On the boundary slip of fluid flow

For hundreds of years, in all the textbooks of classical fluid mechanics and lubrica- tion mechanics it is assumed that there was no wall slip (boundary slip) at a liquid-solid interface, i.e. no relative motion between liquid and solid at the interface. This is the no-slip boundary condition. It has been widely applied to engineering and experiments and to almost all the rheology or viscosity measurements of fluids. Rheology is one of the most important bases for fluid mechanics and lubricati…     

双面对称角度楔形镜的超光滑表面加工方法

对两个通光面均为超光滑表面的双面对称角度楔形镜的加工提出了一种新工艺方法,并根据零件的特点对工艺方法进行了改进。利用组合楔板工装、粘接上盘等方式对零件进行成盘加工,不仅使零件的角度、厚度得到了很好的保证,而且还避免了光胶上盘对已加工表面的损伤,使通光面的疵病、面形、粗糙度、一致性等指标有很大的改善,超光滑表面粗糙度rms均优于0.2 nm (AFM测量),表面疵病达到0级,角度精度达到15,一次交检合格率达到85%以上,有效地解决了生产中的瓶颈问题。     

Acoustic gas slip induced by surface waves

A boundary kinetic effect has been predicted on the basis of a model of interaction between Rayleigh surface acoustic waves (SAW) and a gas. The effect resembles some classic boundary effects such as thermal or diffusion gas slip. The functional dependence of the effect on gas and SAW parameters is presented. The slip phenomenon takes place due to angular restrictions of the scattered gas molecules because of the deformation of the solid surface.     

Theoretical and numerical studies of non-equilibrium slip effects on a catalytic surface

A new concentration slip model to describe the rarefied gas effect on the species transport in microscale chemical reactors was derived from the approximate solution of the Boltzmann equation. The present model is more general and recovers the existing models in the limiting cases. The analytical results showed that the concentration slip is dominated by two different mechanisms, the reaction induced concentration slip (RIC) and the temperature slip induced concentration slip (TIC). The magnitude of RIC slip is proportional to the product of the Damköhler number and Knudsen number. The impact of the velocity, concentration and temperature slips on the coupling between the surface catalytic reactions and the homogeneous gas phase reactions was examined using the detailed chemistry of hydrogen and methane within a wide range of accommodation coefficients in a two-dimensional microscale chemical reactor. The results showed that the impact of reaction induced concentration slip (RIC) effects on catalytic reactions strongly depends on the Damköhler number, the Knudsen number and the surface accommodation coefficient. It was found that the TIC slip had a strong effect on the fuel oxidation rates and the RIC slip dramatically changed the mass fraction distributions of radicals, especially when the mass accommodation coefficients were far less than unity.     

光楔加工检测及测量误差分析

提出了用于光楔加工中楔角检测的一种新型装置及测角系统。结合锗晶体元件的光学特性 ,在综合分析各种测角装置的结构特点后 ,形成了此装置及系统。实际使用中该装置测角性能良好。对测量中可能产生的误差进行了较详细的分析。经过对标准楔块的检测 ,可满足实际使用要求。该装置的特点 :采用多个微动机构 ,在微机控制的细分驱动方式下 ,利用搜索逼近的方法完成对楔角的测量。该装置除用于红外光楔的锗晶体测量之外 ,也可用作其它光学玻璃的角度测量和分度使用     

Effective boundary slip and wetting characteristics of water on substrates with effects of surface morphology

ABSTRACT

In the present study, molecular dynamics (MD) simulation was used to investigate the relationship between wetting behaviour and slip length on patterned substrates. We adopted two solid surfaces of Si(100) and graphite due to similarities in their intrinsic contact angle. Contact angle and apparent slip length were obtained using discrete simulations with the same thermodynamic states. In the present study, a number of questions regarding surface roughness and the problem of contact angle (θ) and slip length (L_s) are discussed. These questions include the relationship between θ and surface roughness, the characteristics used to describe the difference between static and dynamic fluid fields and the reason for a lack of multilayer sticking observed in the current cases. Our results indicate that the quasi-universal θ ? L_s equation proposed by Hung et al. (2008) is applicable to cases involving a Cassie-like nanoscale roughened surface. In contrast, in cases with a Wenzel-like nanostructure, the no-slip boundary conditions are independent of variations in the contact angle. The adoption of a Wenzel–Cassie hybrid model helped to verify that the fluid density inside the cavity is a critical indicator of wettability of the wall–fluid interface. Our results also demonstrate that ρ_{f, cav} is a critical property in the measurement of hydrodynamic effects and thus its importance as an indicator of the validity of the equation θ ? L_s. The average time that water molecules are trapped and the number of averaged hydrogen bonds within cavities in a dynamic fluid field were also investigated.

     

Analytical studies of gain optimization in CO2-N2 gasdynamic lasers employing two-dimensional wedge nozzles

An analytical method has been proposed to optimise the small-signaloptical gain of CO₂-N₂ gasdynamic lasers (gdl) employing two-dimensional (2D) wedge nozzles. Following our earlier work the equations governing the steady, inviscid, quasi-one-dimensional flow in the wedge nozzle of thegdl are reduced to a universal form so that their solutions depend on a single unifying parameter. These equations are solved numerically to obtain similar solutions for the various flow quantities, which variables are subsequently used to optimize the small-signal-gain. The corresponding optimum values like reservoir pressure and temperature and 2D nozzle area ratio also have been predicted and graphed for a wide range of laser gas compositions, with either H₂O or He as the catalyst. A large number of graphs are presented which may be used to obtain the optimum values of small signal gain for a wide range of laser compositions without further computations.     

Boundary layer flow and heat transfer of a Casson fluid past a symmetric porous wedge with surface heat flux

The aim of this paper is to investigate numerically the boundary layer forced convection flow of a Casson fluid past a symmetric porous wedge. Similarity transformations are used to convert the governing partial differential equations into ordinary ones. With the help of the shooting method, the reduced equations are then solved numerically. Comparisons are made with the previously published results in some special cases and they are found to be in excellent agreement with each other. The results obtained in this study are illustrated graphically and discussed in detail. The velocity is found to increase with an increasing Falkner-Skan exponent whereas the temperature decreases. With the rise of the Casson fluid parameter, the fluid velocity increases but the temperature is found to decrease in this case. Fluid velocity is suppressed with the increase of suction. The skin friction decreases with the increasing value of Casson fluid parameter. It is found that the temperature decreases as the Prandtl number increases and thermal boundary layer thickness decreases with the increasing value of Prandtl number. A significant finding of this investigation is that flow separation can be controlled by increasing the value of the Casson fluid parameter as well as by increasing the amount of suction.     

Partial slip effect on non-aligned stagnation point nanofluid over a stretching convective surface

The present study inspects the non-aligned stagnation point nano fluid over a convective surface in the presence of partial slip.Two types of base fluids namely water and kerosene are selected with Cu nanoparticles.The governing physical problem is presented and transformed into a system of coupled nonlinear differential equations using suitable similarity transformations.These equations are then solved numerically using midpoint integration scheme along with Richardson extrapolation via Maple.Impact of relevant physical parameters on the dimensionless velocity and temperature profiles are portrayed through graphs.Physical quantities such as local skin frictions co-efficient and Nusselt numbers are tabularized.It is detected from numerical computations that kerosene-based nano fluids have better heat transfer capability compared with water-based nanofluids.Moreover it is found that water-based nanofluids offer less resistance in terms of skin friction than kerosene-based fluid.In order to authenticate our present study,the calculated results are compared with the prevailing literature and a considerable agreement is perceived for the limiting case.     

Diffraction of plane waves by a black wedge

The scattering of plane waves by a black wedge is examined. Two methods are considered for the solution of the problem. A closed-form series solution is derived by performing the technique of the separation of variables using boundary conditions of Macdonald. The second approach is the method of the modified theory of physical optics. The results are compared numerically.     

Design of a wedge plate for polarization-preserving angular shifter

It is shown that by using a wedge plate, the incident direction of light propagation can be rotated as necessary while still preserving beam polarization. The basic conditions of these preservations of polarization are deduced. For numerical demonstration, it is shown that a collimated beam with +45° linear polarization can be guided to any pre-settled direction where the square of ellipse ratio variation in the polarization is less than 0.0001%, while the variation of squared ellipse ratio of a right circular polarization beam is kept under 0.1%.     

冲击波实验用铝楔形靶加工技术

采用单点金刚石车削技术制备加工铝楔形靶,发现金刚石车削加工楔形靶实际轮廓为圆锥面。通过Veeco NT1100白光干涉仪对表面轮廓及粗糙度进行了测量,结果表明平面部分表面粗糙度小于50 nm,最大峰谷值小于100 nm,斜面部分表面粗糙度小于200 nm。分析认为斜面部分粗糙度测量数值较大是由刀具工作角度变化导致的,而测量轮廓线非圆锥体母线又导致粗糙度测量结果大于实际值。     

冲击波实验用铝楔形靶加工技术

采用单点金刚石车削技术制备加工铝楔形靶,发现金刚石车削加工楔形靶实际轮廓为圆锥面。通过Veeco NT1100白光干涉仪对表面轮廓及粗糙度进行了测量,结果表明平面部分表面粗糙度小于50 nm,最大峰谷值小于100 nm,斜面部分表面粗糙度小于200 nm。分析认为斜面部分粗糙度测量数值较大是由刀具工作角度变化导致的,而测量轮廓线非圆锥体母线又导致粗糙度测量结果大于实际值。     

Imaging properties of a tetra wedge readout

The decoding principle of a tetra wedge anode, which is a development of the wedge and strip anode, is described. The influence of charge cloud size on decoding accuracy is studied using the Monte Carlo method. Simulation results show that the decoding error is large when the size of charge clouds collected by the anode is small. Thus, the charge clouds collected by the tetra wedge anode should reach a necessary size to ensure accurate decoding. Finally, using the ultraviolet photon counting imaging system, the linearity and the spatial resolution of the system are tested. Experimental results show that the system has a good linearity and the spatial resolution is better than 100 μm.     

点光源劈尖干涉的条纹分布特征

在有限远的点光源照射下,导出了劈尖干涉的明、暗纹条件,通过Matlab软件,用数值分析方法给出了劈尖表面条纹分布特征,讨论了光源距离对表面条纹分布的影响.     

自组建激光干涉仪测量平行板楔角

在光学实验平台上组建激光干涉仪,给出了测量微小楔角的原理和测量方法,导出了测量公式并进行了实际测量.     

Accurate step wedge calibration for densitometry of electrophoresis gels

Accurate step wedge calibration is important for reliable quantitative densitometry of electrophoresis gels. In this work, we outline the theory and verified by experiment, the effect that the nonlinear response of detectors at low irradiance levels has on accurate optical density (OD) calibration of step wedges. It was found that OD value departures from stated do exist and thus supports the case of calibration. Halogen broadband light was shown to be generally unsuited as light source for step wedge calibration even though applied at highest illumination before saturation, unless correction approaches which add complexity to the process are applied. Monochromatic light was determined best suited for use, provided that the irradiance level was high enough for the calibration to be conducted fully in the detector’s linear range.     

微系统中转矩及电渗流作用下的微粒子电动旋转操控

微粒子的电动旋转操控是表征分散系中微粒子介电特性的有效方法.低雷诺数微系统中,以Maxwell-Wagner极化理论为基础,进行了转矩作用下的微粒子电动旋转机理研究,推导了此机理作用下微粒子电动旋转峰值速度所对应的特征频率,分析了弛豫时间对粒子旋转方向的影响,对转矩作用下的微粒子电动旋转速度进行仿真;以双电层理论为基础,对电渗流导致的微粒子电动旋转机理进行定性分析,提出具有金修饰的粒子表面更适合电渗流作用下的电动旋转研究.分别以羧基修饰的聚苯乙烯微球以及表面被金修饰的聚苯乙烯微球为操控对象,进行电动旋转实 关键词： 微系统 电动旋转 转矩 电渗流     

测劈尖角度及折射率的研究

介绍了一种利用光的干涉测量劈尖角度及折射率的方法。