thermal conductivity

Physical

2022

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

Thermal conductivity is the property of certain materials capable of transmitting heat.

What is thermal conductivity?

Thermal conductivity is a property of certain materials capable of transmitting the heat, that is, allow the passage of the Kinetic energy of its molecules to other adjacent substances. It is an intensive magnitude, inverse to thermal resistivity (which is the resistance of certain materials to the transmission of heat through their molecules).

The explanation for this phenomenon lies in the fact that when a material heats up, its molecules increase its kinetic energy, that is, they increase its agitation. The molecules, then, are able to share that extra energy without causing movements global matter (in that it differs from the thermal convection of theliquids Ygases), this capacity being very high in the metals and in continuous bodies, generally, 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 made based on the following formula:

λ = q / grad. T

where what is the heat flux per unit of weather and area, andgrad.T is the gradient of temperature.

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

Thermal conduction methods

Conduction occurs when heat is transmitted from one body to another through contact.

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

  • Driving. It occurs when heat is transmitted from one body to another with a different temperature through mere contact, without the occurrence of a displacement of matter.
  • Convection. It occurs through the movement of particles of the substance that transmits heat, so it must always be a fluid (liquid or gas), either by natural or forced movement.
  • The radiation. It occurs when heat is transmitted between two solid of different temperatures without any contact point or solid conductor between them. The heat is transmitted in emission of electromagnetic waves to the speed of light.

Units of measurement for thermal conductivity

Thermal conduction is measured, according to International system, from the relation W / (K.m), where W are watts, K kelvin and m, meters. This unit is equivalent to Joules on meter per second per Kelvin (J / m.s.K).

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

Examples of thermal conductivity

Some examples of thermal conductivity are:

  • The steel. With a conductivity of 47 to 58 W / (K.m).
  • Water. With a conductivity of 0.58 W / (K.m).
  • The alcohol. With a conductivity of 0.16 W / (K.m).
  • The bronze. With a conductivity of 116 to 140 W / (K.m).
  • Timber. With a conductivity of 0.13 W / (K.m).
  • Titanium. With a conductivity of 21.9 W / (K.m).
  • The Mercury. With a conductivity of 83.7 W / (K.m).
  • Glycerin. With a conductivity of 0.29 W / (K.m).
  • Cork. With a conductivity of 0.03 to 0.04 W / (K.m).
  • Gold. With a conductivity of 308.2 W / (K.m).
  • The Lead. With a conductivity of 35 W / (K.m).
  • The diamond. With a conductivity of 2300 W / (K.m).
  • Glass. With a conductivity of 0.6 to 1.0 W / (K.m).
  • Lithium. With a conductivity of 301.2 W / (K.m).
  • The wet earth. With a conductivity of 0.8 W / (K.m).
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