Search Results (15)

Agitated bioreactors are the subject of many studies regarding their design and scale-up to enhance the productivity in various chemical and biochemical industries. In this regard, accurately predicting their power consumption is very important, because it influences the mass transfer rate and flow uniformity inside the bioreactor. A literature review revealed that no study has been conducted to investigate the performance of coaxial bioreactors in terms of their power consumption using a machine learning method. In this study, a computational fluid dynamics (CFD) model was developed and validated against experimental data. Subsequently, 500 simulations at different aeration rates (2–6 L/min), anchor impeller speeds (3.5–9.5 rpm), central impeller speeds (60–150 rpm), and rotating modes (co-rotating and counter-rotating) were conducted. The data from these simulations were utilized to train and test various machine learning models. Initially, the k-nearest neighbor (KNN) classification model was employed to categorize the coaxial bioreactors into different rotating modes. It was found that with just the torque value and central impeller speed, the model achieved successful classification. In addition, various regression models, including multi-layer perceptron (MLP), KNN, and random forest, were developed to predict the torque that would be produced by the coaxial bioreactor. For all models, the hyperparameter tuning and cross-validations were performed. The mean squared error (MSE) evaluation showed that the random forest model had superior performance compared to its counterparts. Full article

Coaxial bioreactors are known for effectively dispersing gas inside non-Newtonian fluids. However, due to their design complexity, many aspects of their design and function, including the relationship between hydrodynamics and bioreactor efficiency, remain unexplored. Nowadays, various numerical models, such as computational fluid dynamics (CFD) and artificial intelligence models, provide exceptional opportunities to investigate the performance of coaxial bioreactors. For the first time, this study applied various machine learning models, both classifiers and regressors, to predict the torque generated by a coaxial bioreactor. In this regard, 500 CFD simulations at different aeration rates, central impeller speeds, anchor impeller speeds, and rotating modes were conducted. The results obtained from the CFD simulations were used to train and test the machine learning models. Careful feature scaling and k-fold cross-validation were performed to enhance all models’ performance and prevent overfitting. A key finding of the study was the importance of selecting the right features for the model. It turns out that just by knowing the speed of the central impeller and the torque generated by the coaxial bioreactor, the rotating mode can be labelled with perfect accuracy using k-nearest neighbors (kNN) or support vector machine models. Moreover, regression models, including multi-layer perceptron, kNN, and random forest, were examined to predict the torque of the coaxial impellers. The results showed that the random forest model outperformed all other models. Finally, the feature importance analysis indicated that the rotating mode was the most significant parameter in determining the torque value. Full article

Plant-based proteins are gaining popularity because of their appeal to vegetarians and vegans, alignment with scientific and regulatory recommendations, and the environmental impact associated with livestock production. Several techniques are employed for the separation, isolation, and purification of plant-based proteins including membrane-based separation, diafiltration, centrifugation, chromatography, electrophoresis, micellar precipitation, and isoelectric precipitation. Despite decades of application, these techniques still have some limitations such as scale-up challenges, high solvent consumption, chemical/biological disposal, and the possibility of protein loss during precipitation or elution. Membrane separation processes are the most effective purification/concentration technology in the production of plant-based protein isolates and concentrates due to their selective separation, simple operational conditions, and easy automation. Membrane separation processes yielded products with higher protein content compared to isoelectric precipitation, and all concentrates presented good functional properties with expected variability among different legumes. This review critically focuses on the membrane technology advances and challenges for the purification of plant-based protein isolates. This study also highlights the plant-based diet trend, the market, composition, and the protein isolate of the faba bean, in addition to the emerging technologies for the elimination of antinutritional compounds. Full article

An in-depth analysis of the flow patterns and mixing dynamics in a twin-paddle blender with bi-disperse non-spherical particles was investigated using the discrete element method (DEM) and experiments. This study aimed to explore the mixing efficiency of a twin-paddle blender containing two different shapes of non-spherical particles. The study focussed on the demonstration of the applicability of the GPU-based DEM model. To achieve this, calibration tests were performed using a classical rotary drum to validate the accuracy of the DEM model. The next step was to examine the impact of various operating parameters on the mixing performance, such as impeller rotational speed. The relative standard deviation (RSD) was employed as a measure of mixing performance. Results revealed that the rotational speed of the impellers had a significant impact on the mixing performance. Full article

The performance of gas-liquid mixing processes in agitated vessels is commonly measured by the degree of gas dispersion, and local measurements of this parameter can provide a more accurate description of the mixing, especially for non-Newtonian fluids. For instance, the fluid flow of complex yield-pseudoplastic solutions is highly affected by the local shear stress, leading to a non-homogeneous air distribution throughout the mixing vessel. Coaxial mixers have demonstrated energy-efficient characteristics for non-Newtonian fluids that improve mixing homogeneity due to the independent rotation of a central impeller and a close-clearance impeller. Therefore, this work aims to investigate the axial profile of the local gas holdup in a PBT-anchor coaxial mixer containing xanthan gum solutions, which is a biopolymer widely utilized as an emulsion stabilizer, dispersing agent, and thickener. The rheological behavior of the solutions was described by the Herschel-Bulkley model, and the effect of the xanthan gum concentration on the gas holdup distribution was analyzed. Electrical resistance tomography (ERT) was employed to obtain the gas holdup from the conductivity measurements of the mixture in each of the four horizontal planes. Results show that the gas holdup increased downward for all solutions, and a lower xanthan gum concentration reduced the non-homogeneity in gas distribution and the overall gas volume fraction. In contrast, higher xanthan gum concentrations enhanced gas holdup in high shear stress regions while weakening air dispersion distant from those regions due to higher viscous forces. Full article

The gas–liquid mixing phenomenon that occurs in a mixing tank containing a non-Newtonian fluid is an important process in many industrial applications, such as chemical and biochemical processing. The design and optimization of an aerated mixing tank with such characteristics is a challenging task. Most of these challenges are due to the non-Newtonian behavior of the fluid, which can lead to compartmentalization of the mixing tank and the formation of oxygen-segregated zones. These issues become more pronounced at larger scales. Therefore, the primary objective of this study was to identify the mixing dead zones and determine their impact on the overall mixing process in a coaxial mixing system at two different scales. This research focused on the evaluation of the hydrodynamics attained by a coaxial gas–liquid mixing tank through numerical and experimental methods. The study was conducted using computational fluid dynamics (CFD) and the electrical resistance tomography (ERT) method. The effects of the aeration rate, inner impeller speed, and rotating mode on the creation of dead zones were investigated. Full article

The design parameters of a mixing system have a major impact on the quality of the final product. Therefore, identifying the optimum parameters of mixing systems is highly relevant to various industrial processes dealing with particulate flows. However, the studies on the influences of the mixer’s design features are still insufficient. In this study, the Discrete Element Method (DEM) is used to examine the impact of paddle angle, width, and gap on the mixing performance of a twin paddle blender. The mixing performance and particle flow are assessed using the relative standard deviation (RSD) mixing index, velocity field, diffusivity coefficient, granular temperature, the force acting on particles, and the mixer’s power consumption. The mixing performance is highest for a paddle angle of 0° at the cost of the highest forces acting on particles. The paddle width is indicated as a critical factor for achieving better mixing quality. In contrast, the powder mixing efficiency and the mixer’s power consumption are not significantly affected by the paddle gap. The results regarding the power consumption denote that the mixer using the paddle angle of 60° has the minimum power consumption. Moreover, increasing the paddle width results in the enhancement of the mixer’s power consumption. Full article

Biodegradable membranes with innovative antifouling properties are emerging as possible substitutes for conventional membranes. These types of membranes have the potential to be applied in a wide range of applications, from water treatment to food packaging and energy production. Nevertheless, there are several existing challenges and limitations associated with the use of biodegradable membranes in large scale applications, and further studies are required to determine the degradation mechanisms and their scalability. Biodegradable membranes can be produced from either renewable natural resources or synthesized from low-molecular monomers that increase the number of possible structures and, as a result, greatly expand the membrane application possibilities. This study focused on bio-sourced and synthesized biodegradable polymers as green membrane materials. Moreover, the article highlighted the excellent antifouling properties of biodegradable membranes that assist in improving membrane lifetime during filtration processes, preventing chemical/biological disposal due to frequent cleaning processes and ultimately reducing the maintenance cost. The industrial and biomedical applications of biodegradable membranes were also summarized, along with their limitations. Finally, an overview of challenges and future trends regarding the use of biodegradable membranes in various industries was thoroughly analyzed. Full article

In this study, we have investigated the mixing kinetics and flow patterns of non-spherical particles in a horizontal double paddle blender using both experiments and the discrete element method (DEM). The experimental data were obtained using image analysis from a rotary drum containing cubical and cylindrical particles. Then, the experimental data were used in order to calibrate the DEM model. Using the calibrated DEM model, the effects of operating parameters such as vessel fill level, particle loading arrangement, and impeller rotational speed on the mixing performance were examined. The diffusivity coefficient was calculated to assess the mixing performance. Full article

Coaxial mixers have shown a uniform energy dissipation rate throughout the mixing tank and a high mass transfer rate. However, to the best of our knowledge no investigation has been conducted on the scale-up of aerated coaxial mixers. In this study, the gas hold-up profile, energy dissipation rate profile, power consumption, and mixing hydrodynamics were explored to keep the mass transfer of the large-scale mixer the same as its small-scale counterpart. The effects of the impeller type, impeller speed, pumping direction, and aeration rate on the reliability of the proposed scale-up technique were explored through electrical resistance tomography, a simplified dynamic pressure method, and computational fluid dynamics. Full article

The development of effective gas-liquid mixing systems in mechanically agitated vessels is typically evaluated in terms of the degree of bubbles dispersion. For instance, adequate gas distribution reduces the formation of oxygen-deficient regions and ensures suitable metabolic pathways in bioreactors. In this regard, the gas holdup is a direct measurement of the process performance because the bubbles’ characteristics determines the gas volume fraction inside the vessel. The accurate estimation of this parameter using empirical correlations provides a better insight and a rapid prediction of the mixing process characteristics, which is crucial for designing stirred tanks. However, a challenge in obtaining empirical correlations is related to the experimental ranges of geometrical and process system conditions. In fact, the existing gas holdup correlations have not considered gas dispersion in yield pseudoplastic fluids using a coaxial mixer that comprises concentric shafts rotating independently. As an opportunity in mixing process system design, this study aims to develop empirical gas holdup correlations for an aerated anchor-PBT coaxial mixing system containing a xanthan gum solution, which behaves as a yield stress fluid. The electrical resistance tomography technique was employed to measure the gas holdup based on the conductivity variation throughout the vessel. A central composite design of experiments was conducted to account for the effect of central impeller speed, anchor speed, and gas flow rate on the mixing performance. The results demonstrated a non-monotonic effect of the central impeller speed on the gas holdup, which indicates a variation in the flow regime. Furthermore, the results showed that the gas holdup was increased by decreasing the anchor speed or increasing the aeration rate applied to the system. The developed correlations were statistically assessed and a good agreement with the experimental data was verified, which enabled us to accurately estimate the gas holdup within the range of operating variables investigated. Full article

Gas dispersion in non-Newtonian fluids is encountered in a broad range of chemical, biochemical, and food industries. Mechanically agitated vessels are commonly employed in these processes because they promote high degree of contact between the phases. However, mixing non-Newtonian fluids is a challenging task that requires comprehensive knowledge of the mixing flow to accurately design stirred vessels. Therefore, this review presents the developments accomplished by researchers in this field. The present work describes mixing and mass transfer variables, namely volumetric mass transfer coefficient, power consumption, gas holdup, bubble diameter, and cavern size. It presents empirical correlations for the mixing variables and discusses the effects of operating and design parameters on the mixing and mass transfer process. Furthermore, this paper demonstrates the advantages of employing computational fluid dynamics tools to shed light on the hydrodynamics of this complex flow. The literature review shows that knowledge gaps remain for gas dispersion in yield stress fluids and non-Newtonian fluids with viscoelastic effects. In addition, comprehensive studies accounting for the scale-up of these mixing processes still need to be accomplished. Hence, further investigation of the flow patterns under different process and design conditions are valuable to have an appropriate insight into this complex system. Full article

Two modeling approaches, the scaling-law and CFD (Computational Fluid Dynamics) approaches, are presented in this paper. To save on experimental cost of the pilot plant, the scaling-law approach as a low-computational-cost method was adopted and a small scale column operating under ambient temperature and pressure was built. A series of laboratory tests and computer simulations were carried out to evaluate the hydrodynamic characteristics of a pilot fluidized-bed biomass gasifier. In the small scale column solids were fluidized. The pressure and other hydrodynamic properties were monitored for the validation of the scaling-law application. In addition to the scaling-law modeling method, the CFD approach was presented to simulate the gas-particle system in the small column. 2D CFD models were developed to simulate the hydrodynamic regime. The simulation results were validated with the experimental data from the small column. It was proved that the CFD model was able to accurately predict the hydrodynamics of the small column. The outcomes of this research present both the scaling law with the lower computational cost and the CFD modeling as a more robust method to suit various needs for the design of fluidized-bed gasifiers. Full article

Vapex (vapor extraction of heavy oil and bitumen) is a promising recovery technology because it consumes low energy, and is very environmentally-friendly. The dispersion of solvents into heavy oil and bitumen is a crucial transport property governing Vapex. The accurate determination of solvent dispersion in Vapex is essential to effectively predict the amount and time scale of oil recovery as well to optimize the field operations. In this work, a novel technique is developed to experimentally determine the concentration-dependent dispersion coefficient of a solvent in Vapex process. The principles of variational calculus are utilized in conjunction with a mass transfer model of the experimental Vapex process. A computational algorithm is developed to optimally compute solvent dispersion as a function of its concentration in heavy oil. The developed technique is applied to Vapex utilizing propane as a solvent. The results show that dispersion of propane is a unimodal function of its concentration in bitumen. Full article

An optimal design strategy of a network of fixed bed reactors for Methanol Production (MP) is proposed in this study. Both methanol production and profit spanning a production period of eight years have been set as objective functions to find the optimal production network. The conservation of mass and energy laws on a heterogeneous model of a single industrial methanol reactor was first developed. The model was solved numerically and was validated with industrial plant data. Different reactor network arrangements were then simulated in order to find an optimal superstructure. It was found that a structure of four reactors (two in series in parallel with another two in series) provide maximum production rate. The application of the more realistic objective function of profit showed that a configuration of two parallel reactors is the best configuration. This optimal structure produces 92 tons/day more methanol than a single reactor. Full article