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Through Euler/Euler large eddy simulation (LES) modeling, it is demonstrated that turbulent dispersion of bubbles can effectively indicate the impact of turbulent eddies on the bubble dynamics, i.e., the bubble oscillation behavior. This finding builds on previous work using the Euler/Lagrange LES modeling approach and leads to a significant improvement in predicting bubble lateral dispersion. Spatially filtered terms were proposed for the subgrid‐scale (SGS) turbulent dispersion and added mass stress force models, with a modification made to the SGS eddy viscosity to reflect bubble turbulent dispersion and oscillations. The proposed model substantially improves the prediction of bubble volume fraction distribution, bubble and liquid phase velocity profiles, the turbulent kinetic energy spectrum, and mass transfer. [ABSTRACT FROM AUTHOR]

• Considering the effects of bubble induced turbulence in the bubble breakage model. • κ −3 scaling has been identified on bubble induced turbulence kinetic energy spectrum. • Mean turbulent velocity and number density of turbulent eddies have been modified. • Influence of characteristic length scale on daughter bubble PDF is illustrated. • Effect of eddy-bubble contact on mass transfer in the bubble column is demonstrated. A quantitative description of the interaction between the turbulence eddies and bubble groups is crucial for the prediction of the bubble size distribution in bubble columns when adopting the population balance model (PBM) to estimate the heat and mass transfer across the interfaces between bubbles and carrier liquid. The majority of breakage kernels that are currently adopted focus on the shear turbulence in the liquid phase and model the kinetic energy contained in the arrival eddies that hit the bubbles by using the classical single-phase turbulence Kolmogorov −5/3 scaling law. In bubble columns, eddies that collide with bubbles and cause the bubble breakage are mainly generated by bubble-induced turbulence (BIT). The present work focuses on the influence of κ −3 scaling of the bubble-induced turbulence energy spectrum on the bubble breakage due to the eddy-bubble collision in bubble columns. A modified breakage model accounting for the bubble-induced turbulence is proposed. The proposed breakage model considers the mean turbulent velocity of eddies under the influence of bubble-induced turbulence and the characteristic wavenumber/length scale that corresponds to BIT. A comparison of the simulation results with the experimental data clearly demonstrate that the modified breakage model appropriately describes the bubble breakage events occurring under the influence of bubble-induced turbulence in bubble columns. It is also shown that the interaction of bubbles with the bubble-induced turbulence eddies has an impact on prediction of the mass transfer in bubble column flows. [ABSTRACT FROM AUTHOR]

CO 2 absorption by a confined free film has been investigated using the CFD approach. Particular attention focuses on the relationship between mass transfer and flow behaviour of the confined free film. Simulation results show that the average K L value grows 26.9% for the open window region and 17.4% for the lower-wall region, respectively, in comparison to the values in the upper-wall region, and the average K L value of confined free film along the flow direction is about 19.2% higher than the value of wall-bounded film, which affirms that the use of an open window can significantly enhance mass transfer performance and such effect also has impact on the entire regions. It was revealed that there exist two types of vortices inside the film, inner vortices and interfacial vortices. In addition, a correlation coefficient R Ωc is proposed to provide a quantitative measure to characterise the relationship between the local mass concentration profile and vorticity distribution of confined free film. Simulation shows that the average value of R Ωc is 0.93, indicating that the two parameters are highly correlated. Furthermore, the cause of lower correlation coefficient value is discussed. [ABSTRACT FROM AUTHOR]

• E-E LES modelling on three CO 2 chemisorption cases in bubble columns was conducted. • Modified SGS turbulent dispersion (TDF) and added mass stress (AMS) models proposed. • Impacts of the SGS-TDF and SGS-AMS terms on the interfacial mass transfer were assessed. • Scaling laws of turbulent kinetic energy and species concentration spectra were discussed. It has been generally recognised that the turbulent dispersion force plays an important role in interphase momentum transfer. However, the effect of the added mass stress on the momentum and mass transfer in bubble column bubbly flow has not been addressed appropriately. As the turbulent eddies in the surroundings of bubbles interact strongly with the rising bubbles in bubble column bubbly flow, such interactions will bring out the change of interfacial areas between the bubbles and carrier fluid, consequently leading to changes in the interfacial mass transfer. When employing large eddy simulation for modelling bubbly flow coupled with the chemisorption process, the SGS filtered velocity fluctuations of liquid phase can be interpreted as the turbulent eddies that continuously hit the surfaces of bubbles, causing bubble deformation and the variation of bubble interfacial areas, which give rise to the turbulent dispersion and added mass stress forces. The present study will demonstrate through Euler/Euler large-eddy simulations (LES) modelling that by considering the turbulent dispersion force (SGS-TDF) and added mass stress (SGS-AMS), the bubble dynamics and mass transfer under the chemisorption conditions can be better indicated, which leads to remarkable improvements in the prediction of bubble lateral dispersion and the interfacial mass transfer. The turbulent dispersion and added mass stress related to the spatially filtering were proposed with a modification on SGS eddy viscosity to reflect turbulent dispersion due to bubble-induced turbulence. A comprehensive assessment of the effects of these additional filtered stress terms on the time-averaged velocity and bubble volume fraction profiles, flow patterns, mass transfer and the pH variation during CO 2 chemisorption and the turbulent kinetic energy and species concentration spectra was conducted. [ABSTRACT FROM AUTHOR]

The process of CO2 absorption in many currently used chemical devices can be typically characterised and analysed by mass transfer across a thin falling film gas-liquid interface. There is still a lack of general predictability of the transfer quantity based on the basic hydrodynamic parameters involved in such mass transfer processes, and certain important phenomena associated with the transfer still remain unexplained. A novel concept that utilises the correlation between the vorticity neighbouring the falling film gas-liquid interface and the gas concentration to characterise CO2 absorption mass transfer by the falling film is proposed in this work. Numerical simulations using a volume of fluid (VOF) approach were performed for a vertical falling film arrangement. The wave hydrodynamics and the associated mass transfer are discussed, and the numerical results are compared with the existing experimental empirical relationships. In particular, the mass transfer across the falling film interface is interpreted as the passive scalar entrapment and entrainment by the interfacial vortices. The numerical simulation clearly indicates that two types of vortices exist: wall-bounded vortices associated with primary shear in the falling film and interfacial vortices associated with weaker shear in the vicinity of the interface. The numerical simulation reveals that mass transfer across the falling film is highly correlated with the interfacial vorticity Ω i, thus indicating the use of Ω ¯ is able to characterise the mass transfer across the falling film gas-liquid interface. [ABSTRACT FROM AUTHOR]

• Shear turbulence generated in a turbulent swirling Rankine vortex flow reactor. • Damkӧhler number Da describing particle synthesis strongly correlated with the ReT. • Mass transfer of synthesis enhanced by shear turbulence and ultrasound irradiation. The mass transfer in the shear controllable synthesis process of nano-sized particles using a swirling vortex flow reactor is investigated. This type of a reactor is able to generate a strong 'Rankine vortex-like' flow with a great shear gradient in the radial direction, trapping the synthesised aggregated nano-particles into the vortex core to form aggregation. The aggregated particles are further agglomerated to form larger particles with high uniformity under the action of turbulent shear and subsequent mass transfer due to engulfment occurred in the turbulent eddies. The mass transfer is enhanced by engulfment between the slabs of the liquid streams tangentially entering into the reactor while the local shear in the turbulent eddies with the length scales down to the Kolmogorov scale shape the particles, yielding well spherical morphology and narrower size distribution. In addition, the mass transfer performance can be further improved by intensifying the local turbulent shear by applying the ultrasound to the synthesis process. The instantaneous collapse of cavitation bubbles in the vortex due to the introduction of ultrasound results in intensified micro-turbulent streaming. The particle characteristics, chemical reaction and mass transfer performance are found to be correlated with the local turbulence characteristics in the vortex. The mass transfer can be characterised using the film refresh model via the Sherwood number by considering the agglomerated particles response to the turbulent eddies. Both numerical simulation and experimental results clearly indicate the existence of the correlation in synthesis of aggregated nano-particles in swirling vortex reactor between the mass transfer and turbulence shear by using ultrasound irradiation. [ABSTRACT FROM AUTHOR]

It has been recognised that turbulence shear can be used to effectively control and affect the synthesis of micro/nano particles. The present study focuses on turbulence-assisted shear controllable synthesis of silica (SiO 2) micro/nano particles and investigates such shear controllable synthesis process using a counter axial-swirling impinging jet flow vortex flow reactor. Two counter swirling flow streams impinge in the reaction chamber to significantly intensify the local turbulence shear with the aid of ultrasound irradiation. The consequence of the turbulent shear leads to either the trapping of nano-particle nucleus into the turbulent eddies to form the aggregated micro/nana particles or the confinement of the growth of agglomerated micro/nano particles so as to form highly uniform and better morphological micro/nano particles. The experimental results have affirmed the postulation that the local turbulent shear generated by the turbulent eddies with the length scales down to the Kolmogorov length scale may directly interact with the aggregated SiO 2 micro/nano particles, influencing the particle spherical morphology and size distribution. In addition, it has been found that synthesis performance can be further improved by intensifying the local turbulent shear through the ultrasound irradiation in the synthesis process. Both CFD simulation and experimental results clearly indicate the existence of the correlation in the synthesized SiO 2 micro/nano particle characteristics with the local turbulence shear and mass transfer occurring in counter swirl impinge jet flow. [Display omitted] [ABSTRACT FROM AUTHOR]

FePO 4 (FP) particles with a mesoporous structure amalgamated by nanoscale primary crystals were controllably prepared using an ultrasound-intensified turbulence T-junction microreactor (UTISR). The use of this type of reaction system can effectively enhance the micro-mixing and remarkably improve the mass transfer and chemical reaction rates. Consequently, the synergistic effects of the impinging streams and ultrasonic irradiation on the formation of mesoporous structure of FP nanoparticles have been systematically investigated through experimental validation and CFD simulation. The results revealed that the FP particles with a mesoporous structure can be well synthesised by precisely controlling the operation parameters by applying ultrasound irradiation with the input power in the range of 0–900 W and the impinging stream volumetric flow rate in the range of 17.15–257.22 mL·min−1. The findings obtained from the experimental observation and CFD modelling has clearly indicated that there exists a strong correlation between the particle size, morphology, and the local turbulence shear. The application of ultrasonic irradiation can effectively intensify the local turbulence shear in the reactor even at low Reynolds number based on the impinging stream diameter (Re < 2000), leading to an effective reduction in the particle size (from 273.48 to 56.1 nm) and an increase in the specific surface area (from 21.97 to 114.97 m2·g−1) of FP samples. The FP irregularly-shaped particles prepared by UTISR exhibited a mesoporous structure with a particle size of 56.10 nm, a specific surface area of 114.97 m2·g−1 and a total pore adsorption volume of 0.570 cm3·g−1 when the volumetric flow rate and ultrasound power are 85.74 mL·min−1 and 600 W, respectively. [ABSTRACT FROM AUTHOR]

• Twin-liquid film flow has been observed on a spoked rotating disk reactor. • Interplay between the confined free film and wall-bounded film leads to mass transfer intensification. • The circumferential length of the opening window should be accommodated to fluid viscosity. Spoked rotating disk reactor is a common gas–liquid mass transfer equipment for highly viscous fluids. The hydrodynamics of the twin-liquid film on the disk is numerically investigated. The simulated film thickness, which agrees well with the experimental results, shows that film flow patterns shift at different rotational speeds. The alternation between the windows and spokes brings diverse film flow pattern, i.e. , twin-liquid film, where a confined free film and a wall-bounded film coexist and interplay. The twin-liquid film results in 70% thinning of the film thickness and 30% increase in the surface renewal frequency compared to the wall-bounded film. Based on the trajectory of the tracking particles, intense velocity fluctuations within the twin-liquid film can be observed. Given the pressure gradient within the opening window increasing exponentially with fluid viscosity, we suggest that the circumferential length of the open window be proportional to fluid viscosity. The results demonstrate good adaptability of the optimization strategy, which can guide the scaling-up of the spoked rotating disk reactors for highly viscous fluids. [ABSTRACT FROM AUTHOR]