建筑外墙外保温材料热解及火蔓延特性研究

采用阻燃和非阻燃XPS保温材料,并于10℃/min、15℃/min、20℃/min和30℃/min等4种升温速率,在空气氛围中进行热重实验,研究外墙保温材料的热解特性。研究结果表明:两种X P S材料的热解过程可分为3个阶段,即稳定、快速失重和慢速失重阶段。两种X P S材料的初始热解失重温度、热解最大速率温度以及热解结束温度,都会随着升温速率的增加而增加。

Multilayered Ti-Al intermetallic sheets fabricated by cold rolling and annealing of titanium and aluminum foils

Multilayered Ti-Al based intermetallic sheets were fabricated by sintering alternately layered titanium and aluminum foils.The microstructure and phase formation of the obtained sheets under different sintering conditions were evaluated by various techniques.The results reveal that when the sintering temperature is above the melting point of aluminum,the self-propagating high-temperature synthesis reaction occurs between Ti and Al,and forms various phases of Ti-based solid solutions including α-Ti Ti3Al,TiAl,TiAl2 and α-Ti including TiAl3,etc.When the sintering time increased,Ti-based solid solution,TiAl2 and TiAl3 disappeared gradually,and the sheet containing Ti3Al and TiAl phases in a multilayered structure formed finally.A lot of voids were also observed in the sintered structures,which were caused by the melting Al,Kirkendall effect and the difference of molar volumes between reactants and products.The voids were eliminated and a dense sample was obtained by the following hot press.

FDS analysis of smoke spreading in the tunnel with flue under fire

Based on a new type of tunnel configuration model with flue in the top of it, the paper simulated the smoke pervasion when fire happens in this type of tunnel by FDS. The results show that the setting up of the flue outlet reduces the backing up distance of combustion smoke, and the distance of people fleeing is also shortened. But under this condition the smoke density inside and outside of the two flue outlet increases evidently. However, when the exhausted fans are designed at smoking outlet, the smoke movement is accelerated and almost moved into the upper space. This configuration makes the fire smoke density outside of the flue outlet reduced greatly. When the exhausted velocity increased up to a certain critical level, the smoke concentration outside of the flue outlet will reduce at the value which is no harmonious to people＇s life. This situation will offer a relatively safe space for people fleeing, and fire rescuing can also be carried out from two directions. Therefore, this tunnel configuration mentioned in this article give a new reference mode for personnel flee, fire rescuing and tunnel maintenance.

Evaluation of deriving fire cycle of forested landscape based on time-since-fire distribution

Estimation of fire cycle has been conducted by using the negative exponential function as an approximation of time-since-fire distribution of a landscape assumed to be homogeneous with respect to fire spread processes. The authors imposed predefined fire cycles on a virtual landscape of 100 cell×100 cell, and obtained a mosaic composing of patches with different stand ages （i.e. time since fire）. Graphical and statistical methods （Van Wagner 1978; Reed et al. 1998） were employed to derive fire cycle from the virtual landscape. By comparing the predefined and the derived fire cycles, the two methods and tested the effects of sample size and hazard of burning （i.e., stand＇s susceptibility to fire in relation to its stand age） were evaluated on fire cycle deviation. The simulation results indicated a minimum sample size of l0 times of the annual burnt area would be required for.partitioning time-since-fire distribution into homogeneous epochs indicating temporal change in fire cycle. Statistically, there was significant difference among the imposed and the derived fire cycle, regardless of sample sizes with or without consideration of hazard of burning. Both methods underestimated the more recent fire cycle without significant difference between them. The results imply that deviation of fire cycle based on time-since-fire distribution warrants cautious interpretation, especially when a landscape is spatially partitioned into small units and temporal changes in fire cycle are involved.

Surface Fires： No Wind, No Slope, Marginal Burning

The first aim of this work is to provide an analytical expression to calculate the rate of spread of surface fires under no wind and no slope conditions. A previous simplified model was improved for this particular case of fire propagation. The test of this proposed model was performed by using two complete sets of experimental results with several fuel beds and variable parameters such as moisture content or bulk density. The second aim of this article is to highlight two conditions that allow stopping a fire： the low leaf area and the high value of the moisture content.

STUDY ON THE COMBUSTION CHARACTERISTICS OF MINE FIRES

Based on the distribution state of the combustibles and the scale of the fires in underground mines, mine fire sources are divided into two types in this paper,namely, fixed point fire source and movable linear fire source. By analying a lot of ex periment results of mine fires, the authors studied the combustion characteristics of the two types of fire source, and have set up their mathematical models. The models have further been applied to calculate the concrete mine instances and the obtained re sults corresponded with the reality.

THE COMBUSTION CHARACTERISTICS OF A MOVABLE LINEAR FIRE SEAT IN MINE FIRES

Because of the difficulties of describing the process of combustion of underground mine fires, usually the fire seat is considered as a fixed point in the methods of mine fire computer simulation, however this is not in keeping with the feature of the distribution of the combustibles and the process of combustion in mine fires. A conception about movable linear fire seat is put forward first by the authors, together with the calculated models of the thermal decomposition rate, flame spreading velocity and the steady burning length of a linear fire seat etc. The paper also introduces the results of the application of these models.

Evaluation on Combustion Characteristics of Finishing Materials for Exterior Walls

Existing fire test methods reply on measurement of the energy released rate to identify the combustion properties of a material. However, they are inadequate when assessing combustion characteristics of a composite material characterized by vertical flame spread and different inside/outside combustion behaviors. In addition, major factors that affect the flame spread outside the building include the combustion characteristics of materials used as well as air flow around a skyscraper. However, since it is highly difficult to analyze and forecast the air flow from a fire engineering viewpoint, an investigation of the flame spread characteristics of exterior walls of a building depends primarily on the combustion characteristics of materials. Hence, this study examined, using ISO 13785-2 testing method, the temperature changes and vertical flame spread behaviors of one of the finishing materials for exterior walls--（generic ＆ fire-resistant） aluminium panels by a real-scale combustion experiment. According to the results of real-scale experiment, the maximum heat temperature of 987.7 ℃ was recorded seven minutes after the fire test was initiated while the fire-resistant aluminium panels showed the maximum heat temperature of 850.2℃ after exposed for approximately 12 min. The vertical flame spread properties put more emphasis on the time required to reach the maximum temperature rather than its magnitude and there was a five minutes difference between the materials.

Flame Spread over Aviation Kerosene with an Obstacle in Liquid Phase

The phenomena of flame spread over aviation kerosene with an obstacle in liquid phase are investigated experimentally through surface temperature measurement by using infrared camera,schlieren images of subsurface flow in front of and behind obstacle and residence time of flame obtained from video recording.Experimental results reveal that obstacle has no effect on gas phase controlled flame spread.But for liquid phase controlled flame spread,flame can be stopped by an obstacle with its top edge flush with oil surface,and the residence time decreases with the increase of initial temperature of fuel.That conduction and radiation only play a subsidiary role in flame spread over liquid fuel was proved by schlieren images and surface temperature profiles.