退火温度对ZnO陶瓷薄膜低压压敏特性的影响

应用新型溶胶-凝胶法制备了ZnO陶瓷薄膜,研究了退火温度对ZnO陶瓷薄膜低压压敏电阻电性能的影响.结果表明,采用溶胶掺杂在550℃退火条件下可形成Zn7Sb2O12及ZnCr2O4相,且在退火温度范围内(550-950℃)基本上没有焦绿石相形成.当退火温度达到750℃以后,Sb2O3已全部转变为稳定性好的尖晶石相,同时存在Bi2O3、ZnO的挥发.采用适当的退火温度,可得到具有优良电性能的ZnO陶瓷薄膜低压压敏电阻,其压敏电压低于5V,非线性系数可达20,漏电流密度小于0.5μA /mm2.

AP/HTPB复合推进剂低压燃烧特性数值研究

为研究AP/HTPB复合推进剂低压燃烧特性,使用二维三明治模型进行了数值仿真研究。该模型使用简化的四步总包反应机理,考虑燃烧过程中的燃面退移,计算时大粒径AP取平均粒径,小粒径AP采用“均质黏合剂假设”,认为其与HTPB组成“均质黏合剂”。在0.02~0.08MPa的压强下进行了仿真,并与高压(5MPa)下的燃烧仿真进行对比。结果表明,低压下固相AP对黏合剂的传热导致了交界面处燃面的下陷,下陷程度随压强减小而增大;随着燃烧的进行,燃面各点燃速趋于一致,燃面形状不再改变。低压下气相反应表现为预混燃烧,初焰为主导反应。低压下燃速仿真与实验值基本一致,压强指数小于高压下的压强指数。

激光辐射下AP/HTPB复合推进剂低压燃烧特性数值模拟

为了研究激光辐射对AP/HTPB复合推进剂低压燃烧的作用机理,建立二维三明治稳态燃烧模型进行数值仿真研究。针对激光辐射强度1.4W/mm^(2),压强30~90kPa的工况下推进剂的燃烧进行仿真计算,并与130~160kPa压强下自持燃烧的仿真结果进行差异分析。结果表明,激光助燃工况下,仿真计算所得燃速与实验基本一致,最大误差不超过4.2%。在激光助燃和自持燃烧工况下,组分扩散速度快,气相火焰均为预混结构。激光助燃工况下,激光辐射的能量使得近燃面处的反应比较充分,初扩散反应在气相反应中占主导地位,气相火焰高温区域离燃面近;自持燃烧工况下,AP预混反应和初扩散反应共同主导气相反应过程,气相火焰温度在垂直于燃面方向上增长缓慢且高温区域离燃面远。激光助燃比自持燃烧时的压强指数低,推进剂燃烧对压强的敏感性较弱。

Cr_2O_3掺杂对ZnO陶瓷薄膜低压压敏性能的影响

为了制备高性能ZnO陶瓷薄膜低压压敏电阻器 ,利用新型Sol Gel方法研究了Cr2 O3 掺杂对ZnO陶瓷薄膜低压压敏性能的影响 .复合先驱体溶液由Bi2 O3 ,Sb2 O3 ,MnO及Cr2 O3 掺杂的ZnO纳米粉体均匀分散于含有Zn(CH3 COO) 2 ,Bi2 O3 ,Sb2 O3 ,MnO及Cr2 O3 的溶胶中制成 .研究结果表明 :利用新型Sol Gel方法制备的ZnO陶瓷薄膜中 ,ZnCr2 O4相在较低的Cr2 O3 添加量时出现 ,当Cr2 O3 的摩尔分数为 0 .75 %时 ,ZnO陶瓷薄膜的非线性系数α为 7,压敏电压为 6V ,漏电流密度为 0 .7μA/mm2 .

低压断路器大电流检测试验设备研究

针对低压断路器的大电流检测试验过程中功耗高、设备寿命短和自动化水平低等问题,对目前国内生产企业和质检机构使用的大电流检测设备进行了调研。对相关国家检测标准和企业检测工艺进行了总结,阐明了大电流检测试验在低压断路器产品检测工作中的重要意义。对此类检测设备的电气原理和机械结构进行了分析,阐述了两种分别基于调压器和电子式电源的电气方案,并分析了电子式电源方案的先进性。从机械设计的角度出发,指出了大电流测试夹具结构在具体设备设计和使用中的优缺点。提出了基于调压器和电子式电源两种方案在功耗、通用性、成本和自动化4个方面的优缺点。研究结果表明,将基于电子式电源的设备方案应用到行业的相关设备,有利于降低设备功耗,提高设备的寿命和自动化水平。

负荷低压释放对低压减载策略的影响

随着系统中对电压敏感的负荷不断增多,用户侧的负荷低压释放问题越来越突出。系统在发生故障而采取低压减载措施的同时,用户侧负荷出现的负荷低压释放将增大系统中的负荷切除总量,导致负荷切除过多,故障后恢复电压过高的不利结果。本文通过对电网用户侧各负荷的低压释放特性的研究,建立了考虑负荷低压释放特性的综合负荷模型,分析负荷低压释放对低压减载影响的机理,通过对10机39节点系统仿真,分析低压释放对低压减载策略的影响。研究表明,用户侧负荷低压释放量、负荷低压是否延时释放以及延时释放时间将对低压减载策略产生影响。

Performance of a Horizontally Mounted Venturi in Low-pressure Wet Gas Flow

The performance of a Venturi tube used in wet gas flow have been explored mainly under higher-pressure condition, but very often, low-pressure test exists in some oil and gas fields in Tianjin Dagang Oil and Gas Field in China. In this study, the performance of horizontally mounted Venturi meters in low-pressure wet gas flow is discussed. Three 50 mm Venturi meters were tested systematically, with fl values of 0.4048, 0.55 and 0.70, the opera- tion pressure of 0.15 MPa, 0.20 MPa, 0.25 MPa, the gas densiometric Froude number from 0.6 to 2.0, the modified Lockhart-Maretinelli parameter from 0.0022 to 0.06, and the ratio of the gas liquid mass flow rate from 0.5 to 0.99. The effects of modified Lockhart-Maretinelli parameter, pressure, gas densiometric Froude number, diameter ratio, and gas-liquid mass flow rate ratio to the Venturi tube are analyzed with new independent data. Furthermore, low-pressure performance was compared with that under high pressure.

影响PLC载波传输速率的信噪分析

为了研究影响PLC中压载波通信速率的主要因素——信噪,在深入了解中压信道特性以及分析现有解决方案OFDM利弊的基础上,通过选取代表性强的,由若干开关站、变电亭和环网箱构成的测试环境,获取载波组网具有可比性的测试数据,来对信噪产生的影响进行分析并介绍测试结果。测试结果的分析可以为我们配置最佳的载波输出频率提供有力的依据。

Effect of loading rates on the characteristics of thermal damage for mudstone under different temperatures

The uniaxial compression tests for mudstone specimens are carried out with four different loading rates from room temperature to 400℃ by using the Rock Mechanics Servo-controlled Testing System MTS810 and high temperature furnace MTS652.02.The mechanical properties of mudstone with various loading rates are studied under different temperature conditions.The results show that when temperature increases from room temperature to 400℃ and loading rate is less than 0.03 mm/s,the peak strength of mudstone specimen decreases as loading rate increases,while the various peak strengths show significant differences when loading rate exceeds 0.03 mm/s.At room temperature,the elastic modulus decreases at the first time and then increases with loading rate rising.When the temperature is between200 and 400℃,the elastic modulus presents a decreasing trend with increasing loading rate.With increasing the loading rate,the number of fragments in mudstone becomes larger and even the powder is observed in mudstone with higher loading rate.Under high loading rate,the failure mode of mudstone specimens under different temperatures is mainly conical damage.

稳定可靠的闸流管触发开关电路的研究

报道一种能满足封离型氮分子激光器低压特性的、工作稳定、可靠的闸流管触发开关电路的研究及其结果。

Effects of Probe Support on the Stall Characteristics of a Low-Speed Axial Compressor

In order to investigate the effects of probe support on the stall characteristics of micro compressors, an experiment was carried out on a large-scale low-speed research compressor according to the principle of geometric similarity. A cylindrical probe support intruding to 50% blade span was mounted at 50% chord upstream from the rotor blade leading edge. The static pressure rise characteristic of the compressor is measured, with and without the probe support respectively. The dynamic compressor behavior from pre-stall to full stall was also measured. The results indicate that the stability margin of the compressor is lowered after installing the probe support. The stall inception is aroused by modal wave disturbances. The disturbances developed into two stall cells smoothly before installing the probe support, while the disturbances first developed into a single stall cell then splitting into two stall cells after installing the probe support. The presence of probe support lowers the initial intensity of the rotating stall of the compressor, while it doesn't alter the intensity of the rotation stall after the compressor enters into full stall.

Heat Transfer and Aerodynamics of Complex Shroud Leakage Flows in a Low-Pressure Turbine

A numerical investigation on over-shroud & inter-shroud leakage flow has been carried out to explore the underneath flow physics at the stage of shrouded Low Pressure(LP) turbine.Compared with the No inter-Shroud gap's Leakage flow Model(NSLM) and With inter-Shroud gap's Leakage flow Model(WSLM),the aerodynamic characteristics and the heat transfer performance have been studied.Through the aerodynamic point of view,it is concluded that due to the pressure difference between the rotor's passage and the over-shroud cavity,in the stream-wise direction,flow structure has been modified,and the inter-shroud leakage flow may even cause flow separation in the vicinity of the blade passage's throat.In the circumferential direction,separation flows appear over the rotor's shroud surface(upper platform of the shroud).Meanwhile,from the point of view of heat transfer,further provision on contour maps of the non-dimensional Nusselt number reveals that the reattachment of leakage flow would enhance the heat transfer rates and endanger the rotor's labyrinth fins over the shroud.However,due to the limited amount of inter-shroud leakage flow(current computational model),temperature distribution variation along the blade surface(near the rotor's tip section) seems to have only minor insignificant differences.At the end of the paper,the author puts forward some recommendations for the purpose of future successful turbine design.

Characteristic investigation of permanent magnet actuator for vacuum contactors operating with an intrinsically safe low voltage

This paper reports a new application of permanent magnet actuator for vacuum contactors.A novel permanent magnet(PM) actuator to drive a vacuum contactor with intrinsically safe and low supply voltage is proposed.PM is mounted on the static iron of the contactor to enhance its holding force and reliability.While only one coil is used to break the vacuum contactor,two series coils are deployed to yield a high magnetomotive force to realize the making operation.The electrical circuit equation,mechanical equation and magnetic field are all coupled in the simulation.A prototype is manufactured and tested to validate and showcase the performance of the contactor which is equipped with the proposed PM actuator.