A global soot model developed for fires: Validation in laminar flames and application in turbulent pool fires

In this study, a global soot formation model based on the LSP (Laminar Smoke Point) concept in combination with the soot oxidation model developed by Leung et al. [40] is validated in three laminar flames: a non-smoking and a smoking ethylene flame, as well as a non-smoking propane flame, and then applied in two turbulent pool fires fueled by ethylene and methane, respectively. In this global soot model, the sooting propensities of different fuels are accounted for by a pre-exponential factor determined from the LSP height, providing a general and practical solution for soot modeling in multi-fueled fires. The flame fields are solved by FLUENT with UDFs to provide material properties and add additional soot governing equations. A-CSE (Alternative Conditional Source-term Estimation) approach is adopted to handle the interaction between soot chemistry and turbulent flow in the turbulent fires.The model parameters such as the pre-exponential factor, soot inception limits and soot particulate surface area are determined and calibrated against the experimental data. Mixture fraction and temperature are first verified to provide a good premise for soot modeling. Good agreements between the predicted and measured soot volume fraction, as well as the reproduction of transition from non-smoking to smoking flames, demonstrate the capability of current global soot model in accurately predicting soot for both laminar flames and turbulent fires. Using the A-CSE soot modeling approach together with the global soot model, this study presents a general effective yet computationally efficient global soot modeling framework for fires.     

Fire safety research in microgravity: How to detect smoke and flames you cannot see

Any design requiring the application of technology contains a challenge to achieve a safe design. Manned space flight requires the highest degree of attention to crew safety, thus understanding and recognizing all potential risks involved. An important area of concern is establishing design criteria for a reliable fire detection and suppression system. This has been a main target when designing the European pressurized manned module Columbus Attached Laboratory as part of the international space station. This paper describes experiments performed to investigate the behavior of fires and the fluid dynamics of suppression agents in microgravity by means of parabolic flight maneuvers as an aid for the development of a design of a fire detection and suppression system for the manned Columbus Attached Laboratory.Reprinted fromHazard Prevention: Journal of the System Safety Society, Fourth Quarter, Volume 30, No. 4, 1994, with permission from the author.This paper was presented at the Twelfth International System Safety Society Conference in New Orleans, Louisiana, on July 5 through 10, 1994.     

室内火灾旋转火焰理论分析与实验研究

根据涡量传输和火灾动力学等理论,分析室内火灾旋转火焰的形成机理,导出室内火灾产生旋转火焰的控制因素表达式。旋转火焰的产生需要足够的密度梯度、压力梯度和斜压效应。利用小规模室内火灾实验,研究室内火灾旋转火焰的基本特征,比较旋转与非旋转火焰火灾的基本参数。与非旋转火焰的室内火灾比较,旋转火焰室内火灾热烟气层温度、升温速率、燃烧速率、地板所受辐射热通量等的均值与峰值均有显著提高,且峰值出现较早。结合理论分析与实验研究结果,得到了室内火灾发生旋转火焰的条件判据。     

Experimental and numerical evaluation of the influence of the soot yield on the visibility in smoke in CFD analysis

Experimental and numerical analysis have been performed to evaluate the influence of the soot yield parameter on the results of advanced engineering analysis, in regards to visibility. After identifying soot yield as the most influential factor on the results, fuels with various values of Ys have been analysed in a fire chamber and then compared to numerical data. The numerical analysis has been performed using two different CFD packages, ANSYS® Fluent®, and Fire Dynamics Simulator. The numerical analysis itself show an apparent hyperbolic trend of the visibility when changing the soot yield with clear consequences on the ASET (Available Safe Egress Time). Below a cut-off point, that exists at a soot yield value close to Ys =0,10 g/g, a small change in the parameter causes a substantial shift in the results (visibility or ASET time), while above this value an increase to soot yield does barely influence the results. Qualitative assessment of the results shows a need for use of conservative values of Ys in engineering analysis if detailed and precise material data is not available. Additionally to the full-scale experiments, a real case study has been included to show how this research can be translated into the Fire Safety Engineering design process. In this study, change of Ys value below 0,10 g/g caused a significant change of the qualitative assessment of the results of CFD.     

中庭火灾烟气流动的大涡模拟

采用大涡模拟的方法,对中庭火灾烟气的流动过程进行了模拟,了解了中庭烟气的蔓延过程,得到了烟气的速度场和温度场、顶棚射流的速度和温度的详细结果。模拟结果表明,大涡模拟能比较准确地预测中庭内烟气的流动状态,可用于指导中庭建筑的防火设计。     

大型商业综合体防排烟系统设计要点分析

与一般的商业建筑相比,大型商业综合体集购物、餐饮、KTV、电影院等功能于一体,室内空间相对复杂、人员密集、设备用电量较大,发生火灾事故的概率相对较高。一旦发生火灾事故,将会造成非常大的后果。只有做好防排烟系统设计,才能够提高大型商业综合体的火灾防控力度,降低火灾事故所造成的负面影响。基于此,文章针对大型商业综合体的防排烟系统设计进行了详细的分析,以供参考。     

Development of a convective diffusion model for lead pipe rigs operating in laminar flow

As part of achieving lower lead standards water undertakers are utilising lead pipe rigs to quantify the benefit of treatment measures. A convective diffusion model is developed for lead pipe rigs operating in laminar flow, and applied to the three operating steps of flushing, sampling and stagnation. The model is used to determine the appropriate time-scales for each stage, and the sensitivity of the measure to variations in flow-rate. In contrast to rigs operating in turbulent flow the average lead observed leaving the pipe and that in the pipe, after a period of stagnation, are substantially different. Equations are derived for both, and take into account the residual distribution of lead left in the pipe after flushing. It is shown that the lead concentration observed leaving the pipe is well approximated by a single exponential term in contrast to the concentration within the pipe. Predictions are made on the residual lead concentration that can be achieved through flushing, and its dependence on flow-rate. The relevance of the laminar flow model to that in domestic lead pipes is discussed.     

Influence of geometrical and operational parameters on the axial dispersion in an aerated channel reactor

Residence time distribution experiments have been performed on an activated sludge 3000 m³ channel reactor aerated by gas diffusion (for different liquid flowrates under constant aeration rate and constant water depth) and on a bench-scale channel reactor aerated from the bottom (for different liquid and gas flowrates and water depths) in order to characterize their hydrodynamics. Both units can be modeled as plug flow reactors with axial dispersion. A general correlation has been obtained to predict the axial dispersion coefficient as a function of the gas and liquid velocities and the geometrical parameters of the full-scale and bench-scale reactors. Finally, to facilitate the simulation of biological reactions in transient state, an equivalent model based on tanks-in-series with variable back-mixing flowrate is proposed.     

高层建筑火灾时走廊净高对排烟效果的影响

采用k-ε两方程三维紊流模型模拟高层建筑内的烟气流动,利用FLUENT软件对定排烟量情况下不同走廊净高和排烟口风速时的机械排烟进行模拟。对比分析了不同走廊净高和排烟速率情况下,高层建筑内烟气的扩散、走廊内烟气温度和质量分数的变化情况。结果表明,走廊净高为2.4m时,排烟口排烟速率不应大于1.7 m/s;走廊净高为2.7 m时,排烟口排烟速率不宜大于2.8 m/s;而当走廊净高为3 m以上时,排烟口的排烟速率按照《高层民用建筑设计防火规范》(GB50045-95(2005年版))取值,能够符合安全疏散要求。     

高压驱动下非均匀介质内气体输运数值模拟

通过利用商用软件,对地下腔室内的示踪气体在高压驱动下向非均匀围岩介质的输运进行了数值模拟,并分析了影响示踪气体输运行为的主要因素.结果表明,理想的均匀介质可以较好地包容示踪气体,而在实际的非均匀介质内示踪气体更倾向于以较高的浓度沿介质局部薄弱环节向外输运;腔室外的坑道中,采用堵塞段和空段的设计有利于阻止示踪气体向外输运...     

Methods to calculate the response time of heat and smoke detectors installed below large unobstructed ceilings

Recently developed methods to calculate the time required for ceiling mounted heat and smoke detectors to respond to growing fires are reviewed. A computer program that calculates activation times for both fixed temperature and rate of rise heat detectors in response to fires that increase in heat release rate proportionally with the square of time from ignition is given. This program produces nearly equivalent results to the tables published in Appendix C, Guide for Automatic Fire Detector Spacing (NFPA 72E, 1984). A separate method and corresponding program are provided to calculate response time for fires having arbitrary heat release rate histories. This method is based on quasi-steady ceiling layer gas flow assumptions. Assuming a constant proportionality between smoke and heat released from burning materials, a method is described to calculate smoke detector response time, modeling the smoke detector as a low temperature heat detector in either of the two response time models.Nomenclature A g/(c _p T ) - c _p specific heat capacity of ambient air - C _s smoke mass concentration - D effective binary diffusion coefficient - g acceleration of gravity - H vertical distance from fuel to ceiling - I light intensity - I_o initial light intensity - L light beam length - _s smoke gas mass production rate per unit volume - OD optical density per unit length (see Equation 8) - fire energy release rate - energy release rate per unit volume - r radial distance from fire axis to the detector - RTI response time index, the product of the detector thermal time constant and the square root of the gas speed used in the test to measure the time constant.⁹ - t time - t ₂ ^* dimensionless time t/[A^{–1/5 –1/5} H^4/5) - (t ₂ ^* ) _f dimensionless time for time delay for gas front travel - T ambient temperature - T gas temperature at detector location - T _s temperature of detector sensing elements - T T — T - T ₂ ^* dimensionless temperature differences T/[A^2/5(T _f /g) ^2/5 H^–3/5] - U gas speed at the detector location - U ₂ ^* dimensionless gas speed U/[A H]^1/5 - Y _s local ratio of smoke mass to total mass in flow - proportionality constant for t²-fire growth = Q/t² - ambient air density Reference: David D. Evans and David W. Stroup, Methods to Calculate the Response Time of Heat and Smoke Detectors Installed Below Large Unobstructed Ceilings,Fire Technology, Vol. 22, No. 1, February 1985, p. 54. Note: This paper is a contribution of the National Bureau of Standards and is not subject to copyright.     

Measurement and three-dimensional simulation of flow in a rectangular detention tank

There are two main ways to obtain better knowledge of the hydraulics of ponds, namely measurements and simulations. In this study, the applicability of using three-dimensional simulations as an engineering tool in stormwater pond design was investigated. To do this, three-dimensional simulations were compared with measurements of flow pattern and residence time in a large physical model of a detention tank (13 × 9 × 1 m). The agreement between measurements and simulations concerning both flow pattern and residence time distribution curves was found to be good for high flow rates.     

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.     

Characterization and grouping of aquatic fulvic acids isolated from clear-water rivers and lakes in Japan

Characteristics of aquatic fulvic acids (FAs) from 10 clear waters in Japan (around the temperate zone) were revealed by several analytical techniques—high performance size exclusion chromatography (HPSEC), elemental analysis, liquid-state ¹³C NMR spectroscopy, isotopic analyses (δ¹³C and δ¹⁵N), and compared with those of International Humic Substances Society (IHSS) standard samples including FAs from brown waters (Suwannee, Pony, and Nordic FAs). Generally clear-water FAs were different from brown-water FAs in chemical properties. Weight-average molecular weights (Mw) of the clear-water FAs were similar to each other, whereas their elemental compositions and carbon species distribution were different. The clear-water FAs all exhibited a high proportion of alkyl carbons, which may be attributed to microbial activity. δ¹³C and δ¹⁵N values of the FAs indicated that there would be a huge gap between origin and chemical structure of clear-water FA. Results of the chemical structural analyses described above were not always linked to those of the isotopic analyses (δ¹³C and δ¹⁵N). Multivariate statistical analysis, i.e. cluster and principal component analysis was applied to reveal differences or similarities in a more objective manner. The FAs were always classified into two clear-water groups and one brown-water group. Aryl-C and O-Alkyl-C contents were important for the grouping. We speculate that the grouping might depend on the differences of aquatic microbial activity caused by the differences of residence time of water.     

某水电站GIS电缆层中SF6重气扩散的数值模拟

本文以国内某水电站的GIS电缆层为对象,应用CFD数值模拟方法,对以SF_6为代表的重气扩散规律进行研究与分析。着重探讨在不同泄漏量和排风量条件下,SF_6重气在电缆层中浓度的变化及各因素对重气扩散规律的影响,得出了若干结论。相关研究可为后续模型实验研究提供技术指导,也可为同类电站厂房建设提供借鉴与参考。     

煤矸石喷射水泥在工程应用中的几个问题研究

煤矸石喷射水泥主要用于喷射混凝土。针对骨料含水率过大会引起喷射水泥过早凝结的问题,通过比较骨料含水率不同配制的喷射混凝土的抗压强度,确定出骨料含水率的范围为≯0．3％。对地上搅拌与地下喷射之间的时间间隔不同的喷射混凝土的抗压强度进行了比较。结果表明,间隔时间不会对喷射混凝土的抗压强度造成损失。     

电子氡检测仪测定土壤中氡浓度方法的研究

本文使用RAD-7型电子氡检测仪测定土壤中氡浓度,提出了防止检测系统漏气的措施,优化了仪器运行的各种参数,建立了自动化检测系统,是一种快速、准确、简便的测定土壤中氡浓度的方法。     

对建筑给水排水设计规范中几个要点的认识

文中列出常见的几个建筑给水排水设计规范中的要点，并作了具体的分析，提出了实际工程中存在的问题以及解决方法。     

Temperature as an alternative tracer for the determination of the mixing characteristics in wastewater treatment plants

The hydraulic characteristics, i.e. the residence time distributions, of wastewater treatment plant reactors are usually determined using conventional tracers. This paper aims to present an alternative approach based on wastewater temperature. The step in temperature change, e.g. from stormwater events with cold rainwater, is used as a tracer signal. The method was verified using lab- and pilot-scale tests that showed very good agreement of the time series estimated both with conventional and temperature tracer methods. Results from lab-scale tests exhibit a zone with a minor water exchange of about 10% of the volume of all reactors, while the respective zone in the pilot-scale tests was estimated at about 30% of the total volume. The short-circuit flow was more than 50% of the inflow resulting from gaps between the walls inside the reactor cascade. An application example shows the importance of reliable residence time distribution underlying activated sludge modelling and the uncertainty associated with neglecting the determination of appropriate flow-through characteristics.     

An approach to improve the separation of solid-liquid suspensions in inclined plate settlers: CFD simulation and experimental validation

The most important requirements for achieving effective separation conditions in inclined plate settler (IPS) are its hydraulic performance and the equal distribution of suspensions between settler channels, both of which depend on the inlet configuration. In this study, three different inlet structures were used to explore the effect of feeding a bench scale IPS via a nozzle distributor on its hydraulic performance and separation efficiency. Experimental and Computational Fluid Dynamic (CFD) analyses were carried out to evaluate the hydraulic characteristics of the IPS. Comparing the experimental results with the predicted results by CFD simulation implies that the CFD software can play a useful role in studying the hydraulic performance of the IPS by employing residence time distribution (RTD) curves. The results also show that the use of a nozzle distributor can significantly enhance the hydraulic performance of the IPS, which contributes to the improvement of its separation efficiency.