Macroscopic transport models for rarefied gas flows: a brief review

Efficient modelling of gas microflows requires accurate, yet fast to solve, models. For finite but moderate Knudsen numbers, extended macroscopic transport equations offer an alternative to the Boltzmann equation, from which they are derived. Classical and modern approaches for the derivation of these models are reviewed, and the resulting equations are compared for their ability to describe the multitude of known rarefaction phenomena. Among the equations discussed are the Burnett and super-Burnett equations, Grad’s 13 moment equations, and the regularized 13 and 26 moment equations.