基于MEMS技术的微型固态拖动力式测风传感器

为了获得风速风向的信息,制作了一种拖动力式微型固态测风传感器.它包括两个正交封装的单元,每个单元用来独立地测量风速,含有一个薄平板和两个用来连接平板和硅衬底的短悬梁.由于当风从不同角度吹过传感器时悬梁上的应变不同,因此通过测量单个单元悬梁上的应变值可获得风速值,同时通过正交组装两个测风速单元获得风向值.该传感器在ANSYS软件中进行了模拟,用流体力学进行了分析,并在小型风洞中进行了测试.结果表明在输入电源电压为0.5V时传感器最大灵敏度高达60μV/（m·s^-1）,风向测量的线性度小于6%.     

试论提高工业铂电阻测量结果准确性的方法

<正>在实际测量中,工业铂电阻的测量结果容易受到各种因素的影响而产生附加误差。为避免和减小附加误差,提高工业铂电阻测量结果的准确性,现将误差的产生原因及解决方法总结如下:一、自热效应引起的误差利用铂电阻温度计测温时,必须对感温元件的电阻通入工作电流,因此会产生焦耳热,引起温度示值升高,产生测量误差。这种现象叫做自热效应。通过铂电阻的电流越大,其灵敏度和分辨力也越高,由自热效应引起的测温误差也越大。     

(0～419.527)℃一等标准铂电阻温度计检定结果的不确定度评定

按照JJF 1059.1-2012《测量不确定度评定与表示》的要求,对工作在(0～419.527)℃温区的一等标准铂电阻温度计检定结果的不确定度进行评定.包括电测设备引入的标准不确定度分量、标准铂电阻温度计在水三相点、锌凝固点、锡凝固点处阻值的标准不确定度分量,并最终计算电阻比的合成标准不确定度.     

标准铂电阻温度计自热效应对测量结果的影响

为了研究自热效应对标准铂电阻温度计测量结果的影响,分别从定点法和比较法两方面开展研究.针对定点法,统计中国计量科学研究院近3年检定的标准铂电阻温度计数据,计算不同温区的铂电阻温度计自热效应修正前后的测量结果并进行对比,结果表明,在溯源标准铂电阻温度计时自热效应修正与否对测量结果的影响达到了1.5 mK以上,最大达到了6...     

电子计价秤传感器的工作原理和失准校正

电子计价秤采用的是剪应力梁式传感器,梁的横截面加工成工字形,电阻应变片粘贴在工字形的中性层金属弹性体表面上。根据材料力学理论可知,当同一大小的力在梁上的作用点左右移动时,中性层的弯矩要发生变化,与弯矩成正比的弯曲应力也随之变化,而梁上的切力所引起的剪应力与梁的弯矩无关。因此,剪应力梁式传感器可以消除作用点变化引起的误差。电子计价秤传感器上有4个电阻应变片,接成桥式测量电路,其中对角线的两点接上直流电源(+12V,地),另一对角线的两点接上电测仪表。如果在弹性体上加上一重量,电阻将同弹性体一起产生弹性变形,应变片的…     

一米光栅测长机的一种测温装置

我们近年来与其他有关科研单位联合研制成功的一米光栅测长机,是一台配有微处理机进行数据处理和误差修正的高精度测长仪器。该仪器总精度达±3μm,使用环境温度为20±2℃。本机采用微处理机与数字电压表配铂电阻温度计的测温方法,测温系统的极限误差不大于45mK,实际为17mK。一、原理和装置本测温装置测量被测件的温度是基于多支铂电阻温度计(以下简称铂电阻,分别测量一米光栅尺和被测工件的温度)相串联,由恒流源供给直流电流,把多支铂电阻随温度变化的电阻信息换成随温度变化的电压信息,经切换开关分别送入测量显示系统,显示出被测电压量(图1),并由微机进行数据处理后直接显示出玻璃光栅尺和被测工件的温度值。     

微型流量传感器研究

目的　研究微型管道的流量测量技术 .方法　采用热膜技术 ,在石英玻璃棒上镀一层铂电阻膜 ,利用激光将铂膜蚀刻成特定的形状 ,形成 4个独立的铂电阻 ,并构成一基本的电桥 ,电桥通以一定的电流后产生热量 ,由于液体流动的作用会使 4个铂电阻间产生一定的温差 ,从而导致电桥失衡 ,产生一定的输出电势 .结果　研制出的流量传感器的各项技术指标满足设计要求 .结论　微型流量传感器与传统的传感器相比 ,在性能上有了较大的提高 ,并且具有对管道中液体压力损失小的特点     

薄膜铂热电阻特性分析

薄膜铂电阻在温度测量领域应用广泛,使用数量巨大。在很多行业中,已取代了传统的线绕式铂电阻,但由于其原理未被充分掌握,以及特性未被深刻认识,在使用过程中,实际性能指标常常不理想,其高精度和高稳定性未得到充分发挥。为此对薄膜铂电阻工作原理、结构和加工工艺进行了介绍、针对不同于传统铂电阻的电阻温度变化规律、热响应时间和自热效应的特性进行分析,对在开展高精度温度测量应用时需注意的问题予以说明。     

浅析称重传感器的温度自补偿

1 电阻应变计的温度自补偿。对电阻应变计的温度效应来说,主要由两个因素引起,一个是应变合金丝（或箔）材料的电阻随温度变化而变化,另一个是传感器弹性体和应变合金丝（或箔）材料线膨胀系数不同引起的附加变形,使应变计电阻也产生了相应的变化.如果不考虑粘合剂的影响,当温度变化△t时,设应变计电阻丝栅电阻的改变量为△R1,则△R1=Rα△t（1）式中：R为应变计电阻;α为应变合金丝栅的电阻温度系数.     

铂电阻温度计的自热效应研究

对铂电阻温度计在冰水混合物和真空中的自热效应进行了实验研究,提出应用多电流法修正自热效应引起的测量误差.与传统的二电流法和改进的二电流法相比大大降低了自热效应修正给测量结果引入的不确定度.该研究成果对提高真空环境中温度测量的准确度具有重要意义.     

平流层飞艇气动阻力的参数分析

为了研究环境参数及外形布局对平流层飞艇气动阻力的影响,在验证CFD数值模拟方法的基础上,从气动阻力包括压差阻力与摩擦阻力的角度探讨了风速、动力粘度系数、空气密度、Re数、长细比及尾翼对飞艇气动阻力的影响规律及机理。结果表明:气动阻力系数随风速与空气密度的增加而减小,随动力粘度系数的增加而增加;气动阻力系数随Re数减小的趋势,取决于摩擦阻力系数随Re数的减小趋势;随长细比的增加,摩擦阻力系数呈现增加趋势,但气动阻力系数呈现先减小后增加的趋势;尾翼对气动阻力系数的影响主要体现在压差阻力系数的改变。     

Steady Free Surface Flow of a Fluid-Solid Mixture Down an Inclined Plane

The present work is an extension of the investigations performed by Massoudi and Anand (2001). The free surface flow problem is studied here. Numerical solutions for steady free surface flow of a solid-fluid mixture down an inclined plane are presented. The problem is formulated using the mixture theory framework. The resulting set of three coupled nonlinear differential equations is nondimensionalized. A parametric study is conducted to understand the influence of the dimensionless numbers on the velocity and volume fraction. The maximum fluid velocity is found to decrease with increase in the ratio of the drag force to the viscous forces within the fluid phase (D₁). The fluid phase velocity was found to decrease with increase in the ratio of the drag force to viscous force within the solid component (D₂), and the corresponding solid phase velocity was found to increase.     

高层建筑顶部横梁的风效应

结合CFD数值方法和风洞试验分析了高层建筑顶部横梁的气动力和风荷载特性。CFD数值结果显示建筑顶部绕流会显著增大横梁处的气流风攻角;横梁气动力的数值计算结果和风洞试验结果均证实横梁为驰振稳定截面;风振分析显示横梁的峰值升力大于峰值阻力,通过进一步分析广义力功率谱密度函数和频率比对峰值升力的影响,证实横梁在50年重现期强风作用下处于涡激共振状态。     

弹丸头部喷流的风洞实验测试技术

主要阐述了弹丸头部喷流风洞实验中的实验方法、气动力干扰影响及预测方法。介绍了气动力测量、压力测量、底阻测量的关键技术及解决途径。     

Numerical Simulations on Piezoresistivity of CNT/Polymer Based Nanocomposites

In this work, we propose a 3 dimensional (3D) numerical model to predict the piezoresistivity behaviors of a nanocomposite material made from an insulating polymer filled by carbon nanotubes (CNTs). This material is very hopeful for its application in highly sensitive strain sensor by measuring its piezoresistivity, i.e., the ratio of resistance change versus applied strain. In this numerical approach, a 3D resistor network model is firstly proposed to predict the electrical conductivity of the nanocomposite with a large amount of randomly dispersed CNTs under the zero strain state. By focusing on the fact that the piezoresistivity of the nanocomposite sensor is largely influenced by the tunneling effects among neighboring CNTs, we modify this 3D resistor network model by adding the tunneling resistance between those neighboring CNTs within the cut-off distance of tunneling effect, i.e., 1.0 nm in this study. The predicted electrical conductivity by this modified 3D resistor network model is verified experimentally. Furthermore, to analyze the piezoresistivity of the nanocomposite sensor under various strain levels, this modified 3D resistor network model is further combined with a fiber reorientation model, which is used to track the orientation and network change of rigid-body CNTs in the nanocomposite under applied strain. This combined model is employed to predict the piezoresistivity of the nanocomposite iteratively corresponding to various strain levels with the experimental verifications. Some key parameters, which control the piezoresistivity behavior, such as, cross-sectional area of tunnel current, height of barrier, orientation of CNTs, and electrical conductivity of CNTs and other nanofillers, are systematically investigated. The obtained results are very valuable, which can provide guidance for designing the strain sensor of this nanocomposite with enhanced sensitivity.     

Multi-fluid modelling of hydrodynamics in a dual circulating fluidized bed

In this work, a multi-fluid model based on the Eulerian-Eulerian framework is used to study the gas-solid hydrodynamics, such as solid distribution, particle motion and solid velocity, in a three-dimensional (3D) dual circulating fluidized bed (DCFB). The influence of four different drag force models, including two classic models, i.e. Gidaspow, EMMS drag model and two recent drag models, i.e. Rong and Tang drag model, on hydrodynamics in DCFB are assessed. Numerical results show that the characteristics of solid distribution and velocity in different sections are distinct. For qualitative analysis, all the drag models can predict a reasonable radial solid distribution and pressure distribution, but only the EMMS, Rong and Tang drag model can capture the phenomenon of dense solid concentration in the low part. For quantitative analysis, the solid circulating rate predicted by the EMMS drag model is the closest to the experimental value while the Gidaspow drag model shows the most significant deviation. The overall assessments confirm that the drag model selection has a significant influence on the simulations of gas-solid flow in DCFBs. This study sheds lights on the design and optimization of fluidized bed apparatuses.     

翼形表面流动激励载荷特征试验研究

为了研究水下航行体翼形表面流动激励载荷特征,采用柔性基底微型传感器阵列,建立风洞中翼形结构表面流动激励载荷测试方法。分析了翼形表面层流、转捩、湍流发展过程中激励力试验特征,试验结果表明:翼形表面经过层流、转捩、湍流发展过程,随着来流速度的增大,翼形表面转捩区位置逐渐前移直至完全湍流。提出了转捩点预报修正方法,修正后预报值与试验值偏差在 10 % 以内,为水下航行体翼形流动激励力相关研究提供试验基础。     

A Cross-Type Thermal Wind Sensor With Self-Testing Function

A 2-D smart flow sensor with self-testing function was designed, fabricated and tested in this paper. It is composed of cross-structure heaters and four symmetrically located sensing parts. When the flow angle changes in the clockwise direction, the temperature differences among the four parts, namely Mode 1 given by T₁₃(T₂₄) and Model 2 given by T₁₂(T₁₄) will be Sine(Cosine) functions of wind direction. Further study shows that the magnitude of mode 1 is 1.414 times that of Mode 2, and the phase of Mode 2 leads Mode 1 by 45°. By using the fixed phase gap between the two modes, the self-test function can be realized without additional components. In order to achieve a high sensitivity and robust sensor, thermal insulated substrate was introduced to fabricate calorimetric flow sensor instead of silicon wafers. The proposed sensor was fabricated on the Pyrex7740 substrate using single liftoff process. Finally, a wind tunnel test was carried out in constant power (CP) mode, and the test results show reasonable agreement with the simulation curves.     

Hydrodynamic permeability of membranes built up by spherical particles covered by porous shells: effect of stress jump condition

This paper concerns the flow of an incompressible, viscous fluid past a porous spherical particle enclosing a solid core, using particle-in-cell method. The Brinkman’s equation in the porous region and the Stokes equation for clear fluid are used. At the fluid–porous interface, the stress jump boundary condition for the tangential stresses along with continuity of normal stress and velocity components are employed. No-slip and impenetrability boundary conditions on the solid spherical core have been used. The hydrodynamic drag force experienced by a porous spherical particle enclosing a solid core and permeability of membrane built up by solid particles with a porous shell are evaluated. It is found that the hydrodynamic drag force and dimensionless hydrodynamic permeability depends not only on the porous shell thickness, particle volume fraction γ and viscosities of porous and fluid medium, but also on the stress jump coefficient. Four known boundary conditions on the hypothetical surface are considered and compared: Happel’s, Kuwabara’s, Kvashnin’s and Cunningham’s (Mehta–Morse’s condition). Some previous results for the hydrodynamic drag force and dimensionless hydrodynamic permeability have been verified.