Robustness of heat-transfer in confined inclined convection at high-Prandtl-number

TL;DR

This study examines how the heat transfer in inclined convection with high Prandtl number fluids remains largely stable despite turbulence changes, revealing that heat flux is resilient to flow regime transitions.

Contribution

It provides new insights into heat transfer robustness across flow regimes in high-Prandtl-number convection, combining experiments and simulations.

Findings

Heat transfer varies minimally despite turbulence reduction.

Reynolds number decreases significantly in laminar flow.

Large scale circulation influences heat flux in different regimes.

Abstract

We investigate the dependency of the magnitude of heat transfer in a convection cell as a function of its inclination by means of experiments and simulations. The study is performed with a working fluid of large Prandtl number, $Pr \simeq 480$, and at Rayleigh numbers $Ra \simeq 10^{8}$ and $Ra \simeq 5 \times 10^{8}$ in a quasi-two-dimensional rectangular cell with unit aspect ratio. By changing the inclination angle ($\beta$) of the convection cell, the character of the flow can be changed from moderately turbulent, for $\beta = 0^o$, to laminar and steady at $\beta = 90^o$. The global heat transfer is found to be insensitive to the drastic reduction of turbulent intensity, with maximal relative variations of the order of $20\%$ at $Ra \simeq 10^{8}$ and $10\%$ at $Ra \simeq 5 \times 10^{8}$, while the Reynolds number, based on the global root-mean- square velocity, is strongly affected with a decay of more than $85\%$ occurring in the laminar regime. We show that the intensity of the heat flux in the turbulent regime can be only weakly enhanced by establishing a large scale circulation flow by means of small inclinations. On the other hand, in the laminar regime the heat is transported solely by a slow large scale circulation flow which exhibits large correlations between the velocity and temperature fields. For inclination angles close to the transition regime in-between the turbulent-like and laminar state, a quasi-periodic heat-flow bursting phenomenon is observed.