# IGBT Modules - Technologies, Driver and Application (Second Edition) - page 176

164
thermal conductivity is


Km
W
.
shows the
λ
values of some selected
materials.
Fig. 4.4
Thermal resistance of a flat plate
If the cross-section A and thickness d of the medium are known, it is possible to
determine the thermal resistanceR
th
. Theunit of thermal resistance is
W
K
.
A
d R
th
⋅λ
=
Eq. 4.2
If the temperature difference
T of the medium can be derived from its thickness, the
heat flow P
th,C
can be stated together with the thermal conductivity
λ
. The unit of heat
flow is [W], and is describedby the lawof heat conduction, or Fourier's La
:
d
TA
P
C,th
∆⋅ ⋅λ
=
Eq. 4.3
Thismeans tha
canalso bewritten:
C,th
th
P
T R
=
Eq. 4.4
4.1.2.2 Thermal capacity
Thermal capacity C
th
, just like thermal resistance R
th
, is very similar to its electrical
counterparts. Thermal capacity, like electrical capacity, functions as an energy store,
which canbedescribed in terms of physics.
1
Named after theFrench physicist andmathematician JeanBaptiste JosephFourier (1768 - 1830).
1...,166,167,168,169,170,171,172,173,174,175 177,178,179,180,181,182,183,184,185,186,...548