The thermal characteristic length, usually represented by letter
, is a parameter used to describe the
thermal effects at medium and high acoustical frequencies. This
parameter has been introduced by Champoux and Allard [CA91] on
the basis of Johnson, Koplik and Dashen work [JKD87]
related to viscous effects.
Schematic representation of a pore. The thermal characteristic length, controlling the thermal effects at medium and high acoustical frequencies is related to the size of the pores.
The thermal characteristic length can be estimated from standing wave tube measurements or ultrasound techniques.
[CA91] Champoux Y. and Allard J.-F.,
Dynamic tortuosity and bulk modulus in air-saturated porous media,
J. Appl. Phys., 70, 1991, pp. 1975-1979
[JKD87] Johnson D. L., Koplik J. and Dashen R., Theory of dynamic permeability and tortuosity in fluid-saturated porous media, J. Fluid Mech., 176, 1987, pp. 379-402