Numerical Simulation of Light/Dark Cycle Frequency of Microalgae Fluid in a Helical Tubular Photobioreactor for Carbon Dioxide Capture

In the present study, three-dimensional numerical simulations are conducted on hydrodynamics and light-intensity distribution of microalgae fluid flow in a helical tubular photobioreactor for CO₂ capture. The effect of incident direction of the light illumination is discussed and the light/dark cycle frequency experienced by the microalgae fluid in the cross-section of the photobioreactor is investigated. The simulation results reveal the steadily nonhorizontal and unsymmetrical Dean roll-cells of the microalgae fluid flow in the cross-section of the helical tube. The external light projecting onto the helical tubular photobioreactor from the center is a better way for microalgae cultivation. The light/dark cycle frequency of the microalgae fluid flow is calculated based on the light-intensity distribution inside the photobioreactor. The light/dark cycle frequency keeps constant for the same stream trace of the microalgae flow while varies with different flow regions. Meanwhile, the light/dark cycle frequency increases with the increase in microalgae fluid velocity. The suitable demarcation between the light and the dark zone depends on the shape and the location of the Dean roll-cells.