ENERGY-SAVING IN CHAOTIC LAMINAR MIXING

Chaotic mixing in laminar flows at high Schmidt numbers is considered: the time taken for molecular diffusion to erase the concentration gra dient created by advection is estimated. The energy dissipated during mixing in a Stokes flow is calculated, and compared with that for a tu rbulent flow. It is shown that, at high Schmidt numbers, laminar mixin g is more energy-efficient than turbulent mixing. A parameter is then introduced that takes into account both the time spent in mixing and t he energy dissipated during this time: in fact, it is the product of t ime taken and energy dissipated. Again, at high Schmidt numbers, a Sto kes flow is shown to be more efficient even when judged by this parame ter. (C) 1997 Elsevier Science Ltd.