喷淋作用下的自然排烟的效率

通过建立一个简化的数学模型,分析了喷淋作用时烟气的运动情况,在理论上给出了影响自然排烟效率的主要因素.通过一组喷淋与自然排烟作用实验,进一步探讨喷淋对自然排烟效率的影响.结果表明,自然排烟的效率取决于烟气层的厚度与烟气层温度.水喷淋作用后,烟气温度显著降低,自然排烟口的烟气溢出速度大大减小.对于顶部排烟的情况,当喷淋压力在0.15MPa以下时,烟气溢出速度是未设置喷淋时的65%左右.烟气层厚度对自然排烟效率也有着重要的影响,在烟气厚度层很大的情况下,大压力喷淋作用下烟气的溢出速度有可能比小压力喷淋作用时大一些.     

基于蒙特卡洛法的单室火灾热辐射计算

根据CFAST软件模拟简单房间着火后热烟气层温度及高度的变化情况,采用蒙特卡洛法计算热烟气层对房间地板面及地板中心1m2面积上的平均热辐射通量.计算时,分别假设烟气层的辐射能力集中于热烟气层的下表面,或烟气层为温度均匀的灰体,结果表明两种假设的计算结果相近.根据两种假设计算出的地板面上的热辐射通量,预测出室内发生轰燃的时间分别是640s和700s,与CFAST软件的预测结果665s相近.评估中引入热辐射对人体的伤害判据,其结果也可以用来估算安全疏散时间.     

自然通风房间内油池面积变化对细水雾灭火效果影响的数值模拟

采用大涡模拟、混合物分数模拟和欧拉一拉格朗日粒子运动描述法研究了不同油池面积条件下自然通风房间内细水雾与油池火焰作用过程，分析了加入水雾对着火房间速度场和温度场的影响，推导出油池火焰根部空气卷吸速率与油池尺寸的关系，探讨了细水雾在火羽流的不同区域内的灭火机理。模拟结果表明：加入水雾不仅降低了着火房间热烟气层温度，而且显著影响了房间内速度场，在间歇火焰区和浮力羽流区以及热烟气层主要发挥细水雾的蒸发冷却作用，在恒定火焰区则是蒸发冷却和隔氧窒息共同作用，油池火根部的空气卷吸速率与油池边长的四次方成正比。     

墙体节能改造保温层厚度的优化研究

本文以单位造价的节能量△qH/P作为既有建筑节能改造的技术经济评价指标,分析了薄抹灰外墙外保温系统在节能工程中的成本构成.通过改变建筑物的状态系数m、墙体传热系数K0和不变成本P0,着重研究了△qH/P与聚苯板厚度的关系.研究提出了节能改造的新的评价方法及其各参数之间的关系,优化了聚苯板厚度参数.     

2008t/h四角燃烧煤粉锅炉烟温偏差实炉测试分析

大型四角切圆燃烧锅炉的烟、汽温度偏差对其安全运行具有重要影响。在2008t/h锅炉上,对不同负荷工况下炉膛上部屏区烟温及屏式过热器壁温进行了测试。结果表明,汽温左高右低,大致成W型分布形态,而烟温呈M型分布,与汽温分布状态峰谷反向对应。认为炉膛上部空间残余旋转形成沿屏区宽度烟气流量的不均匀分布,因而烟气对受热面的冲刷强度不同,导致屏间烟气换热量存有差异,这是烟、汽温偏差产生的根本原因。     

连杆厚度对裂解的影响分析

结合理论分析与数值模拟研究了连杆厚度对裂解加工的影响,给出了断裂韧性、裂纹区塑性区状态与连杆厚度的关系,并讨论了连杆厚径比对裂解的影响.结果表明:在启裂工步,随连杆厚度的增加,裂纹区的Von Mises应力由狭长的、多个分散集中状态逐渐过渡到趋向中面唯一分布的集中状态,裂尖附近的最大主应力均值逐渐增加,分析了连杆厚度及厚径比与裂解力的关系,得出某规格连杆的厚径比D/R最佳设计范围为3.312～3.438.     

水润滑橡胶轴承振动噪声特性分析

应用ABAQUS有限元分析软件建立了水润滑轴承的振动噪声分析模型,获得了不同条件下橡胶轴承的失稳倾向,重点分析了橡胶材料的摩擦系数、弹性模量、密度和橡胶层厚度对水润滑橡胶轴承振动噪声的影响。研究结果表明摩擦系数越大,失稳倾向绝对值增大,产生摩擦噪声可能性增大;密度较小的橡胶材料失稳倾向的绝对值较小,有利于减小轴承系统的摩擦噪声;而减小橡胶层厚度也有利于减小摩擦噪声,为水润滑橡胶轴承材料选型和结构优化提供了参考和借鉴。     

全氧燃烧浮法玻璃熔窑窑压的数值模拟

采用基于k-ε湍流模型、涡-耗散化学反应模型、P1辐射传热模型的数值模拟方法,研究了玻璃熔窑在全氧燃烧条件下烟气出口面积对窑内压力场和火焰空间的影响规律。研究结果表明,所选用的三维数学模型能够较为真实的反应全氧燃烧玻璃熔窑火焰空间的状态。随着烟气出口面积的增加,玻璃熔窑内压力下降,窑内平均压力与烟气出口面积符合指数衰减关系。当单侧烟气出口面积为0.36 m2时,窑内平均压力约为6 Pa。烟气出口面积改变对火焰形态以及温度场的影响不明显。因此改变烟气出口面积可以作为有效调节全氧燃烧浮法玻璃熔窑窑内压力技术手段,这为指导全氧燃烧玻璃熔窑的设计和运行提供了理论依据。     

宽负荷脱硝SCR入口烟气流场优化系统研究与应用

燃煤机组锅炉在低负荷运行状态下,SCR(选择性催化还原)进口烟道沿宽度方向烟温偏差很大,外侧低中间高,偏差最高可达17~18℃。烟温低的区域处在催化剂低限值下面了,而喷氨枪仍然整个烟道均匀地在喷,造成氨气与烟气混合不均致使脱硝效率降低,同时对催化剂也产生不良影响。针对这一现象,本课题在SCR反应器入口烟道外侧加装均流挡板,使烟气通流面积随负荷变化而变化,充分保证喷氨枪断面上的流速,提高充满度确保烟气流场均匀,与氨气充分混合起到匀质的效果,从而提高脱硝效率。并使外侧催化剂处于休息状态,延长了催化剂寿命。工程改造后进行性能测试,均质后的效果能将NO_x值降低32~40 mg/Nm~3,可实现20 mg/Nm~3的近"0"排放,喷氨流量降低11%左右。获得了环保与经济的双重收益。     

纵向风对通道火灾烟气竖向分层特性的影响

研究了纵向风对通道火灾热分层和烟颗粒分层特性的影响.纵向风可能使通道内的分层流出现Kelvin-Helmholtz流动不稳定性,并导致烟颗粒向下部空间扩散;当纵向风较大时,烟气层的热分层稳定性被破坏,导致烟颗粒与冷空气出现强烈掺混,烟颗粒层显著变厚.通道火灾的热分层和烟颗粒分层特性与Froude数或Richardson数关联紧密.实验初步得到了出现Kelvin-Helmholtz流动不稳定和热分层不稳定的临界条件.     

喷水排烟作用下孤岛火灾行为及烟气运动实验

针对大空间内孤岛火灾安全集中讨论的焦点问题,通过全尺寸实验的方法研究了喷水排烟作用下大空间内孤岛火灾行为及烟气运动过程.分别设置不同火源功率、有无排烟喷水、不同排烟量、不同喷头类型及工作压力等条件而开展了全尺寸的对比性实验,并理论分析了排烟和喷水存在情况下的室内火灾动力学平衡的变化.结果表明:无排烟喷水时孤岛火灾增长迅速,在1.3 MW时可达到轰燃温度;不同喷头类型时孤岛内火灾行为特征及灭火规律表现不同;高速水雾喷头喷射会扩展羽流区半径及加强烟气分界面热分层失稳;喷头类型是灭火关键因素,增加喷头工作压力和排烟量可以降低室内温度,但效果不明显;规范设计孤岛排烟量(20 ACH)和喷水条件(标准喷头、0.05 MPa)存在一定的不足.全尺寸实验验证了排烟喷水作用可以有效地控制孤岛火灾对大空间影响.     

Evolution of liquid and gas phases in multi‐plume spray injection

In this study, the unsteady development of multi‐plume sprays has been investigated by large eddy simulations with Eulerian–Lagrangian multiphase approach for both global spray characteristics and local flow features. Multi‐plume sprays are injected at the injection pressures of 10 MPa and 15 MPa, and the temperature of T_s = 297.65 K into the ambient air at the atmospheric pressure and temperature of T_a = 293.15 K. Experimentally obtained global multi‐plume spray characteristics in terms of spray shape and penetration are used to validate the present numerical simulations. The present numerical predictions for Sauter mean diameter and its temporal variation agree well with the empirical correlations. The predicted droplet size distribution evolves temporally and spatially, and exhibits bimodal distribution, until eventually the mode for small droplet sizes dominates. The spray plumes are found to have limited interaction due to the relatively large orientation angles between the plumes. Because of the momentum transfer from the liquid to gas phase, spray‐induced air jets appear in the multi‐plume sprays. Using vorticity, pressure, and λ₂ − criterion fields, it is shown that the spray‐induced air jets form similar vortical structures as single phase jets. Similarities between the spray‐induced air jets and single phase jets in terms of the shear layer vortical structures such as hairpin‐like vortices improves our understanding of the entrainment and mixing processes in multi‐plume sprays. Copyright © 2016 John Wiley & Sons, Ltd.     

机械排烟控制小室火灾烟气的实验研究

采用全尺寸实验对较大火源功率下机械排烟控制小室火灾烟气的效果进行了研究.根据小室内的温度分布特点以及所稳定的烟气层高度,通过实验数据和计算结果的对比,分析了较大火源功率下3种经典羽流模型在小室机械排烟过程中的适用范围.结果表明,在火源功率大于250 kW时,Heskestad模型的计算值与实验值符合较好,并进一步对实验数据进行拟合,修正了Heskestad模型,从而得出较大火源功率下,控制烟气从小室溢出所需要的风机风量与火源功率以及所控制的烟气层高度之间的半经验关系式.     

喷雾洒水抑制城市二次扬尘的效果分析

临汾市是中国113个环保重点城市和国家环境监测网络城市,道路二次扬尘在对环境空气污染的颗粒物中占到50%左右,抑制扬尘污染已经成为改善临汾市城市环境空气质量的迫切任务。叙述了临汾市采取喷雾洒水抑制道路二次扬尘措施后,取得抑制二次扬尘总量为5366.48t/a,总抑制二次扬尘率为85%的效果。     

细水雾扑灭油池火的临界条件

通过模拟灭火实验发现细水雾灭火过程中由于雾特性参数的变化而形成两种相异的灭火过程,进而通过理论分析与计算得到了细水雾通过火焰冷却扑灭油池火所需的临界条件,并通过实验室尺度实验与全尺度实验对计算结果进行了验证．在实验中还发现对于下喷式系统而言,细水雾能否穿透烟气羽流层对于细水雾系统能否灭火具有至关重要的影响,为此引入了烟气羽流与细水雾的推力比这一概念,并通过实验确定了采用下喷方式时,细水雾灭火的临界推力比大致为10．     

室内火灾机械排烟效果的模型计算与实验研究

研究了机械排烟情况下,室内烟气层保持在一定高度时,机械排烟速率和羽流卷吸速率的关系,并采用不同羽流卷吸模型和溢流模型,计算一定排烟速率下、不同火源功率时烟气层的稳定界面高度．在一个具有一定通风口高度的全尺寸普通房间内进行了实验,通过实验结果和计算结果,分析了机械排烟对烟气的控制效果,讨论了机械排烟情况下受限空间内的羽流模型的适用情况,同时对影响模型计算结果的一些因素进行了分析．     

Flame interactions and smoke containment by downward displacement ventilation

Smoke contamination even from small fires of sensitive components in telephone central offices (TCO) and semiconductor clean rooms has caused disastrous disruptions in services and excessive financial repercussions. Containment and removal of smoke can be achieved by downward displacement ventilation, also used for other purposes in large floor area semiconductor facilities. Downward ventilation reverses the upward flow from the fire and removes the smoke and other combustion products through the floor. Small-scale model experiments under turbulent fire plume conditions investigate the physical parameters such as downward velocity, ceiling clearance, and size of the fire that control the extent of the smoke containment around the fire. The extent of smoke contamination is mapped by measuring the temperatures in several locations on the vertical axis and in the space around the fire. The downward velocities cause oscillation of the fire plume and the flames around the vertical axis. By combining the experimental data with similarity analysis, a characteristic length scale and nondimensional relations are deduced for the extent of the smoke containment and the onset of plume oscillations. These relations allow design of displacement ventilation effective to contain the smoke but not cause fire spread owing to the leaning of the flames. Previously reported discrepancies in the apparent width and behavior of the plume are resolved by examining the experimental data and assessing the suitability of steady state computational fluid dynamics to model the present flow.     

NUMERICAL MODELING FOR INTERACTION OF A WATER SPRAY WITH SMOKE LAYER

Interaction of a water spray with a smoke layer was studied numerically. A one-dimensional model was developed by taking smoke and air as two quasi-steady layers. W ater droplets of the spray were divided into several typical classes based on the droplet distribution function. Spray characteristics such as droplet diameter and velocity, shape of the spray envelope, gas temperature, and flow rate inside the spray envelope were calculated with heat and mass transfer to the induced air flow. The simulated results agreed with the experiments on full cone water spray in a normal atmospheric environment, and indicated some physical principles for using water spray to minimize smoke damage.     

Thin layer electrolyte impregnation into porous anode-supported fuel cell by ultrasonic spray pyrolysis

An ultrasonic spray pyrolyzed thin layer electrolyte impregnates into a porous anode and extends the depth of triple phase boundaries (TPBs) to several times that of the dense thin-layer thickness. This process, without an anode functional layer, improves the conventional repeated impregnation that results in anode porosity blocking and difficult extending to the anode/electrolyte interface. A (La_0.75Sr_0.2Ba_0.05)_0.175Ce_0.825O_1.981 (LSBC) electrolyte thin layer (iLSBC) is deposited on a porous La_0.3Sr_0.7TiO₃ (LST) anode by ultrasonic spray pyrolysis using 0.1 M LSBC precursor at a substrate temperature of 450 °C, while controlling the solution flow rate and spray volume. The spray pyrolyzed iLSBC/LST half-cells co-fired at 1350 °C/6 h exhibit no evident second phase in the X-ray diffraction analysis. The depth profile of iLSBC/LST indicates an approximately 2.75 μm-thick layer with the Ce element line scanning showing a significantly higher impregnation depth. Slight lattice distortion among the impregnated region may be due to the iLSBC diffusion, resulting in the extension of the TPB area and length. The half-cell reaches a low impedance and achieves a power density of 377 mW/cm² at 750 °C.     

基于试验数据的锅炉钢结构高强度螺栓轴力与扭矩关系回归分析

为了解决锅炉机组钢结构高强度螺栓转角法施工过程中量化的检验标准,介绍了采用实验的方法,得到高强度螺栓扭矩与轴力的对应值,并采用线性回归分析方法建立高强度螺栓扭矩与轴力的理论关系模型,结合实际施工、检验条件及要求,为保证检验方便、可行,最终以图或表的形式提供转角法高强度螺栓扭矩与轴力的对应关系.