Q$1.$ A $6-$m$-$long section of an $8-$cm$-$diameter horizontal hot$-$water pipe passes through a large room whose temperature is $20C.$ If the outer surface temperature of the pipe is $70C,$ determine the rate of heat loss from the pipe by natural convection. Given, properties of air at the film temperature of $45C$ and $1$atm:$k=0\mathrm{.}02699\frac{W}{m}K,Pr=0\mathrm{.}7241,$

$u=1\mathrm{.}750{10}^{-5}\frac{m^2}{s}$ and $=\frac{1}{T_f}=\frac{1}{318}{K}^{-1}$