Excess Ultrasonic Attenuation and Volume Viscosity in Liquid Methane

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Abstract
Ultrasonic attenuation in liquid methane has been measured at temperatures between 94 and 146°K with pressures to 87 kg/cm2. The measured attenuation greatly exceeds that accounted for by the dissipation due to shear viscosity and thermal conductivity. This shows a considerable need for the volume viscosity in the attenuation equation of Navier–Stokes. The excess attenuation observed is attributed to the “intrinsic” volume viscosity in liquid methane. The measured attenuation divided by the frequency squared varies from 0.605 × 10−16 cm−1 sec2 at a temperature of 94°K and pressure of 1.65 kg/cm2 to 1.90 × 10−16 cm−1 sec2 at a temperature of 145.6°K and pressure of 8.8 kg/cm2. The intrinsic volume viscosity ranges from 2.26 × 10−3 g/cm·sec to 1.88 × 10−3 g/cm·sec over the same temperature and pressure variations stated above. It is not believed that the internal degrees of freedom in methane are contributing an extra term to the measured attenuation as if by some relaxation mechanism.