
72 Heat Transfer: Thermal Management of Electronics
The radiation heat transfer coefficient and radiation thermal resistance are
hTTTT
h
ssradsurr
2
surr
rad
=+ +
=× ×
εσ()()
..
2
08 567110 914 22 313 15 914 22 313 1
8222−
++W/mK K
24
(. .)(. . 55
51 99
11
51 99 0
)
.
.(
K
W/m°C
W/m°C
2
rad
rad
2
=
==
×
R
hA
..)
.
04
12 02
2
m
°C/W,=
Note that radiation thermal resistance is less than convection thermal resistance in
this case. This is mainly due to the high temperature of the metal cap.
Example 5.4
What are the modified radiation heat transfer coefficient and modified radiation
thermal resistance for the package cap in Example 5.3?
Solution
The modified radiation heat transfer coefficient is ...