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To commercialize large‐scale and high‐density microalgae cultivation, a 10L cross‐flow flat‐plate airlift photobioreactor (CFA‐PBR) was designed and amplified to two types of 40L CFA‐PBRs via different scaling‐up methods. The multiphase flow characteristics and bioreaction process of these CFA‐PBRs were studied by experiments and computational fluid dynamics (CFD) simulation. The results show that the parameters of CFA‐PBRs, such as bubble size, gas holdup, mass transfer, and photosynthetic reaction efficiency, mainly conform to the principle of geometric similarity under the same light thickness and superficial gas velocity, which is significant for large‐scale industrial applications of the efficient high‐density algae cultivation. [ABSTRACT FROM AUTHOR]

Highlights • A novel fractal tree-like photobioreactor was designed and fabricated by 3D printer. • The fractal structure design generated good performances of multiphase flow. • Fractal tree-like photobioreactors had higher efficiency of bio-reaction. • Coupling of fractal geometry and 3D printing provide a potential development for PBR. Abstract Based on the bionic fractal theory, a fractal tree-like photobioreactor (PBR) with high surface area to volume ratio is designed on the basis of bifurcation tree algorithm and manufactured via 3D printing technology. Numerical simulation and experimental results show that the fractal structure has a good flow performance and can lead to secondary flow, which is beneficial to enhance the turbulence and produce smaller bubble sizes. Chlorella culture in the fractal tree-like PBR has a higher Fv / Fm (Chlorophyll fluorescence parameter), close to 0.767, and higher efficiency of photosynthetic growth as well as CO 2 capture, compared with multitubular PBR and conventional acrylic column reactors. Therefore, the fractal tree-like PBR can improve the efficiency of light energy utilization and bioreaction. Combined with 3D printing technology, fractal PBR blazes a new trail for process intensification on the microalgae cultivation. [ABSTRACT FROM AUTHOR]

Highlights • Microbubbles can improve mass transfer and photo bio-reaction. • The scale effect between bubbles and microalgae was studied. • A multiscale bubble combination intake method was proposed. • Multiscale bubbles can provide dual-intensification function. • The multiscale bubbles method can enhance the growth efficiency of Chlorella. Abstract Based on experimental and computational fluid dynamics simulations, the scale effect between the bubbles and the algae for different sizes in the culture process were investigated in a photobioreactor column under single and combined gas intake conditions, including factors such as the bubble distribution, gas holdup and mass transfer coefficient of different scale bubbles (500 μm microbubbles and 5 mm bubbles). In general, microbubbles could improve mass transfer and photo bio-reaction. For microalgae cultures with large particle sizes or high biomass concentration, the mixing ability of microbubbles was weakened, and therefore, the culture efficiency decreased. However, this can be improved by using millimeter bubbles with the strong turbulent characteristic. Therefore, a multiscale bubble combination intake method was proposed. This method can significantly strengthen both the multiphase mixture and mass transfer processes and was beneficial to improving the growth efficiency of Chlorella. [ABSTRACT FROM AUTHOR]

• A gas-liquid bubbling flow and mass transfer CFD model was established by OpenFOAM. • The interphase force models were compared in OpenFOAM simulation. • The PBM and IATE bubble models were compared with the aid of the visual measurements. • The IATE bubble model with mass transfer was agreed with the experimental results well. A general two-phase flow and mass transfer CFD model for bubbling system was established based on OpenFOAM (open-source field operation and manipulation). The influence of each phase parameter of the Blend interface model was investigated to ensure the accuracy and stability of the simulations. The interphase force models (like drag, lift, turbulent) and multi-size bubble models (ie, the population balance equation and the interfacial area transport equation) were studied and compared with aid of the visual bubble measurements. Furthermore, the multi-size bubbling flow coupled mass transfer model was successfully verified by the experiments, which can provide a free open-source modelling method for the industrial application. [ABSTRACT FROM AUTHOR]

• A CFD model was established to describe the gas-liquid 1-hexene hydroformylation. • Simulations showed that microbubble sizes affected the reaction efficiency. • Baffles can enhance the gas holdup, mass transfer, and reaction efficiency. • A petaloid baffle was designed and simulated to achieve a good performance. Based on the micro-bubbling process as an intensification method, an experimental study on hydroformylation of 1-hexene was carried out. Effects of different total pressures, temperatures, partial pressures and substrate concentrations on the conversion rate of olefin and normal-to-iso ratio were investigated and the reaction kinetic coefficients were determined by fitting the experimental data with the model. Using the Euler two-fluid and standard k-ε turbulence model, a computational fluid dynamics model was established to describe the multi-phase flow mass transfer and reaction of olefin hydroformylation. The simulation results were in good agreement with the experimental results. Furthermore, the effects of microbubble sizes and internal components on the overall gas holdup, mass transfer rate, turbulent mixing and reaction efficiency of the multi-phase 1-hexene hydroformylation reaction system were studied, which could be applied to the process intensification and scale-up of the various multi-phase gas-liquid hydroformylation reactions. [Display omitted] [ABSTRACT FROM AUTHOR]

• The effect of micro and macro bubbles in a tree-like photobioreactor (PBR) was compared by CFD simulation and experiments. • Homogeneous dispersed flow pattern could be achieved by the microbubbles (MB). • The photosynthetic capacity and microalgae activity can be enhanced by combining the tree-like PBR with MB. • The bionic fractal structure and MB could intensify the synergistic effect of flow and light field. A bionic fractal tree-like photobioreactor (PBR) with multiscale bubbles was studied to help intensify gas–liquid mass transfer and the microalgal photosynthesis. A numerical simulation and several experiments were conducted to study the hydrodynamic characteristics of the microbubbles (MBs) and large bubbles (LBs) in the tree-like PBR. The characteristics studied included the bubble size distribution, flow pattern, gas holdup, gas–liquid slip ratio, and turbulence. The good flow characteristic of the MBs tended to generate a homogeneous dispersed flow pattern, which intensified the synergistic effect of flow and light fields based on the long residence time, large gas–liquid contact area, and even multiphase mixing in the large-area illuminated fractal reactor. As a result, the photosynthetic capacity and microalgal activity were enhanced by combining the tree-like PBR with MBs, providing a novel valuable technical solution for improving the multiphase photoreaction. [ABSTRACT FROM AUTHOR]

In order to improve the high‐density culture of microalgae, the traditional flat‐plate photobioreactors were modified with parallel baffles with different structures. The mixing characteristics of triphase flow in four types of bioreactors were investigated using the numerical simulation and experiments. The comparison shows that the results of simulations are consistent with those of experiments. The photobioreactor with ladder‐type parallel baffle could produce multiintensification functions of flow mixing, mass transfer, and bioreaction so that its integrated performances on high‐density culture are more prominent than other bioreactors. The culturing experiments were carried out in a bioreactor fed with air containing 10% CO2 at a flow rate of 10 L min−1. The results show that the growth rate of Chlorella vulgaris reaches 0.783 g L−1 d−1 with a total biomass of 7.21 g L−1 within 6 days, further achieving the efficient high‐density prolonged culture with multiperiods, which is significant for industrial applications. [ABSTRACT FROM AUTHOR]