A new correlation for gas temperature inside a burning enclosure

A new correlation for predicting enclosure gas temperature is presented in this paper based on the energy balance for adiabatic conditions, an estimate of the heat flux imposed on the enclosure boundary and the transient thermal response of the boundary. This correlation has been verified being able to predict enclosure gas temperature in both well- and under-ventilated fires in comparison with the existing experimental results. It is also compared with the well-known and widely used McCaffrey, Quintiere & Harkleroad (MQH) correlation.     

Comparison of FDS Prediction of Smoke Movement in a 10-Storey Building with Experimental Data

In this study, the Fire Dynamics Simulator (FDS), a computational fluid dynamics (CFD) model developed by National Institute of Standards and Technology (NIST) is used to simulate fire tests conducted at the National Research Council of Canada (CNRC). These tests were conducted in an experimental 10-storey tower to generate realistic smoke movement data. A full size FDS model of the tower was developed to predict smoke movement from fires that originate on the second floor. Three propane fire tests were modelled, and predictions of O₂, CO₂ concentrations and temperature on each floor are compared with the experimental data. This paper provides details of the tests, and the numerical modelling, and discusses the comparisons between the model results and the experiments. The 10-storey experimental tower was designed to simulate the centre core of high-rise buildings. It includes a compartment and corridor on each floor, a stair shaft, elevator shaft and service shafts. Three propane fire tests were conducted in 2006 and 2007 to study smoke movement through the stair shaft to the upper floors of the building. The fire was set in the compartment of the 2nd floor. Thermocouples and gas analyzers were placed on each floor to measure temperature and O₂, CO₂ and CO concentrations. Comparisons in the fire compartment and floor of fire show that the FDS model gives a good prediction of temperature and O₂ and CO₂ concentrations. In the stair shaft and upper floors there are some small differences which are due to the effect of heat transfer to the stairs that was not considered in the model. Overall the study demonstrates that FDS is capable of modelling fire development and smoke movement in a high rise building for well ventilated fires.     

Effect of cross section and ventilation on heat release rates in tunnel fires

Model scale fire tests were performed in tunnels with varying tunnel widths and heights in order to study the effect of tunnel cross-section and ventilation velocity on the heat release rate (HRR) for both liquid pool fires and solid fuel fires. The results showed that for well ventilated heptane pool fires, the tunnel width nearly has no influence on the HRR whilst a lower tunnel height clearly increases the HRR. For well ventilated solid fuel fires, the HRR increases by approximately 25% relative to a free burn test but the HRR is not sensitive to either tunnel width, tunnel height or ventilation velocity. For solid fuel fires that were not well ventilated, the HRRs could be less than those in free burn laboratory tests. In the case of ventilation controlled fires the HRRs approximately lie at the same level as for cases with natural ventilation.     

The maximum temperature of buoyancy-driven smoke flow beneath the ceiling in tunnel fires

In order to detect a fire and provide adequate fire protection to a tunnel structure, the maximum gas temperature beneath the ceiling to which the structure is exposed needs to be estimated. Theoretical analysis of maximum gas temperature beneath a tunnel ceiling based on a plume theory is given. The heat release rate, longitudinal ventilation velocity and tunnel geometry are taken into account. Two series of model-scale experimental tests were also carried out. The results of both analysis and experiments show that the maximum excess gas temperature beneath the ceiling can be divided into two regions. When the dimensionless ventilation velocity is greater than 0.19, the maximum excess gas temperature beneath the tunnel ceiling increases linearly with the heat release rate and decreases linearly with the longitudinal ventilation velocity. When the dimensionless ventilation velocity is less than 0.19, the maximum excess gas temperature beneath the ceiling varies as the two-thirds power of the dimensionless heat release rate, independent of the longitudinal ventilation velocity. In both regions, the maximum excess gas temperature varies as the −5/3 power of the vertical distance between the fire source bottom and tunnel ceiling. The investigation presented here considers only the cases when the continuous flame region is lower than the ceiling height.     

Determination of the heat release rate inside operational road tunnels by comparison with CFD calculations

Usually, during a fire inside a tunnel, the average heat release rate (HRR) is estimated according to the type of vehicle. Frequently, the overall HRR is considered, however it is also necessary to know its time evolution to design real time systems, particularly ventilation, which respond to fire events or signals as fast as possible. Nowadays, there is not a well established and generally accepted procedure to know the power liberated at each instant of time inside an operational tunnel. That procedure could help in taking the correct actions to adapt the tunnel ventilation in order to diminish the effects of the fire and the smoke. This work shows a method to calculate the heat release rate using sensors that can be installed inside an operational road tunnel. Besides, the location of the fire could also be calculated accurately and quickly. To achieve the previous purposes, a stationary database that depends on HRR, its location, and the ventilation speed is calculated with CFD programs; the data are compared with temperatures measured by the sensors located inside the tunnel. The program used to generate the database is the simplified model UPMTUNNEL. The predictions of the model are compared with the results of calculations carried out using the general purpose code FLUENT, and with measurements done in a tunnel with a real fire, produced with a fuel tray.     

Statistical characterization of the time to reach peak heat release rate for nuclear power plant electrical enclosure fires

Since publication of NUREG/CR-6850 (EPRI 1011989), EPRI/NRC-RES Fire PRA Methodology for Nuclear Power Facilities in 2005, phenomenological modeling of fire growth to peak heat release rate (HRR) for electrical enclosure fires in nuclear power plant probabilistic risk assessment (PRA) has typically assumed an average 12-min rise time [1]. One previous analysis using the data from NUREG/CR-6850 from which this estimate derived indicated this could be represented by a gamma distribution with alpha (shape) and beta (scale) parameters of 8.66 and 1.31, respectively [2]. Completion of the test program by the US Nuclear Regulatory Commission (USNRC) for electrical enclosure heat release rates, documented in NUREG/CR-7197, Heat Release Rates of Electrical Enclosure Fires (HELEN-FIRE) in 2016, has provided substantially more data from which to characterize this growth time to peak HRR [3]. From these, the author develops probabilistic distributions that enhance the original NUREG/CR-6850 results for both qualified and unqualified cables.² The mean times to peak HRR are 13.3 and 10.1 min, respectively, with a mean of 12.4 min when all data are combined, confirming that the original NUREG/CR-6850 estimate of 12 min was quite reasonable.Via statistical-probabilistic analysis, the author shows that the time to peak HRR for qualified and unqualified cables can again be well represented by gamma distributions with alpha and beta parameters of 1.88 and 7.07, and 3.86 and 2.62, respectively. Working with the gamma distribution for All cables given the two cable types, the author performs simulations demonstrating that non-suppression probabilities, on average, are 30% and 10% higher than the use of a 12-min point estimate when the fire is assumed to be detected at its start and halfway between its start and the time it reaches its peak, respectively. This suggests that adopting a probabilistic approach enables more realistic modeling of this particular fire phenomenon (growth time).     

火灾试验用标准燃烧物的制备及燃烧特性

基于典型场所的火灾载荷密度及可燃物,制备了典型的塑料杯组合体和纸杯组合体标准燃烧物,开展两种标准燃烧物的燃烧特性试验研究.结果表明,两种典型的标准燃烧物的燃烧性能稳定,总热值、火灾增长速率数据偏差较小,实验的重现性良好;在一定条件下,塑料杯组合体标准燃烧物可近似代表火灾载荷约为157.8 MJ的近中速火,纸杯组合体标准燃烧物可近似代表火灾载荷约为51.1 MJ的慢速火.     

Measuring rate of heat release by oxygen consumption

This paper provides a comprehensive set of equations and guidelines to determine the rate of heat release in full-scale fire tests based on the O₂ consumption principle. The approach is different from other investigators as the enphasis is on full-scale fire test applications and the use of volumetric flow rates is avoided. Some general equations for flow rate (i.e., applicable irrespective of the configuration of the gas analysis system) are described first. In subsequent sections, distinctions are made between various gas analyzer combinations to derive the equations for rate of heat release. Procedures to calculate net rate of heat release from a specimen exposed to a gas burner or wood crib ignition source are also given. A summary at the end of the paper lists step by step procedures for all cases covered.     

A general calorimetry framework for measurement of combustion efficiency in a suppressed turbulent line fire

The present study seeks to measure suppression effects in a canonical experimental configuration, featuring the exposure of a buoyant, turbulent, methane or propane-fueled diffusion flame to a co-flowing oxidizer diluted with nitrogen gas. Species-based calorimetry measurements, using either oxygen-consumption (OC) or carbon-dioxide-generation (CDG) based methods, are derived and applied to this configuration. Traditional OC models, which cannot account for oxidizer-dilution, are found to significantly overpredict total heat release rate in the present configuration, while traditional CDG models coincidentally give accurate results. Only the present calorimetry formulation, with full accommodation for oxidizer dilution, provides accurate results for both methods. In both methane and propane flames, global combustion efficiency is found to remain close to unity over a wide range of oxidizer dilution, decreasing abruptly only at the onset of global extinction. Similar trends are noted in the net combustion yields of oxygen, carbon-dioxide, and water-vapor. Net yields of carbon-monoxide remain close to zero for both fuels, but increase slightly near the extinction limit. These measurements reveal that despite visible suppression effects in all of the present flames, until the extinction limit is reached, nearly all of the fuel continues to react and combustion products are produced in stoichiometric proportions.     

混凝土动态强度提高因子模型的比较与构建

材料的动态抗力是评价结构安全性的基本依据。混凝土动态力学性能的确定对房屋、大坝、桥梁、公路等结构的设计至关重要。针对混凝土动态强度的应变率效应问题,考虑动态强度提高因子(DIF)这一参数,首先概述比较了已有国内外拉压强度DIF的模型,对不同模型的计算结果进行了比较,并从侧向惯性效应、试件尺寸、摩擦等作用机理对各个模型差异较大的原因进行了讨论。同时,以Cusatis提出的抗拉强度提高因子模型为依据,假定混凝土拉压强度本质应变率效应的机理一致性,将拉压模型联系起来,推导得出了抗压强度DIF模型,并与已有文献中的试验结果进行了比较,结果发现模型计算结果与试验数据吻合良好。     

矩形钢管混凝土轴压短柱中采用不同混凝土材料模型的性能比较分析

介绍了关于混凝土材料本构关系的von Mises,Mohr Coulomb,Drucker Prager,Smeared Cracking和Damaged Plasticity模型,采用这五种材料模型分别对带约束拉杆矩形钢管混凝土(CFT)轴压短柱进行有限元分析,并与试验结果对比。分析表明:采用Damaged Plasticity模型得到的轴压承载力及残余荷载高于von Mises,Mohr Coulomb与Smeared Cracking模型的计算结果,仅低于Drucker Prager模型的计算结果。Damaged Plasticity模型考虑混凝土双轴等压强度,在静水压力下极限强度能适当提高,且采用非相关流动法则,能合理考虑混凝土的塑性体积膨胀,因而能引起钢管及拉杆的约束作用,其计算结果较其它四种模型合理,相对于试验结果较接近,但与试验结果仍有差距。     

Examining the feasibility of prediction models by monitoring data and management data for bioaerosols inside office buildings

Exposure to bioagents can cause several health problems, including acute allergies, infectious diseases, and myctoxicosis. Nevertheless, all conventional methods for measuring airborne bioaerosols have significant limitations such as high cost, prolonged measurement time, and discontinuous measurements.     

双剪类流动模型的非圆形颗粒离散元数值验证

双滑移自由转动模型、双剪模型和双滑移转动率（DSR²）模型这3种双剪类模型均是基于运动理论的塑性模型,其关键区别在于转动率参量的选取。采用改进后的NS2D离散元程序,对长短轴比例分别为1.4和1.7的椭圆颗粒试样进行不排水单剪试验以验证上述双剪类模型中转动率参量选取的合理性。数值试验结果表明：①双滑移自由转动模型中的限定条件因未考虑能量消散过程中颗粒转动的影响而过于严格;②双剪模型中转动率参量为主应力方向变化率的假定与数值试验结果差距显著;③DSR²模型中采用平均纯转动率（APR）可很好地预测转动率参量的变化,且该模型可用于砂土非共轴微观机制的研究;④参量APR能考虑剪切过程中颗粒转动对能量耗散的影响,可将离散介质力学和连续介质力学有机结合起来,是运动模型中合理且重要的参量。     

Developing a one-dimensional heat and mass transfer algorithm for describing the effect of green roofs on the built environment: Comparison with experimental results

This paper investigates the mathematical modelling of the effect of green roofs on mitigating raised urban temperatures. A dynamic, one-dimensional model is developed, describing heat and mass transfer in building materials, considered as capillary-porous bodies, the vegetated canopy, modelled as a combined plant–air canopy layer, the soil and the air. The model is validated with an experiment, conducted in the Welsh School of Architecture, in Cardiff, in summer 2004. The right choice of parameters that affect the accuracy of the model (such as the expression of the convective heat transfer coefficient and stomatal resistance) is discussed. Special attention is given to the comparison between the experimental results and the outputs of only heat transfer algorithms and heat and mass transfer expressions. Taking these comparisons into consideration, conclusions are drawn about developing an accurate algorithm describing the thermal effect of green roofs on the built microclimate.