Effect of Incomplete Accommodation on the Slip Coefficient

摘要

The sensitivity of the value of the slip coefficient obtained from different models of the wall boundary condition was determined by a kinetic theory analysis of the problem of uniform shear flow (Kramer's problem). Solutions were obtained for two models of the wall boundary condition. The first model is that of Maxwell, in which it is assumed that a fixed fraction of the incident particles reflects diffusely and the remainder reflects specularly. The second model is a special case of a more general model previously developed by the author to account for the fact that the nature of the reflection process depends on the velocity of the impinging particle. These solutions were used for determination of the variation of the slip coefficient with the gas-surface interaction parameters. At a fixed value of the tangential momentum accommodation coefficient, the two models may yield significantly different values of the slip coefficient. It is found that the slip coefficient corresponding to the new model is always greater than or equal to the value corresponding to Maxwell's model. The two values differ by a factor of as much as 8/pi at small values of the accommodation coefficients. (Author)