1542Fundamental Concepts

Thermal Equilibrium

A very important law in heat transfer is that under steady-state conditions, the heat flow through any portion of the insulation system is the same as the heat flow through any other part of the system. Specifically, the heat flow through the insulation equals the heat flow from the surface to the ambient, so the temperature difference for each section is proportional to the resistance for each section:

heat flow =

temperature difference resistance to heat flow

Because all of the heat flows Q are equal, this relationship is used to check surface temperature or other interface temperatures. For an analysis concerned with the inner surface film coefficient, the same reasoning applies.

actual outside diameter

Or for a system with two insulation materials involved, the interface temperature tif between the materials is involved.

tif- ta

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