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The thermal conductivity of a material is a measure of its ability to conduct heat.It is commonly denoted by , , or and is measured in W·m −1 ·K −1.. Heat transfer occurs at a lower rate in materials of low thermal conductivity than in materials of high thermal conductivity.
In thermal conductivity, k is defined as "the quantity of heat, Q, transmitted in time (t) through a thickness (L), in a direction normal to a surface of area (A), due to a temperature difference (ΔT) [...]". Thermal conductivity is a material property that is primarily dependent on the medium's phase, temperature, density, and molecular bonding.
A 2008 review paper written by Philips researcher Clemens J. M. Lasance notes that: "Although there is an analogy between heat flow by conduction (Fourier's law) and the flow of an electric current (Ohm’s law), the corresponding physical properties of thermal conductivity and electrical conductivity conspire to make the behavior of heat flow ...
These thermal greases have low electrical conductivity and their volume resistivities are 1.5⋅10 15, 1.8⋅10 11, and 9.9⋅10 9 Ω⋅cm for 860, 8616 and 8617 respectively. The thermal grease 860 is a silicone oil with a Zinc Oxide filler and 8616 and 8617 are synthetic oils with various fillers including Aluminum Oxide and Boron Nitride.
The thermal conductivity is a characteristic of the particular material. Values of thermal conductivities for various materials are listed in the list of thermal conductivities . As mentioned earlier in the article the convection heat transfer coefficient for each stream depends on the type of fluid, flow properties and temperature properties.
Thermal conductivity depends on the material and for fluids, its temperature and pressure. For comparison purposes, conductivity under standard conditions (20 °C at 1 atm) is commonly used. For some materials, thermal conductivity may also depend upon the direction of heat transfer.
Thermal contact resistance is significant and may dominate for good heat conductors such as metals but can be neglected for poor heat conductors such as insulators. [2] Thermal contact conductance is an important factor in a variety of applications, largely because many physical systems contain a mechanical combination of two materials.
For Thermal conductance see: Thermal contact conductance; Thermal conduction; Thermal conductivity; List of thermal conductivities; Thermal conductance and resistance