Models for bulk viscosity in carbon dioxide

Abstract

Bulk viscosity in carbon dioxide is studied using the accurate kinetic theory method. Complex structure of the CO2 molecule and various channels for vibrational relaxation are taken into account while calculating the vibrational relaxation time. It is shown that in the general case, the bulk viscosity coefficient cannot be represented as a sum of independent contributions of rotational and vibrational degrees of freedom. The predicted ratio of bulk and shear viscosity coefficients does not exceed 5 for temperatures lower that 2000â...K. Thus we put in question the widely used assumption about the high ratio of bulk and shear viscosity coefficients in CO2 at low temperature.