
Heat Transfer Mechanisms 63
between zero and one, is a measure of how good the surface is in emitting radiation.
Table 4.3 gives emissivity values for some common surfaces [2].
Equation 4.11 for radiation heat transfer rate between an object and its large sur-
rounding can be written as:
QATT AT TTT
sssradsurrsurrs
=−=++εσ εσ()()(
44 22
uurrsurr
)( ).TT
s
−
If we dene
hTTTT
ssradsurrsurr
=+ +εσ()()
22
, (4.15)
then
. (4.16)
This equation is similar to Newton’s law of cooling for convection heat transfer rate
and h
rad
is called radiation heat transfer coefcient.
Although Equation 4.16 is similar to Newton’s law of cooling it uses ...