基于CFD模拟的不同尺度竖井模型内烟气温度分布相似性的研究

通过小尺寸实验来研究实际建筑结构的火蔓延和烟气控制是一种已经被验证的十分有效的方法。经典方法中尺寸缩放只需要保证Froude数不变即可。采用CFD模拟的方法研究由火灾引起的烟气羽流在高层建筑竖井内的温度分布情况,建立三种不同尺寸高层建筑竖井的相似模型,并对比模拟结果,得出了尺寸缩放的规律:在保证Froude数不变的前提下,还需保证竖井结构内的流动为湍流;同时得到了着火房间通风口无量纲面积大小和火源位置变化对不同尺寸模型内流动相似性效果的影响规律。     

Modeling of pool spreading of LNG on land

This paper presents a source term model for estimating the rate of spreading of LNG and other cryogenic mixtures on unconfined land. The model takes into account the composition changes of a boiling mixture, the varying thermodynamic properties due to preferential boiling within the mixture and the effect of the various boiling regimes on conductive heat transfer. A sensitivity analysis is conducted to determine the relative effect of each of these phenomena on pool spread. The model is applied to continuous and instantaneous spills. The model is compared to literature experimental data on cryogenic pool spreading.     

水面LNG液池扩展模型的分析与对比研究

为了评价在开阔水面上的液化天然气（LNG）火灾和蒸气云爆炸灾害后果,分析了LNG水面扩展动态过程;对比分析了Fay模型、FERC模型和计算流体力学软件FLACS的计算结果,探讨了LNG液池面积随时间的动态变化过程,分析了泄漏量、泄漏速率等参数对LNG液池扩展半径的影响;根据液池扩展模型的计算结果,确定了LNG液池的最大面积,并以此分析了LNG流淌火灾的辐射危害。研究结果表明:对于相同的泄漏条件,3种方法模拟的泄漏LNG水面扩展动态过程相似,一般情况下,FLACS模型,FERC模型和Fay模型所计算的最大液池半径依次增大;由于FERC模型与FLACS软件的模拟结果接近且偏于保守,故此在一般的工程应用时,采用FERC模型即可方便快捷地获得较为准确的结果。     

泥炭粒径对阴燃蔓延速率影响的实验研究

实验研究了自然对流下,不同颗粒粒径(1mm,1mm~2mm,2mm~3mm,3mm~4mm,4mm)的泥炭向下阴燃现象。通过测量泥炭阴燃内部温度,分析了泥炭颗粒粒径大小对泥炭阴燃峰值温度、峰值温度处阴燃蔓延速率、水分蒸发前锋(T=90℃)蔓延速率、泥炭热解前锋(T=312℃)蔓延速率和炭氧化前锋(T=421℃)蔓延速率的影响。实验结果表明:各颗粒粒径泥炭的阴燃峰值温度在510℃到710℃之间变化,平均峰值温度大小呈现随着粒径的增大而减小的趋势。除了粒径1mm的泥炭阴燃实验外,其他粒径的泥炭阴燃稳定蔓延阶段峰值处的蔓延速率随着粒径的增大而增大。实验发现粒径2mm泥炭阴燃蔓延速率随着粒径的增大而增大,而粒径3mm泥炭阴燃蔓延速率随着泥炭粒径的增大而减小,粒径2mm~3mm是一个界限值。     

Experimental study of the evaporation of spreading liquid nitrogen

The investigation of cryogenic liquid pool spreading is an essential procedure to assess the hazard of cryogenic liquid usage. There is a wide range of models used to describe the spreading of a cryogenic liquid pool. Many of these models require the evaporation velocity, which has to be determined experimentally because the heat transfer process between the liquid pool and the surroundings is too complicated to be modeled. In this experimental study, to measure the evaporation velocity when the pool is spreading, liquid nitrogen was continuously released onto unconfined concrete ground. Almost all of the reported results are based on a non-spreading pool in which cryogenic liquid is instantaneously poured onto bounded ground for a very short period of time. For the precise measurement of pool spreading and evaporation weight with time, a cone-type funnel was designed to achieve a nearly constant liquid nitrogen release rate during discharge. Specifically, three nozzles with nominal flow rates of 3.4 × 10⁻² kg/s, 5.6 × 10⁻² kg/s and 9.0 × 10⁻² kg/s were used to investigate the effect of the release rate on the evaporation velocity. It is noted that information about the release rate is not necessary to measure the evaporation velocity in case of the non-spreading pool. A simultaneous measurement of the pool location using thermocouples and of the pool mass using a digital balance was carried out to measure the evaporation velocity and the pool radius. A greater release flow rate was found to result in a greater average evaporation velocity, and the evaporation velocity decreased with the spreading time and the pool radius.     

山地火蔓延过程的三维模拟

本文以林火蔓延的模型为基础,运用OpenGL图形渲染的技术,考虑实时的地形坡度和风向,动态的显示实时火场边界,通过巧妙地将林火蔓延模型转变为计算机中的数据结构,结合粒子系统,在计算机上三维模拟重现了由单个火源引发的林火蔓延过程。这对于林火的辅助应急决策,有效地组织扑救,减少火灾损失,计算火灾引起的损失评估具有重要意义。     

Modeling the vapor source term associated with the spill of LNG into a sump or impoundment area

The recent publication of evaluation protocols for vapor source term models and vapor dispersion models have influenced the modeling approaches that can be used for approval of new and expansion projects at LNG receiving terminals. In the past few years the scientific basis of integral vapor source term models has been questioned with growing concerns regarding their validity. In this paper, the shallow water equations (SWEs) were solved to study the characteristics of the evaporating LNG pool associated with a constant flow rate spill of LNG into a concrete sump. In the early stages of pool spreading, the leading edge thickness profile of the SWE model scales with the square root of the distance from the leading edge as the pool spreads. After the edge of the pool reaches the wall, the reflected wave forms a hydraulic jump that travels back towards the center of the pool at a speed that is considerably slower than the initial spreading of the pool. Once the hydraulic jump reaches the center, the pool assumes a nearly flat free surface for the rest of the spill. The pool spreading and the rate of evaporation from the SWEs were then compared to the solution provided by the integral model, PHAST. The two approaches were found to agree well with one another. The SWE model was also used to demonstrate the influence of an elevated spill source. With an elevated source, the LNG pool spreads faster, significantly increasing the initial rate of vaporization and peak vaporization rate. This increase in the initial rate of vaporization could lead to an increase in the vapor cloud hazard distance. The SWE model was also used to demonstrate the influence of an inclined sump floor in the shape of an inverted cone where the spilling LNG accumulates in the low vertex of the cone. Inclined sump floors can be used to significantly reduce the cumulative evaporation, making them attractive as a possible mitigation approach in cases where a containment sump is located close to a property boundary.     

Investigation of pool spreading and vaporization behavior in medium-scale LNG tests

A failure of a Liquefied Natural Gas (LNG) tanker can occur due to collision or rupture in loading/unloading lines resulting in spillage of LNG on water. Upon release, a spreading liquid can form a pool with rapid vaporization leading to the formation of a flammable vapor cloud. Safety analysis for the protection of public and property involves the determination of consequences of such accidental releases. To address this complex pool spreading and vaporization phenomenon of LNG, an investigation is performed based on the experimental tests that were conducted by the Mary Kay O'Connor Process Safety Center (MKOPSC) in 2007. The 2007 tests are a part of medium-scale experiments carried out at the Brayton Fire Training Field (BFTF), College Station. The dataset represents a semi-continuous spill on water, where LNG is released on a confined area of water for a specified duration of time. The pool spreading and vaporization behavior are validated using empirical models, which involved determination of pool spreading parameters and vaporization rates with respect to time. Knowledge of the pool diameter, pool height and spreading rate are found to be important in calculating the vaporization rates of the liquid pool. The paper also presents a method to determine the vaporization mass flux of LNG using water temperature data that is recorded in the experiment. The vaporization rates are observed to be high initially and tend to decrease once the pool stopped spreading. The results of the analysis indicated that a vaporization mass flux that is varying with time is required for accurate determination of the vaporization rate. Based on the data analysis, sources of uncertainties in the experimental data were identified to arise from ice formation and vapor blocking.     

竖井中羽流前锋上升时间的实验研究

利用PolyU/USTC大空间实验厅内的小尺度竖井实验台,测量了开放和封闭竖井中羽流前锋上升时间,结合理论分析的结果,得到了羽流前锋上升无量纲时间和竖井无量纲高度之间的定量关系式.结果表明,在相同火源、相同竖井尺寸条件下,开放竖井和封闭竖井中的羽流前锋上升无量纲时间分别和无量纲高度的1.03次方、1.50次方成正比,与火源热释放速率的1/3次方成反比.由于烟囱效应的作用,开放竖井中的羽流前锋上升速度最快;非受限空间次之;封闭竖井内最慢.各种决定性因素对羽流前锋上升的影响程度由大到小顺序为:内外压差、壁面导热 粘滞力、空气卷吸.     

侧室－走廊初起火灾下烟气运动的模拟研究

本文用盐水模拟的方法，对典型的侧室－走廊结构建筑内初起火灾时烟气运动规律进行了探讨。所得结果不仅有利于探索烟气运动的盐水模拟准则，还对建筑火灾烟气控制和通风排烟设计有参考作用。     

泄漏液池动态蒸发过程模型研究与分析

指出了现有液体蔓延和蒸发模型的不足,根据质量守恒定律,推导建立了动态液池蒸发模型.在详细分析液池蔓延和蒸发过程的基础上,结合苯的泄漏,利用新建立的数学模型对苯的蔓延和蒸发进行了模拟分析.     

Ecology of drowning risk at a public swimming pool

INTRODUCTION: The fourth-leading cause of death in middle childhood is drowning, but there is remarkably little known about swimmer or lifeguard behavior patterns at public swimming pools. METHOD: This study used non-intrusive observational methodology to examine risk-taking by swimming patrons (predominantly children) and surveillance habits of lifeguards at a public swimming pool. The study also examined whether risk-taking behavior might be associated with density of swimmers, temperature, or lifeguard behaviors. RESULTS: Results suggested risk-taking behavior was common, with dangerous incidents observed over 90 times per hour. Particularly high were rates of running on the deck, which exceeded 100 incidents per hour near the deepest water of the pool, and jumping into the water dangerously close to other swimmers, which was witnessed about once every two minutes in the shallow water of the pool. Lifeguards tended to scan the pool well, and remain attentive to the areas under their responsibility, but they were distracted about 10 times per hour and warned patrons only about once for every 14 dangerous incidents observed. CONCLUSIONS: No consistent correlates to risk-taking behavior by swimming pool patrons were identified. Results are discussed with respect to previous findings and implications for intervention. Impact on Industry: Findings emphasize the need to increase awareness and adherence to safety rules by swimmers at swimming pools; to educate and remind lifeguards about proper swimming pool surveillance techniques; and to consider environmental changes at public swimming pools that might increase swimmer safety.     

庚烷池火多火源燃烧特性的实验研究

多火源燃烧是森林火灾和城市群发性火灾中重要而又特殊的火灾现象,相关研究很少。通过恒定控制液面高度的实验系统,对直径0.1m、0.2m和0.4m的庚烷池火在单个火源、两火源燃烧和三火源线性排列时的火焰高度、火焰体积和燃烧速率等特性进行了实验研究。研究发现,三火源燃烧时中间火源的火焰高度、火焰体积和燃烧速率明显高于两火源燃烧和单火源燃烧,三火源燃烧时边上火源与两火源的燃烧状况难以区分。这些燃烧特性随着火源间距的减小,呈现增大趋势。热量反馈增强和空气卷吸受限这两种火源相互作用机制相互耦合,且随着火源间距的减小而增强,在S/D（S为火源间距,D为油池直径）为2～4时,两种机制强烈竞争,在其他参数范围内热量反馈增强效应占主导作用。研究还发现火焰体积与热释放速率有较好的线性相关关系,单位火焰体积的热释放速率约为1614kW/m3。     

Quantification of source-level turbulence during LNG spills onto a water pond

The use of computational fluid dynamics (CFD) models to simulate LNG vapor dispersion scenarios has been growing steadily over the last few years, with applications to LNG spills on land as well as on water. Before a CFD model may be used to predict the vapor dispersion hazard distances for a hypothetical LNG spill scenario, it is necessary for the model to be validated with respect to relevant experimental data. As part of a joint-industry project aimed at validating the CFD methodology, the LNG vapor source term, including the turbulence level associated with the evaporation process vapors was quantified for one of the Falcon tests.This paper presents the method that was used to quantify the turbulent intensity of evaporating LNG, by analyzing the video images of one of the Falcon tests, which involved LNG spills onto a water pond. The measured rate of LNG pool growth and spreading and the quantified turbulence intensity that were obtained from the image analysis were used as the LNG vapor source term in the CFD model to simulate the Falcon-1 LNG spill test. Several CFD simulations were performed, using a vaporization flux of 0.127 kg/m² s, radial and outward spreading velocities of 1.53 and 0.55 m/s respectively, and a range of turbulence kinetic energy values between 2.9 and 28.8 m²/s². The resulting growth and spread of the vapor cloud within the impounded area and outside of it were found to match the observed behavior and the experimental measured data.The results of the analysis presented in this paper demonstrate that a detailed and accurate definition of the LNG vapor source term is critical in order for any vapor cloud dispersion simulation to provide useful and reliable results.     

乙二醇流淌火燃烧特性及围堵性能研究

为研究乙二醇流淌火燃烧蔓延特性,利用自行设计的流淌火试验平台,开展了乙二醇流淌火实体试验,研究了试验过程中火焰温度、前锋移动、火焰高度等典型参数变化规律。同时,为实现流淌火的有效蔓延控制,开发酚醛泡沫材料模拟乙二醇流淌火围堵处置,评价其围堵效能。结果表明:乙二醇流淌火燃烧速度缓慢,火焰温度低于池火温度;酚醛泡沫材料对可燃液体流淌火展现出较好耐火、阻隔作用,对液体危化品的泄漏围堵具有积极实践意义。     

螺旋隧道火灾特性小尺寸实验研究

为探明螺旋隧道火灾特性,防止人员高温伤害,基于Froude准则,搭建比例1∶67的小尺寸螺旋隧道实验模型,采用模型实验方法研究不同坡度和不同风速下螺旋隧道火灾温度分布规律及烟气蔓延特性。研究结果表明:低坡度条件下,螺旋隧道内高温区以火源为中点呈对称分布状态;随着坡度的增加,隧道内高温区逐渐向下游延伸,火源处拱顶下方温度呈现先增大后降低再升高的变化规律;无论是自然风还是机械纵向通风,新鲜冷空气的吹入对隧道温度的降低起到主导作用,且风速越大,温降幅度越大;随着隧道坡度和自然风速的增加,火羽流由竖直狭长型转变为燃烧不稳定的大截面火焰,同时坡度增加抑制了火灾烟气逆流,促进了烟气向火源下游的蔓延速度,大大提高了排烟的有效性,减少人员伤害。     

The modelling of pool vaporization

This paper describes a mathematical model which calculates the time dependencies of the flow rate and composition of the vapour emerging from a pool. A large variety of accidental cases can be covered: continuous or instantaneous spills, on confined or unconfined ground, ideal or non-ideal liquid mixtures in boiling or evaporating conditions. The boiling, when present, is modelled through an equation system comprising the Rachford-Rice relation and the energy balance of the pool, which is assumed to be well-mixed. In the case of a volatile pool, interfacial mass rates are determined taking into account the Stefan flux, and the thermal resistance inside the liquid phase is also considered. In all situations, the energy balance includes the contribution of ground, sun and air. Known experimental data have been used to validate the model.     

Evaporating liquid flow in a channel (An integral model based on shallow water flow approximation)

Liquefied Natural Gas (LNG) storage facilities generally include channels to convey potential spills of the liquid to an impoundment. There is increasing concern that dispersion of vapors generated by flow of LNG in a channel may lead to higher than limit vapor concentrations for safety at site boundary from channels that may be close to the dike walls. This issue is of recent concern to regulatory agencies, because the calculation of vapor hazard distance(s) from LNG flow in a channel is not required under existing LNG facility siting standards or regulations.An important parameter that directly affects the calculated LNG vapor dispersion distance is the source strength (i.e., the rate of vaporization of LNG flow from the wetted channel surfaces, as a function of spatial position and time). In this paper a model is presented which considers the variation of the depth of the flowing LNG with spatial location and time, and calculates the spatial and temporal dependence of the mass rate of vapor generation. Self similar profiles for the spatial variation of the thermal boundary layer in the liquid wetted wall and liquid depth variation are assumed. The variation with time of the location of the liquid spread front and the evaporation rate are calculated for the case of a constant LNG spill rate into a rectangular channel. The effects of two different channel slopes are evaluated. Details of the results and their impact on dispersion distances are discussed.     

基于pH值和ORP的跳水池池水处理系统的自动控制

为改善跳水池水质的化学安全性和生物学稳定性,保障运动员、教练员以及工作人员身体健康,结合长春市泅渡馆跳水池,阐述了基于pH和ORP的池水处理自动控制系统,确定了自动控制系统的控制参数及其控制范围,为健康跳水池池水处理系统的自动控制系统的设计提供了参考。     

窄带水平集法下林火蔓延仿真研究

火焰锋面的追踪是建立林火蔓延模型及预测锋面位置的关键环节。基于水平集法追踪锋面具有求解灵活稳定、易于处理锋面拓扑结构变化的特点。针对传统水平集法重新初始化过程复杂、计算量较大的问题,根据距离函数定义,提出通过形态学膨胀的方法以锋面点为圆心向外膨胀,获得锋面附近窄带内每个点距离锋面的最近距离,重建窄带内的水平集函数,物理意义明确,有效减小了计算量,在此基础上基于林火速度场经验模型模拟了单火源及双火源的锋面蔓延情况。结果表明,该方法能够有效模拟坡度、风速等因素对火焰锋面的影响,为其在林火蔓延模型中的应用提供了基础。