
207Heat Transfer
a function only of its absolute temperature and is
described by
b
=σ
(10.24a)
b
(10.24b)
where
A is the area (ft
2
or m
2
)
T is the absolute temperature of the body (°R or K)
σ is the Stefan-Boltzmann constant, which has the
value of
σ= °
−
00 0
8
.(./)1714 1Btu hr-ft -R 5 669 1Wm-K
24 -8 24
××
(10.25)
Example 10.4
Given: Surface temperature = 2000°F.
Find: Blackbody emissive power.
Solution
e
b
= σ T
4
= (0.1714 × 10
−8
Btu/h-ft
2
-°R
4
)(2,000 +
460°R)
4
= 62,800Btu/h-ft
2
If all of the radiation received at a solid surface is
absorbed by that surface, the body is referred to as a black-
body and has an absorptivity of one (α = 1). In addition, ...