Ambient air at 20°C flows over a 30-cm-diameter hot spherical object with a velocity of 2.5 m/s. If the average surface temperature of the object is 200°C, the average convection heat transfer coefficient during this process is

(a) 5.0 W/m.K

(b) 6.1 W/m.K

(c) 7.5 W/m.K

(d) 9.3 W/m.K

(e) 11.7 W/m.K

For air, use k = 0.2514 W/m.K, Pr = 0.7309, v = 1.516 × 10−5 m2/s, μ∞ = 1.825 × 10−5 kg/m.s, μs = 2.577 × 10−5 kg/m.s)