(a)
(b)
(c)
(d)
(e)
(f)
Figure 7: Air flow path-lines of the wing-shaped tubes bundle for different fin heights at Re = 1800: (a) = 2 mm, (b) = 4 mm, (c) = 6 mm, (d) = 8 mm, (e) = 10 mm, and (f) = 12 mm.