What Does Thermal Conductivity Mean?
Thermal conductivity is a property of a material that determines the rate at which it can transfer heat. Each material's thermal conductivity is determined by a constant, λ, calculated as:
λ = (Q x L) / (A x t x ΔT)
where Q is heat, L is the thickness of the surface, A is the surface area, t is time, and ΔT is the difference in temperature.
A material's thermal conductivity is a fundamental property. Those materials with high thermal conductivity will transfer heat rapidly, either by receiving heat from a hotter material or by giving heat to a colder material. On the contrary, materials with low thermal conductivity act as thermal insulators, preventing the transfer of heat.
As corrosion is a temperature dependent process, controlling heat transfer is an important design factor of installations. Choice of metal, alloy and corresponding coating materials affect the ability to transfer heat based on each material's thermal conductivity.
Corrosionpedia Explains Thermal Conductivity
Conduction of thermal energy works at the interface between two surfaces, where the higher temperature side transfers energy and heats up the lower temperature side. At a molecular level, the molecules transfer this energy through collisions at the interface. The thermal conductivity of the material is determined by how easily and what mechanisms are available to transfer the energy through the material.
One mechanism of heat transfer through a material is through vibrations. The atoms of a solid material form a lattice and vibrations, known as phonons, propagate through the material by transferring vibrational energy to neighboring atoms. This mechanism is the primary thermal conductance mechanism in non-metallic materials.
For most metallic materials, an additional mechanism for heat transfer is available due to the material's free electrons. This mechanism is related to the electronic conductance of these materials and the ease of which electrons can traverse through the material's conductance band. As such, materials with high electrical conductivity also have high thermal conductivity.
At the two ends of the thermal conductivity scale, there are thermal insulators and heat sinks with low and high thermal conductivities, respectively. Insulators are used to protect against heat transfer, such as coating insulators on materials subjected to extremely high temperature applications or simply to prevent water from freezing inside pipes under cold conditions. Heat sinks, on the other hand, are useful for temperature control and to prevent equipment from becoming too hot or too cold.
In terms of temperature control, the property of thermal conductivity is an important consideration for metal parts of a facility. As corrosion prevention is also a major consideration, the thermal conductivity of protective barriers and coatings must be evaluated. Certain choices regarding corrosion prevention may in turn affect temperature control and vice versa.