$($a$)$ Differentiate between local convection heat transfer coefficient and average

$($overall$)$ convection heat transfer coefficient.

Air stream at $27C$ is moving at $0\mathrm{.}3\frac{m}{s}$ across a $100$ W electric bulb at $127C.$ If

the bulb is approximated by a $60$ mm diameter sphere, estimate the heat transfer

rate and the percentage of power lost due to convection. Take $($i$)$ physical prop$-$

erties of air at $77C$ as Kinematic Viscosity $=2\mathrm{.}08{10}^{-5}\frac{m^2}{s}$; Conductivity $($ k $)$

$=0\mathrm{.}03\frac{W}{m}k$

$($ii$)$ Control equation $=N_{uD}=0\mathrm{.}37R_{eD}^{0\mathrm{.}6}$