Chapter hvac engineering Fundamentals: Part 1 Introduction

18.5.2
Radiant energy transfer
Radiant energy is transferred between two surfaces which can ‘‘see’’
each other and are at different temperatures. One theory holds that
radiant energy transfer takes place continually in both directions but
that the two heat flows are equal at equal surface temperatures. One
general equation for the net radiant heat transfer between two sur-
faces is
4
4
Q
⫽
␴
F F A
(
T
⫺
T
)
(18.9)
e
A
1
1
2
where
Q
⫽
net heat transfer, Btu / h
␴
⫽
Stefan-Boltzmann constant
⫽
0.173
⫻
10
⫺
8
[Btu/(h
䡠
ft
2
䡠
⬚
F)]
F
e
⫽
factor to correct for surface emittances not being equal to
1.0
F
A
⫽
factor to correct for geometric relationship of surfaces
(
F
A
⫽
1.0 if surfaces face each other directly)
Engineering Fundamentals: Part 3
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