Problem $3$

$CL{O}_3$

Duration: $90$ min

The composite wall of an oven consists of three materials A$,$ B and C$,$ The thermal

conductivities of materials A and $B$ are $k_A=20\frac{W}{m}.K,$ and $k_c=30\frac{W}{m}.K$ respectively.

The thicknesses of the three walls are: $L_A=0\mathrm{.}30m,L_B=0\mathrm{.}15m$ and $L_C=0\mathrm{.}15m.$ Under

steady$-$state operating conditions the temperature of the outer surface is $T_{2,0}=20C,$ an

inner surface temperature of $T_{s,1}=600C,$ the temperature of the interface between

materials A and $B$ is $400C,$ and an oven air temperature of $T_{}=800C.$

a$.$ Show the thermal circuit representing the heat transfer situation. Be sure to label

all elements, nodes, and heat rates. Leave in symbolic form

b$.$ Find the inside convection coefficient $h.$

c$.$ Find the thermal conductivity $k_B.$