Determination of smoke layer interface height of medium scale tunnel fire scenarios

Smoke layer interface height is an important parameter in fire safety science. In this paper, a series of experiments were conducted in a 1/6th scale model tunnel for determining the smoke layer interface height in medium scale tunnel fire scenarios. The commonly used approaches, including visual observation, N-percentage rule and integral method are reviewed firstly. Then, considering the subjectivity and empiricism of previous approaches, a buoyancy frequency method is put forward based on the vertical temperature distribution in tunnel, which has definite physical meaning and eliminates the subjectivity of previous methods. The smoke layer thicknesses determined by buoyancy frequency method are compared with the results of visual observation, N-percentage rule (N = 10, 20, 30) and integral ratio method, respectively. The comparison results reveal that the smoke layer thicknesses determined by buoyancy frequency method fit best with the visual values for all the experimental conditions. While the calculated values by integral ratio method are lower than the visual values. In addition, the selection of optimum N values for the N-percentage rule in different cases is also discussed.     

Numerical simulation of transient flow development in a naturally ventilated room

Numerical simulations were conducted to model the transient flow development in a naturally ventilated space containing a centrally located localized source of heat. The simulations were compared with a series of small-scale laboratory experiments and existing theoretical models. The aim of the work was to benchmark CFD models for time-dependent buoyancy-driven natural ventilation against previously published experimental results and theoretical models. The simulations agree well with experimental results during the initial development of the room stratification. The CFD results accurately predict the maximum depth of the hot buoyant layer at the top of the room as well as the steady-state interface height which separates the warm upper buoyant layer from the cooler air below. The simulations also predict well the time taken for the buoyant upper layer to reach its maximum depth. However, at longer times the results diverge. This may be due to thermal diffusion and mixing at the interface between the upper and lower layers due to the inflow from the floor level vents.     

Experimental determination of air-flow in a naturally ventilated room using metabolic carbon dioxide

The paper reports extension to a naturally ventilated room of the metabolic CO₂ method for ventilation measurement. The analysis, which under some circumstances will also be relevant to tracer gas decay measurements, allows assessment of the individual incoming flows of air.     

火源—竖井间距对自然通风隧道火灾烟气流动特征的影响

通过数值计算,研究顶部开口自然通风隧道火灾火源–竖井间距对烟气流动特征与竖井排烟效率的影响。考虑因素有火源–竖井间距、竖井断面尺寸。结果表明：随着火源–竖井间距的增大,竖井前方来流烟气的质量流量增大,且竖井的排烟效率逐渐降低,竖井内空气卷吸量减少;当火源–竖井间距较小时,竖井更有利于排出更多的热量,竖井后方的温度降低幅度更大,烟气可以被控制在更小的范围内。此外,随着竖井截面尺寸的增大,竖井的排烟效率增加,且增大竖井的宽度更有利于增加竖井的排烟量。因此建议当相邻竖井的间距较大时,可适当增加竖井的截面尺寸和竖井高度。     

顶部开口自然通风隧道火灾竖井排烟效率研究

通过数值计算方法,研究了顶部开口自然通风隧道竖井的排烟效率。考虑了火源热释放速率、竖井高度、长度和宽度及竖井位置的影响,并与竖井排烟效率计算模型进行对比。研究结果发现：竖井的排烟效率随竖井高度的增加而略微增大;竖井的排烟效率基本不随火源热释放速率的变化而变化;随着竖井长度和宽度地增加,排烟效率大幅增加;此外,当竖井位于顶棚中央时,排烟效率较位于顶棚一侧的排烟效率高,且烟气控制效果好。此外,竖井排烟效率模型可以较好地预测不同竖井尺寸和位置的排烟效率。     

挡烟垂壁与排烟口设置对烟气层高度的影响

通过N百分比法,理论计算得到了挡烟垂壁与排烟口设置对商业建筑内相邻防火分区烟气层高度变化的影响.分析结果发现,挡烟垂壁凸出越多,烟气层下降速率更为缓慢,后期烟气层高度越高;排烟口距离火源越近,后期烟气层高度越高;排烟口朝向对烟气层高度的变化影响不大.     

Interaction between water spray and smoke in a fire event in a confined and mechanically ventilated enclosure

This work deals with the interaction between water droplet flows and smoke in a fire event in a confined and ventilated enclosure. The objective is to identify the specific effect of water spray in the specific environment of a confined and ventilated enclosure. The study is based on 17 large-scale fire tests performed in one room of 165 m³ ventilated at a renewal rate of 15.4 h⁻¹. The fire source is a propane gas burner with a heat release rate of between 140 and 290 kW. The water spray system consists of two Deluge nozzles with a nozzle coefficient of 26 l/min/bar^0.5. The test parameters are the fire heat release rate, the water flow rate, from 50 to 124 l/min, and the activation time. The study focuses on three topics, the interaction of the droplets with the smoke, the droplet evaporation process and the energy transferred to the droplets. The water spray significantly modifies the smoke stratification by mixing and cooling the gas phase. The rate of droplet evaporation has been determined from the water mass balance and is of the same order of magnitude as the rate of water vapor production by the combustion reaction. Heat transfer from the smoke to the droplets has been investigated using the energy balance equation. For a fire scenario in a confined and ventilated enclosure, the energy released by the fire is mainly transferred to the walls and extracted by the ventilation network. In the event of water spray activation, a significant share, up to 65%, is transferred to the droplet flows.     

高层建筑火灾时走廊净高对排烟效果的影响

采用k-ε两方程三维紊流模型模拟高层建筑内的烟气流动,利用FLUENT软件对定排烟量情况下不同走廊净高和排烟口风速时的机械排烟进行模拟。对比分析了不同走廊净高和排烟速率情况下,高层建筑内烟气的扩散、走廊内烟气温度和质量分数的变化情况。结果表明,走廊净高为2.4m时,排烟口排烟速率不应大于1.7 m/s;走廊净高为2.7 m时,排烟口排烟速率不宜大于2.8 m/s;而当走廊净高为3 m以上时,排烟口的排烟速率按照《高层民用建筑设计防火规范》(GB50045-95(2005年版))取值,能够符合安全疏散要求。     

单室墙角火壁面烟熏痕迹特征研究

为研究单室墙角火火灾壁面烟熏痕迹特征，采用1/3尺寸火灾试验还原单室墙角火火灾，测定壁面不同点的温度及烟气蔓延速度，研究火源在不同位置时的壁面烟熏痕迹特征；利用PyroSim软件模拟烟气蔓延过程。结果表明：火源位于房间中间时，在屋顶呈现圆形痕迹；火源在墙角时，两边侧墙和墙角顶部形成明显烟熏痕迹；墙角火在墙角位置的温度和烟气蔓延速度高于房间中间起火；试验结果与模拟结果吻合。试验结果可为调查墙角火火灾提供理论及试验依据。     

模型车厢内火灾烟气层运动模拟分析

旅客列车车厢内发生火灾时，火灾烟气的运动状况直接影响旅客的人身安全，往往造成重大的人员伤亡和巨大的财产损失。采用模型实验、数值模拟的方法对运行的旅客列车经过隧道发生火灾时车厢内烟气层高度的特征进行了研究，将旅客列车卧铺车厢处理为多个受限空间的组合，研究了车厢内烟气层高度在开口不同状况下的变化规律。模型实验与数值模拟相结合为列车车厢火灾研究提供了理论分析模型和实验研究方法，研究成果为车厢防火设计提供了重要的技术依据。     

大空间建筑喷淋对烟气层的影响

采用PHOENICS软件，研究了大空间建筑水喷淋对烟气控制系统的影响。未考虑燃烧过程以及喷淋对燃烧的影响。采用紊流k-ε双方程模型模拟烟气的运动，用Lagrangian方法模拟热烟气与喷淋水之间相互作用的动能和换热。用具有不同初始速度和直径的液滴来模拟喷淋水。探讨了喷淋流量、喷射角、水滴直径对烟气层的影响。     

Camera-based window-opening estimation in a naturally ventilated office

Naturally ventilated offices enable users to control their environment through the opening of windows. Whilst this level of control is welcomed by users, it creates risk in terms of energy performance, especially during the heating season. In older office buildings, facilities managers usually obtain energy information at the building level. They are often unaware or unable to respond to non-ideal facade interaction by users often as a result of poor environmental control provision. In the summer months, this may mean poor use of free cooling opportunities, whereas in the winter space heating may be wasteful. This paper describes a low-cost, camera-based system to diagnose automatically the status of each window (open or closed) in a facade. The system is shown to achieve a window status prediction accuracy level of 90–97% across both winter and summer test periods in a case study building. A number of limitations are discussed including winter daylight hours, the impact of rain, and the use of fixed camera locations and how these may be addressed. Options to use this window-opening information to engage with office users are explored.     

建筑火灾烟层稳态简化模型排烟效果计算

阐述建筑火灾时期烟气的危害及防排烟的必要性,并应用烟层稳态简化模型对建筑物侧墙开口的排烟效果进行计算。研究表明,烟气的产生量与其沉降速率有关,烟层沉降与否及沉降速率将威胁到室内人员的生命安全。研究可为人员的安全疏散以及房屋的自然排烟设计提供科学依据。     

ISO房间火灾烟气层温度数值模拟工程方法研究

利用场模拟FDS和区域模拟CFAST软件，对ISO房间中55kW和110kW的火灾烟气层温度进行数值模拟，将不同尺寸网格划分条件和区域划分方法的计算结果与试验结果进行分析比较，在保证一定精度条件下，为减少计算所需时间而增大网格尺寸的可能性，并对区域模拟中采用多区域划分方法以提高计算精度的可行性进行了分析，为类似环境的工程应用，单区域划分和多区域划分方法的使用提出了建议。     

Environmental performance of a naturally ventilated city centre library

To tackle climate change it is essential to reduce carbon dioxide emissions. To this end, it is important to reduce the energy demands of non-domestic buildings. Naturally ventilated buildings can have low energy demands but the strategy is difficult to implement in deep plan, urban locations. The Frederick Lanchester Library at Coventry University, UK, incorporates natural ventilation, daylighting and passive cooling strategies. By using lightwells and perimeter stacks to supply and exhaust air, it can be ventilated by natural means despite its deep plan form and sealed façade. This paper describes the building and presents the energy consumption and the internal temperatures and CO₂ levels recorded in 2004/2005. The building's performance is compared to the original design criteria and good practice guidelines. Recommendations for the design of such buildings are made and the likely performance in other UK cities is assessed. It is concluded that the building uses under half the energy of a standard air-conditioned building and yet, in summer, can keep the interior comfortable and up to 5 °C below ambient. The design would perform equally well in the typical weather conditions experienced at 13 other UK cities, but not in London. It is concluded that deep-plan, naturally ventilated buildings with sealed facades, if well designed, could maintain thermal comfort in all but a very few UK locations, whilst consuming much less energy than even good practice standards.     

Thermal analysis of naturally ventilated buildings

A simplified electric analogue method to analyse the thermal performance of naturally ventilated buildings is presented. One of the main features of the method is that empirical constants in some equations account for typical rates of natural ventilation in conventional buildings. Another feature is that a very high degree of lumping is attained by using a special calculation procedure to estimate effective capacity values of building elements. The method is therefore extremely easy to use. Predictions are compared with measurements. The comparison is acceptable for design purposes.     

Empiricism in the thermal analysis of naturally ventilated buildings

Three thermal analysis methods with different degrees of empiricism are quantitatively investigated regarding the ease of use, efficiency, accuracy and redundancy of generated information. From this investigation it is concluded that, for design purposes, a sensitive interplay between experiment and theory can often lead to an optimum method.     

Experimental study based on large-scale smoke propagation fire tests through a horizontal opening connecting two mechanically ventilated compartments

This work describes an experimental study of the flow through a horizontal opening (also referred to as a vent), applicable to specific situations typically encountered in nuclear installations. The configuration consisted of two rooms, which were mechanically ventilated and connected to each other by a horizontal opening, the fire being located in the lower room. The flow was governed by buoyancy due to the heat release from the fire, inertia resulting from the mechanical ventilation, and local momentum from the ceiling jet. Two flow regimes (bi-directional and uni-directional) were encountered depending on the fire power and the ventilation set-up. This study presents 17 large-scale fire tests, investigating the behaviour of the flow at the horizontal opening according to several fire scenario parameters: the fire heat release rate, the fire location, the ventilation configuration and the ventilation flow rate. This range of parameters enabled us to focus on different flow regimes, from pure natural convection (bi-directional) to forced convection (uni-directional). The new set of data obtained, based on detailed flow measurements, offers new insights for understanding the flow and developing sub-models to be used in zone codes.