Apparent thermal diffusivity is measured by the flow method (monotonic two-side heating of the plate) described in ASTM STP 1320 and ASTM STP 1426. Apparent thermal diffusivity is determined by measuring the average temperature difference between thermocouples placed near two surfaces of the plate and in the center. Additional thermocouples (for estimation of errors associated with the non-dimensional temperature field) can be arranged near the other surfaces of the specimen. Solution of Fourier equations at heating velocity close to constant gives the simple formula for apparent thermal diffusivity.
In addition, testing can be performed according to modified method (for semitransparent materials) described in ASTM STP 1426.