Introduction - The second coefficient of viscosity: a brief review of fundamentals

Abstract

The generally assumed relationship between the principal stresses and the principal rates of deformation, at any point of any homogeneous fluid, introduces, as empirical constants, the first ( μ , shear) and second ( μ' , dilatational) coefficients of viscosity. The assumption receives justification only if it can be verified experimentally or if it leads to theoretical conclusions which can be shown to agree with the results of experiments. The relevant experimental evidence seems to come from the phenomena of the absorption of sound energy in so-called ‘liquids’, and from those of acoustical streaming. One important conclusion is that there should be no general correlation between the values of μ and μ' ; the theoretical conclusion that μ'/μ should be equal to - 2/3 has some validity only when referring to ideal monatomic gases. The ideas put forward by Tisza (1942), Eckart (1948), and the experiments of Liebermann (1949) seem to have made a notable advance, but a completely satisfactory explanation of the phenomena is still lacking.