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The defining equation for thermal conductivity is =, where is the heat flux, is the thermal conductivity, and is the temperature gradient. This is known as Fourier's law for heat conduction. Although commonly expressed as a scalar , the most general form of thermal conductivity is a second-rank tensor .
Thermal conductivity, frequently represented by k, is a property that relates the rate of heat loss per unit area of a material to its rate of change of temperature. Essentially, it is a value that accounts for any property of the material that could change the way it conducts heat. [ 1 ]
is the thermal diffusivity, a material-specific quantity depending on the thermal conductivity, the specific heat capacity, and the mass density. The heat equation is a consequence of Fourier's law of conduction (see heat conduction ).
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 ...
Defining equation SI unit Dimension Temperature gradient: No standard symbol K⋅m −1: ΘL −1: Thermal conduction rate, thermal current, thermal/heat flux, thermal power transfer P = / W ML 2 T −3: Thermal intensity I = / W⋅m −2
The plate distance is one centimeter, the special conductivity values were calculated from the Lasance approximation formula in The Thermal conductivity of Air at Reduced Pressures and Length Scales [28] and the primary values were taken from Weast at the normal pressure tables in the CRC handbook on page E2. [27]
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.
The thermal contact conductance coefficient, , is a property indicating the thermal conductivity, or ability to conduct heat, between two bodies in contact. The inverse of this property is termed thermal contact resistance .