The results in Fig. show a small difference between the solutions. To highlight this difference, this case study is modified by considering that, instead of pure natural convection, a light breeze of 5 m s ⁄ blows perpendicular to the outer tube. In this case, for the sake of simplicity, it is assumed that only ℎ 𝑎 is changed and this coefficient is recalculated using the Žukauskas correlation .