A Fundamental Study on the Effect of Surface Roughness Structures on Fluid Flow and Heat Transfer at the Microscale Level

提案题目：表面粗糙度结构对微观流体流动和传热影响的基础研究项目负责人：Kandlikar， Satish g .机构：Rochester Institute of technology提案编号：摘要本项目旨在从微观和宏观两方面改变我们对不可压缩层流中粗糙度的传统认识，并为通过设计粗糙度结构来控制微尺度装置中的输运过程提供新的见解。这项工作包括开发一个理论模型，该模型通过数值模拟以及压降和传热实验进行验证，该实验将结构粗糙度结合在10毫米宽的矩形通道壁上，间隙从0.2毫米到2毫米不等。测试的粗糙度高度涵盖了相对粗糙度范围（定义为粗糙度高度与通道液压直径的比值）从0到30%。我们对粗糙度的传统理解主要来自于Nikuradse和Moody等研究人员几十年前对大直径管的研究。在相对粗糙度低于5%的范围内，流体流动和压降不受壁面粗糙度的影响。尼科拉泽的巨大不确定性是什么？S实验是造成这种差异的主要原因。近五年来在严格控制条件下进行的微尺度流体流动实验表明，层流确实受到壁面粗糙度的影响。关于粗糙度对传热的影响，文献资料很少，对粗糙度对这一重要传递现象的影响缺乏很好的理解。由于微通道的水力直径较小，因此在微通道中经常遇到层流和过渡流，这一点尤为重要。目前尚不清楚这种通道中粗糙度引起的流动结构的变化和不稳定性。前人的研究以及RIT的研究表明，随着相对粗糙度的增加，压降和传热也会增加。粗糙度的存在导致表面积体积比的增加，这在微尺度上已经比传统尺寸的通道大了。低相对粗糙度的影响以前已经在RIT使用润滑理论建模。对于给定的粗糙度剖面，该模型可以预测其对压降的影响。为了准确地模拟较大的相对粗糙度的影响，进一步的壁面修改是必要的。先前的工作表明，粗糙微通道中从层流到湍流的早期转变，这些影响也将用于传热特性的研究。理论工作将辅以数值模拟和先进的实验技术（用水）在热分析和微流体实验室在RIT。这项工作将提供不同类型粗糙表面的基本特征（均匀粗糙度，交叉轮廓和均匀间距的肋骨），以及对表面粗糙度如何影响流体流动，传热和层流和过渡区域微通道和小通道中的层流/湍流过渡的基本理解。计划中的低雷诺数流动控制粗糙度元素的研究将为微尺度流体流动装置的设计提供基础工具。例如，在电子冷却应用中，尽管微通道中的传热系数很高，但更高的值需要更低的水和气流的压降（航空航天领域对空气冷却的新重视）。特别设计的粗糙度元件是提高性能的有效途径。这样的设计师?表面还将增强其他应用中各自的传输过程，例如生物和化学分析系统、微全系统分析、微推进系统、太空探索中的机载微型设备、PEM燃料电池的冷却通道和微混合器。这项工作的结果是，在广泛的参数范围内，从精心控制的微尺度实验中可以获得一套详尽的数据。在教育方面，这项工作将为这一新兴领域的本科生提供令人兴奋的研究机会。它将通过博士生在微系统工程项目中与PI一起工作来巩固RIT的微流体研究基础设施。这项工作的结果将在多学科会议上提出，以促进思想的交流。该项目将在E3展上展出，这是PI自1991年以来为中学生举办的年度活动。PI将继续他对多元化的坚定承诺，今年迄今为止，已雇用了两名少数民族和五名女学生（其中一名有听力障碍）。

Proposal Title: A Fundamental Study on the Effect of Surface Roughness Structures on Fluid Flow and Heat Transfer at the Microscale LevelPrincipal Investigator: Kandlikar, Satish G.Institution: Rochester Institute of TechProposal No: CBET-0829038AbstractThis project aims at transforming our conventional understanding of roughness in incompressible laminar flow at both microscale and macroscale, and providing new insight in controlling transport processes in microscale devices with designer roughness structures. The work includes developing a theoretical model that is validated through numerical simulation as well as pressure drop and heat transfer experiments with structured roughness incorporated on the walls of rectangular channels that are 10-mm wide with gaps ranging from 0.2 mm to 2 mm. The roughness heights tested cover a relative roughness range (defined as the roughness height to the channel hydraulic diameter) from 0 to 30 percent.Our conventional understanding of roughness was derived mainly from the work of researchers such as Nikuradse and Moody several decades ago on the basis of their studies on large diameter tubes. Fluid flow and pressure drop were believed to be unaffected by the wall surface roughness in the relative roughness range below 5 percent. The large uncertainties in Nikuradse?s experiments are largely responsible for this discrepancy. Microscale fluid flow experiments conducted in the last five years under carefully controlled conditions showed that laminar flow is indeed affected by the wall roughness. Regarding the roughness effects on heat transfer, there is very little data available in the literature and a good understanding is lacking on the roughness effects on this important transport phenomenon.Due to the small hydraulic diameter, laminar and transition flows are often encountered in microchannels and are of particular importance. The changes in the flow structure and instabilities caused by roughness in such channels are not well understood at the present time. Previous studies performed by others as well as at RIT indicate an increase in pressure drop and heat transfer with an increase in relative roughness. Presence of roughness leads to an increase in the surface area to volume ratio, which is already larger at the microscale than in conventional-sized channels. The effects of low relative roughness have been previously modeled at RIT using lubrication theory. For a given roughness profile, this model can predict the resulting effect on pressure drop. Further wall modifications will be necessary in order to accurately model the effects of larger relative roughness. Previous work indicates an earlier transition from laminar to turbulent flow in rough microchannels, and these effects also will be investigated for heat transfer characteristics. The theoretical work will be complemented with numerical simulations and advanced experimental techniques (using water) in the Thermal Analysis and Microfluidics Laboratory at RIT.This work will provide basic characterization of different types of rough surfaces (uniform roughness, cross-hatched, and uniformly spaced ribs), and a fundamental understanding of how surface roughness impacts the fluid flow, heat transfer and laminar/turbulent transition in microchannels and minichannels in the laminar and transition regions. The planned work on low Reynolds number flows with controlled roughness elements will provide a fundamental design tool for microscale fluid flow devices. For example, in electronics cooling applications, although the heat transfer coefficients in microchannels are high, even higher values are desired with lower pressure drop penalties for water as well as air flow (new emphasis on air-cooling in aerospace field). Specially designed roughness elements offer an effective way to improve the performance. Such ?designer? surfaces will also enhance respective transport processes in other applications, e.g. biological and chemical assay systems, micro-total system analysis, micro propulsion systems, on-board microscale devices in space exploration, cooling passages for PEM fuel cells, and micromixers. As a result of this work, an exhaustive set of data will be available from carefully controlled microscale experiments over a wide range of parameters. On the educational front, the work will provide exciting undergraduate research opportunities in this emerging field. It will consolidate microfluidics research infrastructure at RIT through Ph.D. students working with the PI in the Microsystems Engineering program. The results of this work will be presented in multidisciplinary meetings for cross-fertilization of ideas. The project will be featured at the E3 Fair, an annual event heralded by the PI for middle school students since 1991. The PI will continue his strong commitment to diversity, with employment of two minority and five female students (one with hearing disability) so far this year.