computational fluid dynamics

In the current study, the flow field and morphology development of a polyethylene (PE) and ethylene vinyl acetate (EVA) blend were investigated numerically during extrusion through a spinneret using Fluent 6.3.26 software. The interface of the two phases was tracked using the volume of fluid (VOF) method. In a conventional spinneret, EVA droplets near the walls break up due to the high shear rate, while the central droplet deforms without breaking up. To enhance the breakup of EVA droplets, the effects of device geometry, including the spinneret angle and the presence of one or two lamps, were investigated in detail. The numerical results indicated that a decrease in the spinneret angle from 60° to 45° causes the central droplet to become more elongated in the flow direction. Additionally, the results showed that the presence of one or two lamps in the conical zone of the spinneret causes a portion of the central droplet to break up.

Computational fluid dynamics (CFD) is one of the methods in which the efficiency of fluids is examined in various ways; For these fluids, equations are considered that are specific to the fluid and its single-phase, biphasic and multi-phase. One of the equations used in these methods is the drag force which has a drag coefficient; The drag coefficient used here is for liquefied gas systems, systems in which the gas bubble and the liquid, which is usually water, come into contact at the separation surface and a slip occurs at this level, which is the drag force. To follow. Among the coordinates used for calculations, Euler-Euler, Euler-Lagrange and etc. The coordinates we are considering are Euler-Eulerian. The equations used in various CFD probes are for Newtonian fluids, usually for sieve trays and etcUsed. In this study, we review the drag coefficients that have been obtained by researchers in this framework over the years.

The accurate simulation of lithium-ion batteries is crucial for optimizing their performance, increasing their lifespan, and mitigating environmental concerns, as they play a vital role in powering electric vehicles, renewable energy systems, and portable electronics. This research presents a novel computational technique for simulating the internal processes of lithium-ion batteries, focusing on the electrochemical equilibrium and dynamics of these batteries. By leveraging the electrochemical method and simplifying complex differential equations through logical assumptions, the study develops a versatile tool for predicting the temporal and spatial distribution of electrode concentration, potential, and electrolyte dynamics in one dimension. The computational approach, executed in a C++ programming environment using computational fluid dynamics and the finite volume method, enables the simulation of diverse lithium-ion batteries.The research addresses the challenges posed by these batteries, including the quest for increased energy and power density, effective heat management, and control and monitoring complexities. By providing valuable insights into optimizing battery performance, this study contributes to the development of sustainable energy storage solutions.The proposed approach has the potential to shape a sustainable energy narrative, particularly in the context of all-electric and hybrid vehicles, and mitigating environmental concerns.

This study presents a computational fluid dynamics (CFD) simulation of two-phase flow patterns in a Y-shaped microfluidic device. The two-phase flow of water and n-butyl acetate is simulated using the volume of fluid (VOF) method in a Y-shaped microfluidic device with different flow rates. A 2D model was used for simulation, and the results were compared to experimental data, showing good consistency. The study also examined the effects of organic (n-butyl acetate) and flow on the overall flow model. The authors observe three different flow patterns, including slug flow, parallel flow, and droplet flow, depending on the flow rate. The results indicate that a slug flow pattern is detected when the flow rates of the aqueous and organic phases are both low and similar. Nonetheless, as the overall flow rate rises, the slug flow pattern shifts to either parallel droplet or plug flow. Similarly, when the flow rate of the aqueous phase is increased while keeping the organic phase flow rate constant, the shift occurs from slug flow to droplet flow. Therefore, this study is significant in providing insights into the different flow regimes that can occur in a microfluidic system. This understanding can be used to design and optimize microfluidic devices for a variety of applications.

An airlift reactor with the external loop (EXL ALFR) is a widely used modified version of a Bubble Column Reactor (BCR). An EXL ALFR can also be used for a three-phase system with the solid phase in a packed or fluidized form. An EXL ALFR provides design flexibility for conventional chemical reactions as well as biological reactions. Shear is an important factor for the reactors handling immobilized enzymes. In the current investigation, the effect of the design variables, like gas hold-up, the velocity of circulating liquid, and the distribution of bubble dimension, was compared for an EXL ALFR and an external loop airlift reactor with a packed bed (EXL ALFR-PB). Particle Image Velocimetry (PIV) was employed for the liquid axial velocity in the downcomer of the reactors, and the computational fluid dynamic with the Population Balance Model (CFD-PBM) was employed. The minimum percentage of errors of 2.3% and 1.2% and the maximum of 4.2% and 3.4% were obtained for the experimental and predicted values of gas hold-up in the EXL ALFR and EXL ALFR-PB, respectively. For the velocity of the circulating liquid, the predicted and experimental values of their minimum percentage error were 1.1% and 0.5% and a maximum of 4.3% and 4.5% in EXL ALFR and EXL ALFR-PB, respectively.  Also, the pressure drops calculated from the Ergun equation and CFD simulation had a 0 to 4% difference, indicating good agreement.

The effectiveness of nitrate removal was assessed in a 9.5 L packed bed column bioreactor through the evaluation of various feeding strategies and initial concentrations. The bioreactor was filled with zeolite mineral particles and initially treated with Thiobacillus denitrificans. Multiple hydraulic retention times were investigated to determine the efficiency of nitrate removal. The results demonstrate that the designed bioreactor is capable of achieving an 87% reduction in nitrate levels within a three-hour timeframe. This indicates that the bioreactor system can effectively remove nitrate ions from water, even when the initial nitrate content is as high as 400 mg/L, which exceeds the standard limit of 45 mg/L. The computational fluid dynamics (CFD) model yielded satisfactory results, confirming the effectiveness of the bioreactor design. It revealed that the optimal length of the bioreactor is suitable for influents containing 400 mg/L of nitrate. However, for influents with lower nitrate concentrations or when employing lower hydraulic retention times (HRTs), the bioreactor can be constructed with shorter heights. This CFD model can serve as a valuable tool for future studies, particularly in scaling up the bioreactor system.

(1) The treatment of hydrocephalus is the use of cerebrospinal shunts. These shunts are made up of different parts. One of the most important parts of these shunts is their catheter, which is placed inside the ventricle of the brain in order to drain cerebrospinal fluid. One of the most important problems of ventricular catheters is their clogging, which causes shunt replacement in 50-80% cases. Although many factors affect this congestion, one of the most important of them is the flow inside the ventricles of the brain with hydrocephalus; (2) The works of many researchers have mentioned the problem of flow inside the catheters, for this purpose two-dimensional simulation has been used. In this research, the two-dimensional image obtained through MRI has been used in the simulation in order to influence the real shape of the ventricles of the brain in the occlusion of the ventricular catheters; (3) According to the investigations, the cause of clogging of most common catheters is the problem in the morphology and the way their holes are located; (4) A new design of catheters by changing the diameter and slope of the holes has been presented. It was found that conventional catheters are very susceptible to being closed by dead cells or cerebral ventricular tissue. Four types of catheters were examined, types 3 and 4 showed better performance with 50% and types 5 and 6 with 100% reduction in the probability of catheter hole closure.

Ejectors offer a cost-effective and practical solution for recovering flare gases, thereby reducing greenhouse gases. Improving the entrainment rate of the secondary fluid can enhance ejector performance. The objective of this research is to identify the optimal ejector geometry to maximize the absorption rate of the secondary fluid. Computational fluid dynamics is used to evaluate a two-phase ejector. Geometric parameters such as throat diameter and length, nozzle diameter, and converging and diverging angles impact the absorption rate of the secondary fluid. Using a multi-objective genetic algorithm, the optimal values for each parameter are obtained. The results show that reducing the throat length and angle of the converging section, as well as nozzle diameter, leads to increased absorption. In contrast, the throat and angle of the divergent section increase absorption. Additionally, energy efficiency is investigated under basic and optimized geometries. The findings reveal that increasing the soak range does not necessarily enhance energy efficiency.

Inclined submerged diffusers that are used to dilute hypersaline and highly contaminated brine, discharged from desalination plants, in receiving marine waters are commonly modeled via semi-empirical, integral, and 3D Computational Fluid Dynamic (CFD) models. The first two models are computationally simple and efficient, but not enough accurate in many cases, and 3D-CFD models which show good agreement with experimental data are time-consuming. To avoid computational costs of 3D models and to present a more precise model than simple ones, a modified 2D-CFD model for stagnant and dynamic ambient is suggested in this study. The results showed that the proposed model can predict the jet behavior in both ambients more accurately than integral models and in shorter computing time than 3D models. The results of this study can be used in order to design environmentally friendly discharge systems by engineers and practitioners for brine or pollutant dilution in the receiving marine waters.

Membrane bioreactors (MBRs) are high-tech systems for water recycling and reusing of unconventional water resources such as municipal wastewater. However, the fouling of polymeric membranes is the main impediment to the market development of MBR. The polyolefin-based membranes are subjected to more severe organic fouling than other hydrophilic membranes due to their inherent strong hydrophobic properties, therefore, proposing efficient, fast, and economic fouling mitigation methods is vital for durable and long-standing performance. In this research, the hydrodynamics of a lab-scale membrane bioreactor with different configurations of aerators and nozzle sizes were used to investigate the air scouring efficiency. It was gained that aerators with higher air flow rates, e.g., 5.5 m/s can produce slug bubbles which are capable of foulant removal from the membrane surface. In comparison with a non-central aerator, the satisfactory scouring zone of the central aerator is narrow and the edge nozzles on both sides of the aerator are blocked. Under constant air flow rate, when the inlet air is injected into the aerator from two and three points, not only the end nozzles are blocked but also the liquid is penetrated into the aerator and the shear stress on the membrane surface decreased to 0.765 Pa. In the case of the non-central aerator, the satisfactory scouring zone becomes wider and neither nozzle blockage nor liquid penetration down to the aerator has occurred. The distribution of bubbles was optically evaluated by video imaging through the transparent plexiglass tank using aerators with different inlet flow rates and various configurations. Numerical simulations and related experimental analyses demonstrated that air inlet velocity has an important role in creating larger slug bubbles. It was shown that a non-central aerator in which the central nozzle in front of the inlet air stream is blocked, produces slug bubbles and sufficient air scoring on the flat sheet membrane. Configuration of a non-central aerator with 4 nozzles not only increased the satisfactory zone of each aerator without blockage of edge nozzles and liquid penetration into the aerator but also provided a higher shear rate over 1.104 Pa under a constant flow rate, which consequently removed the foulant from the membrane surface.

Packed towers are continuous contact systems in which unlike tray towers, the liquid phase is dispersed, and the gas phase is continuous. Packed or packed distillation towers are widely used in chemical industries. The use of such towers is preferable to tray towers, especially in vacuum distillation operations. These columns are suitable in low pressure-drop or low liquid hold up operations. In this study, the pressure drop for the air-water system was simulated, and presented by a 3D model consisting of two layers of Gempak 2A structured packings by using computational fluid dynamics. Computational Fluid Dynamics is a useful tool for scale-up, design and optimization of chemical engineering equipment for its detailed prediction of hydrodynamic characteristics. The BSL turbulence model was used for simulation. The total number of meshes were 1315200. The simulation results were compared with laboratory and existing experimental data. The simulation error of the two-phase pressure drop compared with experimental data was 16.6%. The results of prediction agree well with the experimental data indicating the suitability of the proposed method for the simulation of the hydrodynamics in structured packed columns. The results of this study can be used in the hydraulic design of packed towers containing structured packings.