Study of the hydrodynamics and mass transfer in a rectangular air-lift bioreactor

Process intensification of the ozone-liquid mass transfer in ultrasonic cavitation-rotational flow interaction coupled-field: Optimization and application

A study on the intensification of ozone mass transfer in rotational flow field and UC-RF coupled-field was conducted. Two important operational parameters namely liquid flow rate and ultrasonic power, were optimized with regard to the ozone mass transfer efficiency. Results showed that the mass transfer coefficient (K_La) increased with liquid flow rate (up to 14 L min^-1) and ultrasonic power (up to 1000 W). The maximum K_La value (1.0258 min^-1) was obtained with the UC-RF coupled-field. Moreover, the reinforcement of mass transfer efficiency was promoted by the rotational flow field and UC-RF coupled-field due to the increase in the ozone-liquid contact area, intensification of turbulence, acceleration of interface renewal, and extension of residence time. Ozone microbubbles rose in the reactor in a spiral manner. In addition, the microbubbles produced in the rotational flow field served as cavitation nucleus that helped to generate the cavitation effect. The effective degradation of di-butyl phthalate (DBP) confirmed that its removal was improved by the ozone-liquid mass transfer and the promotion of hydroxyl radicals (·OH) production. The synergistic effect of DBP degradation via ultrasound-enhanced ozonation was significant.

Development of modified airlift reactor (MALR) for improving oxygen transfer: optimize design and operation condition using 'design of experiment' methodology

Oxygen scarcity may significantly affect the process performance since it has low aqueous solubility and high demand by chemical and biological processes. The oxygen mass transfer is therefore necessary to enhance. This work aimed to develop the gas-liquid reactor, named Modified Airlift Reactor (MALR) for improving the oxygen transfer efficiency in terms of internal configurations and aeration parameters by equipping a vertical baffle for creating liquid circulation phenomena, and installing slanted baffles in the reactor riser to extend air-bubbles retention time and to improve their distributions. Since extremum conditions of the investigated factors may inefficient, optimum levels are required to identify. 2 ^k factorial and response surface design of Design of Experiment (DOE) methodology were applied to optimize these complex variables in terms of overall liquid mass transfer coefficient (K _L a) of clean water. As a result, the main effective factors of MALR with their optimum value are amount of baffles (N _b ∼ 3 baffles), baffle angle (α ∼ 50°), position of base area (Y _r ∼ 10 cm), open space on baffle (A _s ∼ 90 cm²), and gas flow (Qg). Increasing Qg resulted better K _L a for the studied ranges (2-18 LPM). At the optimum condition, the improvement of MALR in terms of K _L a coefficient was increased up to 97% and 28% compared to the regular bubble column and airlift reactor, respectively, at a certain gas flow without any extra energy. The correlation models of K _L a coefficient with significant variables and power consumption were constructed for future estimation purposes.

Bubbly flow in degassing cyclones and potential applications

A degassing cyclone is a separator that is widely used for the removal of bubbles and dissolved gas from liquids. Gas bubbles move toward the swirling center region in a degassing cyclone due to centrifugal force. The dissolved gas is desorbed due to a decrease in the saturated solubility resulting from the pressure gradient in the degassing cyclone. Additional carrier gas bubbles with lower partial pressure lead to mass transfer at the turbulent bubble interface. The final state of the dissolved gas and carrier gas bubble in degassing cyclones is an important issue that can be used to develop a theoretical foundation for green separation engineering. The feasible development of this technology and potential applications are discussed in this work.

Computational fluid dynamics modeling of carbon dioxide capture from air using biocatalyst in an airlift reactor

In this work, a novel three-phase and three dimensional CFD model based on the Euler-Euler approach developed for modeling the hydrodynamic, mass transfer and CO₂ fixation using microalgae in an internal loop airlift reactor with internal sparger. The main objective of this work was to development of CFD codes in order to simulate the CO₂ biofixation process under different input gas velocity during 11 days of culture time and simulate the unsteady state mass transfer based on Surface-Renewal-Stretch (SRS) model. The CFD results were compared with the our previous experimental work and they showed good agreement with a margin of less than 10%. This paper illustrated the ability of the CFD in complex process simulation such as CO₂ biofixation in the airlift reactor and provided a useful basis for further study.