Thermal Conductivity

Thermal Conductivity (TC)


The conductivity is a property that have elements that are conductive. This is the name of those materials that have the ability to transmit electricity or heat.

When a material allows electricity to pass through itself it is said to have electrical conductivity. On the other hand, if it allows the passage of heat, we speak of thermal conductivity.

It can therefore be indicated that thermal conductivity is the property of those elements that enable the transmission of heat. This physical property implies that, when a matter has thermal conductivity, the heat passes from the higher-temperature body to a lower-temperature body that is in contact with it.

According to, this heat transfer involves an internal energy exchange (combining potential energy and kinetic energy) of electrons, atoms, and molecules. The higher the thermal conductivity, the better the heat conduction. The inverse property is thermal resistivity, which indicates that the lower the thermal conductivity, the more insulation from heat (more resistivity).

With regard to potential energy, we can say that it is the mechanical energy that is associated with the location of a body in a force field (in this case we speak of electrostatic or gravitational energy, among others) or the presence of a field of forces within the body itself (in such a case, the energy would be elastic). In other words, the potential energy is the result of the system of forces that affects a given body being conservative, that is, its total work on a particle is zero.

The kinetic energy of a body, for its part, is what it has thanks to its movement. This is the work that is needed to get its acceleration from rest to a given speed. When the body reaches this energy throughout acceleration, it maintains it unless it alters its speed. To return to the state of rest, it is necessary to do negative work with the same magnitude.

By heating matter, the average kinetic energy of its molecules increases, and this increases their level of agitation. At the molecular level, heat conduction occurs because the molecules interact with each other, exchanging kinetic energy without making global movements of matter. It is worth mentioning that at the macroscopic level it is possible to model this phenomenon by means of Fourier’s law.

Fourier’s law indicates that thermal conductivity carries a proportional flow by conduction of heat transfer (the process by which heat spreads in different media), in an isotropic medium (a space in which physical properties are not tied to the direction in which they are examined), which is proportional and opposite to the temperature gradient in that direction.

The Fourier law formula states that the heat flux that occurs on a given surface, measured with a given unit, is equal to the thermal conductivity times the temperature gradient within the material, all multiplied by -1.

The metals are good thermal conductors: thus used in those industrial processes where it is intended to maximize heat transfer. Other materials, such as fiberglass, have such low thermal conductivity that they are used as insulators.

The capacity of heat conduction states through a known magnitude coefficient of thermal conductivity. This coefficient, in the International System of Units, is expressed in watts / (meter x kelvin). It can also be expressed in BTU / (hour x foot x Fahrenheit) in the Anglo-Saxon system and in kilocalories / (hour x meter x kelvin) in the technical system.

Thermal Conductivity