共查询到19条相似文献,搜索用时 140 毫秒
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为研究不同升温速率下油漆稀料与PET塑料共热解特性的变化规律,使用同步热分析仪,测定不同升温速率(10、20、30 K/min)条件下油漆稀料和PET塑料共热解过程中失重(TG)、焓变(DSC)的变化,并采用Coats-Redfern法对样品进行热动力学分析,探究油漆稀料和PET塑料两种材料的共热解行为受升温速率的影响。结果表明:在氮气气氛中,样品的热解过程存在明显的滞后现象;油漆稀料和PET塑料热解过程只存在1个主要失重阶段,混合物存在2个主要失重阶段;油漆稀料和PET塑料的热解活化能随着升温速率的提高而减小,混合物在升温速率低于30 K/min时热解反应受到抑制,在30 K/min升温速率下活化能最低,热解反应最彻底,最终样品残余量为8.4%,火灾危险性强。 相似文献
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为研究废旧竹制地板的热解特性,采用热重分析法对废旧竹制地板颗粒进行热解实验,并利用控制变量法,得到地板颗粒在不同粒径、升温速率和气氛下的热解参数及热重曲线,使用Coats- Redfern 积分法进行热动力学分析,并选择最佳机理函数。结果表明,废旧竹制地板的热解分为4 个阶段,各阶段温度区间分别约为20~100、100~200、200~384、384~800 ℃。通过对热解条件的研究,粒径大小可对热解主要质量损失阶段造成影响,会使该阶段的发生延后,升温速率对热解的影响主要体现在第三阶段,升温速率越大,反应越剧烈,空气对热解有促进作用,可使反应更加充分,质量损失更大。 相似文献
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摘 要:为探究不同升温速率下5种典型乔木可燃物的热解特性,加快和完善内蒙古大兴安岭地区森林燃烧性研究,以白桦、黑桦、兴安落叶松、蒙古栎、山杨的小枝为主要研究对象,基于OFW热重分析法,在空气气氛中,以氧气为载气,加热区间为30~600 ℃,首先升温至100 ℃并保持5 min,气体流量为20 mL/min,然后分别以40,60,80 ℃/min升温速度率升温。通过TG-DTG曲线分析试样的热解过程,利用OFW法对试样的快速热解阶段进行动力学分析并绘制参数趋势图。结果表明,升温速率对热解过程的影响主要集中在失重阶段,随着升温速率的增加,热解特征温度增加,试样失重率增大。在此阶段,升温速率为60 ℃/min时,5种典型乔木可燃物热解程度排序为:兴安落叶松>蒙古栎>山杨>白桦>黑桦;OFW法分析下的5种典型乔木可燃物活化能随转化率变化,活化能计算结果可靠,模型较优。山杨活化能区间为659.788~712.664 kJ/mol,调整后的R2为0.962 6~0.999 7,活化能随转化率的增加呈现先减少后增加的趋势,反应进程中后段依然保持良好的放热反应。 相似文献
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利用热重—差热同步分析仪研究随机、单向、织布 3种铺层结构碳纤维/环氧复合材料在不同升温速率下的热解特性。氮气气氛(50 mL/min),升温速率取 5、10、20、30、40 ℃/min,实验温度范围为 25~800 ℃。研究表明:3 种铺层结构碳纤维/环氧复合材料均只有 1 个热解阶段,热解温度范围及到达失重速率峰值温度几乎相同,但铺层结构对热失重速率峰值及质量剩余率有较大影响。随着升温速率的增加,热解反应各阶段终止温度、最大失重速率温度均向高温方向移动。采用 Kissnger 法对不同铺层结构碳纤维/环氧复合材料的热解动力学进行计算,得到其表观活化能。 相似文献
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《消防科学与技术》2017,(2)
利用热重—差热同步分析仪研究典型高强玻璃纤维/环氧树脂复合材料在不同升温速率、不同载气气氛影响下的热解特性规律。升温速率取5、10、20、30、40℃/min;气氛取空气及氮气气氛(50 mL/min);实验温度范围为25~800℃。研究表明,随着升温速率的增大,热解反应各阶段起始温度、终止温度、最大失重速率温度均向高温方向移动。空气气氛下,玻纤复合材料热解分为两个阶段,分别是环氧树脂基材热解的两个阶段,玻璃纤维自身不分解;氮气气氛下,玻纤复合材料热解反应一步完成。相同升温速率下,玻纤复合材料与环氧树脂基材的热解初始分解温度、热解温度范围基本一致,玻纤复合材料的热解终止温度及热解各阶段失重速率明显小于环氧树脂基材。运用Kissinger法和Flynn-Wall-Ozawa法进行热解动力学分析,得到玻纤复合材料热解各阶段的表观活化能,两种计算方法所得结果基本一致。热解第二阶段表观活化能明显高于第一阶段,其热稳定性在热解过程中逐渐增强。 相似文献
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以内蒙古自治区阿尔山市内沟塘草甸为研究区域,选取典型草本羊草为研究对象,运用热重分析法以通氧速率10、20、30 mL/min,在升温速率分别为40、80 ℃/min的条件下进行热失重行为研究。使用TG-DTG曲线分析样品的热解过程,利用Coats-Redfern(CR)积分法和Flynn-Wall-Ozawa(FWO)积分法对样品的快速热解阶段进行动力学分析,得出在不同氧气浓度下样品的热解活化能和指前因子并求得相应参数。结果表明羊草热解过程分为:失水阶段、快速热解阶段、炭化阶段。其中快速热解阶段为350~450 ℃,此阶段中升温速率越快,温度滞后现象越明显;通氧速率越快,温度超前现象越明显。热解过程及动力学参数分析表明,Flynn-Wall-Ozawa法更适用于羊草热解过程,引发火灾危险程度的通氧速率为:30 mL/min>20 mL/min>10 mL/min。 相似文献
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A computational model of flashover is presented that closely follows the experimental setup at CNRS-ENSMA-Poitiers. A propane burner with thermal power of 55 kW is used as a primary source of fire and square beech wood samples (30 mm×30 mm×5 mm) as fire spread targets. The computational model describes the wood pyrolysis with a progress variable. Using the conservation of heat fluxes at the solid–gas interface, the thermal diffusion in the wood samples is coupled with the convective and the radiative heat transfer in the ambient gas phase. The incoming heat flux at the upper surface of the wood samples reaches values between 20 and 30 kW/m2. With the ignition and subsequent combustion of the pyrolysis volatiles, the heat flux increases by approx. 12 kW/m2. The results show that the ignition of the wood samples is triggered at an approx. surface temperature of 650 K. Due to large local variations in incident heat flux, significant differences in the ignition times of the wood samples are observed. The comparison of the calculated and the experimentally measured temperature shows a good agreement for the first wood sample and the model predicts the ignition time very well. But for the second and the third wood samples the model overpredicts the temperature, which leads to a premature ignition of these wood samples. 相似文献
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Experiments on the thermal decomposition of wet wood in air were carried out in this work. The samples (typically 100×100 mm exposed surface, 15 mm thick) of several species with moisture content from 5% to 30% were subjected to a uniform heat flux 20–70 kW m−2. A one-dimensional pyrolysis model is proposed to examine the influence of heat flux, species and moisture content on the process of thermal decomposition of wet wood. Temperature profiles at different points and solid conversion are calculated and compared with experimental data. There is good agreement between the experimental and calculated results. 相似文献
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Pyrolysis experiments were conducted on medium density fibreboard (MDF) in inert atmosphere and different ambient pressures, to investigate the char shrinkage and cracking. It is found that the char cracking under uniform heat flux is a typical thermal shock process induced by unbalance shrinkage along the sample thickness during pyrolysis. To predict the number of char fissures, the critical stress criterion and energy conservation theory are used to develop mathematical models under plane constitutive stress state, which reveal that under the same surface degradation the number of char fissures (blisters) strongly relates to the pyrolysis depth at cracking time. Increasing external heat flux decreases the pyrolysis depth and increases the number of char fissures. Both experiments and numerical modelling are used to validate the models. The experimental results show that the horizontal shrinkage is 11% of original length and the micro-structure of char fissures of MDF is less uniform compared to the one of natural wood with a cellular pattern. The surface stresses after cracking are found similarly close to the tensile strength under different heat fluxes, while the surface stresses are very different assuming no crack, which indicates the cracking process reduces the surface stress to lower than the tensile strength. The modelled cracking times are different from the observed cracking time as the fissures are hard to identify at its initial stage and only when they have expanded to certain size the fissures are visually observed. Using the modelled cracking time, the number of char blisters can be well correlated with the pyrolysis depth. 相似文献
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为探讨自然劣化对文物建筑木质构件热性能的影响,采用傅立叶变换红外光谱(FTIR)与差式扫描量热分析法(DSC)对4种文物建筑木质构件样品与云南松现代材样品进行官能基团和热稳定性能测定,讨论了自然劣化对其的影响。结果显示,较软木松而言,硬木松即使在自然劣化后仍然有着较好的耐燃性能。同时,木质构件在自然劣化过程中主要发生了木质素与半纤维素的分解。清代劣化材由于木质素含量减少,干燥阶段与固相燃烧阶段所需温度都有大幅度提前,更易热解。另外,虫害情况越严重,老化材纤维素含量越少,放热量随之降低,同时木构件化学结构越不稳定,劣化材干燥阶段所需温度随之降低,热解反应越剧烈。 相似文献
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The modelling of the pyrolysis of wet wood provides more realistic fire scenarios for structural fire design by taking into account variable thermal properties of wood which are beyond the scope of conventional structural fire design codes. The proposed numerical methodology has been written in MATLAB environment. A 2D nonlinear finite element analysis (FEA) is performed to model the pyrolysis of wet wood subjected to high temperature. The varying of thermal proprieties of wood are discussed from the point of view of changes of structure and chemical composition under fire condition. The validity of the model is established by comparing the predicted results with results from fire resistance tests presented in literature. Qualitatively, the model provides good agreement with the experimental data. It is shown that the model can handle layers of a wooden composite structure. Temperature profiles at different points in the wood sample and the two-dimensional charring depth of Laminated Veneer Lumber (LVL) panels are calculated and compared with experimental data. 相似文献