Experimental and numerical study on water mist suppression system on room fire

Full-scale experiment and numerical simulations are carried out on a room fire to study water mist suppression system with heat release rate of 6 MW. A computational fluid dynamics (CFD) model of fire-driven fluid flow, FDS (Fire Dynamics Simulator), is used to solve numerically a form of the Navier–Stokes equations for fire. A fire experiment without water mist is performed and the temperatures are measured to validate the predictions of FDS code against the experimental data. Then a fire experiment with water mist suppression system is performed and the temperatures and extinguishing time are measured. The validated numerical model is used to simulate the experiment; the temperatures, oxygen concentration and extinguishing time are compared and studied. In numerical simulations, the cell size sensitivity is analyzed. The experimental results of temperatures and extinguishing time are compared with the results of numerical simulations. It appears that the numerical results are in good agreement (qualitatively) with the experimental data in temperature fields. These useful data can be helpful in accomplishing the design of water mist suppression system and the design regulations for fire safety management.     

细水雾控制高层住宅烟道火灾的有效性及参数优化

为了有效控制高层住宅厨房烟道火灾,构建细水雾控制厨房食用油火和带分支烟道的高层住宅厨房烟道油垢火的FDS数值模型,分析高层住宅厨房烟道细水雾灭火系统有效性的影响因素及最佳设计参数。结果表明,如果未能即时扑灭高层住宅底层厨房食用油火,在强烈的烟囱效应作用下,高温火焰和烟气会引燃烟道内油垢,造成火势的迅速蔓延。本文所建的30 m高厨房烟道火模型中,最佳细水雾灭火系统运行模式为关闭厨房抽油烟机,即时开启厨房灶台上方和主烟道内分段设置的细水雾喷头,雾流量分别为0.6,10 L/min,细水雾最佳参数为喷射流速10 m/s、喷射角度60°、水雾粒径500 μm。     

直线加速器间细水雾灭火系统设计与分析

针对直线加速器间作为医疗建筑中的重要设备房间,其设备贵重、设置空间的辐射防护要求特殊,为解决其灭火系统不同常规的设计要求研究了设计对策。建立了灭火系统选择安全性、适用性、经济性的原则,结合应用场所的需求对各种灭火系统进行了分析,研究了直线加速器间应用细水雾灭火系统的适用性和合理性,建议采用高压细水雾灭火系统的单联锁预作用系统。以某医疗中心的直线加速器间为例,从系统选型、应用方式和设计参数等方面,说明了其高压细水雾灭火系统的设计。就设计中关注的误喷、系统的压力和水雾粒径、设计参数的问题进行了分析,并探讨了值得注意的几个问题。     

Experimental and numerical study of high-pressure water-mist nozzle sprays

The performance of extinguishment of fires by water sprays is strongly influenced by the characteristics of the sprays produced by nozzles. Computational fluid dynamics (CFD) based fire models are a tool that can be used for the characterization of sprays. However, it is necessary to evaluate the capability of a CFD based fire model in predicting the behaviour of sprays before using it for such characterization. One of the basic parameters that is important in characterising the water mist spray is the distribution of flux density of water droplets impinging on the floor. This paper reports the study on the characterization of water mists, in terms of distribution of flux density of sprays, produced by a single and a multi-orifice high-pressure jet nozzle. Full-scale experiments were conducted and the distributions of volume flux density of sprays were measured. The sprays were also modelled using a CFD model, Fire Dynamic Simulator (FDS), version 6, to investigate the capability of the model in predicting the distribution behaviour of the spray. The numerical results of distribution are compared with those obtained experimentally. The predicted results of FDS has show good agreement with the experimental results.     

Fixed Fire Protection Systems in Tunnels: Issues and Directions

Fire protection practices for highway tunnels have been undergoing significant changes in the last decade, largely in response to a number of catastrophic fires that caused tunnel authorities to thoroughly review their fire safety assumptions. One of the fire safety issues currently receiving much attention includes the installation of “active” fire protection systems in addition to the “passive” fire protection features that were until recently considered to be sufficient to mitigate fire risk in tunnels. Passive fire protection measures include the use of fire resistive construction materials which help protect the critical structural elements from damage due to high temperatures. Active fire protection systems include fixed piping systems to deliver water sprays, such as deluge sprinklers and water mist, or other water-based agents such as compressed air or high expansion foam (CAF or Hi-Ex respectively). Active fire protection systems for tunnels are currently referred to as water based fixed fire fighting systems, or FFFS for short. Fire research suggests that measures based solely on passive protection are not likely to be sufficient to protect life and property to the degree warranted by the high monetary and strategic value of modern tunnel infrastructure. Full-scale fire testing and engineering analysis indicate that FFFS have the potential to reduce the impact of a severe fire on the tunnel structure from catastrophic to manageable at an affordable cost. Fire testing with CAF and Hi-Ex foam systems has shown them capable of actually extinguishing very large fires, including hydrocarbon pool fires. Systems based on water sprays on the other hand are not expected to extinguish fires, but rather to control the fire, limit fire growth and heat release rate, prevent fire propagation and provide thermal management. Although there are a few years of experience internationally that have proven sprinkler and deluge sprinkler system to be effective in mitigating tunnel fires, recent testing of FFFS in Europe has concentrated on water mist. One reason is the perception that water mist systems may involve less complex piping and agent storage than CAF or Hi-Ex foam, and may provide equivalent or superior performance with less water and smaller pipes than conventional sprinkler deluge systems. However, many engineering challenges remain to be resolved, such as how much credit to grant to the FFFS in terms of reduced criteria for passive protection, and how exactly to integrate active protection systems with traditional fire safety measures such as the ventilation systems. This article examines some recent developments in understanding how active fire-fighting systems might alter the impact of fires in tunnels.     

Assessment of the Fire Dynamics Simulator for Modeling Fire Suppression in Engine Rooms of Ships with Low-Pressure Water Mist

Water mist-based fire-extinguishing systems are gaining acceptance for the protection of ship machinery spaces. The use of simulation tools presents a great potential for taking a performance-based design (PBD) approach to these fire scenarios. The Fire Dynamics Simulator (FDS) is the most frequently used and validated fire modeling software; however, studies of low-pressure water mist fire suppression modeling in ship engine rooms are rare. This paper contributes to the current literature by using the FDS to model a series of fire suppression scenarios defined by the International Maritime Organization (IMO) Circulars, including spray and pool fires with heptane and diesel oil, as well as exposed and obstructed fires. The simulation results are compared to data from full-scale tests conducted at recognized fire testing laboratories. Furthermore, an analysis of both the experimental and model uncertainties is carried out to assess the simulations performance. In general, a good agreement in compartment temperature evolution and fire extinguishing time is found for the modeled fire scenarios. The results support the application of FDS in a PBD approach for the design of water mist fire extinguishing systems for machinery spaces in ships. In this way, designers and engineers could model different machinery volumes and nozzles spacings that differ from those prescribed for a one story square engine room of the IMO, and, thus, predict the evolution of temperatures and extinguishing times for get the authorities approval.     

Development of a computational model simulating the interaction between a fire plume and a sprinkler spray

Numerical simulations to predict actual delivered densities (ADDs) of early suppression fast response (ESFR) sprinklers in heptane spray fire scenarios were sought. First, in order to supply input data for the development of numerical models and experimental data for validation of the models, four sets of measurements were carried out: the momentum and water flux distribution of two ESFR sprinkler sprays without fire; the temperature and axial velocities along the axis of free-burn fires; and the actual delivered densities. Then, a numerical model for a sprinkler spray was completed by assigning the representative drop size, mass flow rate, discharge speed and discharge angle of 275 trajectories in such a way that they produced reasonable agreement with the measured water flux distribution and spray momentum in the absence of fire. A numerical model for the free-burn fire was created by assigning a heat flux distribution on a horizontal surface and simulating a central, vertical air jet used in the experiment, varying parameters until a reasonable match was established with the measured temperatures and the axial velocities along the axis. Numerical computations of actual delivered densities were carried out by combining the water spray model and the free-burn fire model for different water flow rates of the sprinklers. The ADDs obtained from the simulations compared reasonably well with those from the measurements.     

原木楞堆细水雾灭火过程数值模拟

采用FDS模拟对原木楞堆细水雾灭火过程.通过分析雾滴直径、喷雾速率和喷头与楞堆顶面距离不同情况下楞堆燃烧周围温度的变化规律,选定了贮木场楞堆细水雾化灭火系统的合理参数.模拟结果表明,雾滴直径在100～150 m、喷头与楞堆顶面距离约5m时,细水雾灭火系统的灭火效果最好;雾滴速率为30～70 m/s时对灭火能力的影响不走,在设计细水雾灭火系统时可不予考虑.     

航天飞船地面试验舱灭火系统设计

针对低气压和富氧的条件,航天飞船试验舱灭火系统选用基于高效冷却作用的Novec1230和细水雾系统.结合工程设计,介绍了两种系统的灭火机理、工艺流程、系统组成、控制方式以及灭火特点等.     

高压细水雾灭火对古建筑木构件的水渍损失研究

高压细水雾灭火系统喷雾后会对木构件造成一定的水渍损失,为了探明木构件的水渍损失情况,对10 种木材喷雾后含水率、阴干速率和腐朽状态进行研究。通过搭建实验平台进行模拟实验,测定了不同大气湿度、环境温度下高压细水雾喷雾后实验木块含水率变化情况,分析了实验木块的含水率变化趋势、阴干速率和腐朽状态。实验结果表明,高压细水雾灭火系统喷雾后实验木块含水率测定值在35%以内,阴干2 h 后木材含水率下降至20%,阴干5 h 后木材含水率下降至河南地区平衡含水率以内,封存45 d 后实验木块肉眼观察无腐朽症状。通过对济渎庙玉皇殿消防改造工程的介绍,阐明高压细水雾灭火系统在古建筑消防改造中的技术优势,为古建筑消防系统的设计提供参考。     

不同工况下细水雾灭火效能影响的数值模拟

采用FDS对单室火灾中细水雾与火焰相互作用过程进行数值模拟分析,探讨细水雾与火焰相互作用过程中不同区域的细水雾灭火机理,分析粒径分布、速度和雾化角度对细水雾灭火产生的影响.模拟结果表明:在细水雾与火焰相互作用过程中粒径分布对灭火效能影响显著;细水雾在粒径小于100 μm时不能实现有效灭火;当粒径为200～400 μm时细水雾能有效抑制火焰发展并熄灭火源;在细水雾灭火机理中,相对于气相冷却和隔氧窒息,细水雾的表面冷却作用起到主导作用;细水雾喷射速度对灭火效果影响较大,细水雾动量不小于火羽流动量是火灾发展得到有效控制的重要前提;细水雾有效雾通量随着雾化角度增大而逐渐减小,雾化角度增大不利于细水雾灭火效能提高.     

细水雾扑救电气火灾有效性和安全性实验研究

为探究工作压力对高压细水雾扑救电气火灾有效性和安全性的影响,在 4 m × 4 m × 5 m 的封闭环境中,针对同一型号的细水雾喷头在不同喷射压力下进行灭火实验。结果表明：增大喷头工作压力可增强细水雾灭电气火的有效性;不同工作压力下的细水雾,绝缘电阻下降率不同;随着工作压力变大,绝缘电阻下降速度呈现先减小后增大的趋势;喷头工作压力超过一定值时,细水雾对绝缘电阻的影响更显著。对于特定高压细水雾喷头,存在灭火效果好且水渍污染小的适合工作压力。     

综合管廊电缆舱灭火系统效果研究

针对某综合管廊的电缆舱室,采取全尺寸实验和数值模拟结合的方法,探究综合管廊内电缆舱的火灾特性,对比分析干粉灭火系统和高压细水雾灭火两种灭火系统的灭火效果.将火源功率为0.7 MW的乙醇火设置于电缆架底部,观察火灾发展和烟气蔓延情况,分析电缆舱火灾特性;对比两种灭火系统开启后管廊内的温度和烟气变化规律,分析灭火效果.在实...     

Modeling and Simulation of High Pressure Water Mist Systems

This paper describes work done to improve and validate the capability of fire dynamics simulator (FDS) to predict the dynamics of water mist sprays. Three single orifice and five multi-orifice spray heads are modeled with FDS based on information on the flow-rate, spray angle, operating pressure and experimentally determined particle size distribution. The capability of FDS to predict the drop size, velocity, mist flux and number concentration profiles within the spray cone is assessed. The effects of turbulence modeling on the predictions of the spray dynamics is investigated. The capability of FDS to predict the air entrainment by high-speed water sprays is validated using experiments in rectangular channels with open ends.     

Measurements of spray-plume interactions for model validation

Fire suppression using automatic fire sprinklers is tremendously successful in reducing loss of life and property in the event of a fire. With the increasing computing power available, as well as the spread of performance-based design methods, the ability to accurately model spray dispersion and suppression is desirable. In this study, experiments were conducted to quantify spray dispersion and spray-plume interactions for model validation. Numerical simulations of these spray interactions were performed using FireFOAM. These simulations were distinguished by the use of comprehensive highly-resolved initial spray measurements to generate the numerical spray. The experimental Sprinkler Array Facility (SAF) used in this study consisted of a centrally located, well-characterized, forced air jet (simulating the updraft from a real fire plume) providing a challenge to the spray. Reliable model boundary conditions were established from detailed measurements of the air jet injection velocities and detailed measurements of the initial spray using the Spatially-resolved Spray Scanning System (4 S). Measurements of volume flux as well as optical measurements of drop size and velocity were obtained at various locations within the air jet. Four flow conditions were investigated with the intent of providing model validation data; close and far sprinkler spacing, each with quiescent air and strong jet conditions. The strong jet was capable of overwhelming the smallest drops within the spray, reversing their direction, and reducing the volume flux at the floor. Computational simulations (informed by detailed initial spray measurements) demonstrated good agreement with the spray dispersion and plume penetration experiments.     

国内某地铁加装细水雾灭火系统方案

对行业内自动灭火系统进行对比,提出细水雾灭火系统在城市轨道交通车辆上应用的优势。通过在国内某地铁加装细水雾灭火系统的实例,介绍了细水雾灭火系统的方案、系统组成及细水雾装置的配置方案,依据地方标准的要求,通过对灭火时环境参数的分析,验证了加装的细水雾灭火系统达到了设计要求,起到了灭控火的目的。     

Study of cooling system with water mist sprayers: Fundamental examination of particle size distribution and cooling effects

A cooling system that sprays micro water droplets could prove useful in mitigating temperature increases in urban areas by using the heat of water evaporation, a process that consumes only small amounts of water and energy. If water mist is sprayed in a semi-outdoor area, for example, under a canopy, it could potentially improve conditions on hot days. However, there is little reference data concerning the design or control of such systems. In order to propose a method for designing and predicting the performance of a water mist system, we discuss differences in cooling effects in the context of particle size distribution of water mist. The results of numerical fluid analysis showed there is no significant difference in temperature reduction for different particle sizes. However, the water particles remained in a lower position with larger particles.     

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.     

A Study of Total Flooding Water Mist Fire Suppression System Performance Using a Transient One-Zone Computer Model

Due to the intense R&D activity in the field of water mist fire suppression during the past decade, the qualitative and quantitative understanding on the performance of water mist has increased significantly. This development has led to a point in which quantitative theoretical models describing large-scale water mist fire suppression systems begin to emerge. This paper describes the composition and validation of one such model, designed for total flooding water mist applications, especially against flammable liquid hazards in enclosures. The basic construction of the model is first described, followed by an example on the validation of the model using full-scale experimental data. The model is then used to investigate the limitations to the maximum possible mist concentration in the protected space. The potential of the model as an engineering tool is illustrated by making predictions on the scaling laws associated with water mist systems in the framework of IMO MSC/Circ.668/728 as the enclosure volumes and ventilation conditions are varied. The predictions are found to be in agreement with what is indicated by the recent US Coast Guard test series in very large machinery spaces.