CHAOTIC MIXING OF IMMISCIBLE IMPURITIES IN A 2-DIMENSIONAL FLOW

Experiments compare the chaotic mixing of miscible and immiscible impu rities in a two-dimensional flow composed of a chain of alternating vo rtices. Periodic lime dependence is imposed on the system by sloshing the fluid slowly across the stationary vortices, mimicking the even os cillatory instability of Rayleigh-Benard convection. The transport of a miscible impurity is diffusive with an enhanced diffusion coefficien t D that depends on the size of ''lobes'' which are, in turn, depende nt on the oscillation amplitude. The lobes play an important role in t he transport of immiscible impurities well. In this case, the impurity is broken into a distribution of droplets, whose areas determine the nature of the transport. If the characteristic long-term droplet areas are appreciably smaller than the lobe areas, then there is long-range transport with D equal to that for the miscible case with the same f low conditions. If the droplet areas remain larger than the lobe areas , then there is no long-range transport. (C) 1998 American Institute o f Physics.