用超音速电弧等离子体射流合成金刚石膜

本文简要地介绍用超音速电弧等离子体射流合成金刚石薄膜的原理、装置、性能、特点及目前进展。     

等离子体射流控制机翼气动力矩的实验研究

为考察火花放电等离子体射流控制机翼气动力矩的效果,在NACA0021平直机翼模型上安装火花放电等离子体射流发生器,通过改变射流发生器安装位置、射流角度及加载电参数,研究其控制机翼模型气动力矩的性能及机理。在NACA0021机翼模型近前缘处,布置2个火花放电等离子体射流发生器,采用气动力测量技术,在来流风速为20 m/s时测得,攻角-4°~10°时,滚转力矩系数最大减小了0.0024,攻角为12°~16°时,滚转力矩系数最大增加了0.0021;偏航力矩系数最大减小了0.00097。实验研究结果表明:等离子体射流可改变机翼模型横航向气动力矩,并可通过改变射流角度和加载电压频率调节等离子体射流控制横向气动力矩的效果。     

等离子体射流法制备高纯竹节状碳纳米管

以乙醇为碳源，二茂铁为催化剂，氮气为电弧工作气体，利用等离子体射流在常压下制备高纯度竹节状多壁碳纳米管。用TEM和HRTEM等技术对所得产品进行表征。发现在电弧电压140V～150V，电流220A～240A，将二茂铁和乙醇混合溶液（质量比为1：100）以50mL／min速度连续加入反应器，反应120S后，即可批量制备纯度在90％以上的竹节状碳纳米管；这些竹节状碳纳米管的管径尺寸均匀，为20nm左右，长度为数微米，其管壁呈典型的鱼骨状。产品中含有部分分叉结构，呈Y形竹节状碳纳米管。认为竹节状碳纳米管的形成涉及以下几个步骤：乙醇在等离子体射流中裂解产生大量碳活性物种，同时溶解在乙醇中的二茂铁生成催化剂颗粒：碳活性物种在催化剂颗粒上溶解、扩散并从催化剂颗粒上析出堆积成为碳纳米管管壁碳层，由于催化剂颗粒运动与碳层生长速度的差异，最终形成竹节状结构的碳纳米管。     

脉动冲击射流的传热特性研究

为了深入理解脉动冲击射流的传热传质特性,研究脉动流的温度相关热物理性质对于靶面局部努塞尔数分布的影响,分别对正弦和方波非稳态脉动冲击射流进行了数值模拟.结果显示单个正弦脉冲的强化传热并不明显,而方波脉冲的强化传热效果却十分明显.对于脉动冲击射流中的流场分析表明,靶面上的瞬态换热效率与非线性热力学和水力学边界层随时间的发展密切相关.     

多股射流入射水垫塘点面脉动压力特性

本文首次对１：１００大比尺的水垫塘模型在多股射流入射时的底板点面脉压进行了多组次量测，对点面壁压的自相关特性，点面脉动强度关系及点面关系的频谱特性进行了分析，得到点面壁压脉动强度均化系数Ｃｐ与承压面积Ｓ和水垫塘水垫深度ｈｔ的经验公式。这些结果为工程设计提供了重要的依据。     

大气压等离子体射流装置及应用研究进展

大气压等离子体射流(APPJ)能够在开放空间而不是在狭窄放电间隙中产生高活性非平衡低温等离子体,APPJ已经成为国际上等离子体科学与技术领域的研究热点之一。本文首先介绍了4种典型的等离子体射流装置,包括单针、针-环、单双环以及微腔结构,并分析了各自的结构特点。然后介绍了APPJ近几年的研究进展,包括射流装置结构、活性粒子探测方法、射流与外界物质相互作用及应用等方面。最后对APPJ面临的一些关键问题和发展方向进行了展望。     

常压下超音速等离子体射流的数值模拟

数值模拟研究了在二维轴对称情形下,超音速等离子体射流喷射于常压环境中的湍流流动,其中考虑了等离子体物性随温度的大幅度变化,还考虑了粘性耗散。等离子体射流的数学模型采用了Navier-Stockes方程,对湍流的模拟采用了κ-ε方程。计算方法以SIMPLER方法为基础,引入密度修正,得到适用于可压缩流体的p＇方程和p＂方程。p＇方程用来更新现有压力场和密度场,p＂方程用来修正速度场以保证质量守恒。计算结果对常压下超音速等离子体射流的进一步研究有重要的参考价值     

微波等离子体射流处理有机废气回收纳米碳粉

在自行设计的常压微波等离子体射流装置上进行了丙酮模拟的有机工业废气的分解处理实验,利用Raman光谱、XRD、HRTEM和EDAX对回收到的样品成分、结构和形貌进行了分析。实验结果表明,有机废气在常压等离子体射流的作用下分解为单质碳和无害气态产物。单质碳的主要成分为纳米片状石墨以及碳包覆纳米铜颗粒。该技术可用于有机工业废气的分解处理和特殊纳米材料的制备     

气体流速对等离子体射流长度的影响

为了研究气体流速对大气压低温氩等离子体射流长度的影响,确定实际应用中最佳射流条件,首先建立二维轴对称模型,进行数值仿真,然后根据仿真结果进行了实验研究.实验结果与仿真结果基本吻合.气体流动处于层流时,射流几乎不能被观察到;气体流动处于过渡态时,射流比较好,射流长度最长;气体流动处于湍流状态时,射流尖端变得不稳定,射流长度有所减小.     

低温等离子体射流制备二氧化钛薄膜及其光催化活性的研究

利用大气压低温等离子体射流技术,以空气为放电气体,四氯化钛为钛源,在玻璃载玻片基底上制备了二氧化钛薄膜。利用扫描电镜及椭圆偏振仪分析测量了薄膜的表面形貌与沉积速率。利用紫外光照射硬脂酸分解速率评价所制备薄膜的光催化活性,结果显示在同一放电输入功率及气体流量条件下,四氯化钛前驱体引入位置距射流枪枪口越近,所制备的二氧化钛薄膜光催化性能越高。在同一反应位置时,放电输入功率的增加有助于提高二氧化钛薄膜的光催化活性。     

直流电弧等离子体法制备TiO2纳米超细粉

采用直流电弧等离子体法直接制备了晶态的TiO2纳米超细粉,粉体中的晶粒既有锐钛矿结构,也有金红石结构;既有单晶结构的TiO2,也有多晶结构的TiO2.当热处理温度低于600℃时,粉体颗粒的长大较为缓慢,粒径在20nm以下;温度高于700℃时,颗粒迅速长大,锐钛矿向金红石结构的转变明显;当温度达到800℃时,样品转变为单晶结构的金红石型TiO2,颗粒大小在40-120nm之间.     

An Investigation of Titanium Nitride Prepared by a DC Arc Plasma Jet

The properties of a titanium nitride film prepared by a DC arc plasma jet were investigated by microscopic observations, composition analysis, and hardness measurements. Scanning electron microscopy showed that the film was composed of three phases, designated the A, B, and C regions from the outer surface. The existence of three regions was also supported by composition analysis and hardness measurements on the cross section. XRD patterns showed the presence of -TiN in the A region. In the B region, a number of voids were observed, which have never been reported in previous papers. These were made up from specific crystallographic surfaces. The C region also had a few voids which were somewhat different from those in the B region. In the matrix, an acicular texture was found and identified as -Ti solid solution by XRD. The cross section of the film changed the color determined by the nitrogen content.     

直流非转移弧等离子喷枪中电弧的工作特性研究

利用计算机数值模拟技术，采用有限容积方法，针对自制的低能耗、高效率内送粉等离子喷涂设备，对喷枪内部电弧长度及其对流体特性的影响进行了分析研究。结果表明，通过增加进气流量和减少电流的大小，均使得等离子电弧长度增加，阳极弧根位置逐渐向下游移动，但是产生这两种现象的机理以及对气流温度和速度的影响是不同的。     

底喷式等离子体发生器的输出特性研究

等离子体点火是发射药燃烧的一种新型点火方式,等离子体发生器性能会影响等离子体的输出效果。为了实现发射药高效的等离子体点火作用而研究等离子体发生器的输出性能。通过调整底喷式等离子体发生器内部关键参量,分析了发生器输出特性影响规律,优化了等离子体发生器内部结构参数,并在30 mm火炮中进行了试验。结果表明:等离子体发生器效率和输出电压及等离子体射流压强随毛细管孔径增加而下降,但随放电通道长度增加而增加;增加脉冲功率源的充电电压能够提高等离子体射流动能和压强峰值;聚乙烯(PE)和聚四氟乙烯(PTFE)两种材质对等离子体发生器输出特性影响不显著;经优选后的底喷式等离子体发生器能够在火炮装置中有效地点燃发射药。     

超音速等离子与HVOF喷涂WC-Co涂层的冲蚀磨损性能研究

用超音速等离子喷涂(HEPJet)和两种进口高速氧燃气火焰喷涂(HVOF)设备(JP-5000 和DJ-2700)制备WC-Co涂层,进行了孔隙率、显微硬度、结合强度及30°和90°攻角的冲蚀磨损对比实验,分析了涂层的SEM磨损形貌.结果表明,超音速等离子喷涂WC-Co涂层综合性能与JP-5000喷涂WC-Co涂层相当,优于DJ-2700;在30°冲蚀磨损条件下,WC-Co涂层的失效行为表现为疲劳剥落和微切削两种特征;在90°冲蚀磨损时,涂层的失效主要是垂直表面的磨粒冲击力导致涂层疲劳剥落.     

Enhancement of Particle Removal Performance of High-speed Air Jet by Setting Obstacle in Jet Flow

Surface cleaning using high-speed air jet can be applied to cleaning of an object with concavo-convex shape. In such cases, the distance between the air jet nozzle and the surface becomes on the order of cm. An increase in the distance causes a decrease of the air velocity at the surface resulting in deterioration of the particle removal performance of the air jet. Therefore, a method to enhance removal efficiency is required. In this study, we investigated two methods for the enhancement of removal efficiency: one is to set a wire in the air flow and the other is to set two cylindrical rods. Although the wire set at the center of the jet flow deteriorates the removal efficiency, experimental results imply that the wire has a positive effect on the efficiency when it is set at a position where it does not interfere with the main flow of the jet. On the other hand, when two cylindrical rods are set at a theoretical periphery of the air jet, it shows clearly an enhancement in removal efficiency. This fact implies that the removal efficiency can be enhanced by controlling flow fluctuation by means of setting an obstacle.     

Diamond Film Synthesis with a DC Plasma Jet： Effect of the Contacting Interface between Substrate and Base on the Substrate Temperature

The contacting interface between the substrate and water-cooled base is vital to the substrate temperature during diamond films deposition by a DC （direct current） plasma jet. The effects of the solid contacting area,conductive materials and fixing between the substrate and the base were investigated without affecting the other parameters. Experimental results indicated that the preferable solid contacting area was more than 60% of total contacting areal; the particular Sn-Pb alloy was more suitable for conducting heat and the concentric fixing ring was a better setting for controlling the substrate temperature. The result was explained in terms of the variable thermal contact resistance at the interface between substrate and base. The diamond films were analyzed by scanning electron microscopy （SEM） for morphology, X-ray diffraction （XRD） for the intensity of characteristic spectroscopy and Raman spectroscopy for structure.     

A lattice Boltzmann-Based Study of Plasma Sprayed Particles Behaviours

Axisymetric lattice Boltzmann (LB) model is developed to investigate the interaction of momentum and heat between plasma hot gas and Alumina powders. The plasma flow is simulated using a double population lattice Boltzmann model and the plasma-particles interaction is modeled based on a Lagrangian approach for the motion and heat transfer equations. The present results show that the LB method is an efficient and powerful tool to comprehend and explain the very high complexity of the plasma jet physics as well as it preserves effectively the computational cost. The present results for the centerline temperature and velocity profiles agree well with the previous experimental and various numerical approaches findings. Furthermore, our results for the plasma-particles interactions are in good agreement with the Finite-Differences results of the Jets&Poudres code for particles motion and heat-up.     

喷雾半干法脱硫塔内射流卷吸特性的数值模拟

喷雾半干法烟气脱硫塔内射流卷吸特性对塔内烟气与吸收剂的混合以及流场分布均匀有着重要影响。该文通过数值模拟的方法,分析双流体雾化喷嘴的射流卷吸混合特性,得到喷雾半干法烟气脱硫塔内射流流场分布。结果表明：双流体雾化喷嘴在塔内流场呈现中间大两边小的对称分布,并且在靠近塔壁的两侧产生了回流;射流流体与周围气体发生动量交换,对周围气体有明显的卷吸作用,沿着射流轴线方向,射流卷吸量逐渐增加,随着伴随风量的增加,射流卷吸量也逐渐增加。     

反应等离子喷涂TiC/Fe涂层的摩擦磨损性能研究

采用等离子喷涂前驱体热分解技术制备的Fe-Ti-C系反应热喷涂粉末,在低碳钢基体上沉积TiC/Fe金属陶瓷复合涂层.利用SEM和X射线衍射仪对涂层的显微组织结构、磨损表面及其相组成进行分析;采用SRV型往复式摩擦磨损试验机评价喷涂涂层的摩擦磨损性能.结果表明: TiC理论含量为53%(质量分数)TiC/Fe金属陶瓷涂层的耐磨粒磨损性能较好,相比基体提高了约25倍;反应等离子喷涂TiC/Fe陶瓷涂层的磨损机制主要为粘着磨损和轻微的剥落.