Side-wall gas ‘‘creep’’ and ‘‘thermal stress convection’’ in microgravity experiments on film growth by vapor transport

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Abstract
While ‘‘no-slip’’ boundary conditions and the Navier–Stokes equations of continuum fluid mechanics have served the (moderate-to-‘‘high’’ pressure) vapor transport community well until now, it is pointed out that transport conditions within highly nonisothermal ampoules (e.g., those used to grow organic solid thin films in microgravity experiments) are such that the nonisothermal side walls ‘‘drive’’ (rather than damp) the dominant convective flow, and the familiar Stokes–Fourier–Fick laws governing the molecular fluxes of momentum, energy, and (species) mass in the ‘‘continuum’’ field equations will often prove to be inadequate, even at Knudsen numbers as small as 10−3. The implications of these interesting gas kinetic phenomena under microgravity conditions, and even under ‘‘Earth-bound’’ experimental conditions, are outlined here, along with a tractable approach to their systematic treatment.