Bulk viscosity of dilute monatomic gases revisited

Extensive research has been carried out in the past to estimate bulk viscosity of dense monatomic fluids; however, little attention paid same dilute gas regime. In this work, we perform precise Green-Kubo calculations molecular dynamics simulations argon gas. The investigated temperature and pressure range is 300 750 K 0.5 1.5 bar respectively. It observed that estimated $O(10^{-10})$ Pa s, which several orders magnitude smaller than other diatomic polyatomic gases, but nonetheless, not an absolute zero as typically assumed. implies Stokes' hypothesis true for gases only approximate rather sense. variation with pressures at constant temperatures also studied found be quadratic nature. obtained values are reported reduced Lennard-Jones units enable extension present results noble well. becomes independent very low densities.