Numerical modeling of natural convection heat transfer from a horizontally positioned tube layer immersed in a tank

Abstract

This study addresses the problem of heating heavy fuel oil (HFO) in ship storage tanks. The 3D natural convection heat transfer from a horizontally positioned tube layer immersed in a tank for heating the HFO was investigated in the Rayleigh (Ra) number ranges of 10⁵≤Ra_H≤10⁷, 170≤ Ra_D≤16990. The effect of the ratio of computational domain height (H) to width (W), (A = H/W), on heat transfer by natural convection was also examined. Analyses were performed for 3 different H/W (1.66, 2.5 and 3.33). The governing equations of heat transfer by natural convection in the tank were solved using the finite volume method. The function related to the variation in the HFO viscosity with temperature was compiled into a finite volume solver. The flow and thermal fields inside the tank were obtained by the isosurface technique. The average Nusselt numbers ($\overline{\text{Nu}}$) on the tube and horizontal walls were calculated. The findings of the study are that the Ra number increased, the $\overline{\text{Nu}}$ in the tube and the top horizontal walls increased, but there was no significant change in the $\overline{\text{Nu}}$ numbers for the bottom wall. Additionally, the $\overline{\text{Nu}}$ values for the tube increased in the 10⁵≤Ra_H≤10⁶ range as the H/W ratio increased. At Ra_H = 10⁷, the increase in the H/W ratio from 2.5 to 3.33 had no effect on the heat transfer rate in the tube. As a result, the effect of the H/W ratio on the heat transfer rate in the tube gradually decreased with the increase of Ra number. Correlations between Ra number, aspect ratio and $\overline{\text{Nu}}$ were developed.