Thermal Conductivity

In this section, we introduce thermal conductivity with examples of products exploiting the conductivity of aluminium.
Definition
The thermal conductivity of a material is the measure of a material’s ability to conduct heat. High conductivity = good thermal conductor; low conductivity = good thermal insulator.

The thermal conductivity is important in engineering for conditions of steady-state heat flow - i.e. when the imposed temperatures are stable, and the designer needs to know how much heat is being conducted down a thermal gradient. In a heat exchanger we wish to transfer as much heat as possible between two fluids, one hot, the other cold; in a window frame, we aim to lose as little heat as possible from a heated home to the environment.

The mathematical formula defining thermal conductivity λ (or sometimes k) is:

where q is the heat conducted per second (or power), per unit area, and dT/dx is the temperature gradient (K m−1) in the direction of heat conduction.

Units and values

Thermal conductivity is measured in W m−1 K−1. Aluminium alloys have values in the range 75-235 W m−1 K−1, at the top end of the range for metallic alloys (5-390 W m−1 K−1). Only copper has a higher thermal conductivity, while steel has values in the range 10-55 W m−1 K−1.


Nadia.