径向导热条件下圆柱状样品金属导热系数的测定

由于棒状样品轴向导热法测定导热系数的实验中无法准确测定棒表面的散热,故实验结果误差较大;而稳态平板法又不能用于金属导热系数的测定。另外,这两种方法均无法反映导热系数随温度的变化;故此类方法的意义有限。本文尝试采用圆柱状样品径向导热法来测定金属的导数系数。实验结果显示该方法取得了初步成功。一、轴对称区域上的稳态导热稳态导热条件下,各向异性区域内的温度分布满足▽·(λ▽T)=0 (1) 由于导热系数λ仅为温度的函数,故(1)式可化为     

用Origin处理导热系数测定实验的数据

基于用稳态法测量不良导体的导热系数实验,为了求得更为精确的导热系数,用origin软件处理实验数据,拟合出温度和时间的曲线,并求得冷却速率及导热系数.     

硅晶体热传导性能的分子动力学模拟

基于硅色散关系的实验值,给出硅晶体导热系数的经典分子动力学模拟所必需的温度、导热系数的量子化修正曲线。应用平衡态分子动力学算法模拟了硅晶体在 300～700 K温度区间内的导热系数,模拟结果表明,理想硅晶体的导热系数比自然硅高60％～75％,但随着温度的下降,模拟结果的准确性下降。     

导热系数测量实验中平衡温度的测量技巧

测量不良导体导热系数实验中的稳定导热条件下的温度时,在选取温度范围内通过反复升温降温的方法,即可迅速准确测得平衡温度,加快了实验速度,减小了实验测量误差。     

光纤温度传感器实验的改进与分析

本文利用价格低廉的1310 nm商用光纤分束器、铝箔导热等对光纤温度传感器实验装置进行了改进,并测量了改进后传感器的温度系数,发现改进后的温度系数更加稳定,导热条件对温度系数的测量影响较大.最后对此实验的教学提出了建议.     

计算热物性参数的导热反问题

本文作者根据现场测得的、生产过程中钢锭模内部若干点温度变化规律,用有限差分求解导热反问题的方法计算了钢锭模材料的导热系数及其随温度的变化。同时,对同种材料在“通电法测量导热系数”的试验台上进行精确测量,计算结果与实验结果对比表明:计算得到的导热系数落在实验数据分散度范围之内。     

二乙二醇二甲醚液相导热系数实验研究

本文利用瞬态单热线法对温度区间233～373 K、压力区间0.1～30 MPa的二乙二醇二甲醚(DMDE)的导热系数进行了实验研究,为替代燃料研究提供了基础数据,导热系数测量不确定度为±2%.实验数据拟合成导热系数关于温度和压力的方程,实验数据与拟合方程计算值的最大偏差为-2.56%,平均绝对偏差为0.91%.     

树脂基碳纤维复合材料各向异性导热系数研究

本文通过实验测试与数值预测结合研究了平纹、斜纹树脂基碳纤维复合材料的各向异性传热性能。实验方面,采用基于电加热膜加热的稳态"三明治"结构进行测试,得到了材料厚度与面内方向导热系数随温度的变化规律。模拟方面,观测复合材料内部微观结构,重构建立了代表性单胞模型,在三维方向分别模拟其一维稳态导热过程来预测材料不同方向的导热系数。研究结果表明,实验获得的树脂基碳纤维复合材料厚度与面内方向导热系数均随材料热面温度升高而近似线性增大,面内方向导热系数约为厚度方向的2.8倍,因密度相近,平纹、斜纹机织结构材料各主轴方向导热系数偏差小于10%。数值预测结果与实验结果基本符合,并对引起实验与数值结果偏差的来源进行分析。     

稳态法测量冰的导热系数

基于保护热板法原型,使用干冰-乙醇和乙二醇混合浴制造不同温度稳定低温环境之间的传热代替传统的加热传热,设计了冰的导热系数测量装置,在较大的温度范围(-70～-30℃)内实现了冰的导热系数稳定可靠的测量.同时充分借助电子式温度计高效测量数据,测得了冰在不同温度下和含有不同杂质情况下的导热系数变化规律,实验结果与参考值符合较好.利用杂质对冰的导热系数的影响规律,可以按需求调节冰的导热系数.     

良导体导热系数实验中稳态时间、稳态温度与水流量的相关性

通过改变参数进行实验测定,分析了稳态法测量良导体导热系数实验中系统达到稳态的时间、水流量、稳定温度及测得导热系数结果的准确性等相关问题,提供了可供参考的经验数据,对学生实验过程有指导作用.     

Three-dimensional simulation of electric field and space charge in the advanced hybrid particulate collector

The advanced hybrid particulate collector (AHPC) is an efficient hybrid system that combines the electrostatic precipitator (ESP) and the bag filter in a unique approach. In this study, an unstructured finite volume method (FVM) is used to compute the three-dimensional distributions of the electric field and the space charge density in an AHPC setup for two cases: without the perforated plate and with the perforated plate. The current–voltage characteristics of the AHPC setup are measured. The current on the bag plate has a mean value 7.82 μA without the perforated plate and 0.08 μA with the perforated plate for the measured voltages. The total currents are used to calculate the charge density at the corona wire according to the Peek's formula. For both cases, the numerical predictions of the current–voltage relations of the plates of the model AHPC agree well with the measurements. When the AHPC has the perforated plate, numerical results show that the electric field and space charge density distributions on the perforated plate have the same number of peaks corresponding to the holes. The electric field on the bag plate surface is lower than that of the top plate and the perforated plate. Though the bag plate has low current, its surface still has high space charge density. When the AHPC has no perforated plate, the electric field is higher than six times and the space charge density is higher than three times that of the case with the perforated plate on the bag plate surface.     

Heat Transfer from a Hot Moving Steel Plate by Air-Atomized Spray Impingement

Air-atomized spray cooling of a hot moving AISI 304 steel plate of 6 mm thickness has been investigated experimentally by varying water flow rate and plate velocity at a fixed nozzle-to-plate distance. It is found that the heat transfer coefficient is a non-linear function of surface temperature. The result shows that the cooling rate increases with an increase in the water flow rate. The highest cooling rate has been found for the static plate, whereas for a moving plate, an increasing cooling rate trend has been observed with increasing plate velocity.     

爆轰驱动的飞片熵增

在高能炸药与飞片直接接触的能量转换装置中,炸药爆轰推动飞片,飞片获得动能的同时,其熵值亦增加。本文数值模拟计算了平面一维系统。计算结果给出,适当选取空腔长度和飞片厚度,可实现飞片熵增明显下降的同时,飞片获得的动能不仅不减少还有一定的增加。     

Experimental and numerical investigation on the exergy and entransy performance of a novel plate heat exchanger

There has been increased attention on various types of plate heat exchangers because of their high efficiency and compactness. This article presents an investigation of heat transfer and fluid flow performance of a novel plate heat exchanger based on numeric studies and experimental tests. Parameters of the novel plate heat exchanger are analyzed and discussed. The thermo-hydraulic transfer performance of different plate heat exchangers is comprehensively analyzed using the exergy and entransy principle. The results indicate that the novel plate heat exchanger has better thermo-hydraulic transfer performance than the smooth plate heat exchanger. The result of this study provides a paradigm for the optimal design of plate heat exchangers.     

折反射系统中的梯度折射率校正板

本文给出了一种类似于施密特非球面校正板作用的梯度折射率介质平板,这种介质是一种弱径向梯度折射率介质。     

Interactions between the Euler,Helmholtz, and Rayleigh Instabilities

The static bending of a thin plate that separates two liquids with different densities and velocities has been considered under the assumption that the liquids and the midsurface of the plate are incompressible. Wavelengths in this simple model are small compared to the sizes of the plate and liquid-filled spaces. Static interaction between the Euler, Helmholtz, and Rayleigh instabilities as a function of the compression force acting on the plate normally to the contact boundary has been studied. The ranges of the corresponding parameters have been found for the cases when the flatness of the plate and contact boundaries becomes stable and unstable.     

小型平板蒸汽腔的实验研究

平板蒸汽腔的加工工艺一直都有待改进,其工艺的质量直接影响着工作性能.本文基于平板蒸汽腔的工作原理,设计、加工了一种小型平板蒸汽腔,并进行了实验研究.文中介绍了其工作原理,加工工艺以及实验结果.结果表明:该小型平板蒸汽腔具有较好的工作性能,其厚度为5 mm,当输入热流为22.1 W时,平板蒸汽腔的热阻低至0.01°C/W...     

用于储罐底板缺陷检测的超声兰姆波模式研究

从超声兰姆波的声场方程出发,得到板材表面离面位移(法向位移)为零的条件,即当超声兰姆波的相速度等于板材介质的纵波声速时,在板材表面的离面位移为零。在给定适当频厚积的条件下,分别数值模拟了仅有切向位移而无离面位移的A1、S1、A2和S2兰姆波模式在有液体负载的单层钢板中的传播情形。结果表明:离面位移为零的S2模式频散较小且对板中缺陷更为敏感。     

In-plane attenuation zone and its optimization in a plate with periodic holes

It is difficult to design a plate with wide attenuation zones in low frequency region based on Bragg scattering mechanism. A plate with periodic rhombic holes is optimized and designed. Based on the finite element method under periodic boundary conditions, the in-plane dispersion curves of periodically perforated plate are calculated via COMSOL. The frequency responses of periodically perforated plate axe investigated via ANSYS simulation. The plates with periodic holes are suspended and dynamically tested under sinusoidal excitations. The results show that a periodically perforated plate with rhombus holes has wider attenuation zones than plates with circular and hexagonal holes. Material properties have a great influence on attenuation zones: nitrile-butadiene rubber and silicon rubber can easily obtain low-frequency zones, while increasing porosity creates lower and wider zones. The width of attenuation zone increases as the horizontal angle of the rhombus holes increases. An analysis of the attenuation zones* generation mechanism shows that the plate with periodic holes exhibits characteristics of Bragg scattering and local resonant phononic crystal, indicating an inherent relationship between two types of mechanisms. The optimized plate has a complete attenuation zone ranging from 5281.76-8824.30 Hz. The vibrations are significantly reduced when the number of periods is no less than two. The attenuation range obtained via the numerical method is generally consistent with the experiment. The research sheds light on the noise insulation plate and has the potential to improve the sound environment in various applications due to its simple manufacturing.     

准随机点阵二值化Gabor波带片聚焦特性的数值计算

 Fresnel波带片有多个焦点,作为单色器波长选择元件使用时会受到高级衍射的影响。而Gabor波带片只有一个焦点,有更好的聚焦特性,但制作难度较大,准随机点阵二值化Gabor波带片概念的提出则解决了这个问题。介绍了准随机点阵二值化Gabor波带片的设计,并利用优化的程序分别对Fresnel波带片和准随机点阵二值化Gabor波带片的聚焦特性进行了模拟计算,通过对计算结果进行分析比较,发现准随机点阵二值化Gabor波带片具有抑制高阶衍射的特性。