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What is thermal conductivity?

What is thermal conductivity?

Thermal conductivity refers to the ability of a given material to conduct/transfer heat. It is generally denoted by the symbol ‘k’ but can also be denoted by ‘λ’ and ‘κ’. The reciprocal of this quantity is known as thermal resistivity. Materials with high thermal conductivity are used in heat sinks whereas materials with low values of λ are used as thermal insulators.

Fourier’s law of thermal conduction (also known as the law of heat conduction) states that the rate at which heat is transferred through a material is proportional to the negative of the temperature gradient and is also proportional to the area through which the heat flows.

The heat transfer characteristics of a solid material are measured by a property called the thermal conductivity, k (or λ), measured in W/m.K. It is a measure of a substance’s ability to transfer heat through a material by conduction. Note that Fourier’s law applies for all matter, regardless of its state (solid, liquid, or gas), therefore, it is also defined for liquids and gases.

The thermal conductivity of most liquids and solids varies with temperature. For vapors, it also depends upon pressure.

Effect of Temperature on Thermal Conductivity

Temperature affects the thermal conductivities of metals and non-metals differently.

Non-Metals

The thermal conductivities of non-metals are primarily attributed to lattice vibrations.

The mean free path of the phonons does not reduce significantly when the temperatures are high, implying that the thermal conductivity of non-metals does not show significant change at higher temperatures.

When the temperature is decreased to a point below the Debye temperature, the heat conductivity of a non-metal decreases along with its heat capacity. The crosslinked pe foam  is a kind of plastic foam, which has minimum Thermal Conductivity of 0.039 W/m.K, if you want to information on the TDS, welcome to contact Meishuo by e-mail: info@msfoam.com, Tel: +89-572-2691805.

Metals

The heat conductivity of metals is attributed to the presence of free electrons. It is somewhat proportional to the product of the absolute temperature and the electrical conductivity, as per the Wiedemann-Franz law.

With an increase in temperature, the electrical conductivity of a pure metal decreases.

This implies that the thermal conductivity of the pure metal shows little variance with an increase in temperature. However, a sharp decrease is observed when temperatures approach 0K.

Alloys of metals do not show significant changes in electrical conductivity when the temperature is increased, implying that their heat conductivities increase with the increase in temperature.

The peak value of heat conductivity in many pure metals can be found at temperatures ranging from 2K to 10K.

Besides, heat conductivity (K-value) is also have an equation with R value, as follows:

R = 1/C = L/K 

High conductivity, K, indicates rapid heat flow, and low conductivity indicates low heat flow. Thicker pieces of the same material cause heat to flow more slowly than thin pieces. So actual thermal performance depends on both the conductivity and the thickness of the material. A piece of material with a conductivity K and thickness L has a conductance of C = K/L, which indicates how well heat can flow through a specific piece of that material such as a wall. In buildings, you are often concerned with stopping heat flow, or insulating.

 

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Post time: Sep-02-2021