ON LAGRANGIAN CHAOS BETWEEN ELLIPTIC CYLI NDERS

A viscous fluid is introduced into the annular space between two conce ntric, confocal ellipses. The inner and outer walls can be displaced a long their circumference. A small quantity of fluorescent dye is intro duced into the fluid and deformation and mixing are studied for the ca se of periodic boundary movement. An analytical solution in elliptical coordinates has been previously derived for creeping flow conditions. Poincare sections for a given set of parameters indicate that counter -rotation leads to a more chaotic behaviour than co-rotation, this res ult is confirmed experimentally. This geometry can also be used as a h eat exchanger. By a suitable choice of the parameters, the heat transf er for steady boundary motion can be increased by more than 50% with r espect to the concentric cylinder system. If the inner and outer walls are displaced time-periodically, the heat transfer rate obtained can be more than double the rate obtained between concentric cylinders.