Unsteadiness in non-transferred dc arc plasma generators

Non-transferred dc arc plasma generators are widely used in materials processing. They are generally considered steadily-operating devises. However, unsteady phenomena do exist in them, and may cause non-ideal effects in processes which require high controllability and reproducibility. These unsteady phenomena can cause parameter fluctuations in the arc and the plasma jet, some of which have been studied in recent years. Several types and mechanisms of these phenomena have been identified. This paper reviews the research progress in this specific area, hoping to present a more complete picture of this subject

Wear Resistance of Cast Iron Remelted by Non-Transferred Laminar Plasma Jet

对在大气压条件下用非转移弧层流等离子体射流熔凝强化处理的W-Mo-Cu铸铁表面,采用光学显微镜、显微硬度计、磨损试验机、扫描电镜等,观察和测试了熔凝试样的表面层组织、硬度、耐磨性和磨损形貌.结果表明,熔凝后铸铁表面为初晶渗碳体和莱氏体组成的过共晶组织,硬度和耐磨性有了明显的提高

小功率氮电弧推力器的性能

采用自然辐射冷却结构的小功率电弧推力器,实现了以氮气为推进剂的长时间稳定运行。采用间接测力方法得到推力,利用铜镜反射法拍摄喉道处的放电状态,结合测量的弧电压、弧电流和气流量数据以及导出的比冲和推力效率,对推力器运行性能和放电特性进行了研究。结果显示:在气流量为100~700 mL/min,输入功率为35~55W的条件下,最大推力约为24 mN,最大比冲接近175 s,当弧电流为80~120 mA范围内变化时,弧电压变化范围为420~520V,并且弧电压随气流量的增加呈现出先下降后上升的趋势

丁苯酞软胶囊联合阿托伐他汀钙片治疗脑梗死的效果

目的观察丁苯酞软胶囊联合阿托伐他汀钙片治疗脑梗死的临床疗效。方法选取福建中医药大学附属人民医院2015年1月～2018年6月收治的脑梗死患者186例,随机分为A、B、C组,每组各62例。A组给予丁苯酞软胶囊治疗,B组给予阿托伐他汀钙片治疗,C组给予丁苯酞软胶囊联合阿托伐他汀钙片治疗。采用美国国立卫生研究院卒中量表(NIHSS)评价患者的神经功能缺损情况,采用Barthel指数评定量表评价患者日常生活能力,采用经颅多普勒超声测量缺血区域脑血流量。治疗1个月后,观察比较3组患者的NIHSS评分、Barthel指数、缺血区域脑血流量及临床总有效率。结果 3组患者治疗后的NIHSS评分、Barthel指数和缺血区脑血流量比较,差异均有统计学意义(F=6.48、5.78、15.69,P<0.05)。3组患者治疗后的NIHSS评分均低于治疗前(t=2.523,P<0.05;t=3.016,P<0.05;t=2.642,P<0.05),Barthel指数均高于治疗前(t=2.232,P<0.05;t=2.694,P<0.05;t=2.086,P<0.05),缺血区脑血流量均高于治疗前(t=5.962,P<0.05;t=4.672,P<0.05;t=5.214,P<0.05)。治疗后,C组NIHSS评分低于A、B组(均P<0.05),Barthel指数和缺血区脑血流量均明显高于A、B组(均P<0.05)。C组治疗总有效率为82.26%,高于A、B组的58.06%、53.23%(χ~2=5.342,P<0.05;χ~2=4.163,P<0.05)。结论丁苯酞软胶囊联合阿托伐他汀钙片能有效治疗脑梗死

100W级小功率电弧推力器性能研究

卫星小型化的应用发展对其在轨精确定位的推进技术提出了迫切需求。目前应用于空间微推进技术的主要还是冷气推进和电阻加热推进,其中主要的原因是,很多先进的推进技术虽然可能产生较高的比冲,却很难保证运行性能的稳定性和可控性,或者推力器的体积和重量难以减小到适用于微小卫星,或者系统复杂,以及使用的电源与卫星供电系统兼容性差,等等。然而不管是冷气推进还是电阻加热推进,都存在比冲低的不足,同样的任务需要携带更大量的气体以及气体贮存装置,降低有效载荷。电弧等离子体推力器具有结构简单,工作电压低,容易与卫星供电系统协调、推力功率比高,在技术实现难度及可靠性等方面具有一定优势,也正是由于这些特点,以肼为推进剂的千瓦级电弧加热推力器在国外大、中型卫星,特别是用于通讯和监测等用途的地球同步轨道卫星上,得到了较为大量的应用[1]。由于小卫星通常难以提供中低功率电弧推力器所需的较大输入电功率需求,因此100 W(甚至几瓦)以下稳定工作的Arcjet近年来得到了广泛关注。本文在实验室已有工作的基础上,自行研制了小功率的电弧推力器。推力器阳极喷管的喉道直径为0.3mm,喉道与阳极喷管出口的面积比为200,阳极喷管的扩张半角为20°。实验所用真空室的极限真空可达1×10-4Pa,推力器工作时的最大腔压小于0.8Pa。在气流量100~600 m L/min、工作电流80-180 m A的范围内实现了以氩气、氮气和氨气为推进剂的电弧推力器的持续稳定放电;采用测量冲击力的间接测力方法[2],系统测量了推力器在不同工作参数条件下的推力数据,结合弧电流、弧电压的测量数据,导出了对应条件下推力器的比冲和推力效率,并对推力器性能进行了分析。结果显示,在相同的气流量、工作电流条件下,推进剂为氨气时得到的比冲最大,最大比冲超过300s。三种推进剂条件下获得的弧电压都远高于1k W级电弧加热推力器的电压值。在氮气和氨气条件下,弧电压随气流量的增加先减小而后增大,呈现出不同于1k W级电弧加热推力器的复杂放电特性

热等离子体加热的长时间超高速稀薄气体流动地面模拟

在高层临近空间(100 km附近)以接近第一宇宙速度(7.9km/s)巡航的新型飞行器对我国国家战略安全以及空间和平利用具有重大意义,是实现我国空天科技跨越式发展的关键之一。100公里高度空域属于大气层边缘,稀薄气体效应、真实气体效应、化学/热非平衡效应显著。地面模拟该区域超高速流动的相似准则从传统的马赫数、雷诺数相似转变为双尺度律,即来流绝对速度以及来流密度与飞行器特征尺度的乘积相同。同时,由于稀薄气动力热的时间累积效应,持续数分钟的长时间稳定来流条件成为提高测试数据准确度的必要保障。在持续有喷流的情况下仍要维持相对较高真空度以满足稀薄相似的需求,这对地面模拟系统提出了苛刻要求。本文利用优化结构的热等离子体发生器,实现了高比焓能量注入;基于自由分子流的真空流导分析和数值模拟,对有载条件下0.01~1Pa范围的长时间维持真空系统进行了优化;获得了满足相似准则的来流条件,可为新型过渡流区超高速巡航飞行器的气动特性研究提供参考

Modeling study on the flow, heat transfer and energy conversion characteristics of low-power arc-heated hydrogen/nitrogen thrusters

A modeling study is conducted to investigate the effect of hydrogen content in propellants on the plasma flow, heat transfer and energy conversion characteristics of low-power (kW class) arc-heated hydrogen/nitrogen thrusters (arcjets). 1:0 (pure hydrogen), 3:1 (to simulate decomposed ammonia), 2:1 (to simulate decomposed hydrazine) and 0:1 (pure nitrogen) hydrogen/nitrogen mixtures are chosen as the propellants. Both the gas flow region inside the thruster nozzle and the anode-nozzle wall are included in the computational domain in order to better treat the conjugate heat transfer between the gas flow region and the solid wall region. The axial variations of the enthalpy flux, kinetic energy flux, directed kinetic-energy flux, and momentum flux, all normalized to the mass flow rate of the propellant, are used to investigate the energy conversion process inside the thruster nozzle. The modeling results show that the values of the arc voltage, the gas axial-velocity at the thruster exit, and the specific impulse of the arcjet thruster all increase with increasing hydrogen content in the propellant, but the gas temperature at the nitrogen thruster exit is significantly higher than that for other three propellants. The flow, heat transfer, and energy conversion processes taking place in the thruster nozzle have some common features for all the four propellants. The propellant is heated mainly in the near-cathode and constrictor region, accompanied with a rapid increase of the enthalpy flux, and after achieving its maximum value, the enthalpy flux decreases appreciably due to the conversion of gas internal energy into its kinetic energy in the divergent segment of the thruster nozzle. The kinetic energy flux, directed kinetic energy flux and momentum flux also increase at first due to the arc heating and the thermodynamic expansion, assume their maximum inside the nozzle and then decrease gradually as the propellant flows toward the thruster exit. It is found that a large energy loss (31-52%) occurs in the thruster nozzle due to the heat transfer to the nozzle wall and too long nozzle is not necessary. Modeling results for the NASA 1-kW class arcjet thruster with hydrogen or decomposed hydrazine as the propellant are found to compare favorably with available experimental data

利用收缩扩张喷管实现电弧弧根气动分散

电极烧蚀是影响电弧等离子体发生器寿命和性能的关键因素,这与电弧的近电极行为密切相关。相较于集聚型的弧根贴附,扩散型的弧根更利于减小热烧蚀,从而提高电极寿命并提高放电稳定性。弧根的贴附行为与电弧在电极壁面附近的输运特性以及弧根所受的气动力和电磁力相关。本文分析了利用收缩-扩张喷管实现弧根气动分散的关键影响因素

Modeling study to compare the flow and heat transfer characteristics of low-power hydrogen, nitrogen and argon arc-heated thrusters

A modelling study is performed to compare the plasma °ow and heat transfer char- acteristics of low-power arc-heated thrusters (arcjets) for three di®erent propellants: hydrogen, nitrogen and argon. The all-speed SIMPLE algorithm is employed to solve the governing equa- tions, which take into account the e®ects of compressibility, Lorentz force and Joule heating, as well as the temperature- and pressure-dependence of the gas properties. The temperature, veloc- ity and Mach number distributions calculated within the thruster nozzle obtained with di®erent propellant gases are compared for the same thruster structure, dimensions, inlet-gas stagnant pressure and arc currents. The temperature distributions in the solid region of the anode-nozzle wall are also given. It is found that the °ow and energy conversion processes in the thruster nozzle show many similar features for all three propellants. For example, the propellant is heated mainly in the near-cathode and constrictor region, with the highest plasma temperature appear- ing near the cathode tip; the °ow transition from the subsonic to supersonic regime occurs within the constrictor region; the highest axial velocity appears inside the nozzle; and most of the input propellant °ows towards the thruster exit through the cooler gas region near the anode-nozzle wall. However, since the properties of hydrogen, nitrogen and argon, especially their molecular weights, speci¯c enthalpies and thermal conductivities, are di®erent, there are appreciable di®er- ences in arcjet performance. For example, compared to the other two propellants, the hydrogen arcjet thruster shows a higher plasma temperature in the arc region, and higher axial velocity but lower temperature at the thruster exit. Correspondingly, the hydrogen arcjet thruster has the highest speci¯c impulse and arc voltage for the same inlet stagnant pressure and arc current. The predictions of the modelling are compared favourably with available experimental results