Measurements of wall shear stress of a turbulent boundary layer using a micro-shear-stress imaging chip

Measurements of wall shear-stress streaks of a turbulent boundary layer in the channel flow were carried out using a MEMS-based micro-shear-stress imaging chip, which contains about 100 sensors. The chip is designed and fabricated by surface micromachining technology. One arrray of 25 micro-shear-stress sensors in the chip that covers a length of 7.5 mm is used to measure the instantaneous spanwise distribution of the surface shear stress. The statistics of high shear-stress streaks were established. Based on the measurement, the physical quantities associated with the high shear-stress streaks, such as their length, width and peak shear-stress level, were obtained. We found out that a high correlation exists between the peak shear-stress level and front-end shear-stress slope of a high shear-stress streak. This important property is currently being applied to the deisgn of a real-time flow control logic.     

以陶瓷厚膜为绝缘层的红色ZnS:Sm,Cl电致发光器件

报道采用高介电常数的陶瓷厚膜作绝缘层、ＺｎＳ：Ｓｍ,Ｃｌ作为发光层的红色薄膜电致发光器件。测量了器件的电致发光光谱和亮度电压曲线,研究了发光机理和效率电压等特性。制备的器件在电驱动下１６Ｖ启亮,最大亮度为１８．４ｃｄ／ｍ＾２,最大效率为０．０６１ｍ／Ｗ。     

采用端壁边界层抽吸方法抑制时栅二次流的效果分析

１前言叶栅端壁边界层和叶片表面边界层的发展及其产生的各种旋涡和分离流动对二次流损失有着重要的影响［１,２］,采用端壁边界层抽吸可以控制叶栅端壁上边界层的发展,从而降低二次流损失并改善出口气流的均匀性。同时,在汽轮机湿蒸汽静叶栅中有时也需在端壁上开设抽...     

Electrophysical properties of double‐layer nickel‐base and vanadium‐base films within the intermediate temperature range

Phase composition of the double‐layer Ni‐base and V‐base films obtained and annealed in vacuum of 10^‐4–10^‐5 Pa within the temperature range of 700–900 K is studied by technique of electronography and transmission electron microscopy. Temperature dependence of resistance and temperature coefficient of resistance (TCR) was investigated. Comparison of TCR experimental data with the calculated data was made at T = 300 K on basis of semiclassical and macroscopic models and formula for TCR of alloys. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

General solutions of axial symmetrical ring shells

This paper gives the general solutions of axial symmetrical ring shells for all values of slenderness ratio. This solution is newly brought out, and can be used to solve various practical problems, including corrugated tubes, thermal expansion joints, Borden tubes, etc.     

Electrochemistry of capillary systems with narrow pores. I. Overview

In capillary systems with narrow pores the Helmholtz electrochemical double layer located at the pore wall extends over the entire cross section of the pores. It loses its character as the “charge on the wall”. It will be shown that not only the electrokinetic phenomena but also the electrical conductivity and the dialysis potential of membranes with narrow pores can be understood from the same point of view, namely: the electrolyte solution in the pores of a membrane with narrow pores is considered to be an approximately homogeneous solution in contact with immobilised charges located at the pore wall. In this case the electrochemical equations contain the fixed ion concentration as a parameter instead of the ζ potential. This makes it possible to describe quantitatively to a good approximation data on the electroosmosis, the electrical conductivity, the streaming potential and the dialysis potential taken from the literature, as well as results of our own measurements, by using a single membrane constant.     

Comparison of polyelectrolyte multilayers built up with polydiallyldimethylammonium chloride and poly(ethyleneimine) from salt-free solutions by in-situ surface plasmon resonance measurements

Polyelectrolytes offer a widespread potential for the defined modification of planar inorganic or polymer surfaces. Essential parameters for the regular adsorption of subsequent polymer layers by electrostatic interactions are the charge of polyelectrolyte and of the outermost surface region, the surface of the substrate, and the molar mass of the polyelectrolyte. To study such effects in mono- and multilayers we used poly(diallyldimethylammonium chloride (PD) with a molar mass from 5000 to 400000 g/mol as a strong polycation and poly(ethyleneimine) (PEI) with 75000 g/mol as a weak polycation and poly(sodium styrenesulfonate) (PSS) from 70000 to 1Mio g/mol in the diluted and semi-diluted region. The characterization of the layers was performed by streaming potential, in-situ SPR and UV-Vis spectroscopy. Thereby the layer built up at the solid/liquid-interface could be followed and quantified at the molecular level. SPR revealed that the thicknesses of the multilayer depends strongly on pK values of the polyelectrolyte (strong or weak) and the molar masses. We observed a linear growth if both polyelectrolytes are strong and an exponential growth if one polyelectrolyte is weak. The thickness increased with higher molar masses of the polyelectrolytes. The process was followed in-situ in short time steps.     

45~#碳钢表面激光铬镍合金化及其耐磨性的研究

作者利用1.1kW CO_2激光器对45~#碳钢表面进行了激光铬镍合金化处理。通过对合金层的成分和相组织分析,以及对合金层和基体的硬度与耐磨性的研究认为,激光铬镍合金化层的组织是胞状枝晶,其相组成为马氏体加残余奥氏体。测试结果表明,合金层的显微硬度是45~#碳钢基体的2～3倍,耐磨性也明显地比基体材料的好。     

流速比对颗粒在液固两相平板混合层中沉降的影响

本文采用流动显示的方法对平板混合层中上下层流体速度比对固体颗粒在混合层中沉降的影响进行了研究。实验中分别采用粒径小于 ４０ ｕｍ,粒径 ９８～１０４ｕｍ,粒径 １５４～１６０ｕｍ的玻璃微珠以及环氧树脂作为固相颗粒,对这些颗粒在速度比分别为１：１．２、１：２和１：２．８的液相混合层中的运动进行了显示。结果表明混合层中大涡结构对固体颗粒的沉降具有迟滞作用,其作用程度取决于混合层中上下层流体速度比。速度比越大,颗粒的沉降越慢。     

多孔涂层横向抽吸效应强化膜状凝结换热的研究

研究多孔涂层界面抽吸效应对强化膜状凝结换热的影响。考察了多孔涂层的特性参数对凝液膜厚度和换热系数的影响。与Nusselt理论预示值对照表明,多孔涂层界面抽吸效应是强化膜状凝结换热的重要因素。