Comment on Cercignani’s second-order slip coefficient

Abstract
Cercignani’s second-order slip model has been neglected over the years, perhaps due to Sreekanth’s claim that it cannot fit his experimental data. In this paper we show that Sreekanth’s claim was based on an incorrect interpretation of this model. We also show that Cercignani’s second-order slip model, when modified and used appropriately, is in good agreement with solutions of the Boltzmann equation for a hard-sphere gas for a wide range of rarefaction. Given its simplicity, we expect this model to be a valuable tool for describing isothermal micro- and nanoscale flows to the extent that the hard-sphere approximation is appropriate.