Air entrainment into balcony spill plumes

New plume formulations have been developed for assessing air entrainment into thermal plumes that spill over a balcony edge into an atrium void.     

非封闭式天井开口对火灾烟气蔓延的影响

本文采用数值模拟软件FDS模拟了不同开口尺寸、数量及位置对非封闭式天井内火灾烟气蔓延规律的影响。研究表明,非封闭式天井温度（烟囱效应）随开口宽度增大先缓慢下降（减弱）,然后迅速降低（减弱）,当开口宽度达到一定比例后,温度（烟囱效应）几乎不变。开口总宽度相同,仅有1个开口时,开口处巻吸气流较为集中,对火灾烟气蔓延的扰动较大,开口数量增加到2个和3个时,火灾烟气受开口数量的影响较小。与开口位于火源同侧相比,开口位于火源不同侧更容易产生火旋风,更有利于火灾烟气竖向蔓延。     

Air entrainment and turbulent fluctuations in hydraulic jumps

A hydraulic jump is the sudden transition from a high-velocity impinging flow into a turbulent roller in an open channel. Substantial amounts of air are entrapped at the impingement point, and significant free-surface fluctuations take place above the roller. In the present study, some physical modelling was conducted in a relatively large sized facility. The flow conditions included a wide ranges of inflow Froude numbers and Reynolds numbers (3.8 < Fr₁ < 10.0, 2.1 × 10⁴ < Re < 1.6 × 10⁵). The fluctuating features of free-surface and roller position were investigated non-intrusively with a series of acoustic displacement meters. The characteristic frequencies of the fluctuating motions were documented, and some major roller surface deformation patterns were revealed. The air-water flow properties were investigated with an intrusive phase-detection probe. The void fraction and bubble count rate data were documented in the jump roller, together with the interfacial velocity distributions. The rate of air entrainment was estimated based upon the void fraction and interfacial velocity distribution data. Some simultaneous measurements of instantaneous void fraction and free-surface fluctuations as well as longitudinal jump front oscillations were conducted. The relationship between the rate of air entrainment and turbulent fluctuations is discussed. Both the turbulent fluctuation and aeration properties are basic design parameters in urban water systems in which a hydraulic jump may take place. The present work provides relevant information for water systems including covered channels and partially-filled pipes.     

Maximum temperature of smoke beneath ceiling in tunnel fire with vertical shafts

To assess the impact of heat smoke in tunnel with vertical shafts, the maximum temperature of smoke beneath ceiling is researched theoretically and experimentally in this paper. A theoretical prediction model for maximum temperature of smoke beneath ceiling is built using dimensional analysis. A numerical model is built and calibrated with the full-scale experiment data. The calibrated numerical model is used to simulate the maximum temperature of smoke under different conditions with different shaft geometry. At last, the proposed theoretical model was formulated and compared with Kurioka model, experimental data and simulation data. The results show that the proposed theoretical model can give a better prediction for the tendency. It can be used to predict the maximum temperature of smoke beneath ceiling of tunnel with vertical shafts by taking the shaft geometry and arrangements effect into account.     

Air entrainment and thermal radiation from heptane pool fires

An experimental study was made to explore the air entrainment into heptane pool fires and the smoke blocking effect on thermal radiation from fire. Heptane was burned in five different sized tanks 0.3 m, 0.6 m, 1 m, 2 m, and 6 m in diameter, and its burning rate, flame temperature, vertical hot gas velocity, and thermal radiation were measured. It was found that the total amount of air entrainment is about 5 times the stoichiometric air requirement. A smoke block effect appeared at tank diameter of 2 m or more.     

Two-layer zone model including entrainment into the horizontally spreading smoke under the ceiling for application to fires in large area rooms

A model for smoke filling in a large room was developed that considers entrainment into the horizontally spreading smoke under the ceiling. This was accomplished by incorporating a simple model for the spreading ceiling jet into the two-layer zone model. Here, the proposed model was validated by focusing on the horizontal smoke spread phase on the basis of the previous experimental data of smoke spread in a large office room. The calculated results were in good agreement with the experimental data. In addition, a case study on the smoke filling in a large room was conducted to clarify the characteristics of the proposed model. As a result, the proposed model can predict the underside of the smoke layer to be lower than the two-layer zone model.     

耦合电梯门狭缝流动的高层竖井火灾烟气模拟

利用FDS 建立17 层高层办公楼数值模型,考虑狭缝的小开口流动,耦合了基于开口流动理论的HVAC 模型,研究高层建筑内烟气通过电梯竖井的蔓延过程,得到了高层建筑内烟囱效应诱导的火灾烟气蔓延规律。高层建筑内较低层发生的火灾会显著加热电梯竖井中的气体,形成烟囱效应,高层建筑内部会形成中性面。通过将HVAC 模型与基于标准流量系数的模型进行比较,可以发现这两种方法计算的质量流量相差约1.5 倍。这是由于采用的HVAC 模型并没有考虑狭缝处的开口流动损失。通过进一步修正,取开口损失系数K 值为3.56 能得到较好的模拟结果。     

Full-scale experimental study on smoke flow in natural ventilation road tunnel fires with shafts

Three full-scale burning tests were conducted in a natural ventilation city road tunnel with shafts. Fire sources were placed to be at different locations but its peak release heats were all around 5 MW. Results showed that large amounts of smoke and heat were released through shafts. The maximum smoke temperatures under the ceiling were below than 100 °C, and being lower than 110 °C at the safe height farther 3 m away from fires. The maximum smoke spreading horizontal lengths were less than 240 m both in the upwind and downwind. During the late stages, many smoke particles descended from the ceiling and downdraught occurred at shafts due to low smoke temperatures, but the visibility was not very bad and people needn’t evacuate. All These results are valuable for fire protection and construction of natural ventilation road tunnel with shafts.     

扁平大空间机械排烟全尺寸试验研究

利用全尺寸热烟试验,研究了机械排烟系统在典型扁平大空间中的排烟有效性.通过改变防烟分区面积、排烟量、排烟口位置和排烟口数量,研究不同工况下烟控方式的有效性.研究发现,排烟距离对排烟效果影响很大,超出一定距离后,烟控效果较差.当防烟分区内有均匀分布两个以上排烟口时,排烟效果明显优于单个排烟口的排烟效果.同时,理论公式算得的排烟量能够有效控制烟气蔓延,我国规范规定的排烟量计算方法相对较为保守.另外对试验中存在的烟气弥散和烟气回填现象进行了探讨和分析.     

成都地铁浅埋区间隧道自然通风排烟方式的热烟试验研究

区间隧道采用自然通风的方式进行排烟在国内尚属首次.采用熬烟试验方法在建成的实体隧道现场,验证了成都地铁浅埋区间隧道现有的通风竖井间距和通风面积能够满足隧道排烟的要求.烟层高度高于人体特征高度,烟气通过区间隧道最近的两个通风竖井排出,烟气蔓延区域控制在两个通风竖井之间,来自隧道内外的自然风对排烟效果的影响不大.     

某高大空间热烟试验研究

对大空间的防排烟设计主要参考中庭的要求进行设计,消防验收中对其防排烟系统的有效性只能依据是否符合规范来评定.许多大空间建筑超出了规范涵盖的建筑形式,参考规范中中庭的要求进行防排烟的设计和评价已不再适宜.在澳大利亚热烟试验标准的基础上对某大空间的烟控系统进行测试,通过对烟气层高度和烟气层温升变化等数据的分析,研究大空间烟控系统的排烟效果.结果表明:热烟试验能够模拟火灾烟气的流动,可用于评价大空间排烟系统的有效性及消防验收.     

通风对竖井型隧道火灾烟气特性影响试验研究

通过隧道火灾模型试验,研究纵向通风对竖井排烟效果及隧道内纵向烟气温度分布的影响。试验考虑不同火源热释放速率和纵向风速。结果表明：纵向风速对正庚烷池火热释放速率存在影响,对于较小正庚烷池火（≤11 cm）,火源热释放速率基本不随纵向风速而改变;对于较大正庚烷池火（≥14 cm）,火源热释放率随风速的增加先降低后基本保持恒定。此外,当隧道内风速较小时,竖井内烟气附壁排出,竖井后方烟气温度较低,控烟效果较好;当隧道内风速较大时,竖井内烟气出现边界分离,竖井后方温度升高,烟气蔓延距离增加,竖井排烟效果较差。因此,建议当竖井型隧道内发生火灾时,应尽量采用自然通风或较低的内部通风,避免较高风速。     

热水供暖系统的积气和排气

１系统积气的原因①在热水供热系统充水前,系统中存有空气。在系统充水时,空气逐渐被挤到系统的末端和顶部。这时,打开系统顶部放气阀排出空气,水即充至顶部。但系统内的空气不可能完全排出,在系统的某些部位会存有空气。②水中溶有空气。当水逐渐升温时,空气会逐渐...     

地下大空间步行街火灾自然排烟有效性热烟试验

采用热烟试验方法研究某地下大空间步行街区采用自然排烟模式的有效性。火源面积为 2 m2 ,火源的功率约为1 500 kW,设置 3 处典型火源位置。结果表明,在自然排烟模式下,大部分烟气在热浮力作用下通过火源上方的自然排烟口排出至室外,仅在局部区域产生少量烟气的聚集、沉降现象。在模拟计算的人员疏散时间内,疏散路径及疏散出口能见度高,总体控烟排烟效果明显,烟气流动沿程的温度变化对人员疏散行为的影响不明显。     

热烟测试用于评价建筑烟控系统的讨论

烟气是火灾中导致人员伤亡的最主要因素，建筑的消防系统中必须包括有一个良好的烟气控制系统。目前在国内烟气控制系统的有效性评判一般是根据相关规范的规定来得到，而对于超出规范范围的建筑，大都是利用数值模拟来给出其烟控系统的有效性评判，极少通过现场烟气实验来对烟控系统进行测试，且国内尚未形成现场测试的相关标准或规范。介绍了澳大利亚用于烟气控制系统现场测试的热烟测试标准，利用其对一个高大中庭的烟控系统进行了测试。测试过程和结果表明，热烟测试可以较好地用于对建筑烟气控制系统有效性的评判，是一种在消防测试中值得推广的现场实验方法。     

高层建筑防排烟系统风量调试

在理论分析的基础上，提出了高层建筑防排烟风量测定和系统调试的方法。针对调试中发现的问题，给出了解决措施。     

预测FTIR光谱中烟气毒性组分体积分数的定量模型

分析烟气中毒性组分FTIR图谱的定量方法很多，鉴于每种方法都有其独特的优缺点，着重介绍了经典最小二乘法(CLS)和偏最小二乘法(PLS)。     

对防烟楼梯间及其合用前室分别加压送风防烟方案的流体网络分析

应用流体网络分析法,对现行高层建筑防火规范第8章第8.3.2条表8.3.2-2中的风量控制数据进行了校验性计算,揭示了分别加压送风的流动特性。计算结果表明,向防烟楼梯间加压是徒劳的,因为加压送风会直接从防烟楼梯间的疏散外门流失。     

Modeling for predicting the temperature distribution of smoke during a fire in an underground road tunnel with vertical shafts

In this study, fire experiments using a 1:20 model-scale tunnel were conducted to investigate the performance of natural ventilation in an underground road tunnel with six vertical shafts. The experimental parameters were the heat release rate of a fire source and the height of the shafts, and nine experiments were conducted in total. Furthermore, simple models were developed for predicting the temperature distribution of the smoke flowing under the tunnel ceiling. The following results were obtained: (1) In the experiments, the form of the smoke exhausted from the shaft became plug-holing when the shaft height was 1.0H_t, and became boundary layer separation when the height was 0.24H_t. (2) The average efficiency of heat exhaust was 0.16 when the form was plug-holing, and was 0.12 when the form was boundary layer separation. (3) When the form was plug-holing, the ratio of entrainment of fresh air became almost constant regardless of Ri. On the other hand, when the form was boundary layer separation, the ratio of entrainment of fresh air was smaller than that under the condition of plug-holing. (4) The temperature distribution under the tunnel ceiling predicted by the models agreed with that measured by the fire experiments in all cases.