Three modes of a direct-current plasma jet operated underwater to degrade methylene blue

A direct-current air plasma jet operated underwater presents three stable modes including an intermittently-pulsed discharge, a periodically-pulsed discharge and a continuous discharge with increasing the power voltage. The three discharge modes have different appearances for the plasma plumes. Moreover, gap voltage-current characteristics indicate that the continuous discharge is in a normal glow regime. Spectral lines from reactive species（OH, N2, N2^＋, Hα,and O） have been revealed in the emission spectrum of the plasma jet operated underwater.Spectral intensities emitted from OH radical and oxygen atom increase with increasing the power voltage or the gas flow rate, indicating that reactive species are abundant. These reactive species cause the degradation of the methylene blue dye in solution. Effects of the experimental parameters such as the power voltage, the gas flow rate and the treatment time are investigated on the degradation efficiency. Results indicate that the degradation efficiency increases with increasing the power voltage, the gas flow rate or the treatment time. Compared with degradation in the intermittently-pulsed mode or the periodically-pulsed one, it is more efficient in the continuous mode, reaching 98% after 21 min treatment.

Direct Numerical Simulation of Particle Dispersion in Gas-Solid Compressible Turbulent Jets

A numerical method was developed to directly simulate the compressible, particle-laden turbulent jets.The fourth order compact finite difference schemes were used to discretize the space derivatives. The Lagrangian method was adopted to simulate the particle motion based on one-way coupling. It is found that the turbulent intensity profiles attain self-similar status in the jet downstream regions. At the Stokes number of 1, particles are concentrated largely in the outer boundaries of the large-scale vortex structures with the most uneven distribution and the widest dispersion in the lateral direction. Particles at the much smaller Stokes numbers are distributed evenly in the flow field, and the lateral dispersion is also considerable. Distribution of particles at much larger Stokes numbers is more uniform and the lateral dispersion becomes small. In addition, the inflow conditions have different effects on the particle dispersion. The direct numerical simulation (DNS) results accord with the previous experiments and numerical studies.

Numerical Simulation of Direct-contact Condensation from a Supersonic Steam Jet in Subcooled Water

直接接触的冷凝作用的现象，在驾驶的蒸气使用喷气注射者，核反应堆紧急情况核心冷却系统和直接接触的热 exchangers，被在使过冷的水里为蒸气的直接接触的冷凝作用介绍一个热平衡模型计算地调查。介绍的冷凝作用模型是在接口的双方上照顾热转移过程并且使用一条可变蒸气水泡直径的二个抵抗模型。在使过冷的水坦克的超声的蒸气喷气的注射用 Euler-Euler 多相的流动模型被模仿流畅与冷凝作用模型一起的 6.3 代码合并了。模拟与出版试验性的数据和相当好的同意相比的计算液体动力学(CFD ) 的调查结果被观察在之间二，因此验证冷凝作用模型。为羽毛从 2.73-7.33 改变的蒸气的无尺寸的穿入长度的 CFD 模拟的结果，当冷凝作用热转移系数从 0.75-0.917 MW 汯敹桴牥?晬湯 ? 变化时 ???? 琠楲敭潳汹？？

Discussion of Direct Numerical Simulation Method for Supercritical Carbon Dioxide Jet Flow

A kind of direct numerical simulation method suitable for supercritical carbon dioxide jet flow has been discussed in this paper. The form of dimensionless nonconservative compressible Navier-Stokes equations in a two-dimensional cartesian coordinate system is derived in detail. High accurate finite difference compact schemes based on non-uniform grid system are introduced to solve the equations. The simulation results of the three vortex pairing phenomenon of plane mixing layer and a compressible axisymmetric jet flow field show that the discussed numerical simulation method is feasible to calculate the supercritical carbon dioxide jet fluid. And it is found that the difficulties of splitting the convective terms in conservation Navier-Stokes equations, which are brought by the supercritical carbon dioxide fluid pressure state equation, can be avoided by solving the nonconservative compressible Navier-Stokes equations.

直射喷嘴结构对超低温氮气射流温度和速度的影响

液氮冷却低温切削是实现钛合金等难加工材料的绿色、高质量加工的有效手段之一。为实现面向超低温氮气射流过程温-速控制的喷嘴结构优选,采用数值模拟结合实验研究的方法,探析锥直型喷嘴入口直径D、出口直径d、收缩角α0以及长径比l/d对出口射流场温-速分布的影响规律。研究结果表明:存在一核心结构场使得场内射流速度和温度与喷嘴出口处的一致,而核心结构场外速度衰减幅值与温升幅值随出口直径d增加而减小。在实验条件下,当d从2.0 mm增至4.0 mm时,射流速度衰减幅值自386.3 m/s降至40.1 m/s,射流温升幅值自92.7 K降至41.1 K;射流速度核心区长度sn1和射流温度核心区长度sn2与d呈线性正相关,且sn1的变化率为sn2变化率的1.4倍;相较于l/d,d对出口轴心射流速度um的影响更显著。随着d从2.0 mm增至4.0 mm,um降低了74.9%;随着长径比l/d从1增至4,um增加了3.2%,表明减小喷嘴出口直径和增大长径比有利于提高锥直型出口射速。

稀薄流高超声速钝化前缘逆向射流流场特征研究

为准确预测稀薄过渡区逆向射流对稀薄大气的干扰流动特征,本文采用直接蒙特卡洛算法(DSMC),在自由流马赫数为7的情况下,对稀薄流中逆向射流干扰下的高超声速流动进行了数值模拟。计算中考虑了60~90 km高度的典型大气环境,研究了压比和自由流克努森数对压力、剪切力和热流密度的影响规律。结果表明,逆向射流改变了流场结构,且具有明显的热防护性能,但减阻效果不明显。逆向射流对高超声速稀薄来流的影响随压比的增加明显增强,形成的马赫盘大小也随之增加。高度的增加伴随稀薄效应不断增强,自由流克努森数增大,导致弓形激波厚度随高度增加而增加,壁面处的回流区范围不断减小至消失。这项研究初步揭示了稀薄流中逆向射流/高超声速流动相互作用的机制。

船用微引燃甲醇发动机喷油器参数对燃烧和排放特性的影响

[目的]为改善大功率船用发动机燃烧、性能及排放,采用柴油微喷引燃甲醇喷射方式,研究发动机缸内燃烧和排放特性。[方法]基于一台大缸径船用ACD320中速柴油机,建立柴油微喷引燃甲醇发动机三维仿真模型,研究喷油器参数(喷孔数与甲醇喷雾夹角γ)对大缸径船用甲醇发动机燃烧性能与排放特性的影响。[结果]研究结果表明:随着喷孔数的增加,缸内甲醇雾化效果较好,使缸内工质混合较充分,CA50提前,燃烧持续期缩短,获得了较高的指示热效率和较好的燃油消耗率,并有助于降低碳烟排放,但会导致NO_(x)排放量升高。但随着甲醇喷雾夹角的增大,指示热效率增大,能够获得较好的燃油经济性和较低碳烟排放量。当甲醇喷雾夹角位于柴油喷雾夹角时(γ>60°),缸内火焰传播速度较快,指示热效率较大,燃料燃烧较充分,获得碳烟最低排放量和最优燃油消耗率。[结论]分析结果可为发动机喷油器布置提供了理论依据。

导向槽定向水力压裂煤层增透强化瓦斯抽采技术及应用

针对低透气性高瓦斯煤层预抽瓦斯困难问题,提出导向槽定向水力压裂煤层增透技术,通过理论推导计算煤层段扩孔后塑性区分布,分析穿层钻孔煤层段水压裂缝的起裂与扩展,揭示导向槽定向水力压裂煤层增透的力学机制,研发导向槽定向水力压裂煤层增透装备。在山西中兴煤矿进行现场应用,结果表明:利用水射流方法对穿层钻孔煤层段进行扩孔,使得煤中产生形似圆柱孔洞,穿层钻孔围岩塑性区半径与钻孔半径成正比,钻孔扩孔是增大塑性区范围的一种有效方法,裂隙扩展明显,瓦斯采出率提高。同时研发了一种导向槽定向水力压裂防突成套装备,主要部件有移动高压水力泵站、喷头、喷嘴、螺旋辅助排渣水射流高压钻杆、孔口防喷装置以及高压旋转接头,结合井下水力化作业远程监测和控制,现场监测结果表明,通过增透作业钻孔的方法,平均瓦斯浓度和瓦斯抽采混合量提高到常规孔的2.75倍和1.81倍,说明采取导向槽定向水力压裂措施的增透效果显著。

Preparation of novel Ni-Ir/γ-Al_2O_3 catalyst via high-frequency cold plasma direct reduction process

The novel Ni-Ir/γ-Al2O3 catalyst, denoted as NIA-P, was prepared by high-frequency cold plasma direct reduction method under ambient conditions without thermal treatment, and the conventional sample, denoted as NIA-CR, was prepared by impregnation, thermal calcination, and then by H2 reduction method. The effects of reduction methods on the catalysts for ammonia decomposition were studied, and they were characterized by XRD, N2 adsorption, XPS, and H2-TPD. It was found that the plasma-reduced NIA-P sample showed a better catalytic performance, over which ammonia conversion was 68.9%, at T = 450℃, P = 1 atm, and GHSV = 30, 000 h^-1. It was 31.7% higher than that of the conventional NIA-CR sample. XRD results showed that the crystallite size decreased for the sample with plasma reduction, and the dispersion of active components was improved. There were more active components on the surface of the NIA-P sample from the XPS results. This effect resulted in the higher activity for decomposition of ammonia. Meanwhile, the plasma process significantly decreased the time of preparing catalyst.

煤矿井下连续管钻进管柱分析及射流钻进实验

由于可连续起下钻、不间断循环等优势,连续管钻井已成为近年来发展最快的石油钻井技术之一,开发煤矿井下连续管钻进技术是煤矿实现“少人化”甚至“无人化”钻探的重要技术途径。针对该技术在煤矿井下应用存在的管柱优选、钻进方法等关键问题,提出了连续管射流定向钻进方法,根据煤矿井下钻探用泥浆泵能力和孔深设计,分析了不同管径、不同弯曲比(r0/Rb)连续管流体摩阻;采用数值模拟方法,分析了不同连续管管径与钻孔孔径比(管孔比rc)情况下近水平钻进管柱屈曲形态及与孔壁接触应力;通过旋转射流水力学参数研究和破岩效果实验,给出了最佳射流钻头参数:通过连续管射流定向钻进实验,分析了射流定向钻进造斜规律,不同流量、钻进速度与钻孔孔径的关系。结果表明:?19~?31.75 mm连续管的弯曲半径可满足煤矿坑道空间要求;连续管流体摩阻的主要影响因素为管径和流量,在井下常用泥浆泵流量200 L/min、压力31.5 MPa、钻孔深度200 m情况下,?31.75 mm连续管为最佳管柱方案;管孔比rc=0.454时,连续管与孔壁接触应力稳定,压应力呈线性变化;采用?34.5 mm/5×1.0 mm(5个孔径1.0 mm的喷嘴)喷射钻头+?40 mm液力换向器+?31.75 mm连续管钻具组合钻进,平均增倾角能力0.67 (°)/m,平均降倾角能力为0.61 (°)/m,平均增/减方位能力0.45 (°)/m;通过控制射流流量和钻进速度,钻孔直径可控制在?70 mm左右;研究成果为煤矿井下连续管钻进技术与装备的开发提供了理论基础。

Electric-Jet Assisted Layer-by-Layer Deposition of Gold Nanoparticles to Prepare Conducting Tracks

A suspension of 15nm diameter gold nanoparti-cles has been deposited along a line on a silicon substrate with the assistance of a jet generated in an electric field. In order to control the evaporation of the solvent used to suspend the gold nanoparticles, a heating device was used to change the substrate temperature. Layer-by- layer deposition enabled the direct writing of gold tracks having an electrical resistivity of 1.8 × 10-7 Ωm, only about an order of magnitude above the electrical resistivity of bulk gold.

Electrohydrodynamic direct-writing of conductor–insulator–conductor multi-layer interconnection

A multi-layer interconnection structure is a basic component of electronic devices, and printing of the multi-layer interconnection structure is the key process in printed electronics. In this work, electrohydrodynamic direct-writing （EDW） is utilized to print the conductor-insulator--conductor multi-layer ~nterconne^ction structure. Silver ink is chosen to print the conductor pattern, and a polyvinylpyrrolidone （PVP） solution is util^zed to f^bricate the insulator layer between the bottom and top conductor patterns. The influences of EDW process parameters on the line width of the printed conductor and insulator patterns are studied systematically. The obtained ~es^l~s show that the line width of the printed structure increases with the increase of the flow rate, but decreases with the increase of applied voltage and PVP content in the solution. The average resistivity values of the bottom and top silver conductor tracks are determined to be 1.34 × 10-7 Ω.m and 1.39×10-7 Ω.m, respectively. The printed PVP layer between the two conductor tracks is well insulated, which can meet the insulation requirement of the electronic devices. This study offers an alternative, fast, and cost-effective method of fabricating conductor-insulator-conductor multi-layer interconnections in the electronic industry.

Optical characterization of single-crystal diamond grown by DC arc plasma jet CVD

Optical centers of single-crystal diamond grown by DC arc plasma jet chemical vapor deposition(CVD) were examined using a low-temperature photoluminescence(PL) technique. The results show that most of the nitrogen-vacancy(NV) complexes are present as NV-centers, although some H2 and H3 centers and B-aggregates are also present in the single-crystal diamond because of nitrogen aggregation resulting from high N_2 incorporation and the high mobility of vacancies under growth temperatures of 950–1000°C. Furthermore, emissions of radiation-induced defects were also detected at 389, 467.5, 550, and 588.6 nm in the PL spectra. The reason for the formation of these radiation-induced defects is not clear. Although a Ni-based alloy was used during the diamond growth, Ni-related emissions were not detected in the PL spectra. In addition, the silicon-vacancy(Si-V)-related emission line at 737 nm, which has been observed in the spectra of many previously reported microwave plasma chemical vapor deposition(MPCVD) synthetic diamonds, was absent in the PL spectra of the single-crystal diamond prepared in this work. The high density of NV-centers, along with the absence of Ni-related defects and Si-V centers, makes the single-crystal diamond grown by DC arc plasma jet CVD a promising material for applications in quantum computing.

Three-Dimensional Visualization of Shock Cell Structure and Screech Tone Emission in Underexpanded Circular Jet

The three-dimensional visualization of flow and screech-tone emission from an underexpanded circular jet is first investigated experimentally using high-speed cross-schlieren imaging and microphone measurements in the cross-sectional planes along the jet axis. This experimental technique allows the visualization of the shock-cell structure, directivity of sound intensity, and frequency spectrum in the cross-sectional planes of the screeching jet. The high-speed cross-schlieren observation of the screeching jet shows the occurrence of an asymmetrical shock-cell structure that is generated by the flapping mode in the screeching jet. This contributes to the generation of a screech tone propagating upstream along the jet axis and non-uniform sound intensities around the jet in circumferential direction. These observations by high-speed cross-schlieren imaging were validated by the microphone measurements.

双直喷型柴油JCCI模式的参数优化数值模拟

针对双直喷型柴油射流控制压燃模式,利用三维数值模拟结合优化算法,分析了预喷正时、射流正时、初始温度、初始压力和预喷射能量比等参数对发动机燃烧与排放性能的影响.计算结果表明,射流正时可以有效控制着火相位和燃烧相位,预喷正时主要影响预混合气燃烧后期.当燃烧相位在6~8°CA ATDC区间时,发动机经济性最佳.射流正时和预喷正时均较晚时,燃烧呈现两阶段高温放热过程,整体燃烧速率大于射流正时与预喷正时均较早的单阶段高温放热过程,因此等效燃油消耗率下降6.80 g/(kW·h).

New Formulation for Semi-Empirical Correlations for Penetration Jets

Correlations for the extension of a water vapor jet injected in a liquid pool were historically proposed considering the mass flux (kg/m2/s) as a constant. The results were satisfactory, however adjusting the values by linear regression. Although, it presents the following drawbacks: 1) the formulation is only valid for the specific range of data for what it was created;2) it does not allow the analytical evaluation of the heat transfer coefficient from the extension equation. This paper proposes a new formulation for the calculation of the mass flux, in such a way to remove both of these drawbacks.

基于喷孔布置及喷射参数协调控制的双直喷发动机燃烧及碳烟排放特性研究

通过建立三维计算流体力学(computational fluid dynamic,CFD)柴油/天然气双直喷模型耦合多组分混合物简化化学动力学机理及现象学碳烟模型,模拟研究了天然气射流中心轴线与水平方向夹角α、天然气喷射持续期(natural gas injection duration,NID)的协调作用对柴油微引高压直喷天然气发动机燃烧过程及碳烟生成、氧化过程的影响。结果表明:缩短NID可提高扩散火焰的传播速度,增加燃烧区域的化学反应速率,且最高燃烧压力、峰值放热率、最大压力升高率(maximum pressure rise rate,MPRR)、指示热效率(indicated thermal efficiency,ITE)升高;随NID缩短,A_(4)、C_(2)H_(2)消耗反应速率增加,OH生成峰值增加,碳烟生成降低而氧化增强。增大α促进了大尺度涡旋结构的生成,降低了进入挤气区域的燃料比例,同时利于ITE的改善;较短的NID下,增大α后最高燃烧压力、峰值放热率提升明显;α增大至20°可显著降低A_(4)、C_(2)H_(2)生成峰值,抑制碳烟成核及表面生长反应,降低碳烟生成。综合考虑最高燃烧压力、ITE、MPRR及碳烟排放,确定两个优化方案分别为:α=15°&NID=16.5°及α=20°&NID=21.5°。

外加交变磁场对MIG焊电弧及射流过渡的影响

利用高速摄影系统采集交变间歇磁场下MIG焊的电弧和射流过渡图片。通过受力分析,研究不同磁场方向下电弧和射流过渡的变化。结果表明:保持励磁频率为40 Hz,励磁电流在0~1.0 A范围内,随着磁场方向在纵向由向下到向上的周期变化,电弧绕焊丝轴线呈周期性顺时针、逆时针旋转,且出现扩张和收缩现象。焊丝末端导电流体由液锥、液流束和细小球状熔滴组成。当励磁电流为0 A时,液锥和液流束沿焊丝轴向下垂,未发生偏转,熔滴沿着液流束末端向熔池内平稳过渡。当励磁电流为0.2、0.6 A时,液流束呈短粗状,小角度偏离焊丝轴向做顺、逆时针旋转。当励磁电流达到0.8、1.0 A时,液流束呈细长状,导电流体呈“S”形,大角度偏离绕焊丝轴向做周期性逆时针和顺时针旋转。

高分辨率熔融金属电流体喷印直写工艺

固态金属材料以其高导电性和低成本等特点在柔性电子器件的制造中具有巨大的应用潜力,但现有熔融金属微制造工艺的制造精度有限。为了提高熔融金属在导电结构制备中的分辨率,研发了一种熔融金属电流体喷印直写打印方法。对该方法的基本原理进行阐述。利用自主研发的熔融金属电流体喷印喷头装置,以金属锡为原料进行实验,对打印工艺参数进行了研究。探究了脉冲峰值电压、喷嘴高度、打印速度对锡线成型质量的影响规律,研究结果表明:当脉冲峰值电压4.0 kV,喷嘴高度0.20 mm,打印速度2.0 mm/s时,锡线成型质量最好,能实现线宽约为50μm的锡线制备。最后,结合优化的工艺参数在聚酰亚胺(PI)薄膜上制作了高分辨率导电图案,验证了该方法的可行性,为熔融金属材料在柔性电子器件制造中的应用提供了新途径。

基于缸内压缩空气直喷的工作特性研究

提出压缩空气缸内直喷发动机概念,建立了ADI计算模型和同等燃烧室的传统发动机模型。ADI发动机在常用的中低转速及负荷区域比传统气道进气构型的缸内循环工质的理论计算温度下降约200℃,提高了发动机热效率并降低了NO_(x)原始排放水平,使NO_(x)原始排放值降低超过50%。在排量为1.0 L的ADI发动机上实现了40%的热效率输出,使得开发小型化、高热效率、低排放的混动发动机成为可能。