Find the radiation shape factor F$2-1($Figure $2).$

Figure $2.$

For calculating radiation shape factors use the graph given in Figure $1.$

$[5$ MARKS$]$

c$)$

A long marble plate with a cross$-$section area $(1$m x $0\mathrm{.}3$m$)$ is at $20$oC$.$ Suddenly the top

surface of the plate is exposed to water with a temperature of $10$oC$.$ Determine: The time needed for the temperature to reach $17\mathrm{.}5$oC at the point that is $1\mathrm{.}25$ cm

below the top surface.

ii$)$ The surface heat transfer per unit area.