The mixing of the culture medium in a photobioreactor (PBR) is very important to enhance the cultivation of microalgae since it ensures that microalgae cells can access nutrients and light radiation. In this study, a numerical model of hydrodynamic conditions was developed to investigate the mixing of the culture medium in a hybrid tubular photobioreactor under various operating conditions. The movements of microalgae cells in transparent tubes was simulated. The motion of the cells was

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... ed into a mechanistic model, to simulate the influence of operating parameters on the distribution of light in the culture medium and, consequently, on the production of microalgae. According to the developed multi-physical model, when the flow rate of the culture medium increases, more intensive mixing takes place in the transparent area of hybrid tubular PBR, and microalgal cells are more often exposed to light radiation. Intensification of mixing showed an increase in microalgal biomass production. However, the increase in production was very low because the concentration of microalgal biomass in the culture medium was generally low and therefore the penetration of incident light into the culture medium was not limited.