Mixing and turbulence in floating flexible photobioreactors.

Abstract

Renewable energy initiatives aim to advance global efforts toward a sustainable bioeconomy. The power generation industry is the most crucial sector requiring strategic planning to achieve economic and environmental sustainability. Biodiesel production utilising microalgae as a feedstock yields a ± 400% larger production range compared to traditional feedstocks. Floating flexible photobioreactors (FPBs) aim to provide largescale microalgae enclosures and promote biofuel production's commercial application. FPBs are placed off-shore, where they naturally accelerate microalgae growth by harnessing wave energy, sunlight, waste carbon dioxide and wastewater discharge (as a nutrient source). Microalgae production requires explicit physical and chemical conditions to achieve optimal growth rates. In this study, a physical FPB model is constructed within a laboratory wave flume where the change in the internal fluid motion within the FPB is observed under an idealised wave pressure constriction. Under the influence of an idealised wave, the flexible tube experiences a reduction and expansion in its crosssectional area, which deforms the internal fluid flow. The fluid’s flow structure is analysed using particle image velocimetry (PIV). PIVlab was used to analyse the data. The fluid moves backwards (or towards constriction) when placed under direct tube constriction; however, under unrestricted tube expansion, the fluid is propelled forward in the original direction of the idealised wave, in the form of a bulge wave. Relative to the constriction, the fluid moves negatively on the left-hand side of the peak and positively on the righthand side. Regions of strong shear in which there was a rapid change in the velocity were identified as potential mixing zones.