On Turbulent Rayleigh-Bénard Convection in a Two-Phase Binary Gas Mixture

by Florian Winkel
Doctoral thesis
Date of Examination:2014-10-27
Date of issue:2015-11-27
Advisor:Dr. Holger Nobach
Referee:Dr. Holger Nobach
Referee:Prof. Dr. Andreas Tilgner
Persistent Address: http://dx.doi.org/10.53846/goediss-5396

 

 

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Abstract

English

In this thesis an attempt is made to generate cloud patterns in a laboratory scale experiment. A two-phase binary gas mixture is employed as a physical model system. The fluid mixture is composed of a condensable gas which forms a liquid and a vapor phase and a noncondensable gas which serves as a background or carrier gas. The fluid mixture is confined between a bottom and a top plate. If the fluid mixture is exposed to a constant temperature difference, two intriguing phenomena can be observed. First a film condensation sets in at the cold top plate that results in the formation of a very regular hexagonal droplet pattern. The temporal evolution of the droplet pattern is quantified and it is shown that a stable mass flux is essential in order to the maintain the hexagonal symmetry of the droplet patten. Second cloud-like patterns occur in a thin layer above the liquid-vapor interface. The dynamics of the cloud-like patterns reveal the turbulent flow inside the gaseous phase. An area-perimeter analysis of the cloud-like patterns results in a fractal dimension that is similar to the one obtained by the fractal analysis of two-dimensional cloud and rain areas in satellite and radar data. This thesis is meant as a proof of concept which is why most of the results are still qualitative. However, a physical model system is presented that is appropriate in order to study the dynamics of cloud-like patterns in a turbulent Rayleigh-Bénard convection experiment. The origin of the cloud-like patterns is still a matter of debate. Therefore further experiments that could reveal the nature of these patterns must be performed.
Keywords: Buoyancy-driven flows; Rayleigh-Bénard convection; Interfacial instabilities; Rayleigh-Taylor instability; Gas/liquid flows; Thermal convection
 
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