【作者】 刘志超；

【导师】 刘应清；

【作者基本信息】 西南交通大学 ， 供热供燃气通风及空调工程， 2008， 博士

【摘要】 随着哈龙灭火剂的限用和面临的淘汰,细水雾灭火技术以其无环境污染、灭火迅速、耗水量低、对防护对象破坏性小等特点展示出广阔的应用前景,目前已成为火灾科学前沿研究热点之一。国内现已使用的细水雾灭火系统,其系统压力多属高压范畴,因高压系统结构复杂、工程造价高,已严重影响了细水雾灭火技术的推广应用。在各种细水雾灭火系统中,雾化喷嘴是系统的核心部件之一,喷嘴雾化性能的优劣直接影响着所设计的灭火系统能否满足不同灭火场合的使用要求。目前国内开发的高压雾化喷嘴大都结构复杂,运行参数多且难以控制。因此,研制出一种体积小、重量轻、结构简单,加工、安装方便,在中、低压范围内雾化效果较好的单相细水雾喷嘴,对细水雾灭火技术在我国的推广应用意义重大。在国内火灾科学研究领域,目前尚没有人将喷嘴结构-雾化机理-雾场参数-灭火效果作为一个系统工程开展研究,本研究通过大量的实验获得第一手资料,进而对喷嘴结构、雾化机理、雾场参数、灭火效果之间的关系进行深入探讨,完成的研究工作及取得的主要进展如下:1.本课题在研究过程中,首先设计出了一种结构新颖的中、低压旋流雾化喷嘴,然后采用理论研究、数值模拟、试验验证的方法,对其结构参数进行优化。通过对喷嘴结构和雾化特性参数之间关系的探讨,建立了相应的理论模型,借助于FLUENT软件对喷嘴内外部流场进行数值模拟,研究喷嘴结构参数对雾化性能的影响,为参数优化提供理论依据。2.从雾滴在空气中的受力运动分析入手,建立了雾滴运动方程。针对典型滴径及不同出口初速度的雾滴运动状况进行了数值计算,得出了细水雾雾滴的基本运动规律,确定了终端速度与滴径呈平方关系和线性关系的分界直径为80μm。3.在数值模拟的基础上,进行喷嘴的冷态雾化试验,对模拟结果进行了验证。研究结果表明,经优化设计的中低压单流体直通旋流雾化喷嘴雾化效果良好,在众多的消防灭火场合完全可以替代现有的高压雾化喷嘴和两相流雾化喷嘴,可大幅降低细水雾灭火系统初期投入,同时也使系统的运行安全性得以提高。4.开展了细水雾在外部风流扰动下灭火效果的模拟实验研究和数值模拟。建立了外界风流作用下细水雾的灭火模型,并且进行了验证,结果表明细水雾在无风和扰动风速下均能将火扑灭,在临界风速下不能将火扑灭。5.建立了试验平台,开展了细水雾熄灭受限空间煤油池火试验研究,考察了通风状况、预燃时间及工作压力等因素对灭火时间的影响,得出受限空间燃烧的池火火焰存在核心反应区、通风控制区和燃料控制区。通过试验和定性分析,提出细水雾熄灭受限空间油池火的主导机理为气相冷却和火焰冷却,通过试验验证了室内火灾熄灭分析模型、火灾熄灭理论、临界水流量计算模型等基础假设的正确性。更多还原

【Abstract】 With the limited use and faced elimination of halone fire extinguishing chemical,fire suppression technology employing water mist demonstrates its wide promising potential due to its environmental benign,high efficiency,lower water consumption,less bveakage to the shielded objects and so on.It has become one of the hot topics in fire safety community.In domestic,the currently-used water mist fire suppression systems are featured with complicated design structure and high installation and operation costs mostly due to the high operating pressure.These are significantly detrimental to the generalization of the water mist fire suppression technology.The water mist nozzle is the core part of various water mist fire suppression systems.The performance of the water mist nozzle directly determines whether or not the designed water mist fire suppression system can be effectively applied to various fire scenarios.In China,the most developed high pressure water mist nozzles have not only complex design structure but also too many hard-controlled operating parameters.Therefore,it is significantly important to develop a kind of single-phase water mist nozzle with small size,light weight,simple deign structure, ease-to-manufacture-and-install,and good atomization performance within low-to-medium operating pressure.In domestic fire safety community,there are no literatures combining the nozzle structure,atomization mechanism,spray characteristics and fire suppression effectiveness with the whole systematical engineering for studies.The present work experimentally studied the relationship among the nozzle structure,atomization mechanism,spray characteristics and fire suppression effectiveness. The main works and progresses done in the current study are as follows.1.The present work developed a novel low-to-medium swirl water mist nozzle.The structure parameters of nozzle were optimized through theoretical analysis,numerical simulation and experimental verification.Following the discussion on the relationship between the nozzle structure and spray characteristics,the corresponding theoretical model was developed.The effects of the nozzle’s structure parameters on the spray characteristics had been investigated using the FLUENT code,through which the internal and the external flow fields’ of the nozzle were calculated.The numerical results provided theoretical foundation to parameters optimization of the subsequent design of the water mist nozzle.2.The movement equations of water droplet were established by balancing various forces imposed on the droplet appeared in air.The numerical calculation was performed on the droplets with typical diameter and various exit velocities of the droplet.The basic movement law of the water droplet was then obtained.Dependences of the droplet’s terminal velocity on the droplet diameter between spuared-low and lineear-low was determined,the corresponding critical droplet diameter equal to 80μm.3.On the basis of numericai simulation,the cold field tests on the spray performance of the water mist nozzle were carried out.The experimental results were compared with the numerical calculations.The results showed that the optimized single-fluid and low-to-medium swirl nozzle presented excellent spray characteristics.For most fire scenarios,the current nozzle can replace the high pressure nozzles or two-phase flow nozzles.It not only decreases dramatically the initial investment of water mist fire suppression system but also enhances the safety and reliability of operating the system.4.The fire suppression effectiveness of water mist subjected to external wind disturbance was both experimentally and numerically numerically investigated.The fire suppression model of water mist subjected to external wind flow was established and without wind or with validated.The results showed that water mist can extinguish the pool fire the external disturbed wind flow.However,the fire can not be extinguished at a critical wind velocity.5.The experimental setup was established.The kerosene pool fire suppression tests using water mist in a confined space were performed. The effects of ventilation condition,the preignition time and the operating pressure on fire-extinguishing time were examined.It was concluded that pool fire in confined space showed a core reaction region, a ventilation-controlled region and a fuel-controlled region.Following the experimental results and qualitative analysis,it was found that the principal mechanisms of the pool fire suppression by water mist in confined space were gas phase cooling and flame cooling.Moreover,the basic assumptions of extinguishment model of the chamber fire,the fire extinguishment theory and the model of calculating the critical water flow rate for fire suppression were experimentally verified.更多还原