ABSTRACT
The parameter a was called the thermal diffusivity by Kelvin and the thermometric conductivity by Maxwell, but Kelvin's expression has been generally adopted. It measures the change in temperature that would be produced in unit volume of the substance by the quantity of heat that flows in unit time across unit area of a layer of the substance of unit thickness with unit temperature difference between its faces [3]. It is the parameter that determines the non-steady state temperature distribution in the absence of heat generation and convection and is therefore essential for transient heat flow calculations.
