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Figure 3.6 Heat transfer in composite walls in parallel [1 ]
Heat loss per unit length of the tube according to Equation 3.22:
In the case of multiple-layer walls, in which the heat flow is divided into parallel flows as
shown in Figure 3.6, the total heat flow is the sum of the individual heat flows. Therefore
we have
3.1.6 Overall Heat Transfer through Composite Walls
(3.23)
(3.24)
If heat exchange takes place between a fluid and a wall as shown in Figure 3.7, in addition
to the conduction resistance we also have convection resistance, which can be written as
(3.25)
where O1 - heat transfer coefficient in the boundary layer near the walls adjacent to the
fluids.
Fluid 1 Fluid 2
Figure 3.7 Conduction and convection through a composite wall [1]