$($Ans$.7\mathrm{.}71$ W: $19\mathrm{.}278\%)7.$ A vertical slot of $15$ mm thickness is formed by two $2$m x $2$m square plates. If the temperature of the plates are $120$C and $20$C respectively.PH$17$ Calculate the following: $()$ The effective thermal conductivity: $($it$)$ The rate of heat flow through the slot. $[$Ans$.(1)0\mathrm{.}0317$ W$/$m$$C$,($i$)845\mathrm{.}3$ W$]8.$ Two horizontal plates separated by a distance of $25\mathrm{.}4$ mm contain air at atmospheric pressure. The temperatures of lower and upper panels are $60$C and $15\mathrm{.}6$C respectively. Calculate the free convection heat transfer per m of the panel surface. $($Ans$.167\mathrm{.}2$ W$/$m$2)$