54. A small metal bead (radius 0.5 mm), initially at 100C, when placed in a stream of fluid at 20C, attains a temperature of 28C in 4.35 seconds. The density and specific heat of the metal are 8500 kg/m and 400 J/kg.K, respectively. If the bead is considered as lumped system, the convective heat transfer coefficient (in W/m2.K) between the metal bead and the fluid stream is (A) 283.3 (B) 449.7 (C) 149.9 (D) 299.8