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1
       v  l (1.14.6)
3

1.15 Heat Conduction

When there exists a temperature gradient within a body, heat energy
will flow from the region of high temperature to the region of low
temperature. This phenomenon is known as

conduction heat transfer, and is described by
Fourier's Law (named after the French
physicist Joseph Fourier),

 T
Q    S  t  (1.15.1)
 z
quantity of heat Q transferes in a body

for time t through area S oriented
perpendicular to the direction of heat
transference is proportional to time t ,
S
area  and to the temperature
Figure 1.15.1  T
gradient and  is heat conductivity
 z
factor or coefficient of heat conduction.

2  T K
If  t  1s , S  1m and  then Q  
 z m
(numerically).
J
Measurement unit of heat conductivity factor is  
K  m s 

And now consider we will
derive an expression for the

thermal conductivity.
Consider a gas with a

vertical temperature gradient
(fig.1.15.2) . The lower side
is hot and the upper side is
cold. There is an upward

Figure 1.15.2
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