Numerical Analysis of Steady Smoldering of Biomass Rods

Understanding the steady mechanism of biomass smoldering plays a great role in the utilization of smoldering technology.In this study numerical analysis of steady smoldering of biomass rods was performed.A two-dimensional(2D)steady model taking into account both char oxidation and pyrolysis was developed on the basis of a calculated propagation velocity according to empirical correlation.The model was validated against the smoldering experiment of biomass rods under natural conditions,and the maximum error was smaller than 31%.Parameter sensitivity analysis found that propagation velocity decreases significantly while oxidation area and pyrolysis zone increase significantly with the increasing diameter of rod fuel.

Smoldering charcoal detection in forest soil by multiple CO sensors

Cleaning up residual fires is an important part of forest fire management to avoid the loss of forest resources caused by the recurrence of a residual fire.Existing residual fire detection equipment is mainly infrared temperature detection and smoke identification.Due to the isolation of ground,temperature and smoke characteristics of medium and large smoldering charcoal in some forest soils are not obvious,making it difficult to identify by detection equipment.CO gas is an important detection index for indoor smoldering fire detection,and an important identification feature of hidden smoldering ground fires.However,there is no research on locating smoldering fires through CO detection.We studied the diffusion law of CO gas directly above covered smoldering charcoal as a criterion to design a detection device equipped with multiple CO sensors.According to the motion decomposition search algorithm,the detection device realizes the function of automatically searching for smoldering charcoal.Experimental data shows that the average CO concentration over the covered smoldering charcoal decreases exponentially with increasing height.The size of the search step is related to the reliability of the search algorithm.The detection success corresponding to the small step length is high but the search time is lengthy which can lead to search failure.The introduction of step and rotation factors in search algorithm improves the search efficiency.This study reveals that the average ground CO concentration directly above smoldering charcoal in forests changes with height.Based on this law,a CO gas sensor detection device for hidden smoldering fires has been designed,which enriches the technique of residual fire detection.

Numerical study of forward smoldering combustionof polyurethane foam

A two-dimensional and two-phase numerical model is presented for the smolder propagation in a horizontal polyurethane foam. The chemical processes considered include endothermic pyrolysis and exotherrnic oxidation degradation of polyurethane foam and exothermic oxidation of char. The governing equations are discretized in space using the finite element method and solved by the software package FEMLAB. Predicted profiles of solid temperature as well as evolutions of solid compositions （including foam, char and ash） are presented at an airflow velocity of 0. 28 cm/s. The computed average smoldering velocity is 0. 021 4 cm/s, and the average maximum temperature is 644. 67 K. Based on the evolutions of solid compositions, the packed bed can be obviously divided into four zones： unreacted zone, fuel pyrolysis and oxidation zone, char oxidation zone and fuel burned-out zone. Simultaneously, the effects of inlet air velocity and fuel properties （including thermal conductivity, specific heat, density and pore diameter） are studied on the smoldering propagation. The results show that the smoldering velocity and temperature have a roughly linear increase with increasing inlet air velocity; the fuel density is the most important factor in determining smoldering propagation; radiation has a non-negligible role on the smoldering velocity for larger pore diameters of porous material. The computational results are compared with the experimental data and a general agreement is reached.

Numerical study on the propagation characteristics of forward smoldering in a cellulosic packed bed

Based on a three-step kinetic mechanism, a one-dimensional, time dependent, numerical model is presented for the smoldering propagation in a horizontally packed bed of cellulosic material. The kinetic processes include pyrolysis and oxidation degradation of fuel and oxidation of char. Heat transfer between solid and gas is taken into account, and the diffusion coefficient varies with the temperature. Radiative heat transfer is included by using the diffusion approximation. The effects of airflow velocity and oxygen concentration are simulated on the smoldering velocity and the averaged maximum temperature of smoldering fuel. The results indicate that the spread rate varies linearly with increasing airflow velocity, and the inlet air velocity has little effect on the maximum temperature. The evolutions of gas species and solid compositions are predicted. The effects of frequency factors （A1, A2 and A3） are analyzed. Simulations show that the smoldering spread rate increases with increasing A2 （fuel oxidation）, but decreases with A1 （fuel pyrolysis） and A3 （char oxidation）.

Structure and stability of non-adiabatic reverse smolder waves

The structure and stability of non-adiabatic reverse smolder waves are investigated numerically. First, the 1D steady-state responses of reverse smolder waves in the presence of convective heat losses are studied with the rate of incoming air flow as the control parameter. Based on the 1D steady solutions, the linear stability and the Lewis number effects on the stability are examined by a numerical normal mode analysis. Finally, the dynamical evolution processes of unstable reverse smolder waves are studied by direct numerical simulations. It is shown that, in comparison with the adiabatic case, the presence of heat losses leads to a backward shift of the extinction limit. For varying Lewis numbers, the extinction limit shifts forward with the increase of the Lewis number while the smolder temperature remains unchanged. Furthermore, results of a linear stability analysis show that the maximum growth rate decreases with the increasing Lewis number, implying that increasing the Lewis number tends to weaken the thermal-diffusive instability of non-adiabatic reverse smolder waves. Direct numerical simulation results show that, on the fuel-rich branch, the unstable plane reverse smolder wave gradually develops to a regular steady fingering pattern, whereas on the fuel-lean branch, similar to the adiabatic case, vigorous fragmentation instability occurs, and is accompanied by a substantial local temperature rise, which may be sufficiently high to trigger the transition to flaming combustion.

Characterizing and predicting smoldering temperature variations based on non-linear mixed effects models

Underground fires are slow spreading,long-lasting and low temperature smoldering combustion without flames,mainly occurring in peatlands and wetlands with rich organic matter.The spread of the smoldering is maintained by heat released during combustion and monitoring this is an important approach to detect underground fires.The Daxing'an Mountains region is a hotspot for underground fires in northeast China.This study examined a L arix gmelinii plantation in the Tatou wetlands of the Daxing'an Mountains and determined the maximum temperature variation of humus of varying particle sizes,and the temperature rising process based on non-linear mixed effects models by an indoor combustion experiment.Maximum combustion temperatures up to 897.5°C,increased with humus depth;among the three models tested,Richard's equations were best for characterizing temperature variations;a non-linear equation with three parameters had the highest accuracy in fitting the combustion temperature variations with varying humus particle sizes.These results are informative for predicting temperature variations and provide technical support for underground fire monitoring.

Gastrointestinal amyloidosis in a patient with smoldering multiple myeloma:A case report

BACKGROUND Smoldering multiple myeloma(SMM)is an asymptomatic plasma cell proliferative disorder that can progress to multiple myeloma(MM).Amyloidosis(light chain)(AL)is the most common form of systemic amyloidosis.There are few reports of SMM coexisting with AL involving the digestive tract.CASE SUMMARY A 63-year-old woman presented with lower limb edema,abdominal distension,abdominal pain,and hematochezia.Gastroscopy showed gastric retention,gastric angler mucosal coarseness,hyperemia,and mild oozing of blood.Colonoscopy showed hyperemic and edematous mucosa of the distal ascending colon and sigmoid colon with the presence of multiple round and irregular ulcers,submucosal ecchymosis,and hematoma.Gastric and colonic tissue biopsy confirmed the diagnosis of AL by positive Congo red staining.MM was confirmed by bone marrow biopsy and immunohistochemistry.The patient had no hypercalcemia,renal dysfunction,anemia,bone lesions or biomarkers of malignancy defined as plasma cells>60%in bone marrow.Additionally,no elevated serum free light chain ratio,or presence of bone marrow lesions by magnetic resonance imaging(SLiM criteria)were detected.The patient was finally diagnosed with SMM coexisting with AL.She received chemotherapy and was discharged when the symptoms were relieved.She is doing well at nearly five years of follow up.CONCLUSION This case highlights that high index of suspicion is required to diagnose gastrointestinal AL.It should be suspected in elderly patients with endoscopic findings of granular-appearing mucosa,ecchymosis,and submucosal hematoma.Timely diagnosis and appropriate therapy can help to improve the prognosis of these patients.

Numerical study on waste polyethylene pyrolysis driven by self-sustaining smoldering

Polyethylene is the type of waste plastic that accounts for the most significant proportion of municipal solid waste.Waste polyethylene can be valorized via pyrolysis and produce value-added oil,gas,and char.On the other hand,self-sustaining smoldering is an emerging technical means to deal with sand/soil contaminated by organic matter.The high-temperature heat generated by smoldering can be used as a heat source for pyrolyzing waste polyethylene.Therefore,this study investigates numerically the pyrolysis of waste polyethylene driven by self-sustaining smoldering.A novel 4-step lumped kinetic model is proposed for simulating the pyrolysis of waste polyethylene.The results indicate that the operating parameters can determine the pyrolysis product yields by regulating the pyrolysis temperature and the volatile residence time.Note that higher temperatures and longer residence times favor the generation of shorter-chain pyrolysis products because of the intensified volatiles’secondary cracking.It can be concluded that a high interface-wall heat transfer coefficient(400 W m^(-2)K^(-1)),a low PE content(0.20),a high char concentration(2.4%),and a moderate air velocity(0.040 m s^(-1))are beneficial to oil yield.To some extent,this study may broaden the boundaries for the application of self-sustained smoldering-driven pyrolysis.

基于YOLOv7的红外阴燃火探测算法改进研究

目前,基于机器视觉的火灾检测算法中数据集类型不充分、数据集在时间维度覆盖不全面,致使此类算法难以实现火灾的早期预警,文中提出了基于改进YOLOv7的红外阴燃探测方法.该算法利用EfficientFormerV2模型替换原模型的骨干网络CSPDarknet53,从而增强了模型低延迟、低参数量、易部署的能力;同时,在预测网络中,采用CARAFE轻量化上采样模块代替原模型中的上采样模块,扩大了模型对特征的感受野,改善了阴燃特征的表示能力;此外,还引入了新的NWD度量来提升模型边界框预测能力.结果表明,在自建阴燃数据集上,该算法的平均精度达到92.9%,对阴燃检测的平均精度达到99.6%,比YOLOv7的精度提升了14.4%,较基于手工提取特征的卷积神经网络算法提升了4.6%.研究成果将为阴燃火早期预警提供新思路.

绝热逆向阴燃波的热扩散不稳定性

通过数值方法研究在绝热条件下逆向阴燃的热扩散不稳定性以及失稳后的非线性发展过程.通过正则模态分析方法研究绝热逆向阴燃的线性稳定性,得到以氧气Lewis数和气体流量Mg表征的线性稳定性图谱.结果表明,绝热逆向阴燃随控制参数的变化存在两种不同特征的不稳定性,即元胞(或指状)不稳定性和行波不稳定性,对阴燃波二维非线性失稳过程的模拟印证了这一线性稳定性分析结果.

艾炷阴燃温度检测方法及仿真分析综述

艾灸疗法历史久远,临床上在治疗未病等方面应用广泛。艾炷燃烧产生的温热刺激和生成的烃化物是其实现治疗的关键因素,因此对其阴燃过程中的温度检测和生成物质成分确定具有重要的研究意义。本文主要从温热刺激角度出发,对国内外小体积燃烧体主要是艾炷的阴燃温度检测方法和仿真分析进行了调研;对比分析了其不同类型的测温方法,主要包括热电偶式接触测温和红外热像仪等非接触式测温;并对小型燃烧体的阴燃仿真分析理论进行对比和分析。最后,对艾炷温度检测方法和仿真分析手段进行总结和展望,对实现艾灸阴燃过程量化分析和电子艾灸仪的温度控制特性,提供了依据和参考。

阴燃法处置含油污泥的可行性与应用场景分析

含油污泥具有高含水率、高黏性、半流态化的物理性状,是典型的湿黏性物料。目前主流的含油污泥处置利用技术均存在石油烃残留量高、能耗高和碳排放高的缺点,在我国大力推进“双碳”目标的背景下,亟须开发一种新型的含油污泥低碳处置技术。系统分析了阴燃法处置含油污泥的优势、可行性及应用场景,并对尚待解决的技术问题以及未来需深入开展的研究工作进行了归纳和总结,以期为相关科学技术人员提供参考。

稳定阴燃过程烟气流动的纹影分析

阴燃中烟气流动和氧气扩散是影响传播速度和温度场的关键,目前少有报道。本研究搭建了单镜离轴纹影系统,对不同直径(3、4、5 mm)和不同种类(生物质、炭)棒状燃料的阴燃烟气流动进行了纹影观察和图像记录分析。结果表明:与视觉下模糊的生物质阴燃烟气图像及不可见的炭棒阴燃烟气图像相比,两者的纹影图像较为清晰;纹影图像显示,在稳定阴燃过程棒状燃料周围的烟气流动为层流;相比于生物质棒,炭棒烟气流动的纹影图像更加明显,这可能是由于其CO_(2)浓度更高的原因;生物质棒阴燃最大烟气直径约为其直径的2倍,炭棒最大烟气直径约为其直径的3倍。

A Mathematical Approach to the Property of One-dimensional Steady Solution of Reverse Smolder Waves

The mathematical property of one-dimensional steady solution for reverse smolder waves in the context of a model that permits both fuel-rich and fuel-lean has been studied using the method of analysis. Based on the equations and the boundary conditions some asymptotic properties of the solution at infinity are proved. It is shown that the value of oxygen or the mass of fuel （corresponding to the fuel-rich case and the fuel-lean case, respectively） tends to zero, and the temperature approaches to a fixed value. This is confirmed by other authors using large activation energy asymptotic methods.

木材阴燃传播的自熄与自维持模拟研究

木材阴燃传播会演变成自熄或自维持的火灾形式.基于多组分平行热解氧化的五步反应模型,验证了阴燃前锋深度作为木材阴燃演变临界条件的可行性,并研究了阴燃特征温度、热流和厚度对木材阴燃演变临界条件的影响.模型较好地复现了不同阴燃前锋深度下的木材阴燃自熄和自维持传播.研究发现,临界阴燃前锋深度随着阴燃特征温度和热流的增大而减小,5~10 mm是阴燃传播的特征厚度,在阴燃传播到达到此深度后,自维持的传播更容易发生,且受热流的影响较小.一旦达到临界条件,无论厚度的大小,阴燃始终能够维持传播.

卷烟纸的阴燃过程分析

阴燃速率是卷烟纸的一项重要物理指标,为了解卷烟纸的阴燃过程,本文通过电镜分析观察卷烟纸正、反面结构差异;通过烘箱加热观察卷烟纸正、反面碳化颜色差异;通过CSR-II型卷烟纸阴燃速率测量仪检测卷烟纸正面朝下(非涂助燃剂面)与反面朝下(涂助燃剂面)的阴燃速率结果差异,对卷烟纸的阴燃过程进行分析、讨论。

石油烃污染土壤阴燃反应特性及修复效果研究

石油开采和运输过程中会产生大面积的石油污染场地,亟需修复。本研究以石油烃污染土壤为研究对象,采用自制的阴燃小试装置研究土壤热值、含水率和空气流量等因素对污染土壤阴燃反应特性及修复效果的影响,并探究了石油烃污染物在阴燃过程中降解路径。结果表明:石油烃污染土壤的阴燃反应温度区间为200~600℃,修复率普遍高于98.5%。当含水率增加5%时,阴燃峰面传播速率约减小46.3%,土壤含水率越高则阴燃峰面传播速率越小;当热值增加1.81 MJ/kg时,阴燃平均峰值温度会升高300℃。阴燃峰值温度随污染土壤热值的升高而增加;当空气流量为15~25 L/min时,阴燃峰面传播速率随空气流量的提高而增加。污染土壤阴燃过程中烯烃类物质的双键基团易被氧化断裂生成醛类物质,同时长链烷烃类物质的碳键易断裂生成中链烷烃类物质。研究显示,阴燃对石油烃污染土壤的修复效果显著,并且可以通过对影响因素的调控实现对阴燃过程的控制,相关结果将为有机污染土壤阴燃修复技术的工程化应用提供理论支撑。

热浮力驱动下地下煤火阴燃蔓延模型与机制

地下煤火蔓延模型与机制研究对我国煤炭资源绿色安全开采具有重要意义。目前地下煤火阴燃正向蔓延模型主要存在问题:简化的煤燃烧单步反应忽略了水分蒸发和热解吸热反应对蔓延的重要影响作用;缺乏实验数据验证模型的有效性。为此,构建了包含水分蒸发、煤热解和碳氧化三步反应体系的地下煤火阴燃正向蔓延数学模型;采用COMSOL Multiphysics有限元软件数值计算了该理论模型;开展了不同地裂缝渗透性条件下热浮力驱动地下煤火阴燃正向蔓延实验,进行对比实验和数值计算。结果表明:构建的模型揭示了地下煤火阴燃蔓延供氧控制机制,不仅能预测地下煤火阴燃正向蔓延高温区域的温度和蔓延速率,而且还能合理地预测阴燃多步反应速率以及氧气、煤、碳和灰分质量分数的时空演化。

骨髓浆细胞形态分型与单克隆性的相关性及其对高危冒烟型骨髓瘤的诊断价值

目的:研究浆细胞的形态学分型与单克隆性的相关性,探讨其对高危冒烟型骨髓瘤(HR-SMM)的诊断价值。方法:分析于本院就诊的84例HR-SMM患者的骨髓浆细胞形态特点与其单克隆性的相关性,并进一步验证异常浆细胞形态分型与s FLC比值、二代测序检测结果的一致性,及其与流式细胞术检测的单克隆浆细胞比例的相关性;检测患者的免疫球蛋白类型及血清中非受累免疫球蛋白水平,并观察不同疾病类型患者浆细胞成簇分布情况。结果:成熟浆细胞比例均数按反应性浆细胞增多症(RP)组、意义未明的单克隆免疫球蛋白血症(MGUS)组、冒烟型骨髓瘤(SMM)组、HR-SMM组、多发性骨髓瘤(MM)组的顺序依次减少;而幼稚型、原始型、网状型及火焰型浆细胞占有核细胞的比例均数按RP组、MGUS组、SMM组、HR-SMM组的顺序依次升高,两两组间比较差异均有统计学意义(P<0.05)。HR-SMM患者骨髓浆细胞中异常浆细胞的平均比例为96.2%。HR-SMM患者骨髓异常浆细胞比例与s FLC比值及二代测序检测结果有较好的一致性(kappa=0.879及kappa=0.891,均>0.75),与免疫表型为CD45-/CD38+/CD138+/CD56+/CD19-的单克隆浆细胞有较好的相关性(γ=0.825)。Ig G型、Ig A型及Ig M型HR-SMM患者的非受累免疫球蛋白水平比正常参考范围均减低25%以上,差异有统计学意义(P<0.05)。各疾病组浆细胞成簇分布比例未见明显差异(P>0.05)。结论:在HR-SMM患者中,幼稚型、原始型、网状型及火焰型浆细胞作为骨髓异常浆细胞,与单克隆浆细胞存在较大相关性;异常浆细胞在骨髓总浆细胞中的比例及患者的非受累免疫球蛋白水平减少幅度对HR-SMM的诊断有一定价值。

基于红外图像及环境信息关联的阴燃火探测

针对目前常用的阴燃火检测方法存在检测效率低、准确度低等问题,提出了一种基于红外图像与环境信息关联的卷积神经网络(Convolutional Neural Network,CNN)阴燃火分类预测方法。通过实时获取试验样本的环境信息及红外图像,将目标面积变化率、周长变化率、圆形度和目标移动特性作为特征参数用于阴燃目标探测判别依据;通过随机森林算法(Random forest algorithm,RF)对4个图像特征参数进行重要性评估,依此分配权重并实现图像信息特征融合,进而与环境信息关联并作为CNN的输入参量进行训练测试。结果表明,阴燃早期检测效率及全时段检测准确率均大幅提升,15 s前阴燃检测召回率提升了65%,全时间段内的检测准确率提升了6.25%。研究成果将为阴燃火早期预警提供新思路。