Thermal conductivity, also called heat conduction, is the flow of energy from something of a higher temperature to something of a lower temperature. It is different from electrical conductivity, which deals with electrical currents. Several factors affect thermal conductivity and the rate that energy is transferred. As the Physics Info website points out, the flow is not measured by how much energy is transferred, but by the rate it is transferred.
The kind of material being used in thermal conductivity can affect the rate of energy flowing between the two regions. The greater the conductivity of the material, the faster the energy flows. According to the Physics Hypertextbook, the material with the greatest conductivity is helium II, a superfluid form of liquid helium, which exists only at very low temperatures. Other materials with high conductivity are diamonds, graphite, silver, copper and gold. Liquids have low conductivity levels and gases even lower.
The length of the material the energy must flow through can affect the rate at which it flows. The shorter the length, the faster it will flow. The thermal conductivity may continue to increase even when the length is increased--it may just increase at a slower pace than it had before.
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Thermal conductivity varies depending on temperature. Depending on the material of the conductor, as the temperature rises the thermal conductivity of the material often rises as well, increasing the flow of energy.
The cross-section type, such as round, C- and hollow-shaped, can affect the thermal conductivity, according to the Journal of Materials Science. The article reports that the thermal diffusivity factor of C- and hollow-shaped carbon fiber-reinforced composites showed about two times higher values than those of round-type ones.