Turbulent-convection experiments at extreme conditions using cryogenic nitrogen

PI：Ranjan，Devesh提案编号：1604468当流体被加热并开始上升时会发生自然对流。拟议的研究的重点是调查自然对流在极端条件下的参数是重要的过程。在几个重要的自然和工程流程中发现了应用。大规模的自然系统，如地球的大气层、海洋和地幔，以及太阳等恒星的内部，都不同程度地受到自然对流的影响。用来理解这种无处不在的热传输机制的简化物理模型是瑞利-贝纳德（RB）对流，其是由具有绝热侧壁的实验室的顶板和底板之间的温差驱动的流体流动。尽管这一课题有着悠久的历史，最近在理论、数值和实验领域取得了进展，但许多问题仍然没有得到解决。一个基本的问题是高度湍流对流传热定标，特别是关于过渡到渐进制度的增强传热。其他问题与这些极端流动参数下的流动结构有关，特别是关于不规则多边形结构的存在，这些结构与对流发生时观察到的结构相似。该项目旨在在格鲁吉亚理工学院的一个设施中，通过使用接近其共存曲线的液态或气态氮，从1个大气压下的77 K到其临界点（约126 K和34 bar/500 psi），探索极端参数下的RB对流。拟议的研究将提供可视化的流动结构的条件下，不存在。在这些极端条件下的实验结果似乎是相互矛盾的，拟议的工作有望解决这个问题。除了研究生和本科生的教育活动，还有一个计划，继续与游击队科学，一个专业的外展组织总部设在纽约市和伦敦，其中PI开发和运行流体动力学启发的竞争。目的是吸引年轻学生学习工程学。

PI: Ranjan, DeveshProposal Number: 1604468Natural convection occurs when fluid is heated and starts to rise. The focus of the proposed research is to investigate natural convection at extreme conditions in terms of the parameters that are important to the process. Applications are found in several important natural and engineering flows. Large scale natural systems such as the Earth's atmosphere - its oceans as well as the Earth's mantle - and the interior of stars such as the Sun, are all affected to various degrees by natural convection.The simplified physical model used to understand this ubiquitous heat transport mechanism is Rayleigh-Bénard (RB) convection, which is a fluid flow driven by a temperature difference between the top and bottom plates of an experimental cell with adiabatic sidewalls. Despite the long history of the subject and the recent progress in theoretical, numerical and experimental domains, many questions remain unresolved. A fundamental question concerns the heat transfer scaling in highly turbulent convective flows and in particular regarding the transition to the asymptotic regime of enhanced heat transfer. Other questions are related to the flow structures at these extreme flow parameters, and in particular about the existence of irregular polygonal structures that resemble those observed just above the onset of convection. This project aims to explore RB convection at extreme parameters by using liquid or gaseous nitrogen close to its coexistence curve, from 77K at 1 atm to its critical point (about 126K and 34 bar/500psi) in a facility at Georgia Institute of Technology. The proposed research will provide visualization of the flow structures at conditions for which none exist. Available experimental results at these extreme conditions appear to be in conflict, and the proposed work promises to settle the issue. In addition to graduate and undergraduate educational activities, there is a plan to continue collaborating with Guerilla Science, a professional outreach organization based in NYC and London, with which the PIs developed and run a fluid dynamics-inspired competition. The goal is to attract young students to engineering.