Simulated cell trajectories in a stratified gas–liquid flow tubular photobioreactor

Abstract

The fluid dynamic environment within a photobioreactor is critical for performance as it controls mass transfer of photosynthetic gases (CO 2 and O 2 ) and the mixing environment of the algal culture. At a cellular level, light fluctuation will occur when cells move between the "light", well-illuminated volume of the culture near the light source and the "dark", self-shaded zone of the culture. Controlled light/dark frequency may increase the light to biomass yield and prevent photoinhibition. Knowledge of cell trajectories within the reactor is therefore important to optimize culture performance. This study examines the cell trajectories and light/dark frequencies in a stratified gas-liquid flow tubular photobioreactor. Commercially available computational fluid dynamics software, ANSYS Fluent, was used to investigate cell trajectories within the half-full solar receivers at different liquid velocities and reactor tube diameters. In the standard configuration 96-mm solar receiver tube, the light/ dark cycle frequencies ranged from 0.104 to 0.612 Hz over the liquid velocity range of 0.1 to 1 m s −1 . In comparison, the smaller diameter 48-and 24-mm tubes exhibit higher light/dark frequencies, 0.219 to 1.30 Hz and 0.486 to 2.67 Hz, respectively.

Light/dark cycle enhancement and energy consumption of tubular microalgal photobioreactors with discrete double inclined ribs

“…Cells in the particle tracking model are usually assumed to be inert spheres (Pruvost et al 2008;Gao et al 2017), which are similar to the tracer used in particle tracking experiments conducted by Luo and AlDahhan (2004) and Pruvost et al (2000). In this work, cells are assumed to be inert particles with a uniform diameter (10 µm) and density (1000 kg m −3 ) (Moberg et al 2012;Zhang et al 2015). The virtual mass force and Saffman's lift force are neglected (Moberg et al 2012;.…”

“…In this work, cells are assumed to be inert particles with a uniform diameter (10 µm) and density (1000 kg m −3 ) (Moberg et al 2012;Zhang et al 2015). The virtual mass force and Saffman's lift force are neglected (Moberg et al 2012;. Tube surface is a reflective surface and the outlet is an escape one.…”

CFD simulation for reduced energy costs in tubular photobioreactors using wall turbulence promoters

“…This function is evaluated by using an external Matlab function. The discrete random walk is used in literature as a way to approach the chaotic behaviour of turbulent fluid dynamics [24]. It is an empiric relationship to evaluate what happens in different scenarios.…”

“…Particle tracking is used to characterize microalgae roaming in a turbulent environment. A discrete random walk model is applied to simulate the chaotic effects of turbulence on the mixing and particle path [24] The mixing behaviour can be analysed by methods used in signal processing and control. The first option is to regard periodicity of the particle trajectories, which is expressed by the power spectrum derived from the Fourier transform.…”

Outdoor production of microalgae

“…When comparing the different systems it is important to note that configuration and mixing are completely different [57,79,80]. Slower mixing along the light gradient in the ORP therefore could explain the bigger impact of high biomass concentration on productivity in comparison to the VT and HT.…”