Numerical Investigation of Transient Natural Convection in Air in a Convergent Vertical Channel Symmetrically Heated at Uniform Heat Flux

Abstract

A numerical investigation of natural convection in a convergent vertical channel is accomplished in order to study the thermal and fluid dynamics behavior of the transient regime in this configuration. The convergent channel has the two principal flat plates at uniform heat flux and the numerical analysis is carried out in a two-dimensional laminar regime. Results in terms of wall temperature profile, as a function of the time for inclination angle, between 0° and 10°, aspect ratios in the range of 10 to 58, and channel Rayleigh numbers from 5.0 to 3.8 × 10³, are presented. Dimensionless wall temperature sensitivity to the convergence variation is almost 0° for larger angle values. Maximum wall dimensionless temperature, for all convergence angles considered, changes in a very small range at small values of dimensionless time. Overshoots and undershoots in maximum and average dimensionless wall temperature profiles, as well as for dimensionless mass flow rate, are detected. The Nusselt number decreases remarkably between the initial time and 0.2. According to previous results, for steady-state investigations, a channel with a convergence angle equal to 2° is the best configuration in terms of maximum wall temperature and heat transfer coefficient. Stream function and dimensionless air temperature fields allow analysis of fluid dynamics and thermal behavior for different times.

This study is supported by the Ministerio dell'Istruzione. dell'Università e della Ricera with a 2005 PRIN grant research.