等离子体反应器中传热与流动的三维数值模拟

本文采用我们新发展的三维计算机程序,对有载气和颗粒从单个喷孔侧向喷射的等离子体反应器中的传热与流动以及颗粒的运动轨迹与加热历程进行了三维数值模拟,并与相应的二维数值模拟结果进行了比较。模拟结果表明侧向喷入的载气所引起的三维流动效应相当明显,不同的颗粒在反应器内的运动轨迹与加热历程也有明显差别。     

高频感应热等离子体中粉末颗粒的运动行为研究

建立了高频电感耦合等离子体炬的二维轴对称模型,利用商用软件FLUENT对钛粉颗粒在纯氩热等离子体内的运动轨迹进行了模拟,研究了前驱体粒径及载气流量的变化对粉末颗粒受力过程的影响。研究结果表明,粒径小的颗粒受炬内回流作用的影响较大,颗粒运动轨迹杂乱,而粒径大的颗粒受回流的影响则很小;降低载气流量可以使钛粉的受热更加充分,使得更多的颗粒被加热至熔化,可提高粉末的球化率。     

高频感应热等离子体中粉末颗粒的运动行为研究

建立了高频电感耦合等离子体炬的二维轴对称模型,利用商用软件FLUENT对钛粉颗粒在纯氩热等离子体内的运动轨迹进行了模拟,研究了前驱体粒径及载气流量的变化对粉末颗粒受力过程的影响。研究结果表明,粒径小的颗粒受炬内回流作用的影响较大,颗粒运动轨迹杂乱,而粒径大的颗粒受回流的影响则很小;降低载气流量可以使钛粉的受热更加充分,使得更多的颗粒被加热至熔化,可提高粉末的球化率。     

喷雾参数对溶液热等离子体喷涂的影响

本文应用溶液注入热等离子体喷徐传热和流动过程的三维数学模型.对溶液喷雾喷入参数对溶液喷雾在热等离子体射流中运动和加热历程的影响进行了研究.结果表明以一定的角度逆向喷入溶液可以强化溶液喷雾的加热蒸发过程,在一定范围内提高溶液初始喷入速度,可以使小粒径的液滴获得较大的动量进入射流高温区获得充分加热.结果还表明,为了得到致密...     

层流与湍流等离子体冲击射流特性比较

本文采用数值模拟方法,对层流与湍流氩等离子体射流在空气环境中冲击平板时的流动与传热特性进行了对比研究.结果表明,在平板和射流进口间的距离较大时,平板的存在只对其附近的射流参数分布有较大影响,层流等离子体冲击射流的温度与轴向速度的轴向梯度明显小于湍流等离子体冲击射流情形;由于在平板表面形成的径向壁面射流对引射的附加贡献,层流和湍流等离子体冲击射流对环境空气的引射量明显增加.     

紫外光诱导纳米颗粒胶体微射流碰撞特性（英文）北大核心CSCD

采用流体力学模拟方法,建立了垂直非淹没射流的计算流体动力学模型,研究了在紫外光诱导纳米颗粒胶体射流中用直径D为500μm的微孔光-液耦合喷嘴进行抛光加工的冲击动力学,分析了非淹没射流条件下光-液耦合喷嘴内、外的流场分布情况及其对工件表面的喷射冲击特征,对紫外光诱导纳米颗粒胶体射流冲击动力学过程进行了理论描述。计算结果表明,在1MPa入射压力时,微孔光-液耦合喷嘴口TiO2胶体的喷射速度约为30m/s,其集束匀速喷射距离约为5mm。在此喷射距离时进行垂直喷射,在胶束与工件表面的冲击射流作用区域,其射流静压最大值分布在射流冲击作用中心,但射流动压及射流合成速度在此区域的截面分布呈"W"形状,射流动压及速度最大值出现在胶体射流束的外环直径约2mm处。     

气热耦合多孔气膜冷却流动的数值研究

对具有气膜冷却的某涡轮叶栅,提取中部截面型线进行了平面叶栅的气热耦合数值模拟,研究了多孔射流气膜冷却流动的特点.主流与固壁气流耦合计算表明,冷却气流在冷却腔内的流动过程中,被固体壁面加热,在喷射入主流场之前温度升高幅度较大,使得沿程后部的冷却效果减弱,同时研究了多射流孔附近区域三维定常流动的流场.     

紫外光诱导纳米颗粒胶体微射流碰撞特性（英文）

采用流体力学模拟方法,建立了垂直非淹没射流的计算流体动力学模型,研究了在紫外光诱导纳米颗粒胶体射流中用直径D为500μm的微孔光-液耦合喷嘴进行抛光加工的冲击动力学,分析了非淹没射流条件下光-液耦合喷嘴内、外的流场分布情况及其对工件表面的喷射冲击特征,对紫外光诱导纳米颗粒胶体射流冲击动力学过程进行了理论描述。计算结果表明,在1MPa入射压力时,微孔光-液耦合喷嘴口TiO2胶体的喷射速度约为30m/s,其集束匀速喷射距离约为5mm。在此喷射距离时进行垂直喷射,在胶束与工件表面的冲击射流作用区域,其射流静压最大值分布在射流冲击作用中心,但射流动压及射流合成速度在此区域的截面分布呈"W"形状,射流动压及速度最大值出现在胶体射流束的外环直径约2mm处。     

不同湍流模型对热等离子体射流模拟的影响

本文应用大气压等离子体射流传热与流动的三维数学模型,在相同初始条件下,计算得到了采用不同湍流模型时氩等离子体射流对称轴线上的温度、速度及空气质量分数分布,并与文献中同等条件下的实验结果进行了比较,结果表明采用标准κ-ε模型和Realizableκ-ε模型时与实验结果相差较大,而采用RNGκ-ε湍流模型时模拟结果与实验数...     

屏蔽气体对氩等离子体冲击射流的影响

在空气环境中利用氩等离子体射流进行材料加工时,环境空气卷吸进入射流可能会引起金属材料氧化。采用同轴屏蔽气体保护是减小该不利影响的一种可行方案。为此本文对空气环境中层流氩等离子体冲击射流特性受屏蔽气体影响问题进行了数值模拟研究,重点考察了屏蔽气体速度等对材料加工区氧含量的影响。     

Effect of temperature of supersonic heterogeneous flow on the erosion-spraying transition

This publication is a continuation of works devoted to problems that arise in heterogeneous technologies. The matter of parameters that define the transition from surface erosion to particle spraying onto the surface is addressed. In particular, we experimentally examine the influence of temperature of the supersonic heterogeneous flow (carrier-gas temperature and particle temperature) interacting with the streamlined obstacle on the occurrence probability of either surface damage or particle spraying. This work was supported by the Russian Foundation for Basic Research (Grant No. 05-02-16603).     

喷流冷却复合陶瓷薄片激光器的热特性仿真分析及实验研究

为分析喷流冷却复合陶瓷薄片激光器的热特性,设计用于冷却复合陶瓷薄片的喷流冷却系统.利用湍流换热理论和计算流体动力学仿真方法建立喷流冷却复合陶瓷薄片激光器的流固耦合热仿真模型,定义评价其冷却能力和冷却均匀性的定量参数.根据该仿真模型得到喷流冷却系统的最优设计参数,并进行实验验证.使用163孔喷板,流量为0.2kg/s,入口温度为20℃,在1200 W泵浦时获得359 W激光输出功率,并测得复合陶瓷薄片上表面的最高温度为92℃.激光输出功率与复合陶瓷薄片上表面温度均与泵浦功率呈近似正线性关系,且温度的实验值与仿真值相符度较高.     

The effect of target size on α-Fe nanoparticle preparation by?pulsed laser ablation

Two methods of preparing Fe nanoparticles at atmospheric pressure were conducted using pulsed laser ablation of a 0.5-mm-diameter Fe wire and a bulk Fe target. Passivated α-Fe nanoparticles covered with a shell of γ-Fe₂O₃ were prepared at different process parameters. The influences of average laser power, repetition rate, pulse duration and carrier-gas pressure on the mean particle size for two laser ablation methods were investigated, respectively. The results show that the target size has a large effect on the nanoparticle preparation though we have the same range of laser process parameters. Except the carrier-gas pressure, the influence of the laser parameters on the mean particle size is almost opposite for the two laser ablation methods. Besides, the ablation mechanisms were discussed to understand the variation of mean particle sizes with target size.     

Cold processing of green state LTCC with a CO2 laser

We report a novel “cold” self-cleaning technique for processing low temperature co-fired ceramic (LTCC) in the “green” state at high resolution and high speed, using a low power carbon dioxide laser. A particle ejection process involving both the ceramic grains and the organic binder produces material removal rates of >100 μm per pulse with lateral processing resolution of 50 μm and depth resolution comparable to ceramic grain size with no heat-effected zone or other deleterious thermal effects. The process has been used to drill microvias and to machine arbitrary shapes with high resolution. PACS 79.20.Ds; 42.62.Cf; 42.55.Lt; 81.20.Wk     

Visualization of dilute hydrogen jet flame in air flow

The structure of hydrogen jet flame diluted by CO₂ in air flow is studied by various visualization techniques, such as schlieren, direct photograph, tracer injection and reactive Mie scattering method, which allow understanding of the influence of CO₂ on the characteristics of the hydrogen jet flame. The experimental result indicates that the flame structure consists of laminar fuel jet and surrounding reaction zone near the nozzle exit. When the CO2 fraction is increased, the width of the fuel jet grows and the reaction zone is reduced in size. These observations are further confirmed by quantitative measurements of temperature and velocity fields in the flame, which are evaluated by thermocouple and particle image velocimetry (PIV), respectively. These results indicate that the flame temperature is decreased and the flow rate of the fuel jet is increased by the influence of diluents, which are due to the reduced calorific value and larger density of fuel, respectively.     

冲击载荷下Al2O3抗弹陶瓷的力学性能实验研究

 通过静力学实验得到了Al₂O₃抗弹陶瓷的弹性模量和泊松比。通过一维平面撞击实验，在Al₂O₃抗弹陶瓷材料中进行了冲击波速度、飞片速度的测量和纵向应力、横向应力测量，得到了Al₂O₃抗弹陶瓷的冲击波D-u_p关系，以及抗弹陶瓷在3~11 GPa压力范围内相应的横向应力和纵向应力关系曲线，并根据这一曲线得到了抗弹陶瓷的纵向应力与剪切强度的关系。     

Numerical analysis of nitrogen-mixed argon plasma characteristicsand injected particle behavior in an ICP torch for ultrafine powdersynthesis

A numerical model is presented for the analysis of plasma characteristics of an ICP torch and gas mixing effects on the plasma when a nitrogen gas is added into the argon plasma as a carrier or sheath gas at the torch inlet, The fluid equations describing the plasma flow and temperature fields and the diffusions between two different gases are solved along with a magnetic vector potential equation for electromagnetic fields. The trajectory and the temperature change with time for a particle injected into the plasma are also investigated by a plasma-particle interaction model to find out optimum injection conditions for the synthesis of ultrafine nitride ceramic powders, It is found from the calculations that the nitrogen-mixed argon plasma with a nitrogen sheath gas is more favorable than the plasma with a nitrogen carrier gas for the reaction kinetics of nitride synthesis. It is also found that the radial injection through the holes of the tube wall Is preferable to the axial injection at the torch inlet for the complete evaporation of injected particle and the effective chemical reaction of reactant vapor with nitrogen. For the radial injection in an ICP torch of 20 cm in axial length, the optimum injection locations and initial velocities of 50 μm aluminum particles are found for synthesizing aluminum nitride are in the range of 6~12 cm apart from the torch inlet and over 15 m/s, respectively     

陶瓷材料在压剪联合冲击加载下动态响应的实验研究

 应用57 mm压剪炮和双磁场IMPS粒子测试系统对95%的Al₂O₃陶瓷材料在压剪联合加载条件下的力学行为进行了实验研究，测量得到了材料内部压缩波（P波）、剪切波（S波）的加载、卸载和传播规律。对剪切波的衰减随载荷的变化进行了研究，初步得到95% Al₂O₃陶瓷材料在压剪联合载荷冲击下发生损伤的纵向应力阀值是4.86 GPa。     

Experimental Investigation of Jet Stabilization in Near-Axis Region of Plasma Reactor

The paper presents the results of experimental investigations of aerodynamics and heat transfer in a vortex plasma reactor with gas jet injection along its axis. The process of mixing under quasi-isothermal conditions (injection of slightly heated jet) and inhomogeneous conditions (injection of helium and argon) as well as with the injection along the axis of plasma jet is studied consistently. A detailed comparison of temperature fields and concentrations is presented for these conditions. The process of jet expansion is shown to be defined mainly by three factors — centrifugal mass forces, buoyancy forces and initial velocity shift in a jet at the chamber inlet. The end flows contribute considerably to the process of jet mass transfer with peripheral flow.     

Analysis and optimization of gas-thermal spray process in terms of condensed phase velocity and temperature

The paper presents the experimental results for velocity and tempertaure disibutions of the condensed phase in a plasma jet from the plasmatorch PNK-50 (design from ITAM SB RAS, Novosibirsk). The plasma jet is used at different operational modes for thermal spraying of nickel alloy powder PR-NKh16SR3. The measurements for average velocity (230–280 m/s) and temperature (2290–2410 K) of sprayed particles were matched to data on microhardness (630–710 HV) and porosity (1.7–13.5 %) of samples. Results were transferred into coating properties maps plotted in coordinates “arc current vs. torch offset” and “particle velocity vs. particle temperature”. Experiments demonstrated the change in parameters of condensed phase in the jet after performimg of maintenance job for the plasmatorch. We propose the method for adjusting the operational parameters of thermal spraying equipment using optical methods of control for particle velocity and particle temperature. The exemplary apparatus function of the plasmatorch was plotted; an approach is proposed for optimization and transfer of spraying technology of coatings with specified properties between equipment from different manufacturers, different class and power.