Second Viscosity Coefficient of Liquids

Abstract

It is known that the experimental value of the absorption of ultrasonic waves in most liquids is in excess of the theoretically calculated one. While attempts have been made to explain the discrepancy in different ways, a phenomenological approach is through the second viscosity coefficient. Recently Eckart has discussed the streaming set up in a liquid when a beam of ultrasonic waves passes through it, and has shown that it is dependent on both the bulk and shear viscosities. The conclusions arrived at from an experimental investigation carried out on the basis of Eckart's theory are: 1. The value of the ratio of second viscosity to shear viscosity is positive in conformity with the theory. 2. The agreement between experimental and theoretical values is closer in the case of pure liquids than in the case of solutions. For pure liquids the value of μ′, the second viscosity, appears generally to be greater than the value of μ, the shear viscosity, at ordinary pressures and temperatures. 3. The values of μ′ as obtained by experiment and as calculated from the excess sound absorption data are in fair agreement in the case of the liquids used. 4. In some solutions the two coefficients are either equal or the shear viscosity is the greater. 5. The values of μ′/μ obtained by independent workers with different methods are in fair agreement. Although the anomalous absorption of sound may be accounted for by the second viscosity coefficient, more data are necessary before a final conclusion can be drawn as regards the precise mechanism of the sound absorption.