21-July. Basic Concepts 3. Thermal Resistance

21-July. Basic Concepts 3. Thermal Resistance

From the Heat Flow \(\Phi\) relation

\( \Phi=UA\,\Delta T\)

we get

\( q=U\,\Delta T\)

We can interpret the \(\Delta \)T appearing in this relation as the cause that produces the effect of heat flow density q through the wall.

The constant of proportionality that connects the cause to its effect is U. Once the cause \(\Delta \)T is fixed, the bigger is U, the bigger is the effect (q). We call R the reciprocal of U:

\(R=\frac{1}{U}\).

This time, the bigger R, the lower the effect! That’s why R is called the Thermal Resistance of the wall.

UNITS

Thermal Resistance RKm \( ^2\)/ WWith \(\Delta \)T fixed, the bigger R, the lower the flow density q
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Lorenzo Galante

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