Example $4\mathrm{.}3$ : A $50mm$ i$.$d$.$ iron pipe at $423K(150C)$ passes through a room in which the surroundings are at $300K(27C).$ If the emissivity of the pipe metal is $0\mathrm{.}8,$ what is the net interchange of radiation energy per meter length of pipe? The outside diameter of pipe is $60mm.$

Solution :

Jength of nine $=1m$