A small metal bead $(\text{radius}\: 0.5\: mm)$, initially at $100^{\circ}C$ , when placed in a stream of fluid at $20^{\circ}C$ , attains a temperature of $28^{\circ}C$ in $4.35$ seconds. The density and specific heat of the metal are $8500\:kg/m^{3}\:and\:400\:J/kg.K$, respectively. If the bead is considered as lumped system, the convective heat transfer coefficient $(in\:W/m^{2}.K)$ between the metal bead and the fluid stream is
- $283.3$
- $299.8$
- $149.9$
- $449.7$
