用于火灾探测的离子感烟探测器的设计研究

本文论述了自动火灾离子感烟探测器的结构组成及其电路工作原理。通过对探测器电路的具体分析，进一步阐明自动火灾离子感烟探测器的相关功能。     

Analyzing fire-induced dispersion and detector response in complex enclosures using salt-water modeling

The current investigation examines suitability of the hydraulic analog for analysis of fire-induced dispersion within a complex enclosure. This analog has been implemented using salt-water modeling and planar laser induced fluorescence (PLIF) diagnostics providing quantitative visualization of simulated fire-induced flows. The non-intrusive PLIF diagnostics are used to temporally and spatially characterize dispersion from a buoyant source within a 1/7th scale room–corridor–room enclosure. This configuration is geometrically similar to a full-scale fire test facility, where local fire conditions were characterized near five ionization type smoke detectors placed throughout the enclosure. The full-scale fire and salt-water model results were scaled according to the dimensionless fundamental equations that govern source dispersion.An evaluation of the local conditions and dispersive event times for both the systems was used to explore the ability of the hydraulic analog to predict smoke detector response times. The dispersive event (front arrival) times predicted by the salt-water model, which represents a necessary event for detector activation, were in excellent agreement with the fire test data. A methodology using these front arrival times along with local conditions at the detector location is introduced in this paper. However, the complex nature of detector response and fidelity limitations of the analog make precise predictions of detector response time challenging. The predicted dimensionless response times were within 25% for all detector locations, with the exception of the first-room ceiling detector location. For this latter, a shorter dimensionless response time by less than 40% of that in the actual fire was predicted.     

Predicting the properties of petroleum blends

The aim of this study was to find new correlations to predict the properties of petroleum fractions blends. Several correlations for viscosity, smoke point, freezing point, Reid vapor pressure, aniline point, and cloud point were developed. These new correlations were assessed for their ability to predict the properties by comparing the estimated values with the experimental data as well as other correlations in literature. The developed correlations gave an absolute average deviation of 2.6 mm²/s for viscosity, 0.015 mm for smoke point, 0.05 K for freezing point, 6.47 kPa for RVP, 0.32 K for aniline point, and 0.9 K for cloud point.     

Experimental determination of the discharge flow coefficient at a doorway for fire induced flow in natural and mixed convection

The study is an experimental investigation of the discharge flow coefficient at a doorway‐type opening in the case of a fire in an enclosure open to atmosphere. Natural and mixed convection flows are considered with the use of mechanical ventilation. The discharge coefficient is defined as the ratio between the effective flow rate determined experimentally and a theoretical flow rate based on a Bernoulli approach. The effective mass flow rate is obtained from velocity field measured with stereoscopic particle image velocimetry technique. The theoretical flow rate is calculated from vertical temperature profiles measured from both sides of the doorway. Only inflow rate is considered for the calculation of the discharge coefficient. In natural convection mode, a C_D value of 0.54 ± 0.5 is obtained on a reduced‐scale opening (to be compared with 0.68 at large scale). In a mixed convection case, the discharge coefficient is much lower and reaches 0.26 ± 0.06. This study shows that the discharge coefficient C_D may vary significantly regarding the dimension of the opening and the flow conditions (natural and mixed convection). It illustrates the limits of considering a constant discharge coefficient when dealing with doorway flows in a confined and mechanically ventilated compartment. Copyright © 2014 John Wiley & Sons, Ltd.     

电影院空调通风排烟系统设计探讨

电影院设计不但要使立面效果美观大方,各种影音设施齐备完善,而且应为观众提供一个舒适、安全的观赏环境。论文以一具体工程为例,分析了影院建筑的特点,具体阐述了放映厅和放映机房空调和通风系统的确定,以及影厅消防排烟设计上的特点与要点。为读者提供了一种电影院空调通风及排烟系统设计的思路,并指出了设计时区别于其他类型建筑设计的关键点。     

Exposure to environmental tobacco smoke during pregnancy and infancy increased the risk of upper respiratory tract infections in infants: A birth cohort study in Wuhan,China

We aimed to evaluate the association of the exposure to environmental tobacco smoke (ETS) during pregnancy and infancy with the risk of upper respiratory tract infections (URTI) in infants based on a Chinese birth cohort study. Among 4178 infants who constituted the final study population, 46.8% experienced URTI in their first year of life. The hazard ratios (HR) and 95% confidence intervals (CI) for the risk of URTI were assessed using Cox regression models. Compared with no ETS during pregnancy, continued ETS during pregnancy was independently associated with a higher risk of URTI (HR: 1.36, 95% CI: 1.13, 1.63) after adjustment for potential confounders and also associated with earlier occurrence of URTI (log-rank P = .002). The association remained consistent across the strata defined according to maternal age, number of siblings, sex, and breastfeeding. Exposure to ETS during infancy was associated with URTI only among infants who were breastfed for less than 12 months (P for interaction < 0.05).Furthermore, infants exposed to ETS during both pregnancy and infancy showed the highest HR of 1.46 (95% CI: 1.16, 1.85) for URTI. Efforts should be made to protect pregnant women and infants from the adverse effects of indoor and outdoor ETS.     

Experimental study on the effect of lateral concentrated smoke extraction on smoke stratification in the longitudinal ventilated tunnel

Smoke is the main cause of death in tunnel fires. It is one of the important measures to maintain smoke stratification in the early stage of tunnel fire. This article focused on experimentally studying the combined effect of lateral concentrated smoke extraction and longitudinal ventilation on the smoke stratification, which never be revealed before. The velocity of the smoke layer and air layer, vertical temperature distribution, and the flow patterns of the smoke were measured. It was found that the longitudinal ventilation and lateral concentrated smoke extraction would affect the flow of the smoke and change the shear velocity between the smoke layer and air layer, then, the patterns of the smoke layer will be affected. And the flow patterns with Froude (Fr) number can be classified into three categories: (a)Fr < 0.6 , with stable smoke stratification; (b) 0.6 < Fr < 0.85 , with a stable smoke stratification but the blurring interface; and (c) Fr > 0.85 , the smoke layer is completely unstable. The result can provide a reference for ventilation design of immersed tube tunnels.     

民用建筑走道设置排烟设施限定条件的探讨

基于工程实践,对相关规范和设计手册中涉及的民用建筑走道设置排烟设施的限定条件的内容进行了对比,详细分析了各个文献中表述的涵义及优缺点,并在此基础上给出了作者的阐述。     

Experiments of evacuation speed in smoke-filled tunnel

Among tunnel fire safety strategies, evacuation speed in smoke, which is the basic evacuation performance characteristic, is one of the most important factors when assessing safety. An evacuation experiment in a full-scale tunnel filled with smoke has been done in order to clarify the relation between extinction coefficient up to Cs = 1.0 m⁻¹, which includes Cs = 0.4 m⁻¹ as a Japanese road tunnel fire prevention standard, and evacuation speed. The maximum, minimum and mean values of normal walking speeds are almost constant regardless of the extinction coefficient. As for the emergency evacuation speeds, the maximum speed is largely influenced by extinction coefficient, decreasing rapidly from 3.55 m/s at Cs = 0.30 m⁻¹ to 2.53 m/s at Cs = 0.75 m⁻¹ while the minimum and mean speeds are almost constant with a slight decrease as Cs increases. The maximum evacuation speed trends in the present experiments and those in Frantzich and Nillson (2003, 2004) and Fridolf et al. (2013), lie on the same decreasing logarithmic curve as a function of extinction coefficient.     

Experimental study on the time‐dependent smoke densities at 39 locations in a multi‐floor building through a digital smoke detector system

The objective of this study was to quantitatively investigate some characteristics of the smoke transportation in multi‐floor buildings. Eight experiments were conducted for worst scenario. The effects of an open window in the burning room on the smoke transportation are also analyzed. The time‐dependent smoke densities at 39 locations in a half‐scale building with an atrium were measured through a digital smoke detector system. The results indicate that the chimney effect plays an important role in the smoke transportation in multi‐floor buildings with atriums. For the effects of the open window, the results suggest that the smoke densities at most locations in the building increase earlier when a window is open but have a smaller peak value than those results in the cases without any outer vents. It is suggested that a building without vertical atrium would be safer than those with long ones. More attention should be paid to those spaces when the fire protection systems are designed for buildings with atriums. The data of the time‐dependent smoke densities at tens of locations in the building are useful for the validation of smoke transportation models. Copyright © 2013 John Wiley & Sons, Ltd.