Study of vortex in flow fields induced by surface dielectric barrier discharge actuator at low pressure based on Q criterion

Flow fields induced by a surface dielectric barrier discharge actuator at low pressure of 7 kPa are measured by particle image velocimetry.The distribution of local vortices in the flow field is revealed by the Q criterion.The reason for the generation of vortices is analyzed and the influence of pulse frequency and duty cycle on vortices is studied.The results show that the Q criterion can reveal the small-scale vortices,which cannot be indicated by the streamline.The direction transition zone where the induced jet moves from the vertical to the tangential and the shear layer between the jet and stationary air are prone to the generation of strong vortices.The influence of pulse frequency on vortices is not obvious,but the variation of duty cycle can significantly affect the strength and distribution of vortices.     

The effect of positive/negative ion on the dust grain charging process in a Vasyliunas-Cairns (VC)-distributed dusty plasma system

Charging mechanism of dust particles has been considered as a growing research area in dusty plasma physics because of its exciting results. In this paper, we consider a low-temperature non- equilibrium multispecies plasma model, which consists of Vasyliunas–Cairns (VC) distributed electrons, negative/positive streaming ions, and negatively-charged dust grains to explain the charging mechanism of dust grains. The main theme of this work is to derive expressions of currents for negatively-charged dust grains (considering an equilibrium state position) in the plasma environment comprised of electrons and positive/negative streaming ions using the VC distribution function. Our proposed model shows that the dust grain surface potential is significantly affected by different plasma parameters such as the negative ion streaming velocity (S_n), positive ion streaming velocity (S_i), spectral indices of VC distribution, negative ion charging state (Z_n), positive ion charging state (Z_i), and negative ion number density (ρ).     

Surface Potential of Dust Grains at the Sheath Edge of Electronegative Dusty Plasmas

In this paper we investigate the dust surface potential at the sheath edge of electronegative dusty plasmas theoretically, using the standard fluid model for the sheath and treating electrons and negative ions as Boltzmann particles but positive ions and dust grains as cold fluids. The dust charging model is self-consistently coupled with the sheath formation criterion by the dust surface potential and the ion Mach number, moreover the dust density variation is taken into account. The numerical results reveal that the dust number density and negative ion number density as well as its temperature can significantly affect the dust surface potential at the sheath edge.     

Excited Electron Temperature and Molecular Vibration Temperature During Transition from Filamentary Discharge to Glow Discharge in Surface Discharge in Air

A dielectric barrier surface discharge device was used to investigate the transition from a filamentary discharge to a glow discharge in air at different gas pressures. Discharge images and waveforms of the applied voltage and discharge current were recorded simultaneously, and it was found that the discharge could transit from filamentary to glow with the decrease in pressure. Optical emission spectra during the transition from a filamentary discharge to a glow one were recorded. Excited electron temperature can be determined from the ratios of the relative intensities of spectral lines while molecular vibration temperature can be measured by analysing spectral lines of the N2 second positive band system. The results show that both the excited temperature and molecular vibration temperature increase with the decrease in the gas pressure. Qualitative explanations are given.     

Dust Acoustic Compressive Waves in a Warm Dusty Plasma Having Non-Thermal Ions and Non-Isothermal Electrons

In this article an investigation is presented on the properties of dust acoustic(DA)compressive solitary wave propagation in an adiabatic dusty plasma,including the effect of nonthermal positive and negative ions and non-isothermal electrons.The reductive perturbation method has been employed to derive the lower degree modified Kadomtsev-Petviashivili(mK-P),3D Schamel-Korteweg-de-Vries equation or modified Kadomtsev-Petviashivili(mK-P) equations for dust acoustic solitary waves in a homogeneous,unmagnetized and collisionless plasma whose constituents are non-isothermal electrons,singly charged positive and negative non-thermal ions and massive charged dust particles.The stationary analytical solutions of the lower degree mK-P and mK-P equations are numerically analyzed,where the effect of various dusty plasma constituents on DA solitary wave propagation is taken into account.It is observed that both the ions in dusty plasma play a key role in the formation of DA compressive solitary waves,and also the ion concentration and non-isothermal electrons control the transformation of the compressive potentials of the waves.     

Insulation characteristics of triple mixtures of c-C4F8/N2/CO2 under lightning impulse voltage

This paper has researched the insulation characteristics of 10%c-C₄F₈/N₂/CO₂ mixtures under lightning impulse voltage by experiment. It is shown that the positive and negative lightning impulse breakdown voltages of 10%c-C₄F₈/N₂/CO₂ gas mixtures rise linearly as the electrode gap distance and gas pressure increase and under the same conditions, the positive lightning impulse breakdown voltage of the gas mixtures is always higher than the negative lightning impulse breakdown voltage. As the gas mixtures have a little higher liquefied temperature than SF₆ and the comprehensive GWP is about 5% of SF₆ , and the positive and negative lightning impulse breakdown voltages can both reach 60% of SF₆ , 10%c-C₄F₈/N₂/CO₂ gas mixtures can be applied as insulation gas in electrical equipment such as C-GIS, GIT, GIL and so on.     

A new cluster-ion-beam source for secondary ion mass spectrometry (SIMS) using the electrospray of a pure ionic liquid under high vacuum

Electrospray characteristics were studied using a pure room-temperature molten salt (i.e., an ionic liquid) at pressures around 10^?5 Pa as well as at atmospheric pressure. The ionic liquid N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium bis(trifluoromethanesulfonyl)imide was tested, which has negligible vapor pressure and high conductivity. During electrospray, the ionic liquid was introduced at a constant flow rate into a stainless-steel capillary (i.d. 30 μm). It was demonstrated that stable electrosprayed currents exceeding ±1 μΑ were continuously produced in both positive and negative modes. The electrosprayed currents in a high vacuum were twice those at atmospheric pressure. It was found that gas pressure rose slightly with increasing electrosprayed currents. Residual gas analysis revealed that gas component at negative mode was different from that at positive mode. Experimental results indicate that vacuum electrospray of pure ionic liquids is applicable to a massive-cluster beam source for SIMS.     

HTR-10中石墨粉尘在热气导管中的沉积

分析了10Mw高温气冷堆(HTR-10)中的石墨粉尘在热气导管中的沉积情况,得到了石墨粉尘在热气导管中的沉积率.在分析计算中,考虑了石墨粉尘在热气导管中的紊流沉积和热泳沉积.计算结果发现,石墨粉尘在热气导管中的沉积量非常小,其主要原因是氦气的流速较高.     

断电停机过渡过程中核主泵气液两相流动特性研究

为研究断电停机过渡过程中核主泵气液两相瞬态流动特性,借助CFD技术对不同含气量下核主泵内的气液两相流动变化规律及径向力进行了研究,并对计算结果进行试验验证。结果显示,数值模拟数据与试验数据变化趋势吻合,断电停机过渡过程中,在叶轮背面附近产生旋涡,旋涡的存在使气相区域变大且相应的气体体积分数增加。随着流量的减少和转速的降低,叶轮和导叶内存在大量的气相,导致叶轮转换能量的能力减弱。含气量较小时,叶轮内气体体积分数先达到最大值后开始呈离散状回旋下降。而含气量较大时,叶轮内的气体体积分数随流量的减少而增加。含气量对流道内流体的速度影响较大,尤其是对靠近叶片进口方向的流体。随着含气量的增加,叶轮的径向力不平衡程度开始减弱,其最大不平衡径向力由正负值不等转变为以负值为主。     

竖直向下大、小支管气相夹带起始可视化研究

已有气相夹带起始模型均是基于竖直向下的小支管夹带所得到的，用于分析大支管气相夹带时并不适用。本文基于可视化实验，对竖直向下的大、小尺寸T型管的气相夹带起始点进行对比研究。选择与主管道直径比为0.625和0.1的大、小支管，并采用有机玻璃作为实验管道材料，空气和水为实验工质。其实验现象表明：大、小支管夹带起始均有漩涡，且漩涡现象大致相同，但在大支管条件下会出现气室，夹带气体进入支管后也会在气室下翻腾，且在相同液相折算速度下，大支管夹带起始液位会高于小支管。     

Simulation of Multi-Steady States in Low Temperature Gas Discharge

This article presents hydrodynamics simulation of multi-steady states and mode transition by DC-beam-injected gas discharge, and provides a model approach to hysteresis and distinct forms of multi-steady states. The critical transition conditions of the three discharge modes (temperature limited mode, Langmuir mode, and space charge limited mode) are estimated to be dependent on the gas pressure and the filament temperature. Various forms of the multi-steady states in gas discharge can be uniformly explained by the displacement of the mutant positions.The simulation results are in a good agreement with those of the experiments.     

同位素生产专用设备中气流输运部件内、外流场特性研究

为了研究同位素生产专用设备内部气流输运部件内、外流流场条件,从而计算出专用设备内部气流输运部件（也称为变直径管）能耗,开展了气流输运部件内部、外部流场特性的数值模拟和风洞试验研究。首先采用压力修正的方法对气流输运部件内部流场进行了数值计算,得到了气流输运部件内部气流的速度分布和压力分布云图,发现在其变径区域气流速度发生较大变化,同时与壁面发生作用。气流输运部件设计了变径部分后,整体能耗减小约30%~50%。同时在高超声速风洞中采用瞬态纹影和粒子图像测速（PIV）试验技术对气流输运部件的外部激波、涡结构、速度分布开展了流动显示和定量测量分析,实验结果显示,气流输运部件的头部激波为典型的曲线激波,对气流输运部件头部进行切角处理,在目前研究范围内,激波形式不会发生大的变化,但其附近产生的涡结构形态会发生较大变化,涡量明显减小,且涡结构更加贴近壁面。代入测得速度分布计算,进行头部切角处理后,气流输运部件的能耗较不进行切角处理时减小15%~20%,可以在专用设备中使用。     

中国实验快堆压力和流量反应性效应测量实验研究

在中国实验快堆(CEFR)物理启动过程中,对CEFR压力反应性和流量反应性效应进行了测量研究,并进行初步的误差分析。实验中堆芯反应性测量分别使用周期法和逆动态法。实验结果表明：CEFR压力反应性为正反馈,主容器覆盖气体压力从5 kPa升高至50 kPa过程中引入约+20 pcm反应性,升、降压力过程测量结果的相对偏差小于10%;CEFR流量反应性为负反馈,一回路泵转速从150 r/min升高至989 r/min过程中引入约-49 pcm反应性,升、降流量过程测量结果的相对偏差小于10%。周期法和逆动态法的测量结果符合较好。初步误差分析的结果表明,实验结果的测量精度主要由冷却剂温度测量的精度决定。     

Controlling fine particles in flue gas from lead-zinc smelting by plasma technology

With the aim of controlling the problem of fine particles in the flue gas of lead-zinc smelting, a low-temperature plasma-electrocoagulation and electric bag composite dedusting experimental platform was designed by combining electrocoagulation and electric bag composite dust removal technology based on the research of low-temperature plasma technology. Firstly, the properties of fine particles in flue gas from lead-zinc smelting were analyzed, and the effects of input voltage, filter wind speed, dust concentration, and pulse-jet ash-cleaning cycle on the dust collection efficiency of the integrated device were studied. Then, the energy efficiency of the integrated technology was analyzed, and the control mechanism of the fine particles was revealed. The experimental results show that the integrated technology of low-temperature plasma-electrocoagulation and electric bag composite dust removal achieves a fine particle removal efficiency of more than 99.99% and the energy consumption per unit mass of the dust is only 0.008 k W·h/g. The integrated technology has broad application prospects and farreaching practical significance for the lead-zinc smelting industry to achieve ultra-low emission targets for flue gas and achieve energy-saving and emission reduction effects.     

Various concentric-ring patterns formed in a water-anode glow discharge operated at atmospheric pressure

Pattern formation is a very interesting phenomenon formed above a water anode in atmospheric pressure glow discharge. Up to now, concentric-ring patterns only less than four rings have been observed in experiments. In this work, atmospheric pressure glow discharge above a water anode is conducted to produce diversified concentric-ring patterns. Results indicate that as time elapses, the number of concentric rings increases continuously and up to five rings have been found in the concentric-ring patterns. Moreover, the ring number increases continuously with increasing discharge current. The electrical conductivity of the anode plays an important role in the transition of the concentric patterns due to its positive relation with ionic strength. Hence, the electrical conductivity of the water anode is investigated as a function of time and discharge current. From optical emission spectrum, gas temperature and intensity ratio related with density and temperature of electron have been calculated. The various concentric-ring patterns mentioned above have been simulated at last with an autocatalytic reaction model.     

医用同位素生产堆应急停堆系统设计研究

医用同位素生产反应堆(MIPR)以硝酸铀酰（或硫酸铀酰）水溶液为核燃料，主要生产医用同位素⁹⁹Mo和¹³¹I。反应堆的安全性是需要关注的重要问题。当发生一次冷却水泵故障、误提棒、气回路氢氧复合能力丧失等事故而未能紧急停堆的情况下，由应急停堆系统实现反应堆停堆。本文介绍了应急停堆系统的设计原理及运行方式，并分析了“正压卸料”和“负压卸料”停堆方式应急停堆瞬态过程。结果表明，“正压卸料”应急停堆可在150 s内完成燃料的完全排出；“负压卸料”应急停堆可在700 s内完成燃料的完全排出。“正压卸料”的燃料排出速度比“负压卸料”快，该研究结果可对反应堆临界安全分析提供输入数据。     

Experimental investigation on bubble characteristics entrained by surface vortex

The cover gas entrainment at the free surface of sodium coolant becomes one of the significant issues according to the compact sizing of reactor vessel in the latest reactor design. In the present study, some basic experiments for the gas entrainment due to the surface vortex were performed in order to obtain the fundamental knowledge about the entrained bubble size. Distributions of entrained bubble diameters in several experimental conditions were obtained from bubble images using an image processing technique. Velocity fields around vortices and surface dimple shapes (gas cores) due to surface vortices were measured to grasp those influences on bubble shapes. The result showed that mean equivalent diameters of bubbles were varied from 1.3 to 2.1 mm in the range of present experimental conditions. The bubble sizes were influenced by the thickness of gas core.     

周期性力场作用下窄通道内两相流压降特性

通过实验研究了摇摆造成的周期性附加惯性力作用下矩形窄通道内空气 水两相流压降特性。按分液相雷诺数将流动分为层流区（Re_f <800）、过渡区（800≤Re_f≤1 400）及湍流区（Re_f >1 400）3个区域,并对各区域内附加压降、重位压降和摩擦压降平均值及瞬态值进行了比较。结果表明,附加惯性力对窄通道内两相流整数倍周期内平均摩擦阻力无明显影响。周期性附加惯性力作用下(摇摆周期16 s,摇摆振幅30°),层流区及过渡区气相表观速度、液相表观速度、质量含气率及摩擦压降随时间周期性波动,波动周期等于摇摆运动周期;瞬时摩擦压降相对于其平均值的波动幅值随气液两相流速的增加而减小。湍流区两相流动参数周期性波动不明显。     

气体泄漏幂函数模型在双层安全壳环廊密封性试验中的应用

双层安全壳核电机组的环廊密封性是核安全的重要保证，需在机组装料前完成测试。气体泄漏幂函数模型在计算民用建筑泄漏时比二次函数模型有更大的压力适用范围和更高的精度。本文以气体泄漏幂函数模型为基础，推导了环廊泄漏率的计算模型，以及带环廊负压修正的幂函数拟合方案，并采用某双层安全壳环廊密封性试验实测数据对该计算模型进行验证。结果表明，本文计算模型比带环廊负压修正的二次函数拟合方案和国外某公司使用的线性拟合方案有更高的精度，与双层安全壳实际泄漏情况更加吻合。     

Mode transition induced by gas pressure in dusty acetylene microdischarges: two-dimensional simulation

Radio-frequency microdischarge in acetylene is investigated by use of a fluid model and an aerosol dynamics model in a cylindrical discharge chamber. In this article, the results at a pressure of 100–500 Torr, a voltage of 80–150 V, and an electrode gap of 400–1000 μm are carefully analyzed and discussed. It is shown that two electron heating modes α and γ appear in the microdischarge, and the pressure-dependent transition from α to γ was accompanied by the abrupt decrease of electron density and electron temperature. The mode transition phenomenon is further confirmed by the variation of the electron temperature axial profiles, the profiles vary continuously from a center high at the pressure of 100 Torr to an edge high at the pressure of500 Torr. Furthermore, in the α mode(100 Torr) the plasma density increases linearly with the increase of electrode gap, but decreases sharply with the increase of electrode gap in the γ mode(100 Torr). The gas pressure and applied voltage effects on the nanoparticle density and degree of nonuniformity are also investigated. It has been shown that the gas pressure greatly influences the axial profiles of nanoparticle density and the values of the degree of nonuniformity, while the values of the plasma parameters(electron density and nanoparticle density) strongly depend on the applied voltage.