Bulk viscosity of dilute molecular gases

Abstract

We calculate the bulk viscosity of a dilute molecular gas from a kinetic model which considers the internal degrees of freedom in a semiclassical way. Grad's method is implemented to solve the Wang Chang–Uhlenbeck–de Boer kinetic equations in a 12-moment approximation. Such a kinetic calculation allows us to obtain an expression for the bulk viscosity in the framework of generalized hydrodynamics. As a consequence we observe the role played by the temperature inhomogeneities and we give an estimation of the region in which the diffusion of excited molecules is the leading contribution to the bulk viscosity.