Creeping Flow of a Slightly Rarefied Gas past Two Equal Touching Spheres

Steady creeping flow of a slightly rarefied gas past two equal touching spheres along their line of centers is investigated to an accuracy of the second order in small Knudsen number on the basis of the Boltzmann-Krook-Welander equation and the diffuse reflection of the gas molecules on the surface of the two spheres. Stream lines of the flow are depicted in its hydrodynamical flow field outside the Knudsen layer adjacent to their surface. The drag on the pair of equal touching spheres is also calculated to the same accuracy of approximation.