微米级余弦槽表面疏水性及冷凝传热实验研究

为了研究余弦微槽结构的疏水性和冷凝传热性能,首先制备了不同槽峰高度和槽距的微米级余弦槽结构表面,实验研究了不同结构微槽表面的静态接触角及其对滴状冷凝传热性能的影响,并对冷凝传热过程中液滴在微槽表面合并、脱落过程进行实验研究和热力学分析。结果表明,液滴在微槽表面的疏水性和传热性能都呈现明显的各向异性,横向静态接触角θ⊥明显高于纵向接触角θ∥。同时,冷凝传热过程中竖直纵槽阻碍液滴的横向合并,但其对液滴脱落过程起到极大促进作用,传热性能较光滑表面提高30%~50%,且峰距比越大液滴的脱落半径越小、脱落频率越高,表面传热效率也越高。水平横槽则相反,虽然增大峰距比促进了液滴合并,但却对其脱落过程产生不利影响,导致整体传热性能较纵向槽表面大幅下降,与光滑表面接近。引入表面润湿率对微槽表面的液滴脱落半径进行热力学计算,计算值与实验结果吻合较好,误差在20%以内。     

线张力对接触角影响的理论分析

通过引入“线张力”的概念，分别用力学和热力学的方法导出固体表面上液滴平衡时接触角应满足的条件，即对Young方程进行修正．并得到了液滴系统自由能随接触角变化的曲线，从理论上说明在理想固体表面上线张力可以造成液滴接触角的多值现象．结果表明，由液滴形变作用引起的线张力变化是影响接触角测量准确性的一个重要因素．对于深入认识线张力在液滴运动以及滴状冷凝传热过程中的作用有积极意义．     

基于晶格Boltzmann方法研究微液滴形变中接触角

接触角是常见的自然现象,是液体对固体表面浸润的结果,通过测量接触角可以判断固体表面亲疏液体的性质。从热力学自由能理论出发,采用基于化学势的多相流晶格Boltzmann方法研究表面上微小液滴形变中的接触角变化。通过设置不同的化学势来改变固体表面的亲疏液体性质,模拟计算中既有落在固体表面之上的液滴,也包括悬挂在固体表面下方的液滴。在忽略重力作用的情况下,模拟得到的接触角与球冠法的理论预期一致,并且液滴的接触角可以通过表面化学势线性调节。在考虑重力作用的情况下,虽然不同大小的液滴发生了明显的不同程度的形变,但是模拟计算所得的接触角保持不变,验证了微观接触角与重力无关的理论。     

滴状冷凝研究的进展

本文以大最的资料为依据,并结合笔者近年来的研究结果,对实现滴状冷凝的途径、滴状冷凝的机理及影响给热系数的因素进行了论述。0 概述滴状冷凝足发生在不润湿的表面上的,它与膜状冷凝的区别是,冷凝表面上不是连续的液膜而是大小不一的液滴。蒸汽首先在冷凝表面上的活化中心处冷凝,产生大量的微小液滴,这     

液滴在化学异构表面上侧向弹跳的计算机模拟研究

液滴撞击润湿性不同的表面会产生不同的动态行为,数值模拟是研究该现象的一种有效方法.采用基于化学势的晶格Boltzmann方法,通过调整接触角来改变固体表面的润湿性,对液滴撞击单一接触角的疏水表面以及接触角分布不同的疏水表面所产生的动态行为进行模拟和分析.当给疏水表面施加单一接触角时,液滴的弹跳高度随表面接触角的增大而增...     

蒸汽冷凝初始液滴形成机理研究

蒸汽在过冷表面进行滴状冷凝时的初始液滴形成机理一直是悬而未决的问题.应用电子探针和扫描电镜两种方法对水蒸气冷凝前后镁表面上化学成分的变化进行了检测,发现冷凝后镁表面上氧含量明显增加,而且随着过冷度和冷凝时间的增加而增加.为了深入分析氧含量的增加是整个表面都反应造成的还是仅局部反应导致的,建立了镁与凝液反应的动力学关系,并推算出初始液滴所占面积分率远小于1的结果.同时电子探针的扫描检测结果证明氧元素在镁表面上的分布是不均匀的,凝液所占面积分率的图像处理结果与动力学计算结果相吻合.因此,初始形成的冷凝液仅在表面的局部区域产生,不是以薄液膜的形式覆盖表面,即滴状冷凝初始液滴的形成机理在纳米尺度下符合固定成核中心假说.     

圆形径向梯度表面能材料表面的凝结换热系数

在均质表面上的单个球缺形液滴换热模型和液滴通用尺度分布规律的基础上,结合梯度表面能材料表面上的液滴分布和凝结换热特性,得到了圆形径向梯度表面能材料表面上的滴状凝结换热计算式．在此基础上,研究了壁面过冷度、接触角梯度、工质物性等参数对梯度表面能材料表面滴状凝结换热性能的影响．     

基于晶格Boltzmann方法的接触角实时测量研究

接触角在表面湿润、毛细现象和移动接触线等问题中是基本的特征量。虽然数值计算中已经可以有效地模拟接触角现象,但是在动态模拟中,接触角还不能被实时地精确测量。基于化学势晶格Boltzmann方法,本文设计一种几何的方法实时测量接触角。当忽略重力的影响时,该方法计算结果与球冠模型的理论预期保持一致,而且不受液滴大小的影响;当考虑重力影响时,虽然液滴呈现明显的变形,但是测量所得的微观接触角保持不变,与理论预期相符。当基板倾斜时,液滴的前进角逐渐增大,后退角逐渐减小,接触角迟滞越来越大,而且能够被实时地测量。     

超疏水低黏附微孔表面的制备及其冷凝微滴的高效自去除性能

冷凝微滴在基底材料表面的高效自去除是防结霜的一种有效手段.以硅片为基底材料,采用飞秒激光直写技术制备了微孔阵列结构,经低表面能修饰后,表面水接触角为165°,滚动角为0.6°,液滴在微孔结构表面可以实现多次弹跳.通过冷凝微滴的自去除实验,重点分析了冷凝微滴的成核、生长、合并自去除机制,发现冷凝微滴可以在微孔内部短时间内...     

水平管间溴化锂溶液滴状降膜流动分析

对溴化锂溶液在水平管间的实际液滴流动过程进行了记录分析,以改进目前滴状降膜吸收数值模型中的理想化球形液滴假设.使用高速摄像机,对16 mm管间距下溴化锂溶液滴状流动过程进行了拍摄.采用图像边缘识别技术、样条拟合和二维曲线旋转积分方法,得到了液滴表面积和体积关于时间的变化关系.根据液滴的发展特点,将管间液滴形成划分为悬垂拉伸、不稳定液柱和破裂降落3个阶段,据此提出了不同溶液流量下液滴形成的预测模型.管间液滴表面积和体积发展的预测曲线与实测结果吻合较好.该模型可以在滴状降膜传热传质数值计算中得到应用.     

Markedness and its Interpretation in Language Use

Language markedness is a common phenomenon in languages, and is reflected from hearing, vision and sense, i.e. the variation in the three aspects such as phonology, morphology and semantics. This paper focuses on the interpretation of markedness in language use following the three perspectives, i.e. pragmatic interpretation, psychological interpretation and cognitive interpretation, with an aim to define the function of markedness.     

Features of Women's language

Language is a means of verbal communication. People use language to communicate with each other. In the society, no two speakers are exactly alike in the way of speaking. Some differences are due to age, gender, statue and personality. Above all, gender is one of the obvious reasons. The writer of this paper tries to describe the features of women＇s language from these perspectives： pronunciation, intonation, diction, subjects, grammar and discourse. From the discussion of the features of women＇s language, more attention should be paid to language use in social context. What＇s more, the linguistic phenomena in a speaking community can be understood more thoroughly.     

An Analysis of Catherine＇s Character——Wuthering Heights

Wuthering Heights, Emily Bronte＇s only novel, was published in December of 1847 under the pseudonym Ellis Bell. The book did not gain immediate success, but it is now thought one of the finest novels in the English language. Catherine is the key character of this masterpiece, because everybody and everything center on her though she had a short life. We can understand this masterpiece better if we know Catherine well.     

Lower Paleozoic oil relationships within Williston Basin, Canada

The Williston Basin is a significant petroleum province, containing oil production zones that include the Middle Cambrian to Lower Ordovician, Upper Ordovician, Middle Devonian, Upper Devonian and Mississippian and within the Jurassic and Cretaceous. The oils of the Williston Basin exhibit a wide range of geochemical characteristics defined as "oil families", although the geochemical signature of the Cambrian Deadwood Formation and Lower Ordovician Winnipeg reservoired oils does not match any "oil family". Despite their close stratigraphic proximity, it is evident that the oils of the Lower Palaeozoic within the Williston Basin are distinct. This suggests the presence of a new "oil family" within the Williston Basin. Diagnostic geochemical signatures occur in the gasoline range chromatograms, within saturate fraction gas chromatograms and biomarker fingerprints. However, some of the established criteria and cross-plots that are currently used to segregate oils into distinct genetic families within the basin do not always meet with success, particularly when applied to the Lower Palaeozoic oils of the Deadwood and Winnipeg Formation.     

低渗透非均质砂岩油藏启动压力梯度研究

理论推导与室内实验相结合,建立了低渗透非均质砂岩油藏启动压力梯度确定方法。首先借助油藏流场与电场相似的原理,推导了非均质砂岩油藏启动压力梯度计算公式。其次基于稳定流实验方法,建立了非均质砂岩油藏启动压力梯度测试方法。结果表明:低渗透非均质砂岩油藏的启动压力梯度确定遵循两个等效原则。平面非均质油藏的启动压力梯度等于各级渗透率段的启动压力梯度关于长度的加权平均;纵向非均质油藏的启动压力梯度等于各渗透率层的启动压力梯度关于渗透率与渗流面积乘积的加权平均。研究成果可用于有效指导低渗透非均质砂岩油藏的合理井距确定,促进该类油藏的高效开发。     

On Tragic Consciousness In The Works By Ernest Hemingway

As an American modern novelist who were famous in the literary world, Hemingway was not a person who always followed the trend but a sharp observer. At the same time, he was a tragedy maestro, he paid great attention on existence, fate and end-result. The dramatis personae's tragedy of his works was an extreme limit by all means tragedy on the meaning of fearless challenge that failed. The beauty of tragedy was not produced on the destruction of life, but now this kind of value was in the impact activity. They performed for the reader about the tragedy on challenging for the limit and the death.     

Achieving Unusual States of Matter Under High Pressure

正The periodicity of the elements and the non-reactivity of the inner-shell electrons are two related principles of chemistry,rooted in the atomic shell structure.Within compounds,Group I elements,for example,invariably assume the+1 oxidation state,and their chemical properties differ completely from those of the p-block elements.These general rules govern our understanding of chemical structures and reactions.Using first principles calcula-     

Exchange-Correlation and Electronic Excitation Energies from Pairing Matrix Fluctuations

We have developed an adiabatic connection to formulate the ground-state exchange-correlation energy in terms of pairing matrix linear fluctuations.This formulation of the exchange-correlation energy opens a new channel for density functional approximations based on the many-body perturbation theory.We illustrate the potential of such approaches with an approximation based on the particle-particle Random Phase Approximation(pp-RPA).This re-     

Density Functional Theory for the Response of Periodic Systems to Electric Fields Based on the Vector Potential Approach

正The electronic and nuclear(structural/vibrational)response of 1D-3D nanoscale systems to electric fields gives rise to a host of optical,mechanical,spectral,etc.properties that are of high theoretical and applied interest.Due to the computational difficulty of treating such large systems it is convenient to model them as infinite and periodic(at least,in first approximation).The fundamental theoretical/computational problem in doing so is that     

On the Thermodynamic Limit for Responses to Static Electromagnetic Fields

For molecular systems,the quantum-mechanical treatment of their responses to static electromagnetic fields usually employs a scalar-potential treatment of the electric field and a vector-potential treatment of the magnetic field.Although the potential for each field separately is associated with the choice of an(unphysical)origin,the precise choice of the origin for the electrostatic field has little consequences for the results.This is different for the