Thermal diffusivity measurement of papers by an ac Joule heating method

The thermal diffusivity (α) of paper, a porous and thin material, was determined by an ac Joule heating method developed in our laboratory. With this technique the thermal diffusivity of paper was obtained directly with high reproducibility without the need for special preparations, such as the black coating, required in conventional methods. The thermal diffusivity (α) of paper was obtained as a function of temperature and the apparent density (ρ). The apparent thermal conductivity (λ) of paper was calculated from α, ρ, and the heat capacity at constant pressure (Cp): α decreased with increasing apparent density, but λ did not show a density dependence.