A composite wall of an oven consists of three materials, two of which are of known
thermal conductivity, kA = 20 W/m.K and kC = 50 W/m.K and known thickness, LA =
0.30 m and LC = 0.15 m. the third material, B, which is sandwiched between materials
A and C, is of known thickness, LB = 0.15 m, but unknown thermal conductivity kB.
Under steady-state operating conditions, measurements reveal an iuter surface
temperature of Ts,o = 20 oC an inner surface temperature of Ts,i = 600 oC and an
oven air temperature of T = 800 oC. The inside convection coefficient h is known to
be 25 W/m2.K. Draw the thermal circuit of heat flux and referring to this thermal circuit
determine the value of kB?
Thermal circuit
(6000C)Ts,i kA= 20 W/m.k kB= ? kC= 50 W/m.k Ts,o (200C)
Air ( T, h)
0.3 m 0.15 m 0.15 m
LA LB LC
1
R
2
R
3
R
Ts, i LA /KA LB /KB LC /KC Ts,o
R
T
Q
kA
L
R
(conduction)
hA
R1
(convection)
321
RRRR
*Area not given so assume 1m2
C
C
B
B
A
A
K
L
K
L
K
L
oTsiTs
Q
,,
50
15.015.0
20
3.0
20600
B
K
Q
