ABSTRACT
Fourier’s Law gives a mathematical expression of the observed physical fact that the heat transfer by conduction across a plane is proportional to the area of the cross section of the plane, normal to which the heat flows and the gradient of temperature in the direction of heat flow. The concept of relaxation time was introduced into the process of modifying the Fourier heat conduction equation. The simplest definition of the thermal conductivity of a heat transfer medium is the macroscopic definition from Fourier’s law of heat conduction. The fundamental approaches to the problem of heat conduction have resulted in different models developed for thermal conductivity of solids and fluids, and also of mixtures and suspensions of solids in liquids. A simple expression for thermal conductivity is obtained when the phenomenon of conduction of heat in gases is considered based on the kinetic theory.
