Thermal Conductivity (Meaning and Explanation)

We explain what thermal conductivity is and the methods that this property uses. Also, its units of measurement and examples.

What is thermal conductivity?

The thermal conductivity is a property of certain materials capable of transmitting heat that is, allowing the kinetic energy of its molecules to pass to other adjacent substances. This is an intensive magnitude, inverse to thermal resistivity (which is the resistance of certain materials to the transmission of heat by their molecules).

The explanation for this phenomenon lies in the fact that when a material is heated, its molecules increase their kinetic energy, that is, they increase their agitation. The molecules, then, are capable of sharing that extra energy without causing global movements of the subject (in this it is distinguished from the thermal convection of liquids and gases), this capacity being very high in metals and continuous bodies, in general, and very low in polymers and other insulating materials such as fiberglass.

The thermal conductivity of a material is calculated from a coefficient (referred to as λ) and is different depending on its molecular nature. This calculation is done based on the following formula:

λ = q/deg. T

where q is the heat flow per unit time and area, and grad.T is the temperature gradient.

The higher the thermal conductivity of a material, the better a conductor of heat it will be and the smaller it is, the more insulating the material will be. Temperature, convection, electrical conductivity, and phase changes of the material all influence the thermal conductivity coefficient result.

Thermal conduction methods

There are three methods of heat transfer in nature: conduction, convection and radiation.

The driving It occurs when heat is transmitted from one body to another with a different temperature through mere contact, without a displacement of matter occurring.
Convection It is produced through the movement of particles of the substance that transmits heat, so it must always be a fluid (liquid or gas), whether due to natural or forced movement.
The radiation It occurs when heat is transmitted between two solids of different temperatures without any point of contact or a conductive solid between them. Heat is transmitted by emitting electromagnetic waves at the speed of light.

Units of measurement of thermal conductivity

Thermal conduction is measured, according to the International System, from the relationship W/(Km) where W They are watts, K kelvin and mmeters. This unit is equivalent to Joules per meter per second per Kelvin (J/msK) .

A thermal conductivity of 1 watt per meter per kelvin means that one Joule (J) of heat spreads through a material with a surface area of 1m2 and a thickness of 1m, in 1 second, when the difference between both substances is 1K.