Flame behavior, shock wave, and instantaneous thermal field generated by unconfined vapor-liquid propylene oxide/air cloud detonation

Energy output and heating effects are essential for vapor-liquid fuel/air cloud detonation in the fuel-air explosive(FAE) applications or explosion accidents. The purpose of this study is to examine the dynamic large-size flame behavior, shock wave propagation law, and instantaneous thermal field generated by unconfined vapor-liquid propylene oxide(PO)/air cloud detonation. Based on computational fluid dynamics(CFD) and combustion theory, a numerical simulation is used to study the detonation process of a PO/air cloud produced by a double-event fuel-air explosive(DEFAE) of 2.16 kg. The large-scale flame behavior is characterized. The flame initially spreads radially and laterally in a wing shape. Subsequently,the developed flame increases with a larger aspect ratio. Moreover, the propagation laws of shock waves at different heights are discussed. The peak pressure of 1.3 m height level with a stepwise decline is obviously different from that of the ground with an amplitude of reversed ’N’ shape. In the vast majority of the first 6.9 m, the destructive effect of the shock wave near the ground is greater than that of the shock wave at 1.3 m height. Furthermore, the dynamic instantaneous isothermal field is demonstrated.The scaling relationship of various isotherms in the instantaneous thermal field with the flame and initial cloud is summarized. The comprehensive numerical model used in this study can be applied to determine the overpressure and temperature distribution in the entire fuel/air cloud detonation field,providing guidance for assessing the extent of damage caused by DEFAE detonation.

Modeling of the whole process of shock wave overpressure of freefield air explosion

The waveform of the explosion shock wave under free-field air explosion is an extremely complex problem.It is generally considered that the waveform consists of overpressure peak,positive pressure zone and negative pressure zone.Most of current practice usually considers only the positive pressure.Many empirical relations are available to predict overpressure peak,the positive pressure action time and pressure decay law.However,there are few models that can predict the whole waveform.The whole process of explosion shock wave overpressure,which was expressed as the product of the three factor functions of peak,attenuation and oscillation,was proposed in the present work.According to the principle of explosion similarity,the scaled parameters were introduced and the empirical formula was absorbed to form a mathematical model of shock wave overpressure.Parametric numerical simulations of free-field air explosions were conducted.By experimental verification of the AUTODYN numerical method and comparing the analytical and simulated curves,the model is proved to be accurate to calculate the shock wave overpressure under free-field air explosion.In addition,through the model the shock wave overpressure at different time and distance can be displayed in three dimensions.The model makes the time needed for theoretical calculation much less than that for numerical simulation.

Flow Field Characteristics of the Rotor Cage in Turbo Air Classifiers

The turbo air classifier is widely used powder classification equipment in a variety of fields. The flow field characteristics of the turbo air classifier are important basis for the improvement of the turbo air classifier＇s structural design. The flow field characteristics of the rotor cage in turbo air classifiers were investigated trader different operating conditions by laser Doppler velocimeter（LDV）, and a measure diminishing the axial velocity is proposed. The investigation results show that the tangential velocity of the air flow inside the rotor cage is different from the rotary speed of the rotor cage on the same measurement point due to the influences of both the negative pressure at the exit and the rotation of the rotor cage. The tangential velocity of the air flow likewise decreases as the radius decreases in the case of the rotor cage＇s low rotary speed. In contrast, the tangential velocity of the air flow increases as the radius decreases in the case of the rotor cage＇s high rotary speed. Meanwhile, the vortex inside the rotor cage is found to occur near the pressure side of the blade when the rotor cage＇s rotary speed is less than the tangential velocity of air flow. On the contrary, the vortex is found to occur near the blade suction side once the rotor cage＇s rotary speed is higher than the tangential velocity of air flow. Inside the rotor cage, the axial velocity could not be disregarded and is largely determined by the distances between the measurement point and the exit.

CFD prediction of physical field for multi-air channel pulverized coal burner in rotary kiln

A 3-D numerical simulation with CFX software on physical field of multi-air channel coal burner in rotary kiln was carried out. The effects of various operational and structural parameters on flame feature and temperature distribution were investigated. A thermal measurement was conducted on a rotary kiln (4.5m in diameter, 90m in length) with four-air channel coal burner to determine the boundary conditions and to verify the simulation results. The calculation result shows that the distribution of velocity near burner exit is saddle-like; recirculation zones near nozzle and wall are useful for mixture primary air with coal and high temperature fume. A little central airflow can avoid coal backing up and cool nozzle. Adjusting the ratio of internal airflow to outer airflow is an effective and major means to regulate flame and temperature distribution in sintering region. Large whirlcone angle can intensify disturbution range at flame root to accelerate ignition and mixture. Large coal size can reduce high temperature region and result in coal combusting insufficiently. Too much combustion air will lengthen flame and increase heat loss.

Corona with Streamers in Atmospheric Pressure Air in a Highly Inhomogeneous Electric Field

The paper presents research data on positive and negative coronas inatmospheric pressure air in a highly inhomogeneous electric field. Thedata show that irrespective of the polarity of pointed electrodes placed ina high electric field (200 kV/cm), this type of discharge develops via ballstreamers even if the gap voltage rises slowly (0.2 kV/ms). The start voltageof first positive streamers, compared to negative ones, is higher andthe amplitude and the frequency of their current pulses are much lower:about two times and more than two orders of magnitude, respectively.The higher frequency of current pulses from negative streamers provideshigher average currents and larger luminous areas of negative coronascompared to positive ones. Positive and negative cylindrical streamersfrom a pointed to a plane electrode are detected and successive dischargetransitions at both polarities are identified.

Rapid air film continuous casting of aluminum alloy using static magnetic field

The influences of the cooling style and static magnetic field on the air film casting process were investigated. Ingots of 6063 aluminum alloy were produced by AIRSOL VEIL casting with double-layer cooling water and static magnetic field. Surface segregation, hot crack and variation of solute content along the radius direction of ingot were examined. The results showed that double-layer cooling water can improve the surface quality and avoid of hot crack, which created conditions to increase the casting speed. The electromagnetic casting process can effectively improve the surface quality in high speed casting process, and static magnetic field has a great influence on solute distribution along the radius direction of ingot.

Air breakdown induced by the microwave with two mutually orthogonal and heterophase electric field components

The air breakdown is easily caused by the high-power microwave, which can have two mutually orthogonal and heterophase electric field components. For this case, the electron momentum conservation equation is employed to deduce the electric field power and effective electric field for heating electrons. Then the formula of the electric field power is introduced into the global model to simulate the air breakdown. The breakdown prediction from the global model agrees well with the experimental data. Simulation results show that the electron temperature is sensitive to the phase difference between the two electron field components, while the latter can affect obviously the growth of the electron density at low electron temperature amplitudes. The ionization of nitrogen and oxygen induces the growth of electron density, and the density loss due to the dissociative attachment and dissociative recombination is obvious only at low electron temperatures.

Calculation of flow distribution in air reverse circulation bit interior fluid field by simplifying air flow model

By simplifying the characters in the air reverse circulation bit interior fluid field, the authors used air dynamics and fluid mechanics to calculate the air distribution in the bit and obtained an equation of flow distribution with a unique resolution. This study will provide help for making certain the bit parameters of the bit structure effectively and study the air reverse circulation bit interior fluid field character deeply.

Influence of the 60 Hz Magnetic Field on the Airborne Microbial Distribution of Indoor Environments

The aim of this work was to analyze the effect of the magnetic field generated by the household appliances on the airborne microbial surrounding these equipment located on indoor environments with particular interest in the environmental fungi.A simultaneous environmental study was carried out in locals of three different geographical places of Havana,Cuba,which have televisions,computers and an electric generator.The air samples were made by a sedimentation method using Malt Extract Agar.The concentration of total aerobic mesophilic as well as fungi and yeasts were determined in rainy and little rainy seasons by applying as factors:exposure time of dishes(5 to 60 min)and distance to the wall(0 and 1 m)at a height of 1 m above the floor.The predominant fungal genera were Cladosporium,Penicillium and Aspergillus.In the dishes that were placed at 0 and 0.5 m from the emitting sources were observed that some bacteria colonies formed inhibition halos,a great diversity of filamentous fungi and an increase in the mycelium pigmentation as well as the pigments excretion.In the rainy season,the highest amounts of fungi were obtained in all samples.In the little rain season the count of the Gram-negative bacilli increased three times the Gram-positive cocci.

Evolution of Meteorological Conditions during a Heavy Air Pollution Event under the Influence of Shallow Foehn in Urumqi, China

The air pollution in Urumqi which is located on the northern slope of the Tianshan Mountains in northwestern China,is very serious in winter.Of particular importance is the influence of terrain-induced shallow foehn,known locally as elevated southeasterly gale(ESEG).It usually modulates atmospheric boundary layer structure and wind field patterns and produces favorable meteorological conditions conducive to hazardous air pollution.During 2013-17,Urumqi had an average of 50 d yr-1 of heavy pollution(daily average PM2.5 concentration>150μg m-3),of which 41 days were in winter.The majority(71.4%)of heavy pollution processes were associated with the shallow foehn.Based on microwave radiometer,wind profiler,and surface observations,the surface meteorological fields and boundary layer evolution during the worst pollution episode in Urumqi during 16-23 February 2013 are investigated.The results illustrate the significant role of shallow foehn in the building,strengthening,and collapsing of temperature inversions.There were four wind field patterns corresponding to four different phases during the whole pollution event.The most serious pollution phase featured shallow foehn activity in the south of Urumqi city and the appearance of an intense inversion layer below 600 m.Intense convergence caused by foehn and mountain-valley winds was sustained during most of the phase,resulting in pollutants sinking downward to the lower boundary layer and accumulating around urban area.The key indicators of such events identified in this study are highly correlated to particulate matter concentrations and could be used to predict heavy pollution episodes in the feature.

Flow field in air-sparged hydrocyclone

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Influence of thermal flow field of cooling tower on recirculation ratio of a direct air-cooled system for a power plant

In order to get thermal flow field of direct air-cooled system,the hot water was supplied to the model of direct air-cooled condenser(ACC). The particle image velocimetery (PIV) experiments were carried out to get thermal flow field of a ACC under different conditions in low velocity wind tunnel,at the same time,the recirculation ratio at cooling tower was measured,so the relationship between flow field characteristics and recirculation ratio of cooling tower can be discussed. From the results we can see that the flow field configuration around cooling tower has great effects on average recirculation ratio under cooling tower. The eddy formed around cooling tower is a key reason that recirculation produces. The eddy intensity relates to velocity magnitude and direction angle,and the configuration of eddy lies on the geometry size of cooling tower. So changing the flow field configuration around cooling tower reasonably can decrease recirculation ratio under cooling tower,and heat dispel effect of ACC can also be improved.

大型永磁同步电机内外双循环强化散热性能模拟

针对高铁大型永磁同步牵引电机转子区域散热困难、内部温升分布不均匀的问题,在机壳水冷电机结构基础上的定子铁芯外表面处增设轴向矩形风道,并结合气隙、转子减重孔形成内外双循环散热结构,探究降低定子、绕组部位温升和提升电机内部散热均匀性的影响规律.首先通过Ansoft Maxwell平台仿真得到双循环散热结构在额定工况下各部件损耗值,同时为了更好模拟转子旋转带动气隙中的空气流动,对气隙进行分层处理,采用流-固耦合的有限元分析法模拟研究单、双循环散热结构下电机内部空气流动特性以及温升规律.结果表明,内循环风冷结构使电机内部空气流速显著提高,表面平均换热系数也显著提升,转子区域的热量会随着空气的流动更多地传给温度相对较低的定子区域及机壳,同时减少热量向转子部位传递,从而使转子和永磁体的温升降低.在此基础上,采用正交分析法对矩形通风孔的截面积、数量、高宽比进行结构参数优化,并采用温升分布均匀性系数对电机进行温升评价,得到最优方案下电机最高温升相比单循环散热结构降低12.1K,电机整体温升分布均匀性提升16.54%.

基于CFD-DEM的物料转运过程诱导风流场与产尘因素分析

为了揭示颗粒物料在皮带机转运过程中的粉尘运移规律问题,推导了含有水平初速度的颗粒物料转运过程中的诱导气流方程,并采用CFD-DEM耦合方法对转运过程中的颗粒分布与诱导风流场特性进行了研究,分析了颗粒物料的落料高度、质量流量和初速度对颗粒逸散与诱导气流的影响。结果表明:颗粒在弧形下落阶段速度逐渐提高,挤压碰撞阶段颗粒速度先降低后提高,最后趋于稳定,部分颗粒出现逸散现象;含尘气流在颗粒物料弧形下落阶段和挤压碰撞阶段扩散较为明显;诱导气流速度与颗粒物料质量流量和初始速度呈正比关系,颗粒物料质量流量与诱导气流速度呈幂函数关系,拟合曲线幂指数为0.6~0.74。

超大颗粒肥水田气力深施加速器设计及参数优化

为解决水稻撒施追肥存在的肥料流失、利用率低及机械深施肥工作部件易堵塞、伤根等问题,该研究设计了一种用于水田深施追肥机的超大颗粒肥气力式加速器。该加速器利用双螺旋高压气流,在其与肥料上端构成的近封闭空间内加速超大颗粒肥,实现其高速射入泥壤,并可避免肥料颗粒与管壁碰撞;出口设置渐扩管扩散气流,可减轻对泥壤的冲击,提高施肥位置的稳定性。根据超大颗粒肥参数与加速器功能要求,确定了加速器的结构参数,并根据肥料入泥深度所需的射出速度,分析确定了加速器的工作参数。在此基础上,基于Fluent软件的六自由度重叠动网格建立了加速器仿真模型,以进口气流速度、螺旋角和加速管直径为试验因素,进行单因素仿真试验与三因素三水平Box Behnken组合仿真试验,研究各因素对肥料射出速度与气流扩散率的影响。多因素试验分析及响应面分析结果表明,加速器的最佳工作参数为进口气流速度47 m/s、加速管直径21 mm、螺旋进气口螺旋角43°。在此条件下进行台架验证试验,得到肥料射出速度均值为12.61 m/s,出口气流扩散率均值为85.5%,肥料入泥平均深度为4.7 cm,达到了水稻追肥要求。该研究可为超大颗粒肥水田气力深施追肥机设计提供参考。

气流场驱动喷射3D打印熔融聚乳酸微细纤维及表面浸润性调控

提出了一种高速气流场驱动喷射高效三维(3D)打印熔融聚乳酸微细纤维的方法,分析了高速气流致熔融材料剪切破碎原理,研究了打印工艺中供料气压、气流流速、打印高度等关键参数对微细纤维直径分布及结构孔隙率、截面尺寸的影响规律。并对所获得的聚乳酸微细纤维进行了表面浸润性测试。结果表明,该工艺相对于静电纺丝等微细纤维制造方法,加工效率提高10倍以上。通过控制不同的打印参数,可以有效实现纤维直径在6~18μm、孔隙率在55%~96%范围内的有效调控。通过3D打印工艺,可实现具有宏观路径可控、微观具有高孔隙率微纤维结构的制作。表面浸润性结果显示,打印微细纤维由于材料分子基团及高孔隙率综合作用,具有疏水性及粘附性特征,通过对微观局部进行亲水处理,实现了同一材料局部疏水和亲水共存结构的制作,证明了该方法表面浸润性调控的有效性。

干燥空气绝缘开关柜中应用的固封极柱绝缘结构设计及优化

为了实现气体绝缘开关柜的绝缘介质由SF6向干燥空气等环保型气体转变,开发一种结构小型化、绝缘水平满足要求的干燥空气绝缘开关柜中使用的固封极柱是亟需解决的问题。文中分析了40.5 kV SF6固封极柱置于干燥空气绝缘开关柜中的相间及对地电场分布,结果显示灭弧室动、静端盖板以及绝缘拉杆附近的气—固沿面电场严重超标,易造成沿面闪络。依据气—固复合绝缘理论,采取增加均压屏蔽网、改进绝缘壳体外观结构、重新设计绝缘拉杆等措施进行电场优化。通过仿真分析,优化设计后的固封极柱灭弧室端盖附近沿面最大场强由3.4 kV/mm降至2.03 kV/mm,绝缘拉杆沿面最大场强由4.1 kV/mm降至1.7 kV/mm。对优化前后的固封极柱进行了局部放电和雷电冲击耐压试验,局部放电试验的起弧电压由35 kV提升到62 kV,雷电冲击耐压试验的峰值耐受电压由145 kV提升到218 kV,证明了优化方案的可行性,为后续40.5 kV及更高电压等级的类似固封极柱的研发及优化提供了有关参考。

顶燃式热风炉燃烧过程数学模拟研究

一直以来,工业企业在全球能源消耗中占据着举足轻重的地位。作为这些企业的核心设备之一,热风炉在工业生产中发挥着无可替代的作用。热风炉既是能源消耗的主体,也是工业生产过程中不可或缺的热量提供者。热风炉的工作原理主要是利用燃料燃烧产生的热量,通过热交换器将热量传递给空气,产生高温热风。这些高温热风在工业生产中广泛应用于各种工艺流程,如烘干、烧结、熔炼等,对于提高生产效率和产品质量具有至关重要的作用。在介绍顶燃式热风炉燃烧器结构的基础上,探讨顶燃式热风炉数值模拟现状,重点分析了顶燃式热风炉燃烧几何模型和数学模型,并从速度分布以及温度场分布对数学模拟结果进行分析,望能通过优化燃烧过程,可以提高热风炉的燃烧效率,降低燃料消耗量和能源成本。

风冷干式变压器的热仿真分析及优化

对绕组温升和热点温度的有效预测与分析,是确保干式变压器安全、稳定运行的重要前提。模拟了一台8000 kVA干式变压器在强迫风冷条件下的温度场分布情况,并通过风冷温升试验验证了仿真结果的准确性及可靠性。在此基础上,讨论了模型简化方法和结构优化设计对温升模拟结果的影响规律并进行了误差分析。结果表明,所采用的数值仿真方法能够有效地预测变压器的温度分布规律,可为此类变压器的设计、优化和评估提供参考依据。