The normal incidence absorption coefficient of a matrix of narrow tubes with constant cross-section

Abstract The data from a previous paper in which effective density and resistivity were calculated for various tube cross sections are summarized and used to calculate the normal incidence absorption coefficient of a matrix of uniform tubes. The results of the theory are compared with those from experiments for two of the sections, the right equilateral triangle and the square, and good agreement, for engineering purposes, is shown, over a frequency range including the low frequency Poiseuille flow regime up to the Helmholtz regime. Heat conduction effects have been included only in a simplified way, with the assumption of isothermal conditions for the whole frequency range considered.