•A CFD model is developed for bubble column reactor.•The effects of superficial gas velocity is correctly predicted.•The effect of the physical properties of gas phase on bubble formation is ...introduced.•Effect of physico-chemical properties of gas & liquid phases on bubble rise velocity.
Computational fluid dynamics (CFD) has been widely used to study the hydrodynamics of bubble column reactors. However, the interaction between the different phases, which are in fact intimately linked, and the effect of their physical properties on the dynamics of the bubbles are still not well understood. In this study, the population balance equation (PBE) is coupled with CFD model to investigate the effect of liquid and gas phases physico-chemical properties on bubbles formation and the hydrodynamic characteristics in bubble column reactors. The coupling is realized using AVL FIRE v.2017 software, and the predicted results are validated against published experimental data. User subroutines are written using FORTRAN to incorporate the scalar transport equation source term for bubble break-up and coalescence. The predicted results were in reasonable agreement with experimental observations and available literature results, since the model has been able to predict the effect of gas flow rate on the gas holdup in bubble column within the range of ±7%. The simulations showed that the average gas holdup increase with the increase in superficial gas velocity and gas phase density, and decrease with the increase in liquid phase density. It was also found that Sauter mean bubble diameter increases with the increase in liquid density and decreases with the increase in gas density. Finally, the bubble rise velocity increased when water was used as a continuous phase. On the other hand, the increase in gas density causes a decrease in the bubble rise velocity.
A growing appreciation of the metabolic artifacts of cell culture has generated heightened enthusiasm for performing metabolomics on populations of cells purified from tissues and biofluids. ...Fluorescence activated cell sorting, or FACS, is a widely used experimental approach to purify specific cell types from complex heterogeneous samples. Here we show that FACS introduces oxidative stress and alters the metabolic state of cells. Compared to unsorted controls, astrocytes subjected to FACS prior to metabolomic analysis showed altered ratios of GSSG to GSH, NADPH to NADP+, and NAD+ to NADH. Additionally, a 50% increase in reactive oxygen species was observed in astrocytes subjected to FACS relative to unsorted controls. At a more comprehensive scale, nearly half of the metabolomic features that we profiled by liquid chromatography/mass spectrometry were changed by at least 1.5-fold in intensity due to cell sorting. Some specific metabolites identified to have significantly altered levels as a result of cell sorting included glycogen, nucleosides, amino acids, central carbon metabolites, and acylcarnitines. Although the addition of fetal bovine serum to the cell-sorting buffer decreased oxidative stress and attenuated changes in metabolite concentrations, fetal bovine serum did not preserve the metabolic state of the cells during FACS. We conclude that, irrespective of buffer components and data-normalization strategies we examined, metabolomic results from sorted cells do not accurately reflect physiological conditions prior to sorting.
•Subjecting cells to FACS introduces oxidative stress and alters cellular redox state.•The concentrations of many metabolites change during cell sorting.•FBS and BSA do not prevent these perturbations during FACS.•Metabolic changes are non-uniform and cannot be corrected by simple normalization.
•A CFD model is developed for flotation column.•The effects of superficial gas velocity and solid concentration are correctly predicted.•The effects of particle type and concentration on bubble ...hydrodynamics are studied.•The attached particle density with different operating conditions is presented.
A Computational Fluid Dynamics (CFD) model of flotation column was developed and validated against published experimental data. The model is based on an Eulerian multi-fluid formulation with k–ɛ turbulence model and includes three phases: gas bubbles, liquid and solid particle suspended in the liquid. The model is developed by writing FORTRAN subroutine and incorporating then into the commercial CFD code AVL FIRE, v.2014. The gas holdup in flotation column was predicted as a function of superficial gas velocity and solids concentration. The effect of particle type, density, wettability and concentration on gas holdup and bubble hydrodynamics (i.e. bubble size distribution, and attached particle density) were studied. The rate of removal of particles from the pulp zone was obtained with kinetic equations for the three sub-processes: collision, attachment, and detachment involving number density of bubbles and particle concentrations, which were also calculated in this model. As confirmed by the comparisons with available data, the modelling methodology proposed in this work represents the physics of flotation column consistently, since the CFD model correctly predicts the experimental effects of gas flow rate and solid concentration on gas holdup within the range of ±20%. It was found that the addition of hydrophobic particles to the air/water mixture promotes bubble coalescence and, therefore, reduces the gas holdup, while the addition of hydrophilic particles suppresses bubble coalescence and increases the gas holdup. It was also found that the increase of gas flow rate leads to an increase in the attached particle density due to the increase of the concentration number of bubbles that were available for the attachment process. Further, the increase of hydrophobic particles concentration led to an increase in the attached particle density.
A computational fluid dynamics (CFD) model was used to investigate the influence of solid concentration on bubbles' coalescence rate in flotation cell using Eulerian–Eulerian approach. CFD ...simulations were performed with AVL-FIRE 2009.2, and the existing flow field was modelled for two-phase (gas–liquid) and three-phase (gas–liquid–solids). The liquid phase was treated as a continuum and the gas phase (bubbles) and solid particles were considered as dispersed phases. The population balance equation for bubble break-up and bubble coalescence rate and the interfacial exchange of mass and momentum as well as bubble–particle attachment and detachment have been included in the CFD code by writing subroutines in FORTRAN. This investigation focused on studying the effect of solid particle on bubble break-up and bubble coalescence rate in the flotation cell at different superficial gas velocity values. The results predict that the presence of solid particles reduced the gas holdup in a flotation column. With the increase of the superficial gas velocity the size of gas bubble that were generated inside the cell decreased, leading to increased gas holdup. The result also shows that the Sauter mean diameter of bubbles decreases with the increase of solid concentration. Reasonably good agreement was obtained between simulation and experimental results for the effect of solid concentration on gas hold-up and axial pressure profile. In the current study, the froth zone was neglected, only the pulp zone was simulated. This is a deficiency of the present model, as the pulp is only one part of the flotation process, and it is physically linked to the froth. However, the model is a step towards gaining a complete view to describing the processes within a flotation cell through inspect the impact of presence of solid particles on the bubble coalescence rate under the different operation conditions.
•A CFD simulation of flotation cell•Bubble break-up and coalescence in flotation cell•Effect of superficial gas velocity on bubble sizes•Effect of solids concentration on bubble sizes
Purpose
Many countries worldwide have taken early measures to combat the spread of coronavirus SARS-CoV-2 by implementing social distancing measures. The main aim of the present work is to examine ...the feasibility of social distancing (i.e. 1.5 m) in closed spaces taking into account the possibility for airborne transmission of SARS-CoV-2.
Methods
A 3D numerical model of human respiration activities, such as breathing and speaking within indoor environments has been simulated with CFD software AVL FIRE R2020. The Eulerian-Eulerian flow model coupled with k-Ɛ approach were employed. With regard to breathing mode, the infected individual is modelled to be breathing 10 times per minute with a pulmonary rate of 6 L/min with a sinusoidal cycle. The present investigation considered air and droplets/particles as separate phases.
Results
The predicted results suggested that the social distancing (i.e. 1.5 m) is not adequate to reduce the risk of contracting diseases like COVID-19, especially when staying for a longer period in an indoor environment. The person directly facing the infected person inhaled more than 1000 aerosol droplets within 30 min. The results also showed approximately 65 % decrease in the number of inhaled droplets the room is well ventilated.
Conclusions
Within an indoor environment, 1.5 m distance will not be enough to protect the healthy individuals from the droplets coming from an infected person. Also, the situation may become worse with the change of the air ventilation system.
A new approach for simulating the formation of a froth layer in a slurry bubble column is proposed. Froth is considered a separate phase, comprised of a mixture of gas, liquid, and solid. The ...simulation was carried out using commercial flow simulation software （FIRE v2014） for particle sizes of 60-150 μm at solid concentrations of 0-40vol%, and superficial gas velocities of 0.02-0.034m/s in a slurry bubble column with a hydraulic diameter of 0.2 m and height of 1.2 m. Modelling calculations were conducted using a Eulerian-Eulerian multiphase approach with k-ε turbulence. The population balance equations for bubble breakup, bubble coalescence rate, and the interfacial exchange of mass and momentum were included in the computational fluid dynamics code by writing subroutines in Fortran to track the number density of different bubble sizes. Flow structure, radial gas holdup, and Sauter mean bubble diameter distributions at different column heights were predicted in the pulp zone, while froth volume fraction and density were predicted in the froth zone. The model was validated using available experimental data, and the predicted and experimental results showed reasonable agreement. To demonstrate the effect of increasing solid concentration on the coalescence rate, a solid-effect multiplier in the coalescence effi- ciency equation was used. The solid-effect multiplier decreased with increasing slurry concentration, causing an increase in bubble coalescence efficiency. A slight decrease in the coalescence efficiency was also observed owing to increasing particle size, which led to a decrease in Sauter mean bubble diam- eter. The froth volume fraction increased with solid concentration. These results provide an improved understanding of the dynamics of slurry bubble reactors in the presence of hydrophilic particles.
The available computational fluid dynamics (CFD) models for multi-phase bubble column ignore the effects of attached particles on the dynamics of the bubbles. Bubbles become heavier with the ...attachment of solid particles which has significant impact on their buoyancy, and hence their flow dynamics. The present paper endeavours to simulate multi-phase slurry bubble column accounting for the effect of bubble-particle aggregate density on the flow dynamics in a multi-phase slurry bubble column. A CFD model was developed and validated against air-paraffin oil data at ambient conditions to understand the hydrodynamics of a three-phase slurry bubble column.
Bubble surface area flux (Sb) is one of the main design parameter in flotation column that typically employed to describe the gas dispersion properties, and it has a strong correlation with the ...flotation rate constant. There is a limited information available in the literature regarding the effect of particle type, density, wettability and concentration on Sb. In this paper, computational fluid dynamics (CFD) simulations are performed to study the gas–liquid–solid three-phase flow dynamics in flotation column by employing the Eulerian–Eulerian formulation with k-ε turbulence model. The model is developed by writing Fortran subroutine and incorporating then into the commercial CFD code AVL FIRE, v.2014. This paper studies the effects of superficial gas velocities and particle type, density, wettability and concentration on Sb and bubble concentration in the flotation column. The model has been validated against published experimental data. It was found that the CFD model was able to predict, where the response variable as indicated by R-Square value of 0.98. These results suggest that the developed CFD model is reasonable to describe the flotation column reactor. From the CFD results, it is also found that Sb decreased with increasing solid concentration and hydrophobicity, but increased with increasing superficial gas velocity. For example, approximately 28% reduction in the surface area flux is observed when coal concentration is increased from 0 to 10%, by volume. While for the same solid concentration and gas flow rate, the bubble surface area flux is approximately increased by 7% in the presences of sphalerite. A possible explanation for this might be that increasing solid concentration and hydrophobicity promotes the bubble coalescence rate leading to the increase in bubble size. Also, it was found that the bubble concentration would decrease with addition of hydrophobic particle (i.e., coal). For instance, under the same operating conditions, approximately 23% reduction in the bubble concentration is predicted when the system was working with hydrophobic particles. The results presented are useful for understanding flow dynamics of three-phase system and provide a basis for further development of CFD model for flotation column.
The influence of particle concentration on the drag force of a particle deserves attention when using the Lagrangian particle tracking methods for the prediction of industrial type gas-solid flows. ...The Lagrangian approach is best suited to applications where the solids volume fraction is low and the effect of particle concentration can be ignored. The paper successfully predicted the available experimental findings on the effects of particle arrangements on drag force. These successful predictions lead to the development of a new coefficient of drag for particles in cluster. Then a combined experimental and numerical study of free-falling particles was carried out in this study to investigate the behaviour of particles in cluster. The new coefficient of drag proposed in this study was used in the numerical simulations. The study highlighted the increase in terminal velocities of particles within cluster streams. The numerical simulations, obtained with the newly proposed coefficient of drag, showed improved results for the average size particles used. The improvements obtained for larger particle size particles were not as impressive.
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•The paper successfully predicted the effects of particle arrangements on drag force.•A new drag coefficient for particles in cluster is proposed in this paper.•The use of the proposed drag coefficient improved results for average size particle.•This work highlighted the increase in terminal velocity of particles within cluster.
This research was aimed to delay the staling of wheat bread as one of the most used products globally by adding barley pentosanes, which is neglected and not taken into consideration despite their ...unique and multiple functional properties and their optimum storage temperature. Water-soluble pentosanes (WSP) and water-insoluble pentosanes (WIP)was extracted from barley (Hordeum vulgare) and added to wheat flour at different percentages. Five treatments were prepared: (T1) from flour only, (T2 and T3) adding WSP at levels of (1 and 2%), (T4 and T5) adding WIP at the same levels respectively. All treatments were stored at (20, 4 and -18 °C), for 72 h. The results indicated that the addition of pentosans (WSP and WIP) delayed the staling of bread, especially at the level of addition (2%) for both, when was stored at freezing temperature (-18°C). The results of the control treatment (T1) and the treatments that included the highest addition level (2%) ( T3 and T5) and after 72 hours of storage at (-18°C) were as follows: The moisture content of bread crumbs decreased to (39.44, 43.32 and 43.91%) respectively. While the moisture in the bread crust increased to (31.61, 33.98, 34.28%), respectively. The swelling power of the bread crumbs and the sediment volume also decreased to (0.74, 1.18, and 1.03%) and (23, 32 and 33%), respectively, which indicates the potency of pentosans and freezing temperature to delay the staling of wheat bread during the storage period.
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