That is,
F 11 + F 12 + F 13 + · · · = 1
F 21 + F 22 + F 23 + · · · = 1
.
.
.
F N1 + F N2 + F N3 + · · · = 1
Figure 12.3 shows the differential view factor between two differential areas
i and j, and between area i and differential area j. The differential view factor
between differential area i and differential area j can be obtained as
dq ij
cos θ i cos θ j dA j
dF dAi−dAj =
=
;
J i dA i
πR 2
dq ji
cos θ i cos θ j dA i
dF dAj−dAi =
=
J j dA j
πR 2
View Factor
241
dA j
R
R
dA j
dA i
dA i
n
n
A i
θ i
n
n
θ i
θ j
θ j
FIGURE 12.3
Concept of view factor between two differential areas.