  An experimental study of flows of the green non-motile Chlorella micro-alga
in a plane microchannel is presented. Depending on the value of the cell volume
fraction, three distinct flow regimes are observed. For low values of the cell
volume fraction a Newtonian flow regime characterised by a Poiseuille like flow
field, absence of wall slip and hydrodynamic reversibility of the flow states
is observed. For intermediate values of the cell volume fraction, the flow
profiles are consistent with a Poiseuille flow of a shear thinning fluid in the
presence of slip at the channel's wall. For even larger cell volume fractions,
a yield stress like behaviour manifested through the presence of a central
solid plug is observed. Except for the Newtonian flow regime, a strong
hydrodynamic irreversibility of the flow and wall slip are found. The
calculation of the wall shear rate and wall stress based on the measured flow
fields allows one to identify the mechanisms of wall slip observed in the shear
thinning and yield stress regimes.
