粗糙微通道流体流动特性的分形分析

发布时间：2018-04-24 01:05

本文选题：微通道 + 多孔介质　；参考：《华中科技大学》2015年博士论文

【摘要】：随着现代科技和微电子器件以及微加工技术的发展,流体通过微通道时的输运特性在科学与技术应用领域受到越来越多的关注,如材料科学与工程、油气藏工程、生物医学工程、生物传输现象、燃料电池、环境与工程等。在自然界中,光滑的表面是几乎不存在的,或者说非常罕见的。通过显微镜观测,大部分表面(如工程表面)都是粗糙的。而现实中毛细管、孔的表面或者微通道都是粗糙的。因此选用合适的理论和方法来描述和研究多孔介质中毛细管的粗糙壁面或者粗糙微通道的壁面的轮廓是一项既有科学意义,又有实际应用价值的研究。已有调查证实多孔介质具有自相似的分形特性。因此,运用分形几何理论来描述和研究多孔介质及其固体壁面的微结构特征及其对流动特性的影响已经成为凝聚态物理、复杂性科学、地球物理学以及工程热物理等交叉学科领域的研究热点之一。目前,流体通过表面粗糙的微通道时流动特性的探讨和研究,大部分均采用数值方法或实验方法等。但是这些方法都不能得到流体流动特性,如速度分布、压降等的解析表达式,或者表达式中包含有经验常数等。而本文采用分形几何理论和方法来描述粗糙微通道的表面结构特性,得到的速度分布、压降等不含有任何经验常数的解析表达式。本文第一部分介绍了粗糙表面的分形理论,而后引入了光滑类分形树状分叉网络模型和光滑的毛细管束模型,对流体通过多孔介质的渗透率作出简要概述,最后介绍了流体流动的连续介质模型和哈根泊肃叶定律的推导。针对目前流体通过粗糙微通道中流动特征没有解析表达式的研究现状,结合流体通过微通道中数值模拟和实验研究的现有结果,以及工程表面粗糙元或者接触点满足分形标度律的关系,在本文第二章中,我们将壁面粗糙元简化为圆锥体,运用分形几何理论来表征粗糙元高度(或者底面直径)的分布规律,并探讨了流体通过表面粗糙的微通道中的一些流动特性。给出了微通道中相对粗糙度与表面结构参数之问的关系式,然后推导了流体通过该微通道时的速度分布、流动阻力、摩擦因子以及泊肃叶数与壁面粗糙度的函数关系表达式。本文得到的表达式没有任何经验常数,且每个参数都有具体的物理含义。因为多孔介质的孔隙通常会相互连接,形成弯弯曲曲的毛细管或者出现互相连接或互相作用而形成网络状结构,对此,本文第三章建立了粗糙的毛细管束模型和粗糙的类分形树状分叉网络模型,研究了流体流过粗糙毛细管和树状分叉网络时的流动阻力和渗透率的变化规律,而且得到了相对粗糙度与压降、渗透率的分形模型,探讨了相对粗糙度对流体通过粗糙微通道时流动特性如阻力、渗透率等的影响。流体流经粗糙的固体壁面时,对其传热系数的研究均是基于数值模拟或者实验,没有解析解的报道。因此,本文第四章以第二章所提出的粗糙表面模型为基础,探讨了当流体在粗糙表面发生对流换热时,对流换热系数、对流换热所传递的总热量以及无量纲的等效热导率与粗糙表面的结构参数和相对粗糙度之间的关系,并讨论和分析了相对粗糙度对对流换热系数、等效热导率等的影响。本文第五章介绍了论文的创新点,对粗糙多孔介质中的流体流动特性的研究工作作了展望。
[Abstract]:With the development of modern science and technology, microelectronic devices and micromachining technology, the transport characteristics of fluid through microchannels have attracted more and more attention in the field of science and technology applications, such as materials science and engineering, oil and gas engineering, biomedical engineering, biological transmission, fuel cells, environment and engineering, etc. in nature, smooth The surface is almost nonexistent, or very rare. By microscopic observation, most surfaces, such as the surface of the engineering surface, are rough. In reality, the capillary, the surface of the hole or the microchannel are rough. Therefore, a suitable theory and method is used to describe and study the rough wall or rough microsurface of the capillary in the porous medium. The contour of the wall of the channel is a scientific and practical study. It has been investigated and confirmed that the porous media has a self similar fractal characteristic. Therefore, the fractal geometry theory is used to describe and study the microstructural characteristics of porous media and its solid wall and its influence on the flow characteristics. Science, complexity science, geophysics and engineering thermophysics.
At present, the flow characteristics of the fluid through the surface of the rough micro channel are discussed and studied, most of which use numerical methods or experimental methods. But these methods can not obtain the fluid flow characteristics, such as velocity distribution, pressure drop and so on, or the expression contains empirical constants. The method is used to describe the surface structure characteristics of rough microchannels, and the velocity distribution and pressure drop do not contain any analytical expressions of empirical constants.
In the first part of this paper, the fractal theory of rough surface is introduced, then the smooth fractal tree bifurcation network model and the smooth capillary bundle model are introduced. The permeability of the fluid through the porous media is briefly summarized. Finally, the continuous medium model of fluid flow and the derivation of the law of Hagen poissu are introduced.
In view of the current research status of the flow characteristics in the rough microchannel, combined with the existing results of the fluid through the numerical simulation and experimental study in the microchannel, and the relationship between the surface roughness element or the contact point to meet the fractal scale law, in the second chapter, we simplify the wall rough element to conic. The fractal geometry theory is used to characterize the distribution of the height (or the bottom diameter) of the rough element, and the flow characteristics in the rough micro channel of the surface are discussed. The relation between the relative roughness in the microchannel and the parameters of the surface structure is given. Then the velocity distribution of the fluid through the microchannel is derived and the flow is derived. The dynamic resistance, the friction factor and the function expression of the function of the Poisson's number and the wall roughness. The expressions obtained in this paper have no empirical constants, and each parameter has a specific physical meaning.
Because the pores in porous media are usually connected to each other, forming a curved capillary or connecting or interacting with each other to form a network structure. In this third chapter, a rough capillary bundle model and a rough fractal dendrimer network model are established in this paper, and the fluid flows through rough capillary and tree like bifurcation. The flow resistance and permeability change law of the network, and the fractal model of relative roughness and pressure drop and permeability is obtained, and the influence of relative roughness on the flow characteristics, such as resistance and permeability, when the fluid passes through the rough microchannel is discussed.
When the fluid flows through the rough surface of the solid wall, the study of the heat transfer coefficient is based on the numerical simulation or experiment, and there is no analytical solution. Therefore, the fourth chapter, based on the rough surface model proposed in the second chapter, discusses the convection heat transfer coefficient and the convection heat transfer when the fluid has convective heat transfer on the rough surface. The relationship between the total heat and the dimensionless equivalent thermal conductivity and the structural parameters of the rough surface and the relative roughness are discussed and the influence of the relative roughness on the convective heat transfer coefficient and the equivalent thermal conductivity is discussed and analyzed.
In the fifth chapter, the innovation of the paper is introduced, and the research work on the fluid flow characteristics in rough porous media is prospected.

【学位授予单位】：华中科技大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TK124

【相似文献】