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真空退火对Nd_(0.7)Sr_(0.3)MnO_3外延膜结构和输运性影响 总被引:1,自引:0,他引:1
本文研究了真空退火对Nd0.7 Sr0.3 MnO3(NSMO)外延膜的结构和输运性的影响.X-射线衍射(XRD)和电阻率测量结果显示,随着退火温度的升高,NSMO薄膜单胞沿着c-轴方向拉长,电阻率随退火温度的升高而增大,同时金属-绝缘体转变温度(Tp)降低.上述结果归因于真空退火引起的氧缺失导致了Mn3+/Mn4+离子比例的增大及MnO6八面体的畸变.Kroger-vink的缺陷反应式定性的解释了氧缺失与输运性的关系. 相似文献
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金属化保护的光纤布拉格光栅温度传感模型 总被引:2,自引:0,他引:2
光纤布拉格光栅(FBG)传感器是智能金属结构首选的信息传输与传感的载体,埋入金属材料内部的FBG传感器必须要经过适当保护,金属镀层是最有效的保护方法之一.FBG经过镀前预处理,通过化学镀方法可获得均匀的金属保护镀层.针对金属保护镀层,应用弹性力学基本原理分析了由于镀层与FBG传感器的热膨胀系数不同而产生的热应力,建立了镀层厚度对FBG温度传感性能影响的数学模型.镀镍FBG的升温和降温传感实验表明,升温时的实际温度灵敏度系数与模型值之间误差为6.22%,降温时的实际温度灵敏度系数与模型值之间误差为6.75%.与裸FBG相比,化学镀镍后的FBG温度灵敏度系数提高1倍多.结果表明该温度模型从理论上解释了镀层金属热应力对FBG起到的温度增敏作用. 相似文献
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通过对蒸发式新风机组加干式风机盘管空调系统进行性能研究,改变室外相对湿度及新风量,测试新风机组性能;改变风机盘管供水温度、回风量、水流量,测试风机盘管性能。结果表明,随室外相对湿度的升高,新风机组制冷量、新风机组潜热制冷量均增加,新风机组显热制冷量降低;随新风量的增加,新风机组总制冷量、显热制冷量、潜热制冷量都增加。随风机盘管供水温度的升高,风机盘管总制冷量、显热制冷量、潜热制冷量均降低,其中,最佳供水温度为16℃,既可以保证风机盘管完全处于干工况运行,又可以保证风机盘管最大制冷量;随风机盘管回风量的增加,风机盘管总制冷量、显热制冷量增加,潜热制冷量降低;随风机盘管水流量的增加,风机盘管总制冷量、显热制冷量、潜热制冷量均增加。 相似文献
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本文基于非均匀成核相变动力学理论和热传导方程研究了在极快速升温(1012K/s)条件下金属达到过热状态后发生熔化相变时,通过金属/光学窗口界面温度的演化历史研究了金属内部温度的变化情况.分析结果表明,当金属内部无熔化发生时,界面温度将很快达到平衡,此变化满足理想接触界面模型;而当金属内部有熔化发生时,界面温度受熔化速率的影响不能立即达到平衡而是经历了一个下降的弛豫过程.计算结果与实验观测结果进行比较后发现两者符合得较好,由此可以获得金属在高压下的熔化速率,熔化温度等相关信息.本文的研
关键词:
相变动力学
热传导
金属铁
冲击波 相似文献
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将关于液面凹陷的Young-Laplace方程与关于金属溶池的流体力学方程组及关于金属蒸发的BGK方程联立求解,在给定的电子枪加热条件下,获得了熔池流场和温度场图像及金属蒸气密度、速度和温度分布.数值计算结果表明,随电子枪功率增加,金属的蒸发速率增加,蒸气的密度增大、温度降低而速度升高.与假设液面为平面的情况相比,考虑液面凹陷后求得的液面温度较低,金属的蒸发速率较小,并且这种差别随电子枪功率的增加而扩大.因此对于高功率电子枪加热金属蒸发,必须考虑液面凹陷的影响才能得到符合实际的结果.
关键词:
液面凹陷
Young-Laplace方程
熔池
金属蒸发 相似文献
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This paper presents an experimental investigation on the metal foam for controlling a centrifugal fan noise. Nine samples of metal foam with different types of cells, i.e., open, semi-open and close, are employed to compare their effects on the aerodynamic performance and noise level of the centrifugal fan. Experimental data confirms that the open cell metal foam is the most effective to control the fan noise because it not only significantly suppresses the tonal noise but also attenuates the broadband noise. Moreover, the geometrical parameters of the open cell metal foam, i.e., pores per inch and porosity, are studied to investigate their effects on the aerodynamic performance and noise level of the centrifugal fan. 相似文献
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针对煤矿大型风机设备主轴磨损而影响风机工作效率的问题,在对大型风机设备磨损故障的生成原因分析后,根据系统需求设计实现了系统的硬件模块和软件模块,通过传感器电路对大型风机设备的输入输出功率、出风量、主轴转速等参数进行采集,系统软件在对数据进行综合分析后将检测结果显示在液晶屏上,实时输出大型风机设备的运行状态以及主轴磨损状况,从而保证了风机的运行效率,避免设备故障的发生。通过系统测试表明本系统可以实时输出风机设备的主轴磨损程度监测结果,且风机设备的风量、风压、功率和效率等主要参数的测量精度高。 相似文献
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The paper presents the results of experiments upon the influence of tribocharging of PAO and PAG synthetic motor base oils blended with different additives—friction modifiers (FM) and antiwear agents (AW)—and the effect of an external DC electric field on the braking torque. The experiments are carried out in a rotating shaft–oil–lip seal system which represents a specially built experimental facility to be a simplified model of an engine crankcase in the interior of which a metal shaft rotates. The research is especially aimed at the braking torque of a rotating shaft sealed with a lip seal and a possibility of reduction in the torque under external DC electric fields. DC voltage is applied between the stiffening ring of lip seal and a rotating, earthed shaft. The braking torque of rotating shaft is measured as a function of the oil–additive blend's temperature, the shaft's angular velocity, and the absolute value of the external DC voltage. In general, it is found that an external DC electric field causes the braking torque to change with the increasing DC voltage. The change depends on the additives and base oils used in their blends which in turn causes the torque to increase in the case of the PAO–additive blends or to decrease for the PAG–additive blends. 相似文献
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The paper presents the results of experiments on tribocharging of different mineral, semisynthetic, and synthetic base oils and their blends with additives. An antiwear additive ZDDP (zinc dialkyldithiophosphate) is tested when added to base oils in different percentages by weight. Experiments are carried out on the specially built experimental facility to be a simplified model of an engine crankcase in whose interior an earthed metal shaft rotates at given angular velocities. The potential of a stiffening ring of a lip seal is measured directly with an electrometer. The potential is a measure of tribocharging in a rotating shaft–oil–lip seal system, friction junction, and especially between both interfaces: shaft surface–oil and oil–lip of a lip seal. The experimental results are presented in the form of some characteristics that are relationships of the potential induced in the stiffening ring with oil's temperature for different angular shaft's velocities and additives, contents. The oil's temperature ranges from 60 to 110 °C and is controlled automatically. The angular velocities of a shaft used are 500 and 1500 rpm. The additive contents in the blends with different base oils are 0.1 and 0.2%. The pure base oils of all the types and some lip seals are also examined. Moreover, the influence of an external DC electric field applied between the earthed shaft and the stiffening ring on the braking torque of the shaft is examined for a range of temperatures of the pure oils and their blends with the additive used, angular velocities, and additive contents. The electric field is produced while applying the high DC voltage of both polarities between the shaft and the ring. The absolute value of the voltage is in a range from 500 to 1500 V. 相似文献
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Aero-engines operating with supersonic fan tip speeds generate an acoustic signature containing energy spread over a range of harmonics of the engine shaft rotation frequency. These harmonics are commonly known as the “buzz-saw” tones. The pressure signature attached to a supersonic ducted fan will be a sawtooth waveform. The non-linear propagation of a high-amplitude irregular sawtooth upstream inside the inlet duct redistributes the energy amongst the buzz-saw tones. In most modern aero-engines the inlet duct contains an acoustic lining, whose properties will be dependent on the mode number and frequency of the sound, and the speed of the oncoming flow. Such effects may not easily be incorporated into a time-domain approach; hence the non-linear propagation of an irregular sawtooth is calculated in the frequency domain, which enables liner damping to be included in the numerical model. Results are presented comparing noise predictions in hard-walled and acoustically lined inlet ducts. These show the effect of an acoustic liner on the buzz-saw tones. These predictions compare favourably with previous experimental measurements of liner insertion loss (at blade passing frequency), and provide a plausible explanation for the observed reduction in this insertion loss at high fan operating speeds. 相似文献
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A rotating flexible annular thin disk subjected to the temperature increment of the shaft clamping the disk was modeled in this paper. At disk top and bottom surfaces and free outer edge, the heat convection boundaries were assumed. Disk transverse deflection was considered as a function of both disk radial and circumferential coordinates, and temperature distribution was solved along disk thickness and radial directions simultaneously. As a result, the shaft temperature increment causes thermo-elastic instability of some disk modes. Effects of the shaft temperature increment, ratio of disk convective heat transfer coefficient to thermal conductivity, disk thickness, nodal circle and diameter numbers of disk mode on the natural frequencies, thermo-elastic instability and critical angular speed of the disk were discussed. 相似文献
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同时精确测量高温物体温度及发射率的系统 总被引:4,自引:0,他引:4
利用一种新的方法设计能够同时精确测量高温物体的温度及单色发射率的系统。该系统主要由光学系统、信号放大与处理系统及显示系统三部分组成。介绍了该系统的工作原理与结构,讨论了其中的技术难点及其相应的解决方法,分析了测量波长的选择、扇形板关闭时的L1及开启时的L2的测量精度对单色发射率及温度测量精度的影响 相似文献