Formation of diffuse and spark discharges between two needle electrodes with the scattering of particles

The development of a nanosecond discharge in a pin-to-pin gap filled with air at atmospheric pressure has been studied with high temporal and spatial resolutions from a breakdown start to the spark decay.Positive and negative nanosecond voltage pulses with an amplitude of tens of kilovolts were applied.Time-resolved images of the discharge development were taken with a fourchannel Intensified Charge Coupled Device(ICCD)camera.The minimum delay between the camera channels could be as short as≈0.1 ns.This made it possible to study the gap breakdown process with subnanosecond resolution.It was observed that a wide-diameter streamer develops from the high-voltage pointed electrode.The ionization processes near the grounded pin electrode started when the streamer crossed half of the gap.After bridging the gap by the streamer,a diffuse discharge was formed.The development of spark leaders from bright spots on the surface of the pointed electrodes was observed at the next stage.It was found that the rate of development of the spark leader is an order of magnitude lower than that of the wide-diameter streamer.Long thin luminous tracks were observed against the background of a discharge plasma glow.It has been established that the tracks are adjacent to brightly glowing spots on the electrodes and are associated with the flight of small particles.

Measurement of Diffusion Coefficients of Air in Silicone Oil and in Hydraulic Oil

A piston-cylinder apparatus was established to measure the solubility and diffusivity of air in dimethyl silicone oils and in hydraulic oils based on the PVT state equation of air and the solution of unsteady one-dimensional diffusion equation.The measured diffusivity-temperature relation can be well fitted by the Arrhenius equation for engineering applications.The correlation between the solute diffusivity D and solvent viscosity μ is examined.In terms of Eyring＇s activation theory,the activation in the air-silicone-oil diffusion process is quite different from that in the momentum transport of the silicone oil：the activation entropy of the former is positive while that of latter is negative.However,the activation enthalpies of the two processes are in the same order of magnitude,which leads to the observation that Dμ/T is roughly constant.

Effect of Air Content on the Oxygen Diffusion Coefficient of Growing Media

An important parameter for describing oxygen availability in growing media is the air capacity, but this parameter does not include any information about the gas exchange with the surrounding atmosphere. The oxygen diffusion coefficient fulfills this requirement and may be better suited as a characteristic parameter to describe the oxygen regime. The measurement of the gas diffusion coefficient is a common method to describe the oxygenation in mineral soils, but this method has not been studied well on growing media yet. In this investigation four different growing media were used to measure the oxygen diffusion coefficient at two different bulk densities and four different water tensions in the laboratory. The effect of density and water tension on the oxygen diffusion coefficient in different growing media and the dependence on air content were investigated. The results show that both water tension and density have a major influence on oxygen diffusion. With increasing density and moisture content, a decrease of the oxygen diffusion coefficient can be observed. Between the substrates there are no significant differences regarding the oxygen diffusion coefficient at the same air content. Based on the oxygen diffusion coefficients of the substrates, the models describing the dependence of gas diffusion coefficients to air content in the literature were tested for the transferability to growing media. The Moldrup model [1] shows the best fit. The fit can be slightly further improved by modifying the tortuosity parameter.

An Analytical Air Pollution Model with Time Dependent Eddy Diffusivity

Air pollution transport and dispersion in the atmospheric boundary layer are modeled by the advection-diffusion equation, that is, essentially, a statement of conservation of the suspended material in an incompressible flow. Many models simulating air pollution dispersion are based upon the solution (numerical or analytical) of the advection-diffusion equation assuming turbulence parameterization for realistic physical scenarios. We present the general time dependent three-dimensional solution of the advection-diffusion equation considering a vertically inhomogeneous atmospheric boundary layer for arbitrary vertical profiles of wind and eddy-diffusion coefficients. Numerical results and comparison with experimental data are shown.

Air Pollution Steady-State Advection-Diffusion Equation: The General Three-Dimensional Solution

Atmospheric air pollution turbulent fluxes can be assumed to be proportional to the mean concentration gradient. This assumption, along with the equation of continuity, leads to the advection-diffusion equation. Many models simulating air pollution dispersion are based upon the solution (numerical or analytical) of the advection-diffusion equation as- suming turbulence parameterization for realistic physical scenarios. We present the general steady three-dimensional solution of the advection-diffusion equation considering a vertically inhomogeneous atmospheric boundary layer for arbitrary vertical profiles of wind and eddy-diffusion coefficients. Numerical results and comparison with experimental data are shown.

Mesoscopic numerical computation model of air-diffusion electrode of metal/air batteries

This work creates a droplet battery model based on the electrolyte performance in the porous electrode, studies the current density on the mesoscopic scale, and explains how the mesoscopic structure of the porous electrode influences the current density on the air-diffusion electrode. Near the three-phase line, there is a strong band containing nearly 80% current. For porous electrodes, the total current is proportional to the length of the strong band. Thus, it can be inferred that on the macroscopic scale, the longer the total length of the strong band on unit area is, the larger the current density is.

Laminar Diffusion Flames of Methane in a Co-annular Jet of Oxygen-Enriched Air

Oxygen rich combustion is a mean to increase the energy efficiency and to contribute to CO2 capture. Influence of oxygen enriched air on the stability of methane flames from non premixed laminar jets has been investigated experimentally. The burner consists of two coaxial jets： methane flowing out of the inner, oxidizer from the outer. The flame behavior is studied according to the proportion of oxygen in the oxidizer jet, the oxidizer and the methane jets velocities. The flame is either anchored to the burner, lifted, stationary or not or blown-out. The addition of oxygen produces a decrease of the lift height, a reduction of the length of the reaction zone and an increase in the soot emission. These results have been reported into diagrams of stability where the flame configurations are connected to the competition between the dynamic effect of the injection velocity and the chemical effect of oxygen addition.

我国大气环境模式的研究进展和未来展望

本文针对我国大气环境模式的发展历史和主要特点开展系统综述,并对大气环境模式的研究进行展望,提出未来可能的发展方向.我国自20世纪60年代开始大气环境模式方面的发展和应用研究,历经输送扩散模式、酸沉降模式、空气质量模式、气候-化学耦合模式、地球系统模式等不同阶段,自主发展了具有中国特色的大气环境模式,改进完善了国际先进的大气环境模式,在大气污染防治与管控、重大活动环境保障和气候变化应对等方面发挥了重要作用.未来需要进一步加强大气污染形成机理在模式的应用研究、排放清单反演和动态源排放模式研发、多源观测资料与大气环境模式融合、集合预报技术研发、非结构网格系统研发、基于人工智能的环境大模型研发,全面提升我国大气环境模式的整体性能,积极推进我国大气环境模式的开源化和国际化.

地铁站台公共区弥散送风系统结构参数研究

地铁站台公共区弥散送风系统(DASS)可以提供舒适的热环境,其结构设计参数会影响DASS送风效果。采用数值模拟方法,研究不同弥散送风板开口率、送风口数量、静压室高度以及下部空间高度等结构参数对站台公共区DASS送风效果的影响。结果表明:站台公共区气流分布均匀性和人员热舒适性随弥散送风板开口率和送风口数量的增加而增加;静压室高度在1.1m左右时的送风效果最好;下部空间高度越高,气流分布越均匀,但冷风感越强,综合初投资和系统送风效果,下部空间最优高度为3m。

屏蔽门漏风对地铁站台公共区弥散送风效果的影响研究

弥散送风系统(DASS)能为地铁站台公共区提供舒适的热环境,但地铁实际运行中站台存在屏蔽门漏风,对DASS送风气流的影响需要进一步研究。采用数值模拟方法,对屏蔽门漏风作用下站台公共区DASS的送风效果进行研究,并对DASS送风板开启位置进行了优化。结果表明:不考虑屏蔽门漏风作用时,一侧射流式DASS方案的站台公共区温度分布不均匀,靠近送风口一侧温度高,局部区域高于32℃;列车进站时,送风侧吊顶满布弥散送风板的方案使送风出现短路,部分气流直接从楼扶梯口排出,站台公共区靠近送风口一侧温度高于30℃,温度分布不均匀;楼扶梯附近的吊顶板封闭时,避免了气流短路现象,站台公共区温度在23~30℃范围内,送风效果得到改善;列车离站时,将楼扶梯附近的吊顶板封闭,人员活动区温度在28℃以内,满足热舒适要求。

花椒热风-微波组合干燥失水特性研究

花椒热风干燥降速期水分含量低,水分扩散慢,导致热风干燥耗时长。为提高干燥效率,并通过热风与微波组合干燥,分别进行热风干燥、微波干燥和热风-微波组合干燥实验,探究不同干燥参数对花椒失水特性的影响,以确定合理的干燥转换临界点和最优组合干燥模型,并将傅里叶准则数(F_(0))引入Fick第二扩散定律方程,求解有效水分扩散系数(D_(eff))。研究结果表明:热风和微波单独干燥时,升高风温风速和增加微波功率均有利于缩短干燥时间;热风-微波组合干燥花椒时,热风段转微波段的最佳目标含水率即为热风干燥的临界点含水率(65%(w.b)),且高热风温度和高微波功率均可使微波干燥段获得高失水速率;热风-微波组合干燥花椒热风段和微波段对应的最优模型分别为Wang and Singh模型和Page模型,D_(eff)范围分别为1.908×10^(-9)~3.547×10^(-9)m^(2)/s和1.883×10^(-8)~3.321×10^(-8)m^(2)/s。热风-微波组合干燥方式能够显著提高干燥效率,促进花椒内部水分扩散,干燥模型可为优化干燥工艺和设计干燥设备提供理论依据。

综掘工作面风幕阻尘效果影响因素研究

目前综掘工作面粉尘污染的研究多集中于单一因素对综掘工作面风幕阻尘效果的影响,而未充分考虑各因素间的交互作用,使得压风分流技术的工程应用效果欠佳。为明确附壁风筒径向出风距离、径向出风比及轴向出风距离对风幕阻尘效果的影响,以潘三矿810西翼机巷综掘工作面为研究对象,运用Fluent软件对径向出风距离为10~25 m、径向出风比为0.6~0.9及轴向出风距离为6~12 m条件下的风流分布和粉尘扩散情况进行数值模拟。结果表明:(1)随着径向出风距离增大,径向涡流风幕在巷道内的转变更充分,综掘机司机前端的风流分布越均匀,更有利于形成风速方向均指向工作面的轴向阻尘风幕。当径向出风距离为10 m时,距工作面7 m断面内涡流特性明显,风速方向紊乱;当径向出风距离为25 m时,距工作面7 m断面内,风流分布趋于均匀,风速方向均指向工作面,形成了能够覆盖全断面的轴向阻尘风幕。(2)随着径向出风比增大,整流风筒轴向风流风量减小,轴向风流风速和射流强度降低,轴向风流对综掘工作面前端气流的扰动减弱;径向出风比越大,越有利于形成风流方向指向工作面且能覆盖全断面的轴向阻尘流场,即轴向阻尘风幕。(3)径向涡流风幕的阻尘能力随径向出风比的增大先增强后减弱,轴向阻尘风幕的阻尘能力随径向出风比的增大而不断增强。(4)在采取压风分流风幕阻尘技术后,当压风总量为300 m^(3)/min,吸风量为400 m^(3)/min,附壁风筒径向出风距离为20 m,径向出风比为0.9,整流风筒轴向出风距离为8~10 m时,能很好地将粉尘聚集在吸尘口附近,达到高效控尘除尘的目的。在810西翼机巷综掘工作面进行现场测试,测点风速和粉尘质量浓度实测值与模拟值基本一致,高浓度粉尘被有效阻控于工作面前端,隔尘效果较为明显,验证了数值模拟的有效性。

气体射流冲击干燥对脱盐海参理化特性和微观结构的影响

为改善脱盐海参干燥时间长、干制品品质差的问题,该研究将气体射流冲击干燥(air impingement drying, AID)技术应用于脱盐海参干燥,研究了干燥温度(50、60和70℃)和气流速度(4、6和8 m/s)对脱盐海参干燥速率及干制品水分分布及状态、微观结构、硬度和皂苷含量的影响,并与热风干燥(hot air drying, HAD)进行对比。结果表明,随着干燥温度的增加,脱盐海参的干燥速率增加。AID不同干燥温度下脱盐海参的干燥时间比HAD 60℃的海参干燥时间缩短了6.67%~33.33%。温度为60℃时,风速对脱盐海参的干燥时间影响不显著(P>0.05)。微观结构分析表明,温度升高有利于增加物料表面的多孔结构,相同条件下AID海参样品的表面比HAD海参具有更多更大的多孔结构,使得AID海参干燥速率快于HAD。但随着风速的增加,脱盐海参表面因发生结壳现象阻止了形变,使得干海参孔洞结构变小,干燥速率降低。与HAD相比,AID海参的不易流动水弛豫时间向短弛豫时间移动更快,且峰幅度显著降低;干燥相同时间时(6 h),AID海参的质子密度信号比HAD减少更多,表明AID海参的水分迁移速率快于HAD的海参。随着AID温度和风速的升高,干海参的硬度呈先增加后减小的趋势。AID海参皂苷含量随着温度的升高而升高。AID海参的多孔结构不仅加速了水分迁移,而且利于营养成分渗出,提高了营养成分含量,相同条件下,AID海参的皂苷含量比HAD的海参增加了50.00%。综合考虑干燥效率和品质,温度为70℃,风速为6 m/s为脱盐海参AID的较好条件。研究结果有助于阐明AID提高脱盐海参干燥速率和营养成分保留率的机理,为生产高品质干海参提供理论依据和技术参考。

温度对绿色葡萄干色泽及干燥特性的影响

【目的】研究不同温度条件下热风干燥对葡萄干色泽相关指标、水分扩散系数的影响,为绿色葡萄干的工业化生产加工提供理论和技术支撑。【方法】采用不同温度(30、32.5、35、37.5和40℃)对无核白葡萄进行干燥,分析温度对葡萄色泽、水分扩散系数及制干品质的影响,拟合干燥动力学模型。【结果】干燥温度为35℃时绿色葡萄干比率最高达到64%,色泽与原料的差异最小,色差ΔE仅为6.99,C、h 0、L、a、b等色泽指标分别为18.23、1.4、14.57、2.99、17.95。叶绿素、叶绿素a、叶绿素b、类胡萝卜素、总酚含量分别为0.56、0.19、0.36、0.32、0.18 mg/g。35℃更适宜绿色葡萄干加工。最符合葡萄干燥的模型,决定系数R 2值最大,误差平方和、SSE和均方根误差RMSE均值最小,分别为0.9981、0.0054和0.0077。绿色葡萄干最适宜的有效水分扩散系数为5.3348×10^(-9)。【结论】热风干燥温度为35℃时最有利于无核白绿色葡萄制干,35℃时有效水分扩散系数分别为30、32.5、37.5和40℃的114.13%、110.58%、95.17%和76.58%,Logarithmic模型可以有效的描述热风干燥工艺条件下葡萄果实水分的变化规律。

不同一次风系数下热解气扩散燃烧及NO排放特性数值模拟

利用数值模拟方法,在质量、动量、热量传递及化学反应相耦合的综合CFD模型上,以带有旋流一次风喷嘴的燃烧器为研究对象,得到了不同一次风系数下塑料热解气-空气非预混湍流燃烧的燃烧温度、效率和NO排放数据,并进行了一次风系数的优选。研究结果表明一次风系数对NO排放的影响不只体现在燃烧器最高温度上,同时会通过改变燃烧器内的局部温度和流场分布影响NO排放。在本研究参数范围内,一次风系数保持在0.8~0.9时可满足一定的燃烧效率和较高出口温度下的低NO排放要求。

城市气象条件与重污染扩散精细化预报技术研究

为解决城市气象预报不准确,污染扩散防控不及时等问题,对城市气象条件与重污染扩散精细化预报技术进行研究。在分析影响城市气象条件的基础上,建立重污染扩散影响参数,确定精细化标准。在不同气象条件下分析并计算污染程度,建立气象预报模型区分不同气象环境下污染物的干沉浸率和湿沉积率,获取空气污染物在城市上空的平均停留时间。根据污染物沉积速度及实际降水强度,构建空气污染条件下精细化预报模型,实现空气污染扩散精细化预报。实验结果表明,研究技术能有效预报城市气象变化情况,并实现重污染扩散精准预报。

活性炭强化泡沫钛基空气扩散电极电过臭氧氧化及降解布洛芬效能

为了提高传统污水处理技术对布洛芬这一新型污染物的去除效率,本研究构建了一种基于活性炭强化的泡沫钛空气扩散电极(AC@Ti-F GDE)的电过臭氧处理体系。该体系通过增强传统电过臭氧体系的氧化效能,用于布洛芬的去除。结果表明,相对于传统的电极(Ti-F),微孔泡沫钛空气扩散电极(Ti-F GDE)体系中的HO•相对含量提升了155.7%。在投加活性炭后,AC@Ti-F GDE体系中的HO•相对含量在Ti-F GDE体系的基础上进一步提升了35.4%。这种显著提升的HO•产量得益于AC@Ti-F GDE体系中H2O2的增加,从而进一步强化了电过臭氧的氧化效能。通过精确调控活性炭的投加密度和颗粒粒径,确定了AC@Ti-F GDE电过臭氧体系中最佳的活性炭投加密度为0.8 mg/cm^(3),最佳颗粒粒径为850μm。在此基础上,将AC@Ti-F GDE电过臭氧体系应用于布洛芬污染物的处理,通过对比不同因素下该体系降解布洛芬的程度,得到最佳运行条件:pH值为7.00,电流为150 mA,O3,gas浓度为52.2 mg/L,并采用液相质谱检测布洛芬降解过程中中间产物,得出了该体系的降解矿化机理:布洛芬首先通过羟基化、去甲基化和脱羧等反应逐步氧化支链,随后攻击苯环并开环生成脂肪酸,最终被进一步矿化生成CO_(2)和H_(2)O。AC@Ti-F GDE电过臭氧新体系,强化了传统电过臭氧体系氧化效能,为后续电过臭氧处理布洛芬提供新思路。

污染气体扩散效应的城市土地规划布局优化方法研究

为了提高空气环境质量,提出了考虑污染气体扩散效应的城市土地规划布局优化方法。分析大气污染地面扩散模式,计算风向三维空间的空气污染浓度变化关系,得到扩散大气污染地面轴,利用景观破碎度、优势度和分离度加权计算土地景观干扰程度,设置指标权重,获得生态风险指标与抵抗能力。根据合理的空间布局和适度的绿地空间投入,增加点状方式土地绿色空间体系布局,算出规划面积并均匀调整分布状况,完成城市土地规划布局优化。通过实验分析,证明所提方法能够合理的优化城市土地规划布局,提高污染气体扩散程度,减少环境污染。

脱盐海参气体射流冲击干燥特性及复水品质

为探索干燥条件对脱盐海参气体射流冲击干燥(air impingement drying,AID)特性的影响,提高海参干制品品质、缩短干燥时间,该文探讨AID温度(50、60、70℃)和气流速度(4、6、8 m/s)对脱盐海参干燥特性、有效水分扩散系数(Deff)、活化能(Ea)、干制品复水比和氨基酸含量的影响,用6种常见的干燥模型对干燥曲线进行拟合,并以热风干燥(hot air drying,HAD)为对比。结果表明,风速为6 m/s时,AID不同干燥温度下脱盐海参的干燥时间比HAD 60℃的干燥时间缩短6.67%~33.33%。温度为60℃时,风速对脱盐海参干燥时间影响不显著。不同干燥条件下,复水比无显著性差异。AID海参的氨基酸含量(45.91~47.54 g/100 g)随着温度的升高而升高。相同条件下,AID海参的氨基酸含量比HAD海参增加4.46%。AID脱盐海参的Deff最高为2.134×10⁃9,所需的活化能为16.38 kJ/mol。比较模型预测指标发现,Page模型具有较高的拟合度(R2>0.99),模型预测值和试验值误差仅为2.01%,可较准确地预测AID过程中脱盐海参的水分变化规律。

孔隙率对多孔板弥散送风效果的影响研究

弥散送风系统(DCV)由上部静压室、多孔吊顶板、下部房间三部分组成,送风气流通过多孔吊顶板进入下部房间,吊顶板的孔隙大小与弥散送风过程密切相关,目前缺乏吊顶板孔隙率对弥散送风效果的影响研究。采用CFD数值模拟方法,建立了某采用弥散送风系统的办公室的数值计算模型,分析了不同孔隙率下吊顶板对流和辐射传热、室内热环境、热舒适性和空气龄。结果表明:孔隙率由5%增加至20%时,室内垂直温度梯度随之增加;孔板与下部房间的对流和辐射换热量随孔隙率增加而降低,对流换热量占比由6%降低至-3.2%,辐射换热量占比由32%降至17%;人员的热舒适性和平均空气龄随孔隙率增加而变差,PMV值由±0.5变化至±0.8,空气龄由467s变化至541.4s。