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

提案标题：表面粗糙度结构对微尺度流体流动和传热影响的基础研究首席研究员：Kandlikar，Satish G.机构： 罗切斯特技术研究所提案编号： CBET-0829038摘要本项目旨在改变我们对不可压缩层流中微尺度和宏观尺度粗糙度的传统理解，并为控制具有设计粗糙度结构的微尺度器件中的输运过程提供新的见解。该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，该实验在10 mm宽的矩形通道壁上加入结构化粗糙度，间隙范围为0.2 mm至2 mm。测试的粗糙度高度覆盖相对粗糙度范围（定义为粗糙度高度与渠道水力直径之比）从0到30%。我们对粗糙度的传统认识主要来自几十年前Nikuradse和Moody等研究人员在大直径管道研究基础上的工作。流体流动和压降被认为是不受壁面粗糙度的相对粗糙度范围低于5%。尼库拉兹的巨大不确定性？的实验在很大程度上负责这种差异。在过去五年中，在严格控制的条件下进行的微尺度流体流动实验表明，层流确实受到壁粗糙度的影响。关于粗糙度对传热的影响，文献中的数据很少，对粗糙度对这一重要的传输现象的影响缺乏很好的理解，由于水力直径小，层流和过渡流经常在微通道中遇到，特别重要。在这种渠道中的流动结构的变化和不稳定性所造成的粗糙度没有得到很好的理解，在目前的时间。先前由其他人以及在RIT进行的研究表明，随着相对粗糙度的增加，压降和传热增加。粗糙度的存在导致表面积与体积比的增加，其在微尺度下已经比常规尺寸的通道中更大。低相对粗糙度的影响以前已经在RIT使用润滑理论建模。对于给定的粗糙度分布，该模型可以预测对压降的影响。为了准确模拟较大相对粗糙度的影响，需要进一步修改壁面。以往的工作表明，较早的过渡从层流到湍流的粗糙微通道，这些影响也将被调查的传热特性。理论工作将辅以数值模拟和先进的实验技术这项工作将提供不同类型粗糙表面的基本表征（均匀粗糙度、交叉阴影线和均匀间隔的肋），以及对表面粗糙度如何影响流体流动的基本理解，在层流和过渡区中的微通道和小通道中的传热和层流/湍流过渡。计划中的低雷诺数流动与控制粗糙度元素的工作将提供一个基本的设计工具，微尺度流体流动装置。例如，在电子冷却应用中，尽管微通道中的传热系数很高，但是对于水以及空气流（航空航天领域中对空气冷却的新强调），期望甚至更高的值具有更低的压降损失。特别设计的粗糙度元件提供了一种有效的方法来提高性能。是这样吗？设计师？表面还将增强其他应用中的相应传输过程，例如生物和化学测定系统、微总系统分析、微推进系统、空间探索中的机载微型装置、PEM燃料电池的冷却通道和微混合器。作为这项工作的结果，一个详尽的数据集将可从精心控制的微型实验在广泛的参数。在教育方面，这项工作将在这一新兴领域提供令人兴奋的本科生研究机会。它将通过博士学位巩固RIT的微流体研究基础设施。在微系统工程项目中与PI一起工作的学生。这项工作的结果将在多学科会议上提出，以交流想法。该项目将在E3博览会上展出，这是PI自1991年以来为中学生举办的年度活动。PI将继续坚定地致力于多元化，今年迄今为止雇用了两名少数民族学生和五名女学生（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.