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thermal diffusivity[′thər·məl ‚di·fyü′siv·əd·ē]
a physical parameter of a substance that characterizes the rate of change of its temperature in transient thermal processes. Thermal diffusivity is a measure of the thermal-inertia properties of a substance. It is numerically equal to the ratio of the substance’s thermal conductivity and the product of its specific heat (at constant pressure) and density. Thermal diffusivity is expressed in m2/sec.