Author(s)Pekeris, G. L.
RAREFIED GAS DYNAMICS
MEAN FREE PATH
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AbstractA study was made of the dispersion and attenuation of sound in a monoatomic gas with a density for which the mean free path is comparable to or exceeds the wave length of sound. The data on the propagation of sound in He at pressures of 1 mm and less required the solution of Boltzmann's complete transfer equation. Secular determinants of order 5, 8, 12, and 20 were evaluated in an effort to determine the phase velocity and attenuation coefficient. For each determinant order, the propagation constants were solved from the polynomial of the same degree representing the determinant; the polynomial roots were determined numerically. The results appeared to show that with a determinant of order 20, the computed values for the propagation constants is reliable for R greater than about 3, where R is proportional to lambda/L, the ratio of the wave length of sound to the mean free path. Graphical results are included for the determinant of order 8. Calculations are in progress for the determinant of order 30.