Complex particle trajectories and transport in stationary and periodic convective flows

Preliminary results from experimental and numerical studies of transport in two-dimensional Rayleigh-Benard convection are presented. Two regimes are identified: a diffusion-limited regime for time-independent flows; and an advection-dominated regime for time-periodic flows, in which impurity trajectories are chaotic, with adjacent tracer particles separating exponentially as a function of time. Experimental measurements of transport rates as a function of the velocity of the flow are made for time-independent flows and are compared with theoretical predictions. Numerical studies of particle trajectories in time-periodic flows show evidence of chaotic behavior.