Thermal conductivity
Fourier’s law of heat conduction states that the heat flow by conduction in any direction is directly proportional to the area normal to the direction of flow and temperature gradient and in the direction of the negative gradient.
Mathematically
Heat flow = Q = -kA (dT/dx)
‘k’ is the constant of proportionality and is called thermal conductivity.
The SI units of thermal conductivity is Watt/metre.Kelvin or W/mK
Electrical conductors have good thermal conductivity. Gases have least thermal conductivity.
Thermal conductivity varies with temperature. In good conductors, thermal conductivity decreases with temperature. In insulators, thermal conductivity increases with temperature. Thermal conductivity increases with temperature in case of gases also due to increased random activity of atoms and molecules.
Thermal conductivity of some of the materials at 293°K is
Material |
Thermal conductivity (W/mK) |
Copper |
385 |
Silver |
406 |
Gold |
314 |
Iron |
71.8 |
Aluminum |
204.3 |
Glass |
0.8 |
Concrete |
1.13 |
Water |
0.596 |
Air |
0.025 |