正坡和反坡上的内水跃

本文对于正坡和反坡两种情况,根据上、下层的动量方程和能量方程分析了两层液体的内水跃流动现象,研究并得出了不同流动情况下发生内水跃的条件。     

EFFECT OF DISPERSANTS AND FLOCCULANTS ON THE COLLOIDAL STABILITY OF ASPHALTENES

Since the traditional deasphalting process is expensive, a more economical approach would be to use dispersants or flocculants to control the colloidal stability of asphaltenes. The asphaltene content of fuel oils is defined by testing the n-heptane insolubles following the ASTM D 3279 method. In the presence of dodecylbenzenesulfonic acid, a decrease in n-heptane insolubles precipitation was observed indicating an increase in their colloidal stability. No significant change in n-heptane insolubles precipitation was observed in the presence of dodecylphenol and nonylphenol. Poly(maleic anhydride-1-octadecene) polymer was found to be an effective flocculant. The flocculation of n-heptane insolubles varied depending on the polymer-to-asphaltenes weight ratios. The FTIR results indicate that the flocculation occurs through the H-bonding between the asphaltenes and the polymer molecules. Maleic anhydride was found to continuously increase the n-heptane insolubles precipitation with an increase in its treat rate. The FTIR analysis showed the presence of an acidic C=O group and no presence of an anhydride functional group. The results indicate that the presence of an anhydride and unsaturation makes the maleic anhydride too reactive leading to chemical changes and the precipitation of asphaltenes and other aromatic molecules found in fuel oils.     

A general momentum theory applied to an energy‐extracting actuator disc

A general momentum theory for an energy‐extracting actuator disc modelling a rotor with a multiplicity of blades having radially uniform circulation is presented that includes the effects of wake rotation and expansion. A parallel theory directed at the propeller has been published elsewhere, but not one intended for the wind turbine. The rotation of the wake is shown to be accompanied by a fall in static pressure that is additional to that which occurs across the actuator disc and accounts for the energy extraction from the wind. Energy extraction is recognized in the fully developed wake by the flow regaining the static pressure of the undisturbed wind at the expense of the kinetic energy in the wake. Because the wake is still rotating in the fully developed wake, the additional fall in static pressure appears there also and so does not augment the energy extraction. However, the additional fall in pressure would cause a discontinuity in pressure across the fully developed wake but is prevented by a further slowing down of the wake. The additional slowing down extracts a little more energy from the flow than that predicted by the simple momentum theory, which does not include wake rotation. The overall effect of wake rotation on energy extraction is very small for wind turbines operating at high tip speed ratios but can significantly increase the predicted power output for turbines operating at low tip speed ratios. Copyright © 2004 John Wiley & Sons, Ltd.     

Molecular Thermal Phenomena in an Ultrathin Lubrication Liquid Film of Linear Molecules Between Solid Surfaces

Molecular dynamics simulation has been performed on an ultra-thin lubrication liquid film, where the liquid film of diatomic molecules having a thickness of molecular scale (several nanometers) is sheared by two parallel solid walls moving at different speeds. The Couette-like flow is generated and energy conversion from the macroscopic flow energy to thermal energy, which is the viscous heating in a macroscopic sense, occurs in the liquid film. It was observed in the present simulations that the thermal phenomena in the liquid film are far from the macroscopically expected ones; thermal energy is not distributed evenly to each degree of freedom of molecular motion, and energy transfer in the liquid adjacent to the solid surface is contributed by molecular motion in a manner different from those in a bulk liquid.     

Representational momentum is not (totally) impervious to error feedback.

The influence of feedback on representational momentum for the final location of a moving target was examined in 3 experiments. The presence of binary feedback (correct, error) during practise trials or during larger blocks of experimental trials did not reduce representational momentum, nor did the presence of more informative feedback specifying the direction of error (error—in front of, error—behind) during larger blocks of experimental trials reduce representational momentum. Effects on representational momentum of whether feedback was consistently provided were inconsistent. Even though feedback did not reduce representational momentum per se, feedback did influence the probability of a same response for different probe positions. Implications of the data for R. A. Finke and J. J. Freyd's (1985; J. J. Freyd, 1987) claim that representational momentum is impervious to error feedback, and possible roles of perceptual learning in representational momentum, are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

斜程湍流大气光通信信道的单光子轨道角动量

研究了基于单光子轨道角动量技术的量子光通信系统的大气湍流效应,动用Rytov近似和修正von Kamm折射率起伏谱,建立了单光子轨道角动量斜程湍流大气通信信道中轨道角动量l的测量概率理论模型。本文同时给出了量子信道的单光子轨道角动量平均值l=〈l〉的计算关系。     

Estimation of the radial distribution of the tangential velocity in a vortex chamber

The estimation of maximum tangential velocity becomes a very important factor for the estimation of performances of the vortex chamber. In this paper, a proposed flow model of how to estimate the maximum tangential velocity in the special form of the vortex chamber is described in detail. The pressure drop basing upon the rapid expansion by flowing from the inlet pipe into the cyclone body is estimated as half of the dynamic pressure in the inlet pipe.     

列管反应器中环形分布器内流体均布的探讨

利用动量守恒原理,推导出列管反应器中环形分布器内流体流动的修正动量方程,并在与前人实验结果比较和分析的基础上,提出了与环形分布管相适应的分流和合流动量交换系数式。研究结果表明,环形分布器内流体流动符合变质量流动规律,可采用环形分布器修正动量方程描述分流和集流的静压变化;通过直管分布器实验获得的动量交换系数对环形流道分布器也是适用的,其计算值与实验值的相对误差小于10%,可满足工程设计要求。     

一维畦灌地表水流-土壤水动力学耦合模型Ⅰ：建模

畦灌地表水流-土壤水动力学耦合模型可从物理机制上综合模拟地面灌溉过程中地表水与土壤水系统之间的互动关系,为开展区域尺度地面灌溉系统性能评价提供了基础工具.利用二阶时空离散精度的混合数值解法求解一维全水动力学模型,建立了一维畦灌地表水流运动模型,并利用二阶时间离散精度有限差分法和构建的四阶空间离散精度有限体积法解算一维土壤水动力学模型.同时,以地表水和土壤水质量守恒方程交替迭代计算的地表水深收敛值为基础,利用动量守恒方程获得地表水流速场,实现了地表水-土壤水系统间的有效迭代耦合,构建起基于数值解法和迭代耦合模式同步改进的一维畦灌地表水流-土壤水动力学耦合模型.     

弯管流量计研究动向

本文从工作原理和流量方程式、流量系数、结构类型、产生的差压和压力损失等四个方面述评了弯管流量计的发展趋势。最后提出了关于实现弯管流量计标准化的几点建议,并探讨了今后的研究方向和研究方法。