  We report an experimental and numerical investigation to study the role of
asymmetry in the expansion-contraction of the acinar wall on the particle
transport in the acinus. We model the acinar flow feature using a T-section by
appropriately matching the dimensionless numbers to that in the acinus of
healthy human subjects. We show that asymmetry in the expansion-contraction
process (quantified by $\phi$) is required for chaotic advection. We show the
stretch and fold process leading to chaos for a range of $\phi$ and scaled
oscillation frequency $Sr$. We show a regime map in this generalize $\phi$ and
$Sr$ space and show that most mammalian lungs fall at the boundary of chaotic
regime.
