2015 Volume 43 Issue 3_4 Pages 53-62
Pressure-driven flows of a phototactic microalgae suspension in a transparent circular channel illuminated from its outer side were numerically analyzed. Microalgae were modeled by active phototactic particles and the volume-fraction dependence of the suspension viscosity was expressed by the Krieger-Dougherty model. The light intensity distribution in the tube was computed from the algal density distribution based on the Lambert-Beer law. The phototactic behavior of the microalgae was described using a phototaxis function, which controls both the speed and the direction of the algae, and the algal number density distribution in the tube was calculated. The number density distribution changed with the illumination intensity according to their phototactic behavior and remarkably affected the velocity profile. Non-uniformity in apparent viscosity due to the algal distribution produced an anomalous velocity profile, in which the viscous dissipation decreased around a position where the algal density was high, resulting in a high apparent viscosity. The average velocity with a constant pressure gradient increased or decreased according to the algal distribution. The average velocity tends to increase as the position of high-algal-number-density region moves to the center side because the viscosity distribution approaches to a profile effective to suppress the increase in the total amount of the viscous dissipation.
