Fundamental Study of Nucleate Boiling on Nanostructured Interfaces

纳米结构界面上核沸腾的基础研究

• 批准号: 0853785
• 负责人: Yoav Peles
• 金额: $ 32.5万
• 依托单位: Rensselaer Polytechnic Institute
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-06-15 至 2013-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0853785&HistoricalAwards=false
• 关键词: Fundamental; Study; Nucleate; Boiling; Nanostructured

0853785Peles Boiling of fluids on heat transfer surfaces requires nucleation sites in the form of micro- or nanoscale cavities to promote bubble growth. Heat transfer surfaces, rich in effective nucleation sites, can be formed by depositing nanorods on the surfaces. This can significantly improve the heat transfer process. Specifically, it has been recently shown that nanorods can reduce the surface temperature at the onset of nucleate boiling, reduce the surface temperature following boiling inception (that is, increase the two-phase heat transfer coefficient), and increase the maximum allowable heat transfer rate. However, so far there is no clear understanding regarding why the deposited nanorods affect the nucleate boiling process. This project seeks to develop a fundamental understanding of why nanorod surfaces improve nucleate boiling heat transfer by completing the following tasks. (1) perform an experimental study of nucleate boiling of a nanorod film without microscale surface defects. Such a film is comprised of only an interconnected network of nanopores formed between the nanorod interstices, and does not contain microscale surface cavities. This control experiment will determine whether or not bubbles can nucleate at low superheats from nanopores when they are uncoupled from microscale cavities. (2) Perform experimental studies of surfaces with isolated micro cavities. This will allow us to determine whether or not the micro cavities can generate stable bubble nucleation at low superheats when they are uncoupled from the nanopore network. (3) Investigate the role of the wettability of the nanopores, nanorod size and spacing and the density/size of micro-defects on the bubble ebullition process. We will also perform high-speed, microscopic flow visualization to observe bubble growth, as well as measure the bubble release frequency and departure diameters under various operating conditions. The Intellectual merit of the research is based on the fact that very limited nucleate boiling heat transfer data are available for well defined and engineered nanostructured cavities on heated surfaces. The data to be gathered will reveal the mechanisms that control bubble nucleation and heat transfer improvement on surfaces with morphologies of diminishing length scales. It will also aid the development of new heat transfer surfaces, and provide engineers with superior methods for improving thermal performance, perhaps significantly. The Broader impacts of this research are based on the fact that a growing number of industries (microelectronics, aerospace, chemical, cryogenics, energy) are in pressing need of techniques to increase heat transfer in various high heat flux devices. The results of this study will greatly extend the body of scientific knowledge of nucleate boiling over nano- and microscale cavities, and enable the development of innovative heat transfer surfaces that could have practical applications in a variety of processes that involve boiling. To integrate research and teaching, specially-designed virtual labs will be developed. Outreach includes demonstrations to high school students; this will help to attract a diverse cadre of young students to careers in science and engineering.

流体在传热表面上的沸腾需要呈微米或纳米级空腔形式的成核位置以促进气泡生长。通过在表面上沉积纳米棒可以形成富含有效成核位点的传热表面。这可以显著改善传热过程。具体地说，最近已经表明，纳米棒可以降低核态沸腾开始时的表面温度，降低沸腾开始后的表面温度（即，增加两相传热系数），并增加最大允许传热速率。然而，到目前为止，还没有明确的理解，为什么沉积的纳米棒影响核沸腾过程。该项目旨在通过完成以下任务，对纳米棒表面改善核态沸腾传热的原因有一个基本的理解。(1)对无微尺度表面缺陷的纳米棒薄膜进行核态沸腾的实验研究。这种膜仅由在纳米棒间隙之间形成的纳米孔的互连网络组成，并且不包含微米级表面空腔。该控制实验将确定当气泡与微米级空腔解耦时，气泡是否可以在低过热下从纳米孔成核。(2)对具有孤立微腔的表面进行实验研究。这将使我们能够确定当微腔与纳米孔网络解偶联时，它们是否可以在低过热下产生稳定的气泡成核。(3)研究纳米孔的润湿性、纳米棒的尺寸和间距以及微缺陷的密度/尺寸对气泡沸腾过程的作用。我们还将进行高速，微观流动可视化，以观察气泡的生长，以及在各种操作条件下测量气泡释放频率和偏离直径。 这项研究的智力价值是基于这样一个事实，即非常有限的核态沸腾传热数据可用于加热表面上定义良好的和工程化的纳米结构空腔。待收集的数据将揭示控制气泡成核和传热改善的表面上的长度尺度逐渐减小的形态的机制。它还将有助于开发新的传热表面，并为工程师提供上级方法，以提高热性能，也许显着。 这项研究的更广泛的影响是基于这样一个事实，即越来越多的行业（微电子，航空航天，化学，低温，能源）迫切需要技术来增加各种高热通量设备中的传热。这项研究的结果将极大地扩展核沸腾的科学知识体系在纳米和微米尺度的空腔，并使创新的传热表面，可以在各种涉及沸腾的过程中有实际应用的发展。为了整合研究和教学，将开发专门设计的虚拟实验室。外联活动包括向高中生进行示范;这将有助于吸引各种青年学生从事科学和工程职业。