Turbulent Rayleigh-Bénard convection of compressed gas: effect of sidewall thermal conductance

Turbulent Rayleigh-Bénard convection is experimentally studied for 1.96×10⁹≤Ra≤1.36×10¹² to assess the effect of sidewall thermal conductance on Nusselt numbers and propose a simple yet novel experimental method that eliminates the requirement to correct for this effect. The proposed method relies on power input to a large central-heater located far from the sidewalls for estimating the experimental Nusselt numbers. Experiments are carried out using test cells of varied aspect ratios (width to height, AR (L/H) = 0.61,1,2) placed inside a pressure vessel filled with compressed gas. Nusselt numbers obtained using the proposed experimental method are then compared with the sidewall-corrected Nusselt numbers estimated using two semi-analytical models from the literature. This comparison is found to yield a reasonable agreement (to within ±8.6%) with both the models. Results from the present study are also presented in the form of a Nusselt number - Rayleigh number relation for the investigated range of parameters.