Similarly,
F ji =
1
A j
�
A j
�
A i
cos θ i cos θ j
πR 2
dA i dA j
(12.4)
Therefore, we obtain the Reciprocity Rule
A i F ij = A j F ji
(12.5)
For enclosure N surfaces, as shown in Figure 12.2,
n
j=1
F ij = 1
(12.6)
240
Analytical Heat Transfer
A j
dA j
θ j
n j
n i
θ i
dA i
dω j-i
R
A i
FIGURE 12.1
Radiation exchange between two diffuse isothermal surfaces.
1
2
3
N surfaces
FIGURE 12.2
View factor for a N-surface enclosure.
F ji =
1
A j
�
A j
�
A i
cos θ i cos θ j
πR 2
dA i dA j
(12.4)
Therefore, we obtain the Reciprocity Rule
A i F ij = A j F ji
(12.5)
For enclosure N surfaces, as shown in Figure 12.2,
n
j=1
F ij = 1
(12.6)
240
Analytical Heat Transfer
A j
dA j
θ j
n j
n i
θ i
dA i
dω j-i
R
A i
FIGURE 12.1
Radiation exchange between two diffuse isothermal surfaces.
1
2
3
N surfaces
FIGURE 12.2
View factor for a N-surface enclosure.