Natural 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.
