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The combination of convection and conduction in stationary walls is called overall heat
transfer and can be expressed as
(3.26)
where k is denoted as the overall heat transfer coefficient with the corresponding overall
resistance Rw
(3.27)
Analogous to conduction for the composite wall in Figure 3.7, the overall resistance JRW
can be given by
or
A simplified form of Equation 3.29 is
Calculation of the convection heat transfer coefficient is shown in the Section 3.5.
3.2 Transient State Conduction
(3.28)
(3.29)
(3.30)
The differential equation for the transient one-dimensional conduction after Fourier is
given by
where
T = temperature
t = time
x = distance
(3.31)