Preparation of WC/CoCrFeNiAl0.2 high-entropy-alloy composites by high-gravity combustion synthesis

The WC/CoCrFeNiAl0.2 high-entropy alloy(HEA)composites were prepared through high-gravity combustion synthesis.The preparation method is presented below.First,using a designed suitable multiphase thermite system,the molten CoCrFeNiAl0.2 HEA was fabricated using low-cost metal oxides.The molten HEA was subsequently infiltrated into the WC layer to fabricate WC/CoCrFeNiAl0.2 composites in a highgravity field.The porosity of the WC/CoCrFeNiAl0.2 composites was down-regulated,and their compressive yield strength was up-regulated when the high-gravity field was increased from 600g to 1500g because this infiltration process of a HEA melt into the WC layer is driven by centrifugal force.The WC particles in the composites exhibited a gradient distribution along the direction of the centrifugal force,which was attributed to the combined action of the high-gravity field and the temperature gradient field.The Vickers hardness of the sample was down-regulated from 9.53 to 7.41 GPa along the direction of the centrifugal force.

Method for prevention and control of spontaneous combustion of coal seam and its application in mining field

Spontaneous combustion of coal seam has been and continues to be a big problem in coal mines. It could pose great threat to the safety of the whole mine and all miners, especially when it occurs in or nearby coal mines. Besides, environment of area surrounded mines during combustion can be threatened where large amount of toxic gases including CO_2, CO, SO_2 and H_2S can be leased by fire in mine. Hence, it is important and significant for scholars to study the controlling and preventing of the coal seam fire. In this paper, the complicated reasons for the occurrence and development of spontaneous combustion in coal seam are analysed and different models under various air leakage situations are built as well. Based on the model and approximately calculation, the difficulty of fire extinguishment in coal seam is pointed out as the difficulty and poor effect to remove the large amount of heat released. Detailed measurements about backfilling and case analyses are also provided on the basis of the recent ten years' practice of controlling spontaneous combustion in coal seams in China. A technical fire prevention and control method has been concluded as five steps including detection, prevention, sealing, injection and pressure adjustment. However, various backfill materials require different application and environmental factors, so in this paper, analyses and discussion about the effect and engineering application of prevention of spontaneous combustion are provided according to different backfilling technologies and methods. Once the aforementioned fire prevention can be widely applied and regulated in mines, green mining will be achievable concerning mine fire prevention and control.

A back analysis of the temperature field in the combustion volume space during underground coal gasification

The exact shape and size of the gasification channel during underground coal gasification(UGC) are of vital importance for the safety and stability of the upper parts of the geological formation.In practice existing geological measurements are insufficient to obtain such information because the coal seam is typically deeply buried and the geological conditions are often complex.This paper introduces a cylindrical model for the gasification channel.The rock and soil masses are assumed to be homogeneous and isotropic and the effect of seepage on the temperature field was neglected.The theory of heat conduction was used to write the equation predicting the temperature field around the gasification channel.The idea of an excess temperature was introduced to solve the equations.Applying this model to UCG in the field for an influence radius,r,of 70 m gave the model parameters,u1,2,3...,of 2.4,5.5,8.7...By adjusting the radius(2,4,or 6 m) reasonable temperatures of the gasification channel were found for 4 m.The temperature distribution in the vertical direction,and the combustion volume,were also calculated.Comparison to field measurements shows that the results obtained from the proposed model are very close to practice.

Numerical Simulation of Muzzle Flow Field Based on Calculation of Combustion Productions in Bore

To improve the accuracy of numerical simulation of muzzle chemical flow field,and study the gunpowder combustion productions, the muzzle flow field is simulated coupled with the calculation of combustion productions in bore. The calculation in bore uses the gibbs free-energy minimization method and the classical interior ballistics model. The simulation of the muzzle flow field employs the multi-component ALE( Arbitrary Lagrange-Euler) equations. Computations are performed for a 12. 7 mm gun. From 2. 48 ms to3. 14 ms,the projectile moves in the gun barrel. CO and H2 O masses decrease by 3. 37% and 6. 51%,and H2 and CO2masses increase by 11. 11% and 10. 58%. The changes conform to the fact that the water-gas equilibrium reaction of all reactions plays a dominant role in this phase. After the projectile leaves the barrel,the masses of H2 and CO decrease,and the masses of H2 O and CO2 increase. When it moves to 80 d away from the muzzle,the decreases are 12. 75% and 8. 05%,and the increases are 12. 76% and 36. 26%,which tallies with the existence of muzzle flame. Further,CO and H2 burn more and more fiercely with the muzzle pressure pg increasing,and burn more and more weakly with the altitude rising. When two projectiles launch in series,the combustion of the second projectile muzzle flow field is fiercer than the first projectile. Analysis results have shown that the proposed method is effective for simulating the muzzle flow filed.

Numerical Simulation Study of Goaf Methane Drainage and Spontaneous Combustion Coupling

In order to study the coupling problem between methane drainage and spontaneous combustion of residual coal in the collapsed zone after mining ignitable coal seams with high methane,we have analyzed the effects of differ-ent methane drainage modes on spontaneous combustion of residual coal through numerical simulation. The results show that deep and large flux methane drainage modes increases the air leakage from work faces to the goaf and formed new spontaneous combustion zones induced by drainage near vents,which increases the risk of self-ignition of coal—reducing the self-ignition period and enlarging the scale of self-ignition. The spontaneous upstream combustion oxidation of the main fire zone can be suppressed when both drainage and nitrogen injection were adopted. Our research results provide an effective technical measure and theoretical basis to determine the best methane drainage scheme and drainage parameters.

Study on partition of spontaneous combustion danger zone and prediction of self-ignition in coalmine based on numeric simulation

By solving steady model of air flow diffusion and chemical reaction in loose coal, distribution of oxygen concentration and flow velocity magnitude were obtained. Compared the simulating results with critic value as well as duration of spontaneous combustion from large-scale spontaneous combustion experiment, 'three zones' of spontaneous combustion were partitioned and mining conditions to avoid spontaneous combustion were obtained. The above method was employed to partition 'three zones' in gob of fully mechanized top-coal caving long wall face and got fairly good result. Calculation of the above method is much smaller than simulating the whole process of coal spontaneous combustion, but the prediction precision can satisfy the demand of predicting and extinguishing spontaneous combustion in mining.

CFD simulation of spontaneous coal combustion in irregular patterns of goaf with multiple points of leaking air

Based on the non-linear air leakage seepage equation for an anisotropic porous medium, on the seepage diffusion equation of multicomponent gas and on the seepage synthetic heat transfer equation of a porous medium, the numerical model for field flow problems of irregular patterns of a goaf with multiple points of leaking air is established and simultaneously solved by the upwind mode finite element method (G3 computer program). According to the complexity of irregular patterns of a goaf with multiple points of leaking air, the flow pattern in a large area of such a goaf and the variation in gases of methane, oxygen and CO and in temperature are theoretically described. In the calculation, the goaf is regarded as a caving anisotropic medium and the coupling effect of methane effusion on spontaneous combustion is considered. The simulation results agree well with practical experience. In addition, the spontaneous combustion process is also simulated, indicating that 1) the spontaneous combustion often takes place near the area where fresh air leaks in and 2) the fire sources can be classified into static and dynamic zones. Therefore, in practical fire preventing and extinguishing, we should clearly distinguish the upstream air leaking points from the downstream ones in order to take proper measures for leakage stopping.

Boiler combustion optimization based on ANN and PSO-Powell algorithm

To improve the thermal efficiency and reduce nitrogen oxides （NOx ） emissions in a power plant for energy conservation and environment protection, based on the reconstructed section temperature field and other related parameters, dynamic radial basis function （RBF） artificial neural network （ANN） models for forecasting unburned carbon in fly ash and NO, emissions in flue gas ware developed in this paper, together with a multi-objective optimization system utilizing particle swarm optimization and Powell （PSO-Powell） algorithm. To validate the proposed approach, a series of field tests were conducted in a 350 MW power plant. The results indicate that PSO-Powell algorithm can improve the capability to search optimization solution of PSO algorithm, and the effectiveness of system. Its prospective application in the optimization of a pulverized coal （ PC ） fired boiler is presented as well.

Energy from Combustion of Rice Straw: Status and Challenges to China

As the biggest agricultural country, China has an abundant rice straw energy resource. The characteristics of typical china rice straws are presented as high moisture contents, high volatile contents, high ash contents and low bulk density. At present, rice straw is mainly used as fuel, feedstuff, fertilizer and industrial raw material. With improved living conditions in rural areas, farmers tend to rely more on commercial fuel, which leads to even more open field burning of rice straw, and brings air pollutions and potential energy waste as well. The Chinese government is studying relevant policies on acceleration of comprehensive utilization of rice straw with the goal of utilization rate exceeding 80% in 2015. In this paper, focus is on the combustion of rice straw to extract energy, and related challenges face to china is put forward in this paper also.

Numerical calculation of flow and heat transfer process in the new-type external combustion swirl-flowing hot stove

It is clarified that the important method to improve the blast temperature ofthe small and the middle blast furnaces whose production is about two-thirds of total sum of Chinafrom 1000℃ to 1250-1300℃ is to preheat both their combustion-supporting air and coal gas. The airtemperature of blast furnaces can be reached to 1250-1300℃ by burning single blast furnace coal gasif high speed burner is applied to blast furnaces and new-type external combustion swirl-flowinghot stove is used to preheat their combustion-supporting air. The computational results of the flowand heat transfer processions in the hot stove prove that the surface of the bed of the thermalstorage balls there have not eccentric flow and the flow field and temperature field distribution iseven. The computational results of the blast temperature distribution are similar to thosedetermination experiment data. The numerical results also provide references for developing anddesigning the new-type external combustion swirl-flowing hot stoves.

Bulking factor of the strata overlying the gob and a three-dimensional numerical simulation of the air leakage flow field

The present study examines the results of the researches related to the gob bulking factor carried out at home and abroad.A mathematical function of a three-dimensional gob bulking factor is described based on a three-dimensional gob model.The method of taking value for interstice and permeability ratios is also proposed.The law of air leakage of fully mechanized top coal is researched in this study.The results show that the speed of air flow near the upper and lower crossheadings is higher than that in the central section of the gob at the same distance from the working face.When the amount of air at the working face exceeds a critical amount,the width of the spontaneous combustion zone in the upper and lower crossheadings is also larger than that in the central section.In this situation,the key is preventing the coal left in the upper and lower crossheadings from self-igniting.Reducing the amount of air at the working face can decrease the width of the spontaneous combustion zone,especially the width near the upper and lower crossheadings.This also moves the spontaneous combustion zone in the direction of the working face.It can prevent the coal in the gob from self-igniting by making the coal left in the crossheadings to be inert and by effectively controlling the amount of air at the working face.

Performance evaluation on field synergy and composite regeneration by coupling cerium-based additive and microwave for a diesel particulate filter

In order to reveal the mechanics of composite regeneration by coupling cerium-based additive and microwave for a diesel particulate filter, a composite regeneration model by coupling cerium-based additive and microwave for a diesel particulate filter was established based on field synergy theory. Performance evaluation on field synergy and composite regeneration of the diesel particulate filter was conducted by using the vortex crushing combustion and field synergy mathematical models. The results show that the peak temperature of the particulate filter body reaches 1180-1190 K when the regeneration time is 175 s, and there are optimal coordination degree between the velocity vector and temperature gradient of the filter body and the maximum ratio0.56-0.60 of the best burning regeneration region is obtained. Accordingly, the largest regeneration combustion rate inside the particulate filter body and the highest regeneration efficiency at the moment are achieved.

Local dynamic balance theory and technology of flow field in multilayer gob area

Flow field in multilayer gob area, which formed in small hiden-depth, multi-coal layer groups, close distance, hard coal layer, and hard roof, possesses characteristics such as complex, changeable and unstable. Dynamic balance theory of local flow field in multilayer gob area was built based on the realistic requirement that the serious threat on current mining coal layer by large-scale spontaneous combustion fire on close spontaneous combustion coal layer group of Datong Coal mining area at the ＇di-hard＇ conditions was caused by small coal pit mining. The kernel was in dynamic balance between flow field pressures of working face and local flow field in multilayer gob area was kept by transformation. Corresponding technology and set of devices were developed.

Bonding interface between TiAl intermetallic compound and Ti under the electric field

TiAl intermetallic compound was synthesized and bonded together with Ti substrate synchronously by using fieldactivated and pressure-assisted synthesis （FAPAS） process. The effect of electric field on the microstructure and growth pattern of the diffusion dissolution layer of TiA1/Ti interface was mainly studied. The microstructure of the diffusion dissolution layer was investigated by optical microscope （OM） and scanning electron microscope （SEM）. The elements distribution of the diffusion dissolution layer was investigated by energy dispersive spectroscopy （EDS）. The results show that a fine and homogeneous grain structure is obtained in sintered TiA1 intermetallic compound. Metallurgical bond is formed at the TiAl/Ti interface. The thickness of diffusion dissolution layer between TiAl and Ti changes with conduction time and current density.

自燃煤矸石山火区表面温度场三维重构与实践

【目的】煤矸石山自燃灾害严重破坏生态环境,影响安全生产,已成为我国生态文明建设进程中的瓶颈问题,为科学制定灭火方法及实施灭火工程,自燃煤矸石山火区范围的准确探测至关重要。【方法】提出采用无人机热红外倾斜摄影测量技术探测高温区三维分布的思路,研发热红外图像多尺度高斯滤波细节增强技术,突出目标边缘信息;基于FLIR Tools软件开发工具包SDK (software development kit)开发热红外图像一键式批量化处理软件,利用ThreadPool高效地开展热红外图像的多线程异步处理,全局统一所有热红外图像颜色阈值与温度数值的对应关系;最后采用批量处理后的热红外图像进行自燃煤矸石山火区表面温度场三维重构,并在陕西某煤矸石山火区进行了现场应用。【结果和结论】结果表明:(1)经过多尺度高斯滤波细节增强后,热红外彩色图像细节特征得到显著增强,热红外图像信息熵由6.989提高到了7.624。(2)所开发的热红外图像批量化处理软件可在10 min内对1 000张热红外图像进行快速处理,极大提高了工作效率。(3)上述技术在陕西某煤矸石山火区现场成功构建了一区及二区煤矸石山火区三维表面温度场,分别圈定了11 693 m^(2)和10 800 m^(2)高温区,为火区发展态势评估和后续灭火方案设计提供了支撑。研究成果可应用于煤矸石山火灾、煤田火灾、垃圾填埋场火灾、森林火灾以及建筑火灾等高温场景的温度场三维重构,为火区侦查、火情调查及火源位置诊断提供详实的火场数据支持。

基于MT药剂体系的动力型红外诱饵燃烧流场仿真分析

为得到动力型诱饵燃烧产物浓度场和温度场,在分析了MT药剂体系在空气中的燃烧区结构和主要反应基础上,建立了流场与化学反应耦合的二维轴对称模型。通过数值仿真分析了不同组分、环境压力和进气流速对燃烧流的影响。结果表明,MgF2对MT体系光谱的影响显著,Mg含量的增加有助于提高辐射强度,但随着Mg的进一步增加,更多的Mg没有参与反应,不利于改善辐射强度。环境压力对最高温度影响不大,但会影响温度分布和产物浓度。来流速度对核心反应温度和产物浓度影响较小,但会将高温区和产物限定在较小区域,从而影响辐射强度。上述结果可为动力型诱饵的红外辐射特性设计提供参考。

直播稻播前不同土壤火焰温度条件下杂草种子发芽率试验

杂草的有效控制是降低直播稻稳产风险的重要措施,播前土壤火焰处理是以非化学方法在进行播种前抑制杂草种子萌发的有效手段。为明确土壤火焰处理中温度场对杂草种子发芽率的影响规律,采用数值模拟方法对燃料分流部件中集管结构参数进行了研究,数值模拟和验证试验结果表明,当集管内径d为20 mm、气体输入流量为1.0~3.5 m^(3)/h时,最大流量偏差系数Δη在3.0%以内,支管间气体流量分配较均匀。基于数值模拟结果设计了火焰燃烧装置,研究6种输入流量(1.0~3.5 m^(3)/h)的液化石油气燃料对火焰高度和火焰温度分布的影响,以拖拉机行进速度、燃料输入流量和土壤深度作为试验因素,进行了全因素试验,采用稻田间常见的杂草种子研究温度场对杂草种子发芽率的影响规律。试验结果表明,在常温常压工作环境下,火焰高度和火焰温度最高值均随着燃料输入流量的增大而增大;当拖拉机行进速度为2.36 km/h,燃料输入流量为2.5、3.0、3.5 m^(3)/h时,土壤温度最高值可分别达到92.83、116.58、156.83℃;相比未经火焰处理的对照组,当土壤温度达到92.83℃时,在α=0.05的显著性水平下,千金子、异型莎草种子发芽率显著降低,但马唐、鳢肠种子发芽率受影响不显著,当土壤温度达到116.58℃和156.83℃时,4种杂草种子发芽率均显著降低;当土壤温度达到156.83℃时,马唐、鳢肠、千金子和异型莎草4种杂草种子发芽率分别降低94.82%、87.81%、86.54%和84.05%。田间试验结果表明,土壤火焰处理对稗草、马唐、鳢肠和异型莎草有显著的抑制萌发作用,其相对除草率Y≥80.00%。

一体化加力燃烧室热态流场与特性数值研究

为满足新一代航空发动机的高推重比需求,提出一种支板与混合器一体化加力燃烧室方案,采用数值仿真方法,对比分析进口马赫数Ma (0.3~0.45),涵道比B (0.25~0.37)和不同飞行高度H(0~20 km)对加力燃烧室热态流场特性的影响。研究表明:在研究参数范围内,进口马赫数增大,壁式稳定器回流区及下游区域的燃气温度受到影响,区域内燃气温度逐渐升高,沿程径向温度不均匀性逐渐减小,总压损失增大,燃烧效率逐渐下降,但出口燃烧效率仍基本高于0.90;进口涵道比B增大,壁式稳定器下游及中心锥轴线位置的燃气温度开始下降,沿程燃气总压损失增大,燃烧效率随之升高,B从0.25增大至0.28时,燃烧效率提升较大,继续增大涵道比,燃烧效率提升较少;随着飞行高度升高,整体燃烧效率逐渐下降,在0 km和11 km飞行高度之间燃烧效率下降较少,而在20 km飞行高度时燃烧效率下降相对明显。

异辛烷燃烧过程的声场激励调控特性

从宏观与微观层面分析了超声波对异辛烷燃烧的调控作用机理,利用发动机台架试验验证了原机三维燃烧数值模拟模型,基于燃烧室内物理嵌入动网格声源面方法,实现将20 kHz振幅为300μm超声波成功馈入燃烧室.将有、无超声波馈入燃烧室的工作缸压差值作为超声辐射压力扰动,研究了超声场激励对异辛烷的着火延迟期、中间反应组分及敏感性的影响特性.通过对比分析超声馈入方案S_(1)~S_(3)及无超声馈入方案S_(0),结果表明:S_(1)~S_(3)方案均使燃烧相位得以提前,S_(2)和S_(3)中C_(3)H_(6)、IC_(4)H_(8)和C_(2)H_(4)的峰值摩尔分数分别提升42.1%、24.7%、27.5%和21.5%、9.6%、5.3%,且两者异辛烷燃尽时间均提前0.18 s.当量比为1且初始温度分别为1300 K和1700 K时,着火延迟期分别缩短31.8%和6.4%,且均促进了OH自由基的大量生成.

复杂工况下湿式火驱注入井温度场及腐蚀规律研究

针对湿式火驱注入井井筒温度场变化大、不同阶段腐蚀速率难以确定这一问题,以典型湿式火驱注入井进行研究,建立井筒温度场,计算各个阶段的井筒温度,通过氧腐蚀预测模型对管柱进行敏感性分析得到注气、注水下的油管腐蚀速率。研究结果表明:井筒温度主要受注入蒸汽温度、日注气量、日注水量和油层燃烧影响,注入蒸汽温度达到350℃时,井底温度高达266.1℃;管柱腐蚀速率随注水量增大快速上升,日注水量达30 m^(3)时,井底附近的腐蚀速率高达1.23 mm/a。研究结果可为湿式火驱注入井腐蚀规律分析提供一定参考并为安全生产提供保障。