Numerical Investigation of Variable Property Effects on Laminar Natural Convection of Gases Between Two Horizontal Isothermal Concentric Cylinders

A numerical finite difference investigation has been conducted to determine the effects of variable properties on the laminar natural convection of gases between horizontal isothermal concentric cylinders. Velocity profiles, temperature profiles, and heat transfer rates have been computed for diameter ratios of 1.5, 2.28, 2.6, and 5.0 and Rayleigh numbers based on gap width up to 1.8 × 10⁵. The temperature difference ratio θ_o was varied from 0.2 to 3.0, and the range of validity of the Boussinesq approximation was determined to be θ_o = 0.2. A volume-weighted mean temperature was shown to be the most effective reference temperature to reduce the heat transfer data for each diameter ratio to a single curve of the form k_eq = C Ra_Lⁿ, for 0.2 ≤ θ_o ≤ 3.0 and Ra_L = 2.0 × 10⁵.