倾斜角对液体燃料润湿条件下砂床表面火蔓延的影响

利用纹影系统、CCD相机以及K型热电偶对正丁醇润湿条件下不同角度的砂床表面火蔓延特性进行了研究,分析了不同砂床表面倾角对火蔓延的影响机理。研究结果表明:正丁醇润湿条件下变角度砂床表面火焰是稳定匀速蔓延的,向上蔓延时,火焰的高度、黄色发光区以及蔓延速度随着倾角的增加而增大;向下蔓延时,火焰的高度、黄色发光区以及蔓延速度随着倾角的增加而减小;蔓延火焰前方存在预热区,且预热区随表面倾角的增大而增大:砂层内部存在热边界层,且砂床热边界层厚度随表面倾角的增加而减小。得到的火蔓延特性及燃烧机理为此类液体燃料的储存、使用以及环境保护提供了一定的科学依据。     

Experimental study on flame spread along fuel cylinders in high pressures

Flame spread over solid fuels in high‐pressure situations, such as nuclear containment shells during a pressurized period, has potential to result in catastrophic disaster, thus requiring further knowledge. This paper experimentally reveals the flame spread behaviors over fuel cylinders in high pressures. Polyethylene and polymethyl‐methacrylate cylinders with the diameter of 4.0 mm are used in this study. Ambient gas is air, and total pressures are varied from naturally normal pressure (100 kPa) to elevated pressure (500 kPa). Flame characteristics including flame appearance and flame size and burning rate and flame spread rate are investigated. Results show that in high pressure, the flame appearance is significantly affected. As the pressure increases, the blue flame disappeared, and the color of flame tip changes from luminous yellow to orange as well the orange part extends down towards the base of flame. The dimensionless flame height increases with pressure for pressure below 150 kPa and then decreases with pressure above that level. The burning rates show increasing trend with pressure and are proportional to P^0.6 and P^0.79 for polymethyl‐methacrylate and polyethylene, respectively. Besides, flame spread rates for polymethyl‐methacrylate and polyethylene both were found to be proportional to P^0.5.     

Experimental study of vertically upward flame spread over polymethyl methacrylate slabs at different altitudes

Experiments of vertically upward flame spread over polymethyl methacrylate slabs were conducted in Hefei (with an altitude of 29.8 m) and Lhasa (with an altitude of 3658.0 m). Measurements were taken for the flame heights, the flame heat flux to the fuel surface and the flame spread rate. Two regions were identified for the dependence of the flame height on the heat release rate per unit width . When is less than 22 kW/m, the flame height scales as while it scales as , when is greater than 22 kW/m. The flame heights in Lhasa are approximately 1.34 and 1.25 times, respectively, of those in Hefei for these two regions. The flame heat flux to the fuel surface decreases significantly from the pyrolysis front to the flame tip, whereas it decreases slowly above the flame tip. In both regions, it can be correlated reasonably well with (x ? x_p)/(x_f ? x_p) using the form of . The flame heat flux to the fuel surface in Lhasa is approximately 0.75 times of that in Hefei. The flame spread process can be divided into three stages, which correspond to a flow region of laminar, transitional, and turbulent, respectively. The transition to a turbulent flow is delayed in Lhasa compared with Hefei. The flame spread rate in Lhasa is about half of that in Hefei because of the lower flame heat flux caused by the lower ambient pressure. Copyright © 2015 John Wiley & Sons, Ltd.     

不同放置角度的建筑装饰材料PMMA的火焰蔓延特性

为揭示建筑装饰材料聚甲基丙烯酸甲酯(有机玻璃,PMMA)在不同放置角度下的火焰蔓延特性,通过自主搭建的小尺寸火焰蔓延实验平台,研究了宽3 cm、厚2 mm的PMMA试样在不同放置角度下的火焰蔓延特性. 结果表明,放置角度对PMMA火焰蔓延过程中热解区域及预热区长度影响很大,由15°到30°及由?60°到?75°时(顺流火焰蔓延时放置角度为正,逆流火焰蔓延时放置角度为负),平均火焰倾角增加幅度最大. 顺流火焰蔓延的火焰长度随放置角度增加先略减小后逐渐增加,逆流火焰蔓延的火焰长度随放置角度的绝对值增加而略减小. 放置角度由0°到15°时,顺流火焰蔓延的平均速度呈跃变增长,逆流火焰蔓延的平均速度随放置角度绝对值增加而略降低.     

Experimental and mathematical analysis of fuel penetration through unconsolidated porous media

Flame spread over porous media due to accidental fuel spillage is a major fire safety concern. The behaviour of flame under such conditions greatly depends on the availability of fuel at combustion zone. A combined experimental and mathematical study was carried out to investigate the rate of fuel penetration through porous beds at different fuel ratios. Propanol at three different fuel ratios of 0.1, 0.125 and 0.15 and sand particles ranging in diameters from 0.5 to 5 mm were employed as liquid fuel and porous bed, respectively. Results showed that fuel penetration rate was a function of permeability of porous bed and mass of the liquid fuel. The permeability of porous bed and consequently the rate of fuel penetration decreased as either the tortuosity or the specific surface area was increased. Fuel penetration measurement and mathematical results indicated that the rate of fuel penetration is directly proportional to the fuel ratio. The fuel penetration rate was found to be higher for larger fuel ratios compared with that for small ratios. The difference between the fuel penetration rate for two consecutive fuel ratios for a given particle size was 25%. The predicted results were in good agreement with those acquired experimentally. Copyright © 2012 John Wiley & Sons, Ltd.     

Experimental study of horizontal flame spread over rigid polyurethane foam on a plateau: effects of sample width and ambient pressure

The effects of sample width and ambient pressure on horizontal flame spread over horizontal rigid polyurethane foams are experimentally studied. A series of comparative experiments are conducted at two places with different altitudes in China. The sample surface temperature, spread rate, and height of flame are measured over a range of sample widths from 4 to 16 cm. Experimental results show that the horizontal flame spread rate decreases as the sample width increases in a negative power law at both two altitudes and the flame spread rate in the Hefei plain (at an altitude of 30 m) is larger than that on the Tibetan plateau (at an altitude of 3658 m) of the same width. The horizontal flame spread mechanism on the rigid polyurethane foam is analyzed qualitatively in comparison with the results of the flame spread rate of expanded polystyrene foams. The relationship between the dimensionless flame height (H_f/W) and the sample width (W) is obtained by using Froude number similarity. It is found based on the experimental data under two different ambient pressures that the average value of the exponent of the ambient pressure in the power law for the horizontal flame spread rate is about 1.9, which is in good agreement with the theoretical value 2.0. Copyright © 2014 John Wiley & Sons, Ltd.     

Experimental study of flame spread over PE-insulated single copper core wire under varying pressure and electric current

In this study, the flame spread over a thin wire with overload current (0-16 A) has been experimentally investigated at both normal pressure (Hefei: altitude 50 m, 100 kPa) and reduced pressure (Lijiang: altitude 2400 m, 76 kPa; Lhasa: altitude 3650 m, 64 kPa). Polyethylene-insulated single-core wires, comprising Cu as the inner core of diameter 0.30, 0.50, and 0.80 mm and insulation thickness 0.15 and 0.30 mm, are used as samples. The experimental results clearly indicate that the height of the flame increases with the electric current and ambient pressure, but the flame width changes only slightly. At identical conditions, the finer the wire, the faster the flame spreads. The flame spread rate increases with the electric current and ambient pressure. A simplified thermal balance analysis concerning the load current is developed to calculate the flame spread rate, and the calculated flame spread rates are shown to be fairly consistent with the experimental values at different electric currents for different wires at both ambient pressures. In addition, the coupled effect of electric current and ambient pressure on the flame spread is discussed. These results may be meaningful for promoting the research process of wire fire safety.     

Flame spread over a liquid surface in a channel of finite section under oncoming air-flow conditions

The propagation of a combustion wave over a shallow hot liquid (n-butanol) blown over by an air flow was studied experimentally. The flame spread was accompanied by pulsations, whose amplitude depended on the oncoming gas velocity. Dependences of the average flame speed on temperature and oncoming gas velocity were obtained. The average speed was found to be independent of the liquid depth ahead of the flame within the experimental error. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 1, pp. 29–34, January–February, 2008.     

Some factors influencing fire spread over room linings and in the ASTM E–84 tunnel test

An examination of the correlative relationship between room fire intensity (temperature) and flammability data for materials, ASTM E–84 flame ratings and energy release rate from calorimertry devices is presented for fire spread on lings. The results of the analysis show the significance of two modes of flame spread—wind-aided and opposed-flow spread. The factors important in these spread modes are considered from approximate solutions developed for turbulent flow. As the importance of energy release rate to flame spread in the tunnel test (E–84) and in upward or wind-aided spread is illustrated. The results suggest a possible reason why the ASTM E–84 and in upward or wind-aided spread is illustrated. The results suggest a possible reason why the ASTM E–84 ratings may not be applicable to the performance of low-density combustible linings in wall fires. In the analyses, flame radiation has not been considered. Also the interpretation of energy release rate data for difference scale and orientation effects has been ignored. These two factors must ultimately be addressed.     

Flame stabilization in a planar microcombustor partially filled with anisotropic porous medium

Heat recirculation through the combustor walls is responsible in sustaining flames in microcombustors. Incorporating porous medium into microcombustors helps further enhance heat recirculation via the solid matrix. However, the problem of anisotropy arises when the pore size is comparable to the characteristic length of microcombustors. To quantitatively address the problem, an experimental study on the flame stability limits of premixed H₂/air in a planar microcombustor partially filled with porous medium is undertaken. Three folding schemes, namely, parallel sheets, streamwise flow passage, and streamwise flow blocking, are employed to realize the anisotropic properties. By varying the width (W) and position (L_out) of the porous medium, the effects of folding schemes on the critical flashback (Ф₂), and breaking‐through (Ф₃) conditions are examined. The experimental results indicate that the disturbance to flow velocity in the transverse direction mainly influences Ф₂, while Ф₃ is greatly affected by the blocking normal to the flow direction. © 2017 American Institute of Chemical Engineers AIChE J, 63: 153–160, 2018     

Effect of shielding rates on upward flame spread over extruded polystyrene foam in vertical channel and heat transfer mechanism

Fire hazard of extruded polystyrene (XPS) thermal insulation materials has aroused public concern. In order to develop flame spread theory and the guideline for fire risk assessment of XPS, an experimental study on upward flame spread behavior and heat transfer mechanism of XPS in a vertical channel with different frontal shielding rates was conducted. Maximum temperature at the place 2 cm from XPS surface and at the center of channel first increase and then decrease as the shielding rate rises. The former is higher than the latter. Experimental value of average flame height rises as the shielding rate increases. A model for predicting the flame height is built, and the predicted results are consistent with the experimental results. Moreover, the relation between flame height and pyrolysis height under different shielding rates is obtained. The flame spread rate rises as the shielding rate increases. A prediction model of flame spread rate is established, and its prediction results are more accurate compared with those from previous models. The model also predicts that radiative heat transfer is the dominant heat transfer mode, accounting for 93% of the total heat transfer. This work is beneficial for fire risk assessment and fire safety design of building façade.     

Experimental investigation into the influence of ignition location on flame spread and heat release rates of polyurethane foam slabs

This study presents the results from a set of 11 large‐scale open fire tests performed on flexible polyurethane foam slabs/mattresses. The purpose of the study was to investigate the influence of the ignition location on the fire behaviour of the foam slabs and to generate data on a highly characterised material that could be used for modelling work in the future. A method for obtaining spatially resolved flame spread data for this type of material was presented using a gridded array of 5 × 10 thermocouples placed on the underside the foam slab and from this, flame spread was examined using three different approaches. The heat release rate (HRR) results showed clear shapes forming that were dependent on the ignition location, with two distinct behaviours being observed between the various different ignition locations, this was also observed in the calculated flame spread rate (FSR) data. Results within an individual test, showed the calculated range of FSRs over the geometry of the slab varied between approximately 1 and 8 mm/s depending on the ignition location. The average FSR values between tests varied between 3 and 7 mm/s and the maximum and minimum values were calculated to be approximately 11 and 2 mm/s respectively.     

The effects of transient heat release rate and crosswind on flame length and tilt angle of flames at different positions in the spread of fire over a diesel pool

The spread of fire over liquid fuel is a common phenomenon, and it has been demonstrated experimentally that the flame length and tilt angle change with the transient heat release rate and different positions of the flame. The coupling relationship between these factors is studied in this paper. The experiments are composed of a rectangular pool with dimensions of 80 cm × 6 cm × 5 cm and crosswind with speeds of 0.8 to 2.4 m/s. Diesel is used as the fuel, and a new method is applied to ensure that the initial temperature of the diesel is constant during ignition. The results show that the traditional method of luminous flame intermittency may not be suitable for studying the geometric characteristics of the spread of fire over a pool, and a new method is proposed. In addition, the transient variation of flame length in different positions of the pool is shown to fluctuate around a mean flame length. The evolution of flame tilt angle along the longitudinal direction of the pool exhibits a U‐shaped curve. Moreover, the multivariate nonlinear relationships of mean flame length and tilt angle among the heat release rate, fire position, and wind speed are established, and relevant coefficients are determined.     

乙二胺不同掺杂模式下多孔有机聚合物对CO2的吸附

利用嫁接法和浸渍法分别在以1,3,5-三苯基苯为单体的有机多孔聚合物（nTPB）上成功掺杂乙二胺,分别研究了乙二胺的不同掺杂模式对多孔聚合物的结构性质以及CO₂吸附性能的影响。结果表明,嫁接法和浸渍法皆可在nTPB上均匀掺杂乙二胺,且nTPB的比表面积和孔容均有所下降。在乙二胺掺杂量相同的前提下,由于浸渍法完全利用nTPB的孔道吸收乙二胺,nTPB的孔道堵塞更明显。两种掺杂乙二胺的模式均可显著提升nTPB对CO₂的吸附选择性,但只有嫁接法对nTPB的CO₂吸附量有明显促进（从4.4 mmol/g升高为5.2 mmol/g;0℃,10⁵ Pa）;浸渍法由于过度堵塞nTPB孔道,且乙二胺的吸附位点被包埋,导致CO₂的吸附量反而下降（仅有3.4 mmol/g;0℃,10⁵ Pa）。此外,嫁接法掺杂乙二胺的nTPB表现出与nTPB基质相同的良好重复利用性。     

高效液相色谱—氢火焰检测器测定柴油烃族组成研究

近年来,全球性城市空气污染问题日益严重,许多国家都在研究或启动控制空气质量的项目,由于石油燃料的使用是导致大气污染的主要原因之一,因此为了使用清洁燃料而对燃料配方进行调整便是采取的一项主要措施。例如在我国主要城市,含铅汽油已被禁止使用。柴油是目前使用...     

Heat Transfer in a Liquid-Solid Circulating Fluidized Bed Reactor with Low Surface Tension Media

Heat transfer characteristics between the immersed heater and the bed content were studied in the riser of a liquid-solid circulating fluidized bed, whose diameter and height were 0.102 m (ID) and 2.5 ...