The bulk viscosity coefficient of a liquid

A brief review of the available literature on the bulk viscosity in liquids is given. This quantity first appeared in the equations of hydrodynamics and is closely related to the second viscosity coefficient (η′s). The Stokes relation η′s + 2 3ηs = 0, where ηs is the ordinary shear (or 1st) viscosity coefficient, is valid only for monatomic substances. The first and second viscosity coefficients are analogous to the Lame's constants in elasticity. Some of the existing theories of bulk viscosity are considered. The relation of bulk viscosity to absorption and dispersion of ultrasonic waves is discussed. Possible extension of one of the present theories to the case of resonance absorption of an ultrasonic wave is also considered. Some important experimental methods for the determination of this quantity are discussed. The role of bulk viscosity in other branches of science is also briefly considered. It is pointed out that the bulk viscosity plays an important role not only in the study of gases and liquids but also in the study of solids. © 1970.