Effect of Fin Height and Rayleigh Number with Small Increments on Convective Heat Transfer in a Horizontal Annulus

Abstract

The purpose of this paper is to investigate numerically the laminar natural convection in an annular space bounded by two coaxial horizontal cylinders equipped with two fins of height h, ranging from 0.015 to 0.953. Rayleigh number, Ra, is considered between 10(3) and 10(4). The effect of the fin height and Rayleigh number, both varied with small increments is analyzed. The resulting flow structures and heat transfer rates as well as the effectiveness of the system are presented. The results show that for each Ra the increase in h leads to a decrease or an increase in heat transfer rate depending on the fins height value, and that the case without fins can be more favorable to the heat transfer rate compared to the case with fins for intervals of h obtained as a function of Ra. It is also shown that the increase in the Rayleigh number does not necessarily correspond to an increase in heat transfer rate. In particular, the disappearance of the bicellular regime leads to a decrease of the heat transfer rate when Ra increases.