Metallic bolometers with temperature dependent thermal impedance

The paper gives the solution of a bolometer with thermal impedance, which is a general function of the temperature. The general solution is applied to a bolometer cooled by radiation for which the appropriate expressions fo the resistance, sensitivity and dynamic resistance are derived and the expression for the maximum sensitivity of this type of bolometers from nickel, platinum and electrolytical platinum is given. The case of a bolometer cooled by conduction through the air and radiation is solved as the case of a bolometer with several ways of cooling. The paper also gives a graphico-numerical method for determining all the important parameters of the bolometer from the measured dependence of the resistance on the electric power RI²; an example of the application of this method is given for a conduction and radiation cooled bolometer. Deviations from the theoretical course are explained by convection of heat caused by the flow of air along the bolometer due to the increase in temperature of the bolometer over that of its surroundings. The paper also gives the maximum attainable sensitivity of this type of bolometer and metallic bolometers in general.     

流体直接冷却薄板条介质温度及应力的解析表达

基于对流传热和热传导原理, 建立了流体直接冷却均匀抽运薄板条激光工作介质的热效应分析模型, 采用平面应力近似和最小功原理, 得到了板条工作介质内部温度分布和应力分布的解析表达式. 研究了不同流道厚度时对流热交换系数和冷却液温升与流体流速的关系, 分析了流道厚度对工作介质的温度分布和应力分布的影响规律, 讨论了之字形和直通光路时, 热致波前畸变随产热功率的变化趋势. 结果表明: 层流和湍流时, 较厚的流道可以实现更好的热管理效率; 增益介质中的热分布关于中心平面对称, 纵向最大温升出现在出水口端, 最大应力畸变集中在板条两端及其侧边; 流道厚度较大时, 工作介质更易形成一维的温度梯度, 产生的应力更小; 之字形光路可以明显缓解热光效应导致的波前畸变.     

环保节水型冷却塔的研究

综合湿式冷却塔有热交换效率高且造价低而空气冷却器无水蒸发等特点,提出了环保节水型冷却塔.对该新型塔进行了理论分析,对塔内换热、气动力性能等进行了数值计算,对塔内空气换热器和填料层间的冷却负荷以及与风机性能等进行了耦合匹配,结合北方气候条件的计算分析表明新型塔确有良好的节水和环保效果.     

Laminar free convection heat transfer between vertical isothermal plates

The paper represents results on numerical investigation of flow and heat transfer between two isothermal vertical plates under laminar natural convection. A system of complete Navier–Stokes equations is solved for a two-dimensional gas flow between the plates along with additional rectangular regions (connected to inlet and outlet sections), whose characteristic sizes are much greater than the spacing between the plates. The calculations were performed over very wide ranges of Rayleigh number Ra = 10 ÷ 10⁵ and a relative channel length AR = L/w = 1 ÷ 500. The influence of the input parameters on the gas-dynamic and thermal structure of thermogravitational convection, the local and mean heat transfer, and also the gas flow rate between the plates (convective draft. We determined sizes of the regions and regime parameters when the local heat flux on the walls tends to zero due to the gas temperature approach to the surface temperature. It is shown that the mean heat transfer decreases as the relative channel length AR grows, whereas the integral gas flow rate (convective draft) and Reynolds number in the channel Re = 2wUm/ν increase. The use of a modified Rayleigh number Ra* = Ra · (w/L) (Elenbaas number) leads to generalization of calculation data on mean heat transfer. These data are in good agreement with the correlations for heat transfer [1, 2] and gas flow rate [3]. The reasons of variation of the data in the range of low Rayleigh numbers are discussed in detail.     

Anode plasma structure in a gas discharge with neutral density depleted by ionization

We consider the anode plasma structure in a gas discharge with density of neutral atoms (neutrals) depleted by strong ionization. We obtain analytical solutions of the quasi-neutrality equation for the potential distribution and a condition for the existence of anode plasma in the one-dimensional case for arbitrary potential dependences of the neutral depletion frequency and the electron density. We consider the special cases of a constant neutral depletion frequency, ionization by Maxwellian electrons, and ionization by an intense electron beam under the conditions of collisionless ion motion and Boltzmann thermal electron distribution. The solutions for the first two cases at zero depletion parameter, i.e., at constant gas density, match those obtained in [1] by a power series expansion. In the case of ionization by Maxwellian electrons, the formation of anode plasma at reasonable working-gas flow rates is shown to be possible only at a fairly high electron temperature (if, e.g., xenon is used as the working gas, then T _e ≥ 5 eV). Steady-state solutions of the quasi-neutrality equation under ionization by an intense electron beam exist only if the ratio of the electron beam density to the maximum thermal electron density does not exceed a certain limiting value.     

Experimental investigation of the anode region of a free-burning atmospheric-pressure inert-gas arc I. General characteristics of the discharge. Low-current regime

This paper reports the experimental investigation of the anode region of a free-burning inert-gas arc at atmospheric pressure in the current range from a few amperes to hundreds of amperes. The tungsten thermionic-emission cathode and the large-diameter water-cooled copper anode that were used permitted the anode arc root to assume its natural form. The general characteristics of the discharge are given and results are presented from investigations of the anode region at low currents, where the anode arc root is single and constricted, but erosion-free. Measurements of the plasma parameters as well as the current density in the arc root are reported, and a comparison is made between the values obtained and those characteristic of the region of the cathode arc root. Zh. Tekh. Fiz. 67, 35–40 (January 1997)     

Anode Phenomena in Vacuum and Atmospheric Pressure Arcs

This paper summarizes recent experimental data related to anode phenomena in both vacuum and atmospheric pressure arcs. Currents in the range 10A to 3OkA are discussed, and particular emphasis is placed on the effect of plasma flow from the cathode. For vacuum arcs this plasma flow is the directed motion of metal ions from the cathode spots. These ions reduce the anode voltage drop, and maintain a diffuse anode termination. At atmospheric pressure the ion flow is impeded by gas-atom collisions. However, a plasma flow towards the anode can result from magnetic pinch forces at the constricted cathode termination. In the absence of plasma flow, the anode termination constricts to a vigorously evaporating anode spot. For a typical non-refractory electrode such as copper, the spot operates at a temperature close to the boiling point irrespective of the gas pressure. The spot temperature is dictated by the balance between electrical input power and evaporative losses. These anode phenomena are discussed in relation to vacuum switchgear, arc welding and arc furnaces.     

Effect of nonstationary thermal gravitation-capillary convection on temperature distribution in a thin vertical wall

Time dependences of temperature distributions in a thin metal wall were studied experimentally under two conditions of convective heat transfer in a tank model. In the first case, the vertical working wall was heated from within due to a convective heat flux from the opposite wall heated monotonously, and it was cooled due to heat transfer to the ambient medium. Dependence of the temperature field on a thin wall at the stage of convective flow development was retraced with the help of the thermographic camera and thermocouple sensors. In the second case, the tank wall was heated uniformly by IR radiation from the outside, and non-stationary convective flow and volumetric liquid heating were formed inside. Time dependence of temperature distribution over the wall height is studied. It is shown that the flow structure and convective heat transfer in a fuel layer with free boundary are subjected not only to the buoyancy force, but also to the thermocapillary effect. The local features of the flow affect temperature distribution in a thin wall.     

气流对氮气介质阻挡放电气体温度及放电模式的影响

利用光谱测量和高速照相的方法,对大气压氮气介质阻挡放电进行了研究.在气流的帮助下,2mm气隙中的均匀放电可以长时间得以维持.根据放电电流波形和1μs曝光时间的放电图像,这种均匀放电被判定为汤森放电.用氦氖激光器对实验中所用的光谱仪带来的谱线轮廓展宽进行了标定,并将得到的仪器展宽数据输入Specair软件,计算了不同气体温度下氮分子二正系0—2谱带的谱线轮廓.通过用计算谱线轮廓去拟合实验谱线轮廓,确定了氮分子的转动温度并将其近似为气体温度.结果表明:大气压氮气介质阻挡汤森放电并不能使气体温度大幅上升(ΔTg≤50K),气体温度的小幅上升不会引起热不稳定性而导致放电发展成为细丝放电.气流确实可以降低放电气体温度,但这不是使汤森放电得以维持的原因.通过比较加入气流前后的放电光谱可知,气流降低了气隙中杂质氧的含量,使得更多的氮分子亚稳态N2(A3Σu+)的寿命延长到下一次放电的起始时刻,为汤森放电提供了必需的大量种子电子.     

Numerical simulation of anode heat transfer of nitrogen arc utilizing two-temperature chemical non-equilibrium model

A detailed understanding of anode heat transfer is important for the optimization of arc processing technology. In this paper, a two-temperature chemical non-equilibrium model considering the collisionless space charge sheath is developed to investigate the anode heat transfer of nitrogen free-burning arc. The temperature, total heat flux and different heat flux components are analyzed in detail under different arc currents and anode materials. It is found that the arc current can affect the parameter distributions of anode region by changing plasma characteristics in arc column. As the arc current increases from 100 A to 200 A, the total anode heat flux increases, however, the maximum electron condensation heat flux decreases due to the arc expansion. The anode materials have a significant effect on the temperature and heat flux distributions in the anode region. The total heat flux on thoriated tungsten anode is lower than that on copper anode, while the maximum temperature is higher. The power transferred to thoriated tungsten anode, ranked in descending order, is heat flux from heavy-species, electron condensation heat, heat flux from electrons and ion recombination heat. However, the electron condensation heat makes the largest contribution for power transferred to copper anode.     

Atomic oxygen recombination on the ODS PM 1000 at high temperature under air plasma

High temperature materials are necessary for the design of primary heat shields for future reusable space vehicles re-entering atmospheric planet at hypersonic velocity. During the re-entry phase on earth, one of the most important phenomena occurring on the heat shield is the recombination of atomic oxygen and this phenomenon is more or less catalyzed by the material of the heat shield. PM 1000 is planned to be use on the EXPERT capsule to study in real conditions its catalycity. Before the flight, it is necessary to perform measurements on ground test facility. Experimental data of the recombination coefficient of atomic oxygen under air plasma flow were obtained in the diffusion reactor MESOX on pre-oxidized PM 1000, for two total pressures 300 and 1000 Pa in the temperature range (850-1650 K) using actinometry and optical emission spectroscopy. In this investigation, the evolution of the recombination coefficient is dependent of temperature, pressure level and also of the chemical composition of the surface leading to one order of magnitude for a given temperature. The recombination coefficient is increasing with temperature and also dependent on the static pressure. The surface change due to the plasma exposure is inspected with SEM, XRD and XPS. As chromium oxide is the main part of the oxide layer formed during the oxidation in air plasma conditions, a sintered Cr₂O₃ sample was elaborated from powders to compare the data of the recombination coefficient obtained on PM 1000. Pre- and post-test analyses on the several materials were carried out using SEM, WDS, XRD and XPS.     

Operational characteristics of a MAGPIE coaxial CO2 discharge system

The operational characteristics of a convectively cooled Magnetically stabilized, Photo-initiated, Impulse-enhanced, Electrically-excited (MAGPIE) coaxial discharge system are described. terminal behavior is examined as a function of several parameters, such as gas flow, pulser ionization, and magnetic field strength. In-situ plasma potential measurements are also presented, which indicate that CO₂ attachment effects have considerable influence on the spatial electrical characteristics of the gas discharge.     

Fluctuation of arc plasma in arc plasma torch with multiple cathodes

Fluctuation phenomena commonly exist in arc plasmas, limiting the application of this technology.In this paper,we report an investigation of fluctuations of arc plasmas in an arc plasma torch with multiple cathodes.Time-resolved images of the plasma column and anode arc roots are captured.Variations of the arc voltage, plasma column diameter, and pressure are also revealed.The results indicate that two well-separated fluctuations exist in the arc plasma torch.One is the high-frequency fluctuation(of several thousand Hz), which arises from transferring of the anode arc root.The other is the low-frequency fluctuation(of several hundred Hz), which may come from the pressure variation in the arc plasma torch.Initial analysis reveals that as the gas flow rate changes, the low-frequency fluctuation shows a similar variation trend with the Helmholtz oscillation.This oscillation leads to the shrinking and expanding of the plasma column.As a result, the arc voltage shows a sinusoidal fluctuation.     

空心针-板电极大气压氩气辉光放电的特性研究

大气压均匀放电等离子体在工业领域具有非常广泛的应用前景,它是利用直流电源激励的空心针-板放电装置,以氩气为工作气体在大气压空气中产生均匀稳定的放电。对氩气流量和气隙间距对辉光放电发光特性的关系进行了研究,结果表明放电所产生的等离子体柱连接两个电极,发光较为均匀(观察不到放电丝)。在板电极附近放电等离子体柱直径最大,最大直径随着电流和气流的增大而增大。放电伏安特性研究发现,与低气压辉光放电相类似,两电极间的电压随着电流的增大而减小,并且随气流和气隙间距的增大而增大。对该大气压直流均匀放电在扫描范围为330～450 nm的光学发射光谱进行分析,获得了放电等离子体的分子振动温度和谱线强度比I_391.4/I_337.1随氩气流量和气隙间距的变化关系。I_391.4/I_337.1均随流量和气隙间距的增大而降低。对等离子体柱的I_391.4/I_337.1沿气流方向(等离子体柱轴向)进行了空间分辨测量,并进行了定性分析,结果表明,振动温度及电子平均能量随着远离空心针口距离的增大而增大。这些结果对大气压辉光放电在工业中的应用具有重要意义。     

Spectroscopic determination of the relative particle densities of H<Subscript>2</Subscript>, HD,and D<Subscript>2</Subscript> Molecules in non-equilibrium hydrogen–deuterium plasma: II. Experimental verification

The relative intensities of the Balmer series lines of hydrogen and deuterium atoms and the Q-branch lines in the Fulcher-α band system of the H₂, HD, and D₂ molecules were measured. These lines were emitted by non-equilibrium plasma surrounded by the cylindrical channel of an additional molybdenum electrode located between the cathode and anode of glow (in the deuterium with a minor hydrogen impurity) and arc (in a mixture of D₂, H₂, and Ne in comparable quantities) discharges at pressures of 6–8 Torr and current densities of 0.4 and 8.5–17 A/cm², respectively. The measured intensity ratios and gas temperature were used for the estimation of the relative particle densities of the H₂, HD, and D₂ molecules in the framework of the simple models of the excitation of atoms (models 1a and 1b for the high and low values of dissociation degrees, respectively) and the rovibronic levels of isotopic molecules (model 2). The results obtained by means of models 1a and 2 were in a significant contradiction, whereas the data obtained with the use of models 1b and 2 coincided within error bars. The good agreement between two spectroscopic techniques based on two independent theoretical models and two independent sets of experimental data showed that the techniques proposed are promising for the determination of the isotopic composition of molecules in lowpressure hydrogen-deuterium plasma at least in the case of a low dissociation degree of molecules.     

Glow Discharge Characteristics of Hollow Needle-Plate Electrode in Atmospheric Pressure ArgonSCIEI北大核心CSCD

Atmosphere pressure uniform plasma has the broad application prospect in the industrial field. Using hollow needle cathode - plate anode device excited by direct-current voltage, a uniform and stable glow discharge is generated at atmospheric pressure in ambient air with argon used as working gas. The influence of the experimental parameters (including gas flow rate and the gas gap width) on discharge has been investigated by optical method. It can be found that a glow-discharge plasma column can bridge the two electrodes. The plasma column is uniform, and no filaments can be discerned. Near the plate electrode, the diameter of the plasma column is largest of all positions. The maximal diameter of the plasma column increases with increasing the discharge current or the gas flow rate. Through electrical method, the voltage-current characteristic has been investigated. It has been found that the discharge voltage decreases with increasing the current which is similar with the characteristic of glow discharge in low pressure. It increases with increasing the gas gap width or the gas flow rate. By analyzing the optical emission spectrum scanning from 330 to 450 nm emitted from the direct-current glow discharge, the molecular vibrational temperature and the intensity ratio of spectral lines I-391.4/I-337.1 have been investigated as functions of the gas flow rate and gas gap width. Results indicate that both the vibrational temperature and the intensity ratio of spectral lines I-391.4/I-337.1 decrease with increasing the gas flow rate or the gas gap width. In addition, the molecular vibrational temperature and the intensity ratio of spectral lines I-391.4/I-337.1 have been investigated in spatial resolution along the direction of gas flow(plasma column axial), and give a qualitative analysis as well. It is found that the vibrational temperature and the average electron energy increase with increasing the distance from the hollow needle cathode. These results are important to the industrial applications of glow discharge.     

Numerical Analysis of the Joule Heating Effect on Plasma Heat Transfer

The application of thermal plasmas particularly in the field of plasma chemistry and plasma material processing requires a basic understanding of the heat transfer process. This paper is concerned with an analysis of the heat transfer to a positively biased body exposed to a plasma flow. Because of the induced current flow due to the biasing potential, the plasma surrounding the biased body will experience an increase in temperature caused by Joule heating. The fraction ? of the dissipated heat which is transferred to the body is calculated for an atmospheric argon plasma flow at temperatures between 104 and 2 × 104K and Reynolds numbers of 40 and zero. The results indicate that ? increases with increasing plasma temperature for Re = 40 and decreases slightly with increasing plasma temperature for Re = 0. As the Re number increases at constant plasma temperature ? decreases.     

Zur Mikrowellendiagnostik stromstarker Entladungen mit Skineffekt. Teil II: Bestimmung der Plasmaparameter eines angeströmten Stickstoffbogens bei Atmosphärendruck

Microwave diagnostics of an inhomogeneous, dense, cylindrical plasma column may be used to determine the complex impedance and a mean noise temperature in the range of strong skin effect (theory see part I). This case is realized if the specific d.c. impedance E/I falls below a critical value, e.g. 20 Ω/cm for ω = 10¹⁰. It is shown, that for any radial conductivity profile the complex impedance is a function of E/I only. A formula is derived for calculating the noise temperature of the column as a weighted mean value due to the local plasma temperature and conductivity. In the case of strong skin effect this mean value equals the electron temperature of plasma regions near the boundary of the conducting diameter. These results in connection with spectroscopical diagnostics are use to determine some plasma parameters of an arc discharge in a streaming nitrogen atmosphere at 760 Torr. The temperature profil was obtained from the intensity of the 3371 Å molecular band and then the conductivity profile was calculated using an energy balance equation. The results show that even in the 10 A-case the arc plasma is not in thermal equilibrium, the difference T_e—T_g being about 1,500 ºK. This large difference is due to the flow of neutral gas streaming downward the discharge chamber. The length of the discharge (1·3 cm) is not sufficient for the neutral atoms to reach their equilibrium temperature.     

ARC Ignition Phenomena with a Transpiration Cooled Anode

This paper deals with the problem of ignition to the porous transpiration cooled anode of an arc in 1 atm. argon. This was observed for both porous graphite and sintered porous tungsten anodes, in the latter case causing melt spots to form which limited the useful life of the anode. A study was undertaken to overcome this problem in which the transient behavior of the arc current, voltage, anode surface area coverage and gas flow rate of transpiration gas was observed by high speed electronics and cinematography during the ignition period. From these data a computation of the anode current density vs. time showed abnormally high values during the first second or two following ignition; e.g. 1000 amps/cm2 averaged over the first second for a steady state arc current of 70 amps. The damage was attributed to excessive thermal loading during the arc growth period and eliminated by means of a properly control led ignition sequence.     

Production of long,laminar plasma jets at atmospheric pressure with multiple cathodes

Plasma jets from conventional non‐transferred arc plasma devices are usually operated in turbulent flows at atmospheric pressure. In this paper, a novel non‐transferred arc plasma device with multiple cathodes is introduced to produce long, laminar plasma jets at atmospheric pressure. A pure helium atmosphere is used to produce a laminar plasma jet with a maximum length of >60 cm. The influence of gas components, arc currents, anode nozzle diameter, and gas flow rate on the jet characteristics is experimentally studied. The results reveal that the length of the plasma jet increases with increasing helium content and arc current but decreases with increasing nozzle diameter. As the gas flow rate increases, the length of the plasma jet initially increases and then decreases. Accordingly, the plasma jet is transformed from a laminar state to a transitional state and finally to a turbulent state. Furthermore, the anode arc root behaviours corresponding to different plasma jet flows are studied. In conclusion, the multiple stationary arc roots that exist on the anode just inside the nozzle entrance are favourable for the generation of a laminar plasma jet in this device.