Abstract
Microalgae can be raw materials for the production of clean energy and have great potential for development. The design of the microalgal photobioreactor (PBR) affects the mixing of the algal suspension and the utilization efficiency of the light energy, thereby affecting the high-efficiency cultivation of the microalgae. In this study, a spiral rib structure was introduced into a tubular microalgal PBR to improve the mixing performance and the light utilization efficiency. The number of spiral ribs, the inclination angle, and the velocity of the algal suspension were optimized for single-sided and double-sided parallel light illuminations with the same total incident light intensity. Next, the optimization results under the two illumination modes were compared. The results showed that the double-sided illumination did not increase the average light/dark (L/D) cycle frequency of the microalgae particles, but it reduced the efficiency of the L/D cycle enhancement. This outcome was analyzed from the point of view of the relative position between the L/D boundary and the vortex in the flow field. Finally, a method to increase the average L/D cycle frequency was proposed and validated. In this method, the relative position between the L/D boundary and the vortex was adjusted so that the L/D boundary passed through the central region of the vortex. This method can also be applied to the design of other types of PBRs to increase the average L/D cycle frequency.
Highlights
IntroductionEnergy and environmental issues are a serious concern in the contemporary world
Energy and environmental issues are a serious concern in the contemporary world.The consumption of conventional fossil fuels has brought air pollution, and an impending energy crisis
The results showed that the L/D cycle frequency of the particles obtained in the tube with the helical mixer was 3–25 Hz, which was a significant increase compared to that obtained in a tube without mixers (0.2–3 Hz)
Summary
Energy and environmental issues are a serious concern in the contemporary world. The consumption of conventional fossil fuels has brought air pollution, and an impending energy crisis. Microalgae are coming into view because of their vast potential for substituting for traditional fossil fuels. Many species of algae accumulate carbohydrates during their growth from which ethanol can be produced by the microorganisms’ anaerobic fermentation [1]. Ethanol mixed with gasoline, named biogasoline, is used as an automotive fuel. Microalgae can play a vital role; they can absorb carbon dioxide from waste gas as inorganic carbon and inorganic substances from contaminated water as nutrients [5], which would relieve green-house gas emission and water pollution to some degree
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