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### Thermal conductivity refers to the ability of a given material to conduct/transfer heat.

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 differential form of this law can be expressed through the following equation:

Where ∇T refers to the temperature gradient, q denotes the thermal flux or heat flux, and k refers to the thermal conductivity of the material in question.

An illustration describing the thermal conductivity of a material in terms of the flow of heat through it is provided above. In this example, Temperature 1 is greater than Temperature 2 . Therefore, the thermal conductivity can be obtained via the following equation:

Heat Flux = -k * (Temperature 2 – Temperature 1 )/Thickness

Every substance has its own capacity to conduct heat. The thermal conductivity of a material is described by the following formula:

There exist several methods of measuring the thermal conductivities of materials. These methods are broadly classified into two types of techniques – transient and steady-state techniques.

Thus, there exist various methods of measuring the thermal conductivity of materials, each with their own advantages and disadvantages. It is important to note that it is easier to experimentally study the thermal properties of solids when compared to fluids.

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

Temperature is not the only factor which causes a variance in thermal conductivity of a material. Some other important factors that influence the heat conductivity of substances are tabulated below.

Thus, the definition, SI unit, and measurement of thermal conductivity is briefly discussed in this article along with the effects of some factors on it. To learn more about this concept and other important concepts related to conductance, such as electrolytic conductance , register with StudySolver and download the mobile application on your smartphone.

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When the phase of a material changes, an abrupt change in its heat conductivity may arise. For example, the thermal conductivity of ice changes from 2.18 Wm -1 K -1 to 0.56 Wm -1 K -1 when it melts into a liquid phase

The differences in the coupling of phonons along a specific crystal axis causes some substances to exhibit different values of thermal conductivity along different crystal axes. The presence of thermal anisotropy implies that the direction in which the heat flows may not be the same as the temperature gradients direction.

The electrical conductivity of the material

The Wiedemann-Franz law that provides a relation between electrical conductivity and thermal conductivity is only applicable to metals. The heat conductivity of non-metals is relatively unaffected by their electrical conductivities.

The change in the thermal conductivity of a conductor when it is placed in a magnetic field is described by the Maggi-Righi-Leduc effect. The development of an orthogonal temperature gradient is observed when magnetic fields are applied.

The effect of isotopic purity on heat conductivity can be observed in the following example: the thermal conductivity of type IIa diamond (98.9% concentration of carbon-12 isotope) is 10000 Wm -1 K -1 whereas that of 99.9% enriched diamond is 41,000 Wm -1 K -1