共查询到17条相似文献,搜索用时 734 毫秒
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着火时间是可燃物热解着火过程的重要特征参数.辐射热流直接影响可燃物的着火时间,为了简化解析求解,前人往往认为辐射热流为恒定常数且不进入样件内部,但火灾发生早期,透明可燃物接收到的辐射热流可能是随着时间上升的变化热流.针对此问题,本文以适用于变化辐射热流的透明可燃物热解数值和解析模型为基础,系统研究了辐射热流上升速度、表面吸收、内部吸收等因素对着火时间的影响,比较了两种模型的结果差异并探讨了环境与物性参数对解析模型准确性的影响.结果表明:在上升热流早期,解析法与数值法求解结果符合较好,随着热流与表面温度增加,表面对流换热、辐射、热解等因素开始作用,导致解析与数值结果出现偏差,需根据此偏差修正给定可燃物着火时间解析预测结果. 相似文献
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在热重分析仪上进行了空气气氛、不同升温速率下几种木材的热解动力学过程的研究.对不同升温速率以及木材种类对失重过程的DTG曲线的影响进行了深入分析,在热重实验的基础上建立了"双组分两阶段反应"模型来描述空气气氛下木材的热解动力学过程,并利用C-R方法求得了对应失重阶段的动力学参数.在火灾早期特性实验台上进行了4种木材在空气气氛、不同辐射热流下的热解与燃烧过程的特性研究,通过对高、低热流下几种木材表面温度变化、失重率以及着火时间等参数的对比,发现在较高热流下,固定碳含量相似的几种木材的反应机理及其表观热行为趋于一致. 相似文献
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通过对木材热解与燃烧过程中几何结构变化共性的分析,建立相应的几何物理模型,提出了试样的两个几何结构特性参数(体积收缩系数与开裂系数).选择了3种木材(杉木、桦木与实木地板)试样(尺寸为100,mm×100,mm×15,mm),分别在15,k W/m2、30,k W/m2与50,k W/m2的热流下进行了热解与燃烧过程的试验.定量分析了过程中木材几何结构变化的特性,讨论了热流与试样种类对上述两个特性参数的影响,最后研究了几何结构变化对木材热解与燃烧特性的影响. 相似文献
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实验研究了外加线性变化热流条件下木材点燃时间与热流变化率之间的关系,测量了不同种类木材在不同热流变化率下的点燃时间。通过分析实验数据发现,点燃时间和热流变化率之间符合很好的幂函数关系,而密度是影响木材着火的一个关键因素。 相似文献
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利用非等温热重分析法对两种烟煤的热解特性及富氧下的燃烧特性进行研究.实验结果表明,煤粉中低温下的热解行为对其富氧气氛下的着火机理有明显影响.挥发分初析温度低、热解特性指数D大的煤,随着氧体积分数的增加,着火方式逐渐由非均相转变为均相.而挥发分初析温度高、D较小的煤,着火方式则无明显变化.热解活性高的煤,在着火机理转变后,着火温度显著降低,但燃尽温度基本不受影响.氧体积分数提高后两种煤粉的燃烧特性指数S都有所增大,但相同氧体积分数下不同煤种之间的S相差不多,说明着火机理的改变对S无明显影响. 相似文献
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The ignition of single wooden spheres heated in a hot air stream has been investigated experimentally. Three species of wood were used. The single wooden spheres were oven-dried and exposed to various temperatures and streams of air with different flow rates. The orientation of the grains in the wood was kept either perpendicular or parallel to the air stream. The temperature inside a wooden sphere was monitored by embedded thermocouples. The orientation of grains in the hot air stream had a notable influence on the ignition time, particularly with air at 673 and 773 K. At 873 K neither the flow rate of air nor the orientation of the grain had any effect on the ignition time. Glowing reaction was observed prior to ignition for wooden spheres heated to 773 K, but flaming ignition was found for air at 873 K. A correlation for estimating the ignition times was proposed. A simple one-dimensional model for the pyrolysis of wood, taking account of the heat of pyrolysis and the evaporation of moisture, is capable of predicting the mass loss quite well, but is less satisfactory for predicting the temperature in the period prior to flaming ignition. 相似文献
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《International Journal of Heat and Mass Transfer》2007,50(21-22):4371-4386
A three-dimensional mathematical model for the pyrolysis of wet wood is developed with detailed consideration of moisture evaporation, anisotropic and variable properties, and pressure driven internal convection of gases. Multiple competing reactions are formulated; a single first-order Arrhenius reaction is however applied herein. Transient pyrolysis of a beech wood cube with different initial moisture contents is investigated under various furnace temperatures. Influences of anisotropic properties due to the grain structure on heat and mass transfers are discussed. This model serves as a precursor for Part II: Simulation of piloted ignition of wood in a cone calorimeter of this two-part study. 相似文献
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微波热解生物质废弃物的研究 总被引:2,自引:0,他引:2
利用微波热裂解生物质废弃物,使其转化为可直接利用的能源,是一种非常重要的处理工艺。运用自行研发的单模谐振腔微波设备对生物质废弃物进行热解反应试验,考察了微波功率、反应时间、含水率和物料粒径对木屑热解的影响,得到较优的反应工艺条件:微波功率为2.0 kW,反应时间为8 min,含水量为20%,物料粒径为0.5~0.8 mm。分析研究了固、液、气3种热解产物:固体产物(炭)的性质得到了改善;生物油主要是芳香烃类化合物和呋喃类化合物的复杂混合物;热解气体产物主要为CO,CO2,甲烷等,热值相对较高。 相似文献
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Experimental measurements have tested the effect of an external heat flux on the pyrolysis and combustion of charring materials using a cone calorimeter and a radiation platform, particularly with a small heat flux. Differences in the pyrolysis and burning of wood under strong and weak heat fluxes are discussed. Also, a modified model of pyrolysis for charring materials in a fire is proposed. In this model some special factors that affect pyrolysis, such as heat loss by convection and radiation caused by the surface temperature rising and also shrinkage of the char’s external surface, are considered. The pyrolysis of wood and the time to ignition is predicted using the model, which is also used to explain the mechanism of the pyrolysis of wood exposed to weak external fluxes for long times. 相似文献
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《Combustion and Flame》2001,124(1-2):165-177
Thick wood cylinders have been pyrolyzed with applied radiation intensities in the range 28–80 kW/m2, to investigate the role of wood variety on the degradation characteristics (temperature and weight loss dynamics), product (char, gas, and liquid) yields, and gas composition. Two hardwoods (beech, chestnut) and three softwoods (Douglas fir, redwood, and pine) have been examined. Apart from the higher minimum heat flux needed for softwood pyrolysis, all the varieties present the same qualitative behavior, and the process dynamics tend to become the same for applied heat fluxes above 40 kW/m2, when internal heat transfer is the controlling mechanism. However, quantitative differences remain large in terms of pyrolysis temperature (maximum values of 600–650 K), product yields (minimum char yields of 21–33%, maximum liquid yields of 47–57%), and average devolatilization rate, as a consequence of variations in the chemical composition. 相似文献