、采放的人为扰动对巷道的影响很小, 因而巷道受力、变形亦很小;“原位”沿空巷道的掘进成巷及防漏风是需重点解决的技术问题。“原位”沿空掘巷是一种有发展前途、有理论探讨价值和很有必要进行现场试验的新的巷道布置方式。     

How groundwater seepage and transport modelling software can be useful for studying gaseous transport in an unsaturated soil

The aim of this paper is to show how standard hydrogeologic software, usually used to model contaminant transport in groundwater under unsaturated conditions, can also be used to model gas transport in unsaturated porous media. Physical processes involved in the interaction between the atmosphere and the unsaturated soils are considered: transport by diffusion through the air and the groundwater, exchange between the liquid and gas phases and consumption. These physical processes are incorporated into the governing equations of a groundwater numerical code; by considering air, contained in the unsaturated soil, as water in the seepage numerical model, the air effectively becomes fluid within the numerical code. Then, the investigated gas is defined as the contaminant in the transport model, which is transported by -the air for the modeller-, and -water for the numerical code-. The over-riding assumption is that the air profiles and, therefore, water profiles of volume contents remain constant. The approach is illustrated using two examples, which consider the transport of oxygen. The first deals with oxygen distribution through a laboratory-cell diffusion containing reactive mining tailings. The second deals with the oxygen fluxes through the vadose zone, between the atmosphere and an unconfined aquifer's water table. Both examples consider different cases of oxygen consumption.     

Effect of cross section and ventilation on heat release rates in tunnel fires

Model scale fire tests were performed in tunnels with varying tunnel widths and heights in order to study the effect of tunnel cross-section and ventilation velocity on the heat release rate (HRR) for both liquid pool fires and solid fuel fires. The results showed that for well ventilated heptane pool fires, the tunnel width nearly has no influence on the HRR whilst a lower tunnel height clearly increases the HRR. For well ventilated solid fuel fires, the HRR increases by approximately 25% relative to a free burn test but the HRR is not sensitive to either tunnel width, tunnel height or ventilation velocity. For solid fuel fires that were not well ventilated, the HRRs could be less than those in free burn laboratory tests. In the case of ventilation controlled fires the HRRs approximately lie at the same level as for cases with natural ventilation.     

Multiple-zone ventilation and temperature control of a single-duct VAV system using model predictive strategy

Conventional ventilation control schemes for VAV systems cannot achieve acceptable indoor air quality (IAQ). Ventilation control at the zone level is one of key factors affecting IAQ and also impacts thermal control. This paper proposes a multi-input–multi-output (MIMO) controller to control temperature and ventilation of multiple zones in a building with a model predictive control (MPC) strategy. The controller follows the ventilation rate procedure of ASHRAE Standard 62.1 and meets its ventilation requirements. Simulation-based experiments under four types of typical weather conditions are conducted to evaluate the controller's performance. The experimental results demonstrate that the controller is capable of maintaining ventilation air requirements and temperature of multiple zones.     

A Study of the Effect of Make-Up Air Velocity on the Smoke Layer Height with Symmetric Openings in Atrium Fires

This paper presents full-scale test results and CFD modeling of smoke conditions in atrium fires in the case of symmetric make-up air opening arrangements. The atrium used for the experiments was equipped with a smoke management system capable of exhausting 132 m³/s. Thermocouple trees were installed to measure the temperature along the height of the atrium. The N-percentage method was used to determine the smoke interface height from the measured temperature profiles. Make-up air velocities of 1 m/s, 1.5 m/s and 2 m/s were selected to investigate the effect of make-up air velocity on the smoke interface height in the case of 4-side and 2-opposite side openings. The fire size varied from 1 MW to 5 MW to cover the effect of small, medium and large fires. FDS was also used to simulate the atrium fires in order to compare the predictions with the full-scale test results and evaluate the accuracy of the developed correlations. Results show that the limit of 1 m/s is too restrictive in the case of symmetric opening arrangements. A correlation is proposed based on the full-scale test results that can be used to modify the smoke layer height obtained using plume equations so that the effect of make-up air velocity on the smoke layer height is considered.     

三峡左岸电站暖通空调系统设计与运行

介绍了三峡左岸电站的2个集中空调系统和1个主通风系统的设计特点,并分析了其运行情况。根据所服务区域的特点,1#集中空调系统设计为开式系统,大空间采用球形喷口送风;2#集中空调系统设计为闭式系统,采用双循环管路;为保证系统的可靠性,均考虑了足够的备用设备。主通风系统利用低温廊道降温,送风经两次过滤,由三级风机接力送入空调区域。     

Compartment fire phenomena under limited ventilation

Fire behavior of heptane pool fires were investigated in a small-scale 40 cm cubic compartment with wall vents at the ceiling (top vent) and the floor (bottom vent). The measurements included pressure, mass loss, temperature, heat flux, and gas mole fraction. Flame oscillations, ghosting, and burning at the air inlet were seen. The regime of limited ventilation was examined to study the effect of extinction and the influence of oxygen. A theory based on a critical flame temperature showed that extinction depends on heating as well as oxygen concentration. A complete uniform property model was developed and its solution agrees qualitatively with the measurements.