Nematic–isotropic phase transition in turbulent thermal convection

Abstract

AbstractWe report on turbulent Rayleigh–Bénard convection of a nematic liquid crystal while it undergoes a transition from the nematic to the isotropic phase in a cylindrical convection cell with a height equal to twice the diameter (aspect ratio $\Gamma = 0. 50$). The difference between the top and bottom plate temperature $ \mathrm{\Delta} T= {T}_{b} - {T}_{t} $ was held constant, while the average temperature ${T}_{m} = ({T}_{b} + {T}_{t} )/ 2$ was varied. There was a significant increase of the transported heat when the phase transition temperature ${T}_{NI} $ was between ${T}_{b} $ and ${T}_{t} $. Measurements of the temperatures along the sidewall of the sample as a function of ${T}_{m} $ showed several ranges with qualitatively different behaviour of quantities such as the time-averaged sidewall temperature, temperature gradient, or temperature fluctuations. We interpret these different ranges in terms of properties of the thermal boundary layers close to the top and bottom plates whose stability and nature depends on the location within the sample of ${T}_{NI} $.