
Heat flows across the boundaries of each segment along the z-axis by conduction. Fourie r’s law of
heat conduction states that the conductive heat flow per unit area is negatively proportional to the
temperature gradient in the direction of flow. The heat flow from the constant temperature source at
the bott om to the first segment with temperature T
1
is
Q
0
¼kA
T
i
T
Dz=2
¼
T T
1
R
1
(6:278)
The term in parenthesis is the temperature gradient, and k is the thermal conductivity of the material.
R
1
represents the thermal resistance at the lower boundary and is computed from
R
1
¼
Dz
2kA
(6:279)
The internal heat flows are described by
Q
i
¼kA
T
iþ1
T
i
Dz
¼
T
i
T
iþ1
R
iþ1
,