Effects of thermal stratification on natural convection in a symmetrically heated channel: Comparison of characteristic quantities between air and water

Abstract

We present in this paper a numerical investigation on pure convection flow inside a vertical channel heated at symmetrically uniform heat flux and contained in an enclosure. This study aims to investigate how far we can use water to predict natural convection in an air filled channel especially in presence of thermal stratification. The 2D unsteady Navier–Stokes equations under Boussinesq approximation was solved numerically using Finite Differences Method. The investigation is made for moderate Rayleigh numbers in order to study the effect of stratification at the early stages of the flow development. A comparison in terms of flow and heat transfer characteristics is done between the two fluids. It is seen that natural convection heat transfer in such a configuration is more impacted by thermal stratification when air is used as the working fluid. Traditionally used water models to predict the natural convection of air may give rise to misinterpretations about the real phenomenon especially when stratification occurs. This study should also give some clarifications about the discrepancies raised in the literature between numerical and experimental results when both water and air are used.