Massachusetts Institute of Technology
Cambrige, Massachusetts, U. S. A.
In this talk we consider the interdiffusion of two mutually soluble species possessing different mass densities (In a gravity-free environment) taking place in an otherwise quiescent fluid. It will be shown that the resulting diffusional process necessarily gives rise to a convective fluid motion. In commonly occurring physical circumstances, wherein the Schmidt number, Sc (Sc = kinematic viscosity/molecular diffusivity) is large compared with unity, the resulting flow is a (transient) low Reynolds number flow -- albeit one which is ``compressible'' (I.e., not incompressible)! Some examples of this unique class of diffusion-driven flows, which are of potential interest in connection with microgravity experiments performed on orbiting satellites, are discussed. In many circumstances the resulting low Reynolds number flow will also be a potential flow, albeit one which ``compressible.'') It is pointed out that similar low Reynolds number flow phenomena can arise even in single-component systems within which temperature gradients exist, owing to the fact that the density of the fluid is temperature dependent. The Schmidt number criterion then is then replaced by the requirement that the Prandtl number Pr be large compared with unity.