Numerical investigation of serrated fins on natural convection from concentric and eccentric annuli with different cross sections.

In this paper, the effect of internal serrated fins and eccentricity on natural convection heat transfer between annular spaces with the equivalent circular, square, and triangular cross sections has been studied numerically using control volume method. The annuli's inner and outer walls were maintained at different uniform temperatures of 373 and 327 K, respectively, and Rayleigh number ranges were 10⁵ ≤ Ra ≤ 10⁸. According to the results, although heat transfer coefficient was reduced between the space of fins, fins increased the total heat transfer of both inner and outer walls of annuli. The best heat transfer rate belongs to reverse triangular annulus when fins were mounted on the inner wall. As an example, heat transfer of inner wall of reverse triangular annulus was, respectively, increased about 31 and 10% at Ra = 10⁵ and 10⁸, when serrated fins were mounted on the inner wall. In addition, fin efficiency of inner and outer walls was decreased with the increase in Rayleigh number. Nevertheless, thermal efficiency of reverse triangular annulus was uppermost at all Rayleigh numbers compared to other ones. In addition, eccentric annuli showed better heat transfer rate than concentric ones, in which cases 3.5 and 6.7% thermal improvements have been obtained for 0.6 and 1 mm downward movement of the inner wall at Ra = 10⁸, respectively. [ABSTRACT FROM AUTHOR]