地下采空区顶板安全厚度的确定

利用强度折减技术和二分法原理,以塑性区的贯通作为顶板破坏的标准,当采空区顶板的安全系数等于1.2时,利用FLAC软件计算得出各种跨度空区在不同岩层中的最小安全顶板厚度.     

低压蒸汽管道保温层经济厚度计算

以改造后的14^#低压蒸汽管道为例，采用经济厚度法对其进行了保温层的厚度计算。介绍了热力管网保温厚度的设计原则和保温材料的选择。     

Annular wall layer thickness in circulating fluidized bed risers

The thickness of downward-flowing annular wall layers in circulating fluidized bed risers has been determined in the literature based on measured radial profiles of both local particle velocity and solids flux. The thickness of the wall layer is shown to be larger based on solids flux profiles than when based on particle velocity profiles, because fluctuations in local instantaneous particle velocity are correlated with fluctuations in local solids concentration. A new correlation is developed to predict the time-average thickness of the downflowing particle streamer layer based on solids flux measurements as a function of the cross-sectional average voidage. It successfully accounts for the variation of the wall layer thickness with axial location and solids circulation rate.     

鱼鳔及其鱼鳔胶粘剂(三)鱼鳔胶粘剂的力学性能

实验以三种不同的鱼鳔 ,在考查固胶物化性能的同时 ,探索了胶接工艺对胶接性能的影响 ,结合实际应用对基材试件、胶接试件等有关力学性能作了研究     

MEASUREMENT OF LIQUID FILM THICKNESS ON THE SURFACE OF A PARTIALLY IMMERSED VERTICAL ROTATING DISK USING A GAMMA CAMERA

The liquid film thickness on the surface of a partially immersed vertical rotating disk was determined using a gamma camera imaging system to measure the amount and spatial distribution of a dissolved 99m-Technetium pertechneiate radionuclide tracer. The method allows simultaneous measurement of film thickness in individual regions having a projected surface area of less than 1 cm² and distributed over the entire exposed surface of the disk. Measurement accuracy is limited only by counting statistics, and for these studies was better than ±4% of the absolute film thickness.

Experiments were conducted with a 31.5 cm diameter aluminum disk rotating from 18 to 99 revolutions per minute; seven aqueous solutions of glycerol and polyvinylpyrrolidone (PVP) within the viscosity range 1 to 19.7 cp were used. The average film thickness varied between 0.045 and 0.45 mm, and was a function of solution viscosity and disk angular velocity. Local film thickness was dependent on both radial and angular position, and varied from 0.5 to 3.0 times the average thickness. This variation may be important to the characterization of mass transfer when diffusion through the film is a rate limiting step     

对羟基苯甲酸对HDPE结晶行为及力学性能的影响

采用DSC研究了对羟基苯甲酸(HBA)对高密度聚乙烯(HDPE)非等温结晶行为的影响。分析了HBA的引入对HDPE的结晶行为、晶片厚度分布、结晶度以及力学性能的影响。结果表明，当HBA用量为HDPE的0．5％-1．0％时可以促进HDPE的结晶，从而加快HDPE的结晶速度，提高HDPE的结晶度，降低片晶的平均厚度及其分布，并提高其力学性能。     

截面分析法对界面过渡区厚度的放大作用

在采用截面法分析研究截面过渡区厚度时，由于截平面并不一定正好垂直于集料的表面，导致得到的表观界面过渡区厚度与实际界面过渡区厚度是不同的。以3种规则形状(球形、椭圆形截面以及矩形截面)的集料为例，从几何概率角度研究了截面分析法对界面过渡区厚度的放大问题。研究结果表明，截面分析法得到的表观界面过渡区厚度都大于实际的界面过渡区厚度，平均放大倍数与集料的粒形有关。对正方体性集料而言，平均表观界面过渡区的厚度是实际界面厚度的1．12倍；对球形集料而言，实际界面过渡区厚度被放大了π／2倍。     

针孔阵列厚度对集成成像3D显示观看视角的影响

基于针孔阵列的集成成像3D显示具有成本低,重量小,器件厚度薄,易于实现3D/2D转换等优点。针孔阵列的参数设计是集成成像3D显示器结构设计的关键之一。3D观看视角是集成成像3D显示的关键性能参数之一。本文研究针孔阵列的厚度对3D观看视角的影响。根据针孔阵列厚度与孔径宽度的3种取值关系,分别建立3种集成成像3D成像模型,然后根据几何光学分别计算不同成像模型的3D观看视角,并研制了集成成像3D显示测试装置。实验结果表明针孔阵列厚度存在最优值,且只取决于图像元节距、针孔孔径宽度以及针孔阵列与显示面板的间距。针孔阵列厚度取最优值时,显示面板上每个图像元中所有像素发出的光线都可以通过其对应的针孔,且每个图像元中像素发出的光线都不能通过其他针孔,因此3D观看视角最大,且没有串扰图像。针孔阵列厚度小于最优值时,显示面板上每个图像元中所有像素发出的光线都可以通过其对应的针孔,但是每个图像元中部分像素发出的光线可以通过其他针孔,因此3D观看视角不变,但是会产生串扰图像,且串扰与针孔阵列的厚度成反比。针孔阵列厚度大于最优值时,每个图像元中只有部分像素发出的光线可以通过其对应的针孔,虽然没有串扰图像,但是3D观看视角变小,且与针孔阵列厚度的厚度成反比。     

水平管降膜厚度的电导探针测量方法

为测量水平管降膜分布参数,从而揭示降膜的流动特性,根据气液两相介质的电导特性,设计出一种测量水平管降膜厚度的电导探针系统,利用该系统进行了水平管周向不同位置液膜厚度分布规律的实验研究.结果表明,水平管降膜厚度的电导探针测量方法不仅切实可行,而且还能实现大角度范围测量,可扩展应用于垂直结构外部气液两相流动参数的分布测定.此外,管外液膜厚度随管间距的增加而减小,而且液膜波动加剧.与实验数据对比,发现Nusselt公式可以用来预测圆管上半周的液膜厚度,但下半周的数值明显偏大.在不同工况下,最薄的液膜并不是出现在β=90°的单点处,而是在β=90°~115°的区域内.     

Multiple melting behaviour of poly(ethylene terephthalate)

Differential scanning calorimetry (DSC) and temperature modulated DSC (MTDSC) have been used to investigate the melting behaviour of poly(ethylene terephthalate) (PET). Multiple melting endotherms were observed even at high heating rates, e.g. 160 K min⁻¹ and these have been attributed to the presence of two different distributions of lamella thickness and re-crystallisation (reorganisation) on heating. This has been confirmed by MTDSC—the presence of endotherms and an exotherm in the reversing component of the heat flow during heating. Examination of the endotherms of samples heating stepwise indicated that further crystallisation took place above the isothermal crystallisation temperature (T_c). Some part of this was associated with lamella thickening and crystal perfecting. The multiple melting endotherms observed are a consequence of the balance between the melting and re-crystallisation and the lamella thickness distribution existing within the sample, prior to heating. The triple melting endotherms observed are attributed to the melting of secondary and primary lamellae produced on crystallisation and to thickened lamellae produced during heating to the melting point.