Numerical Study of Natural Convection in Vertical Channels with Adiabatic Extensions Downstream

Recent trends in natural-convection research are the finding of new configurations to improve heat transfer parameters or the analysis of standard configurations to determine optimal geometric parameters in order to achieve a better heat transfer rate. In this article a numerical simulation of natural convection in air in a channel-chimney system heated symmetrically at uniform heat flux is carried out. The regime analyzed is two-dimensional, laminar, and steady-state. Wall temperature profiles, air velocity and temperature profiles, and centerline pressure profiles are presented. A comparison with experimental data given in 141 is accomplished and some differences are observed, but thermal and dynamic behavior for different expansion ratios are the same. Results analysis explains how and why the "chimney effect" worsens. The effect is connected to the cold inflow at the outlet section, and this effect is more marked at higher Rayleigh number, Ra. Consequently, optimal thermal configuration for assigned extension ratio presents a larger value of expansion ratio at the lower Ra values.