A composite wall, having unit length normal to the plane of paper, is insulated at the top and bottom as shown in fig. it is comprised of four different materials A, B, C and D.
Dimensions are
$H_{A}=H_{D}=3cm,$
$H_{B}=H_{C}=1.5cm,$
$L_{1}=L_{3}=0.05cm, L_{2}=0.1m$
Thermal conductivity of the materials are
$K_{A}=K_{D}=50W/m^{2}K$
$K_{B}=10W/mK$
$K_{C}=1W/mK$
The fluid temps and HTC (see fig) are
$T_{1}=200^{\circ}C, h_{1}=50 W/m^{2}K$
$T_{2}=25^{\circ}C, h_{2}=50 W/m^{2}K$
Assuming one dimensional heat transfer condition. Determine the rate of heat transfer through the wall.