Microscopic flows of suspensions of the green non-motile Chlorella micro-alga at various volume fractions: applications to intensified photo bio reactors

TL;DR

This study investigates the flow behaviors of Chlorella micro-algae suspensions in microchannels across different concentrations, revealing distinct regimes including Newtonian, shear thinning with slip, and yield stress-like flow, with implications for bio-reactor design.

Contribution

It provides a detailed experimental characterization of flow regimes of Chlorella suspensions at various volume fractions, highlighting the transition from Newtonian to complex non-Newtonian behaviors.

Findings

Low volume fractions exhibit Newtonian, Poiseuille-like flow with no slip.

Intermediate fractions show shear thinning with wall slip.

High fractions display yield stress behavior with a central solid plug.

Abstract

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.