In order to solve the problems of low dust removal efficiency and excessive particle concentration at the fan discharge port due to the irrational design of the gravity settling chamber,the flow field analysis and structural optimization design of the gravity settling chamber of a certain type of road sweeper was carried out.Firstly,FLUENT was used to simulate the internal flow field characteristics of the settling chamber and the movement of dust particles inside the chamber,and the single-factor effects of the key structural parameters of the settling chamber(angle of the dust shield,width of the dust baffle plate,and the distance of the inlet duct outlet from the top of the chamber)on the settling performance(velocity at the bottom of the chamber,velocity at the front of the outlet,and the along-travel pressure drop)were investigated.Based on Box-Behnken design and regression analysis,a multi-objective response surface optimization of the gravity settling chamber was carried out,and the optimal structural parameters of the gravity settling chamber were obtained.Finally,based on the DPM particle phase model,it was verified that the optimized gravity settling chamber had a better settling effect for dust particles with an equivalent particle size above 0.5 mm.
Based on the plasma fluid theory,the effects of high-frequency source frequency in dual frequency capacitive coupling discharge on the various particles'density and plasma parameters of argon oxygen mixture discharge plasma at atmospheric pressure were studied.We simulate the discharge in different high-frequency source frequencies and have achieved the one-dimensional space-time distribution of the various particles'density,electron temperature,electric field and other parameters,and a better understanding of the influence of high-frequency source frequency on plasma characteristics in dual frequency discharge.The results show that when the discharge voltage is fixed,the electron density increases with the increase of the high-frequency source frequency;The electron temperature,electric field and potential have a downward trend;The density of various argon ions and sub argon atoms increases with the increase of high-frequency source frequency;With the increase of high-frequency source frequency,the density of various oxygen ions increases,the density of oxygen atoms decreases first and then increases,and the metastable density of oxygen molecules increases first and then decreases.Electronic pressure heating,electronic ohmic heating,electronic heating and energy loss are gradually increased due to the influence of high-frequency source frequency.In addition,the effective current density and effective power density generally increase with the increase of high-frequency source frequency.
In order to address the mechanism of leakage rate variation for similar channel-type positive pressure standard leak holes under different operating conditions,a mathematical model was established by filling the channel-type leak holes with porous foam metal.Numerical simulations were conducted to analyze the impact of different operating conditions on the leakage rate of the channel-type positive pressure standard leak holes,and the velocity field distribution inside the foam metal was also provided.The results show that under constant air source pressure,compared with Air,He and D2,H2 has the largest leak rate,and the leak rate of the leak hole increases with the increase of air source pressure.Under the condition of constant pore diameter or porosity,the leakage rate of channel type positive pressure standard leak increases with the increase of pore diameter or porosity,and decreases with the increase of channel type positive pressure standard leak length.Nonlinear change of porosity can effectively improve and control the leakage rate.This study provides valuable reference significance for the production and development of positive pressure standard leaks,leak detection in metrology,and optimizing and designing sealing system performance by controlling leakage rates.
Cryostat is a device that utilizes refrigeration technology to provide and maintain a stable low-temperature environment.It is widely used in the fields of magnetic resonance systems,superconductivity,cryogenic spectroscopy,large scientific devices,and other low temperature tests in the laboratory.The dominant technologies to obtain low temperatures are refrigerants and cryogenic cooling.However,due to the limited cooling capacity of passive cooling,experimental cryostats still predominantly rely on refrigerant and active cooling.This paper presents several common experimental cryostat structures based on cryogenic liquid and active refrigeration,discusses the development of cryostats and associated issues,and analyzes the solutions adopted by leading products in the market.Additionally,the paper also outlines the progress of domestic cryostats and their related technologies,including a self-developed cryogenic thin film resistance test instrument.Finally,the paper provides a brief outlook on the research prospects for cryostats.This study offers technical references for domestic peers/colleagues within the field.
A high-sensitivity pressure sensor with small measurement range was investigated for the failure prediction and health management(PHM)of aircraft oxygen supply,hydraulic,environmental control and fuel systems.The pressure sensor working mechanism and mechanical simulation were carried out using ANSYS software.Based on the simulation results,a novel MEMS piezoresistive pressure sensor was proposed,consisting of a composite structure of curved membrane and metered beam.The membrane was supported by cambered silicon cups.We optimized the design parameters of the sensor and determined the position of the resistors,resulting in a high sensitivity and a good linearity in the measurement range of-2 KPa～12 KPa.The sensitivity of the designed pressure sensor is obtained as 21.801 mV/KPa with a nonlinearity of 0.02％using ANSYS software simulation and analysis.Finally,we summarized the fabrication process of the designed pressure sensor based on the SOI substrate.
Nano TiN films can be used to inhibit the secondary electron multiplication of high frequency ceramic windows,shorten the high power aging time of devices,and improve microwave emission performance.In this paper,nano-titanium nitride(TiN)films were successfully prepared on the surface of ceramic windows by using the DC magnetron reaction sputtering method of coaxial cylindrical target and planar target by special vacuum coating equipment and optimizing the preparation process parameters.Modern analytical methods such as scanning electron microscope(SEM),X-ray diffractometer(XRD)and X-ray photoelectron spectrometer(XPS)were used for testing and analysis.The results show that the surface of the TiN film has fine grain size and good density.The crystal planes(111)and(200)feature diffraction peaks with regular peak shapes and narrow peak widths.The atomic stoichiometric ratio of Ti/N is close to 1∶1.With the increase of the deposition time of the film,the secondary electrons emission coefficient(SEY)gradually increases,and SEY is 1.72 when the sputtering time is 8.4s.With the increase of matrix bias,the ionization efficiency increases,and SEY decreases continuously.When the bias voltage is 350 V,the SEY is 1.89.With the increase of nitrogen flow,SEY changed,and when the N2 flow was 38 mL/min,the lowest SEY was 1.83.
The operating performance of particle accelerators has been seriously affected by the electron cloud effect(e-cloud).The secondary electron yield(SEY)is one of the main factors for judging the e-cloud.The secondary electron emission(SEE)and the e-cloud can be effectively suppressed through laser-etching the inner surface of the vacuum chamber.Oxygen-free copper(OFC)has become the first choice for the vacuum chambers of modern accelerators due to its high electrical conductivity,high thermal conductivity,and effective radiation shielding properties.Due to the long construction period of the vacuum chambers in the particle accelerators,the laser-etched components will inevitably face the problem of long-term storage during their manufacturing,installation and commissioning.In this paper,the oxygen-free copper was treated by laser-etching technique,and the surface characterization and SEY were measured before and after laser-etching.The laser-etched samples were periodically measured for SEY during the two-year storage to study the influence of atmospheric storage on SEE.The results show that the SEY of the laser-etched OFC rises gradually as the storage time increases,which can be ascribed to the change in the surface chemical state.The paper aims to provide a feasible method for the surface treatment of vacuum chambers in modern accelerators and experimental support for the storage of laser-etched components.
In order to improve the etching rate and reduce the roughness of the etched surface,the effects of gas ratio,RF power,total gas flow rate,duty cycle of pulse bias power supply and incident angle on etching rate and roughness in the process of SF6/Ar ion beam etching silicon dioxide were studied by using pulse extraction single gate reactive ion source.The results show that the influence of RF power on etching rate and roughness is different under different conditions.The higher the proportion of SF6 gas,the higher the etching rate.As the total gas flow increases,the etching rate gradually increases,and the roughness changes little.When the duty cycle of the pulse bias power supply is small,the etching rate is relatively stable and the roughness is relatively small.When the incident angle is not more than 60°,the etching rate changes little,and the root mean square roughness changes greatly.When the incident angle is greater than 60°,the etching rate and root mean square roughness decrease significantly.
The hydrocarbon species (CxHy) released by the material have a significant impact on the performance and life of precision instruments. The quadrupole mass spectrometer (QMS) is one of the most established and widely used partial outgassing rate measurement instruments. However, a potential issue with QMS is the high-mass discrimination effect, wherein ions with lower m/z values are transmitted more efficiently than those with higher m/z values. It also leads to a reduction in the sensitivity of QMS when measuring CxHy with higher m/z values. To address this problem, this paper proposes a method using dodecane to correct the high-mass discrimination effect of QMS. To ensure stable injection of dodecane gas and maintain the pressure within the working conditions of QMS, a dedicated sampling device for dodecane gas is designed. Furthermore, to verify the effectiveness of the proposed method, the high-mass discrimination effect of two quadrupole mass spectrometers of the model QMG250 M2 was corrected, and the CxHy outgassing rate of polytetrafluoroethylene (PTFE) was measured by continuous expansion method. The results demonstrate that the method proposed in this paper can effectively reduce the impact of the high-mass discrimination effect on the measurement of CxHy with higher m/z values, while significantly increasing the outgassing rate of CxHy from PTFE.
Field reversed configuration Lorentz force propulsion technology uses a rotating magnetic field to drive plasma to generate field reversed configuration(FRC)and uses Lorentz force to accelerate it to generate thrust.Since this thruster does not use grid acceleration,there is no grid sputtering problem,which greatly extends the working life of the thruster.This technology draws on nuclear fusion technology,with high thrust density and a wide range of power levels,which is feasible for future deep space exploration for high specific impulse,high thrust and long-life propulsion systems.In this paper,the development of field reversed configuration Lorentz force propulsion technology is reviewed,and the working principle,calculation model and key problem are introduced.It provides a reference for plasma thruster technology in China.
In order to study the effect of temperature variation on the vacuum of liquefied natural gas(LNG)cryogenic vacuum pipeline,in this paper,a set of high-precision test benches was designed for measuring the vacuum of LNG cryogenic vacuum pipeline based on the surface temperature method and the temperature field principle.This cryogenic vacuum pipeline vacuum test bench uses high vacuum multilayer insulation as the insulation method,an insulation layer consisting of a multilayer reflective layer and heat insulation layer as the insulation material,austenitic stainless steel as the material of cryogenic insulation pipeline,5A molecular sieve as the adsorbent for adsorbing residual gas,cryogenic liquid container,simulated service pipeline,cryogenic liquid buffer zone,vacuum and temperature test unit to simulate the actual vacuum degree of the vacuum pipeline can be obtained by measuring only the temperature of the outer wall of the vacuum pipeline and the corresponding ambient temperature.The LNG cryogenic vacuum pipeline vacuum test bench designed in this paper solves the problem of being unable to directly measure the pipeline vacuum degree in vacuum pipelines.
为抑制发动机TiAl合金新材料的焊接裂纹、改善接头组织,采用整体预热的方式在300℃和500℃恒温环境下,对TNM(Ti-43.5Al-4Nb-1Mo-0.1B)合金试板进行电子束焊接工艺试验,利用光学显微镜(OM)、扫描电镜(SEM)及电子背散射衍射(EBSD)等方法对焊接接头显微组织进行表征,分析了预热温度对焊接裂纹、焊缝形貌、晶粒尺寸、相组成以及硬度等的影响.结果表明,随着预热温度的升高,焊缝宽度有所增加,并且裂纹在预热温度为500℃时消失;靠近焊缝侧的热影响区晶粒明显长大,而远离焊缝侧的热影响区晶粒出现细化;当预热温度升高,焊缝组织中a2相含量减少,y相含量增加,预热温度为500℃时,γ相含量增加至85.5％,成为焊接接头的主相,同时a2相的类片层状特征消失;通过提升预热温度,TNM合金焊缝位错密度和硬度有明显降低.
当今,国内半导体芯片领域的竞争很大程度上取决于半导体装备以及核心零部件的竞争.设备的抗干扰能力以及稳定性等特性是衡量设备优劣的重要标准.对于射频电源而言,控制回路的精准、稳定以及快速响应是决定射频电源这款产品性能好坏的重要指标.因此,本文基于电容分压采样、电流互感器采样以及运放电路等相关原理,设计了一款纯硬件电路的功率信号检测回路,并用仿真软件Multisim进行模拟仿真实验,得到输出电压在数值上等于输出功率的实验结果.同时,通过改变母线信号的输入功率,得到输出电压和输入功率具有极高的线性相关性,因此该检测回路具有很好的稳定性,能够适用于大量程下的射频电源功率检测.
为解决黄芪加工过程中药效成分流失问题,使用热风真空组合干燥技术加工鲜黄芪以提高干燥品质.以色泽度、总黄酮含量、干燥时间为指标,进行单因素试验,研究切片厚度、热风温度、中间转换点含水率、真空温度对黄芪品质的影响规律;使用Central-Composite响应面法和综合评分法,建立二次回归数学模型,分析获取优化工艺参数.结果表明,各影响因素对黄芪品质的影响主次顺序:真空温度＞切片厚度＞中间转换点含水率＞热风温度.最佳工艺参数:切片厚度4.86mm,热风温度52℃,转换点含水率35％,真空温度69℃,在此条件下色差值为9.89,总黄酮含量为0.78 mg/g,干燥时间105 min,综合评分63.69.研究结果可为黄芪的干燥加工工艺提供参考.
范德瓦尔斯材料是一类由数层相同或不同的共价键原子薄层通过层间微弱的范德华相互作用连接起来的新型薄层材料,其中由超导体1H-TaS2和莫特绝缘体1T-TaS2交替堆叠而成的4Hb-TaS2因其独特的二维层状结构、优良的电子特性和特殊的层间电荷转移备受关注.目前关于如何调控这种特殊层间电荷转移的研究较少,使得4Hb-TaS2的电学性质仍然有.较大的研究空间.在文章中,以开尔文探针力显微术(KPFM)为表征手段,研究了 4Hb-TaS2的表面电势差,结合表面形貌信息可以实现对其表面解理层的分辨.通过高温退火实现了 T-H转化,成功制备了 4Hb-Ta1-xTixS2(x=0.005),并在此基础上探究了不同元素掺杂对4Hb-TaS2表面电学性质的影响.研究发现,通过掺杂不同元素,能够调控4Hb-TaS2中层间电荷转移能力,影响其表面电势差的大小,Ti掺杂后4Hb-TaS2的表面电势差明显增大,而Se掺杂后表面电势差减小.此外,研究发现4Hb-TaS2除了 T层、H层正常交替堆垛外,还存在部分堆垛层错的现象.实现层间电荷转移的可控调控对进一步探究4Hb-TaS2的层间电荷转移具有一定的帮助,同时也对其他范德瓦尔斯材料的层间电荷转移和表面电学性质的研究提供了新启发.
文章提出了一种基于氢氧催化键合技术制作小型光学石英真空腔体的低温封装工艺.通过预实验探讨了键合溶液、固化温度、稳定时间等因素对石英玻璃键合的影响,优选出一套当前实验条件下的最佳键合方案.研究表明,两种实验浓度下的Na2SiO3溶液键合强度普遍高于NaOH;1∶6的Na2SiO3溶液键合在80℃下加速固化能够实现不低于12 MPa的抗拉强度,并将固化时间缩短至1天;Na2SiO3溶液键合的稳定时间比NaOH溶液更短,大概只有30 s但这也足够完成某些应用的对准操作.基于优化方案设计并制作出一种双面通光石英光学真空腔体,测试表明其整体漏率优于5.66×10-12 Pa·m3·s-1并且热稳定性良好.本研究可以为小型化的石英光学真空腔体的制造提供了一种低成本、工艺简单且性能优越的可行方案.
通过实验和模拟方式,对比分析了介质阻挡放电和基于多孔阳极氧化铝的毛细管等离子体电极放电.应用阳极氧化法制备的多孔阳极氧化铝(Porous anodic alumina,PAA)作为介质层进行了毛细管等离子体电极放电.研究了多孔阳极氧化铝介质层对毛细管等离子体电极放电的影响,对比分析了相同几何参量的介质阻挡放电和毛细管等离子体电极放电的放电过程.结果表明:应用多孔阳极氧化铝介质的毛细管等离子体电极放电更稳定,放电中产生的更密的微放电有助于提高放电的稳定性;多孔阳极氧化铝介质层的毛细管等离子体电极放电具有相对于介质阻挡放电高出两个数量级的电子密度和更高的电子温度.等离子体参数具有与多孔阳极氧化铝的孔分布同步的周期性,产生了等离子体射流模式,提高了放电稳定性.
空心阴极的寿命是制约离子推力器寿命及可靠性的关键因素之一,而发射体殆尽失效又是制约空心阴极寿命及可靠性的关键因素.在前面工作中,已建立了 LaB6空心阴极工作在额定发射电流下时发射体的损耗过程及工作寿命预测模型,文章在此寿命预测模型的基础上提出了一种发射体寿命扩展模型,即发射体进一步消耗发射体下游顶端高温区域,利用扩展模型重新计算了发射体耗尽失效模式下空心阴极的寿命,并用威布尔统计规律及分析方法定量分析了空心阴极的可靠性,较基本模型而言,扩展模型中空心阴极的寿命及可靠性均得到明显提升.并且发射体温度分布对发射体寿命及可靠性有重要影响.
某在役风洞5000 m3真空球罐需要新增一个DN1000孔,对新增开孔前后球罐强度、刚度和差异性展开研究,对比各类补强方案的补强效果,得到以下结论:新增开孔将降低球罐整体的刚度和使用寿命,但影响程度有限.增加新开孔的引出管壁厚对球罐整体刚度补强效果明显,只降低自身开孔处的应力峰值;补强圈能够有效降低开孔后原有其他孔部位的应力峰值,对新增开孔后球罐使用寿命有明显的提升,但新开孔部位的局部应力、球罐刚度与补强圈宽度的关系是非单调的,补强圈宽度不宜过宽.研究成果证明某在役风洞5000 m3真空球罐新增DN1000开孔后其性能依然满足设计要求,同时为超大容积真空球罐补强方案的制定提供了理论支撑.
NEG薄膜目前已成为新一代同步辐射光源储存环真空室表面处理的主要手段,HALF光源拟采用镀Ti-Zr-V NEG薄膜的方式以满足储存环真空度的设计要求.在一些情况下,需要打开真空室以更换某些故障件或安装插入件等,这将使NEG薄膜暴露大气,严重损伤薄膜的吸气性能及使用寿命,此外也需要数周时间使真空度恢复到原有水平.因此采取向真空室充入Ne气的方法能在一定程度上保护激活后的NEG薄膜,从而避免再次激活薄膜以延长使用寿命和节省时间,另外进行了充入N2的对比实验.结果表明,充入Ne气后,真空度恢复后能满足静态真空度的要求,无需激活,从而延长NEG薄膜的使用寿命并且节省时间.而充入N2后,真空度恢复后达不到静态真空度的要求.但通过低温激活,NEG薄膜均能恢复一定活性并达到静态真空度要求.相对于N2,在Ne气保护作用下真空度恢复的更好.通过对残余气体的分析,发现低温激活前后Nc的含量均极低,对束流的稳定性不会产生影响,进一步证明了充入Ne气的可行性.
