壁面粗糙度对微平行板间电磁和电渗流动的影响

发布时间：2018-05-21 08:18

本文选题：磁流体动力学 + 壁面粗糙度　；参考：《内蒙古大学》2016年博士论文

【摘要】：随着微全分析系统(micro total ananysis system,简称μTAS):和微机电系统(micro electro mechanical system,简称MEMS)的发展,微流体的驱动和控制技术备受关注.微流控系统通常利用外加的电场和磁场来驱动并控制微管道内导电流体(电解质溶液或液态金属)的流动.这种由外加电磁场作用下产生的流动称为电磁驱动流或磁流体动力学流(magnetohydrodynamic flow,简称MHD流),它的优点是电极电压较低而流量较高且有良好的生物相容性.自20世纪末以来,国内外众多学者从理论和实验方面对微管道内MHD流进行了研究并取得了很多重要的成果,并且已在生物、医学和化学等领域获得了重要的应用.但以上研究均没有考虑壁面粗糙度对MHD流的影响,而设备的制造过程或其他物质(如大分子)在壁面上的沉淀都会引起微管道的壁面粗糙度,在实际问题中,有时为了提高微管道内流体的混合效率,管道壁面上也可能会人为地设计一些粗糙度.在微管道中,壁面粗糙度和管道半径之比大于常规尺度管道内的比值,因此,由壁面粗糙引起的速度扰动能传递到主流区而影响整个微流动。另外,管道内的流体流动时会出现壁面滑移现象,并壁面滑移速度与流体所受的剪切率成正比,即uslip=uslip-uwall=b|αu/αy|wall,其中滑移长度b是微米量级的.在常规尺度管道内的流体研究中,我们可以忽略壁面滑移现象.但是,在微管道内,壁面渭移对流体流动有很大的影响,因此,在微流体研究中,壁面滑移现象是应该考虑的重要因素之一.基于这一现状,本文将围绕壁面粗糙度和滑移对MHD流的影响展开研究,主要采用摄动展开法研究以下几类问题：(1)纵向正弦形壁面粗糙度对平行板微管道内直流MHD流(简称DC MHD流)的影响。纵向壁面粗糙度指的是平行于流体流向的粗糙度.具有纵向正弦形壁面粗糙度的微管道内,管道垂直于流体流向的截面沿流动方向不发生改变.本文采用摄动法展开得到了具有纵向正弦形壁面粗糙度的平行板微管道内DC MHD流的速度和流率的近似解析解。结果表明：粗糙度对DC MHD流的影响随着哈特曼数的增加而减小；当粗糙度波数或哈特曼数充分大时,上下板壁面粗糙度的相位差对流动影响可忽略不计；随粗糙度波数的增加,粗糙度对流动的阻力也会增加；当粗糙度波数小于临界波数并相位差等于πc时,壁面粗糙度能提高DCMHD流的平均速度.(2)横向正弦形壁面粗糙度对平行板微管道内DC MHD流动的影响.横向壁面粗糙度指的是垂直于流体流动方向的粗糙度。具有横向正弦形壁面粗糙度的微管道内,管道垂直于流体流向的截面沿流动方向发生改变。本文利用摄动展开法求出了具有横向正弦形壁面粗糙度的平行板微管道内DC MHD流的流函数的近似解析解,并得到了流率和粗糙度之间的关系.结果表明：对任意给定的粗糙度相位差,流率因横向粗糙度的出现而减小；粗糙度对流动的阻力随相位差和波数的增加而增加,随哈特曼数的增加而减小；当粗糙度波数充分大时,粗糙度相位差对流动的影响可忽略不计.(3)壁面滑移和纵向正弦形壁面粗糙度对平行板微管道内交流MHD流的影响.本文利用摄动展开法求出了具有纵向壁面粗糙度的平行板微管道内时间周期MHD滑移流的速度和电势的近似解析解,并得到了平均速度振幅和粗糙度之间的关系.结果表明：速度和电势分布出现了明显的波动现象；速度和电势之间存在相位滞后(phase lag),且相位滞后随频率、滑移长度的增加而增加,随哈特曼数、波数和粗糙度相位差的增加而减小,而对充分小的频率,相位滞后几乎不存在,当波数充分大时,粗糙度相位差对相位滞后的影响可忽略不计；速度振幅随滑移长度的增加而增加,随频率、波数和相位差的增加而减小,但是,当波数充分大时,相位差对速度振幅几乎没有影响,当频率充分大时,速度振幅不受滑移长度的影响.本文还研究了纵向正弦形粗糙度对平行板微管道内电渗、电磁混合驱动流的影响和三维粗糙度对平行板微管道内电渗流的影响。利用摄动展开法求出了速度和电势近似解析解,分析了粗糙度波数、zeta势、双电层厚度的倒数、哈特曼数等无量纲参数对流动的影响.在本文中得到结果能为微流控设备的设计、优化、发展奠定理论基础.
[Abstract]:With the development of micro total ananysis system (ananysis system), and the development of micro electro mechanical system (MEMS), micro fluid drive and control technology has attracted much attention. Microfluidic systems usually use applied electric field and magnetic field to drive and control the conductance body (electrolyte solution or liquid) in micropipeline. The flow of the state metal. This flow produced by the external electromagnetic field is called the electromagnetic driving flow or the magnetohydrodynamic flow (magnetohydrodynamic flow). Its advantages are the low electrode voltage, high flow rate and good biocompatibility. Since the end of the twentieth Century, many scholars at home and abroad have been from the theoretical and experimental aspects. MHD flow in micropipes has been studied and many important achievements have been achieved, and important applications have been obtained in biological, medical and chemical fields. However, the effects of wall roughness on MHD flow are not considered, and the manufacturing process of equipment or other substances (such as macromolecules) on the wall will cause micro pipes. In practical problems, in practical problems, in order to improve the mixing efficiency of the fluid in the micro pipe, some roughness may be artificially designed on the wall of the pipe. In the microchannel, the ratio of the wall roughness to the pipe radius is greater than that in the conventional pipe. Therefore, the velocity disturbance caused by the wall roughness can be transferred to the mainstream. In addition, the wall slip phenomenon occurs when the fluid flows in the pipe, and the velocity of the wall slip is proportional to the shear rate of the fluid, that is, uslip=uslip-uwall=b| alpha u/ alpha y|wall, in which the slip length B is micrometer. In the fluid study in the conventional pipe, we can ignore the slip of the wall. However, in the micro pipeline, the wall Wei shift has a great influence on the flow of the fluid. Therefore, the wall slip phenomenon is one of the important factors to be considered in the study of the microfluidics. Based on this situation, this paper will focus on the influence of the wall roughness and slip on the MHD flow. (1) the influence of the longitudinal sine wall roughness on the direct current MHD flow (DC MHD flow) in the parallel plate micropipeline. The longitudinal wall roughness refers to the roughness of the flow direction parallel to the flow direction. In the microchannel with the longitudinal sinusoidal surface roughness, the cross section of the pipe perpendicular to the flow direction does not change along the flow direction. The approximate analytical solution of the velocity and flow rate of the DC MHD flow in a parallel plate micro pipe with a longitudinal sinusoidal surface roughness is obtained by the dynamic method. The results show that the influence of the roughness on the DC MHD flow decreases with the increase of the Hartmann number; the phase difference convection of the roughness of the upper and lower plate wall surface is the same as the number of roughness wave or the number of waves. The dynamic effect is negligible; with the increase of the roughness wave number, the resistance of the roughness to the flow is also increased; when the roughness wave number is less than the critical wave number and the phase difference equals PI C, the wall roughness can increase the average velocity of the DCMHD flow. (2) the effect of the transverse sine wall roughness on the DC MHD flow in the flat plate micropipeline. The roughness refers to the roughness perpendicular to the flow direction of the fluid. In a microchannel with the roughness of the transverse sinusoidal wall, the cross section of the pipe perpendicular to the flow direction changes along the flow direction. In this paper, the flow function of the DC MHD flow in the flat plate micro pipe with the transverse sinusoidal surface roughness is obtained by the perturbation expansion method. The relationship between the flow rate and the roughness is obtained. The results show that the flow rate decreases with the appearance of the transverse roughness for any given degree of roughness, and the resistance of the roughness to the flow increases with the increase of the phase difference and wave number, and decreases with the increase of the Hartmann number; when the number of roughness waves is sufficiently large, the roughness is large. The effect of phase difference on flow can be neglected. (3) the influence of wall slip and longitudinal sine wall roughness on the AC MHD flow in the parallel plate micropipeline. In this paper, the approximate analytical solution of the velocity and potential of the time periodic MHD slip flow in a parallel plate micro pipe with the longitudinal wall roughness is obtained by the perturbation expansion method. The relationship between the average velocity amplitude and the roughness shows that the velocity and potential distribution have obvious fluctuations, and there is a phase lag between the velocity and the potential (phase lag), and the phase lag increases with the increase of the frequency and the slip length, and decreases with the increase of the Hartmann number, the wave number and the phase difference of the roughness. When the wave number is large, the phase lag effect of the roughness is negligible when the wave number is large. The velocity amplitude increases with the increase of the slip length, and decreases with the increase of the frequency, wave number and phase difference, but when the wave number is sufficiently large, the phase difference has little effect on the velocity amplitude, when the frequency is filled. In addition, the velocity amplitude is not affected by the slip length. The influence of the longitudinal sinusoidal roughness on the electroosmosis in the parallel plate micropipeline, the influence of the electromagnetic mixed driven flow and the three-dimensional roughness on the electroosmotic seepage in the parallel plate micro pipe are also studied. The effect of the dimensionless parameters, such as the zeta potential, the reciprocal of the thickness of the double layer and the Hartmann number, on the flow, can be obtained in this paper to lay a theoretical foundation for the design, optimization and development of the microfluidic equipment.
【学位授予单位】：内蒙古大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：O441;O357.3

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