Thermal Conduction - Conductance

Conductance

Writing

where U is the conductance, in W/(m2 K).

Fourier's law can also be stated as:

The reciprocal of conductance is resistance, R, given by:

and it is resistance which is additive when several conducting layers lie between the hot and cool regions, because A and Q are the same for all layers. In a multilayer partition, the total conductance is related to the conductance of its layers by:

So, when dealing with a multilayer partition, the following formula is usually used:

When heat is being conducted from one fluid to another through a barrier, it is sometimes important to consider the conductance of the thin film of fluid which remains stationary next to the barrier. This thin film of fluid is difficult to quantify, its characteristics depending upon complex conditions of turbulence and viscosity, but when dealing with thin high-conductance barriers it can sometimes be quite significant.