Mixed Flow Pattern Research Articles

Effect of differences in proximal neck angles on biomechanics of abdominal aortic aneurysm based on fluid dynamics.

This study aimed to analyze the effect of proximal neck angulation on the biomechanical indices of abdominal aortic aneurysms (AAA) and to investigate its impact on the risk of AAA rupture. CT angiography (CTA) data of patients with AAA from January 2015 to January 2022 were collected. Patients were divided into three groups based on the angle of the proximal neck: Group A (∠β ≤ 30°), Group B (30°<∠β ≤ 60°), and Group C (∠β > 60°). Biomechanical indices related to the rupture risk of AAA were analyzed using computational fluid dynamics modeling (CFD-Post) based on the collected data. Group A showed slight turbulence in the AAA lumen with a mixed laminar flow pattern. Group B had a regular low-speed eddy line characterized by cross-flow dominated by lumen blood flow and turbulence. In Group C, a few turbulent lines appeared at the proximal neck, accompanied by eddy currents in the lumen expansion area following the AAA shape. Significant differences were found in peak wall stress, shear stress, and the maximum blood flow velocity impact among the three groups. The maximum blood flow velocity at the angle of the proximal neck impact indicated the influence of the proximal neck angle on the blood flow state in the lumen. As the angle of the proximal neck increased, it caused stronger eddy currents and turbulent blood flow due to a high-speed area near the neck. The region with the largest diameter in the abdominal aortic aneurysm was prone to the highest stress, indicating a higher risk of rupture. The corner of the proximal neck experienced the greatest shear stress, potentially leading to endothelial injury and further enlargement of the aneurysm.

Fluid–Solid Mixing Transfer Mechanism and Flow Patterns of the Double-Layered Impeller Stirring Tank by the CFD-DEM Method

The optimization design of the double-layered material tank is essential to improve the material mixing efficiency and quality in chemical engineering and lithium battery production. The draft tube structure and double-layered impellers affect the flow patterns of the fluid–solid transfer process, and its flow pattern recognition faces significant challenges. This paper presents a fluid–solid mixing transfer modeling method using the CFD-DEM coupling solution method to analyze flow pattern evolution regularities. A porous-based interphase coupling technology solved the interphase force and could be used to acquire accurate particle motion trajectories. The effect mechanism of fluid–solid transfer courses in the double-layered mixing tank with a draft tube can be obtained by analyzing key features, including velocity distribution, circulation flows, power, and particle characteristics. The research results illustrate that the draft tube structure creates two major circulations in the mixing transfer process and changes particle and vortex flow patterns. The circulating motion of the double-layered impellers strengthens the overall fluid circulation, enhances the overall mixing efficiency of the fluid medium, and reduces particle deposition. Numerical results can offer technical guidance for the chemical extraction course and lithium battery slurry mixing.

Identification of oil–water-gas flow patterns by super-sparse near-infrared wavelengths sensor

This paper puts forward a method of using two wavelengths of near-infrared light to identify the oil–gas-water mixed flow patterns. Propose a new method of multiple correlation algorithm (MCA) to solve the sensor super-sparse representation problem. Use MCA results as input layer parameters, use BP neural network to train the voltage signal and identify different flow patterns. The experimental results show that the recognition degrees of water, oil bubble, and oil flow patterns have reached 96.77%, 98.39%, and 100%, respectively, and the recognition rate of the water–gas phase has 78.38%. Using a correction model can further improve the accuracy. Test the samples with water cut from 90% to 70%, and the average RMSE = 1.59e-2. This method can be applied to the detection of the water cut of crude oil in oil fields and has a certain reference value for the wavelength selection of near-infrared light sensors.

Analyzing mixing behavior in a double paddle blender containing two types of non-spherical particles through discrete element method (DEM) and response surface method (RSM)

The discrete element method (DEM) and experiments were used to examine the mixing mechanisms and flow patterns in a twin-paddle blender containing two types of non-spherical particles. The applicability of the GPU-based DEM model was demonstrated through calibration tests using a classical rotary drum. Afterward, the calibrated DEM model was utilized to investigate the impact of factors such as the vessel fill level, paddle rotational speed, and particle number ratio on mixing performance. The relation between mixing performance and the operational parameters was predicted using the Response Surface Method (RSM). An escalation in the fill level, coupled with a reduction in impeller speed, led to a rise in the overall number of particles that came into contact with one another, suggesting an increase in the compactness of the mixture. The computed Peclet numbers and diffusivity coefficients revealed that diffusion was the prevailing mixing mechanism.

A Pictorial Essay on Ultrasonography of Lymphadenopathies in Children

The purpose of this review is to become familiar with ultrasound (US) characteristics of normal and pathological lymph nodes and with diagnostic imaging approach to lymphadenopaties. Lymphadenopathy is a common finding in the paediatric population. Due to the many pathologies that can present in a similar fashion, imaging is a valuable method used in diagnostic process. Ultrasound is the modality of choice for lymph node detection in children, with a high safety profile as it does not use radiation. In this review the US appearance and characteristics of normal lymph nodes, and of some more common lymphadenopathies, are presented. Special attention is paid to distinguishing between benign and malignant lymph nodes on the basis of US characteristics. All findings must always be correlated with clinical and laboratory findings, and frequently followed by fine-needle aspiration or excisional biopsy as some US morphologies of benign and malignant nodes may overlap. However, the criteria that raise suspicion for malignancy are round shape, predominantly hypoechoic echogenicity, heterogenous echotexture, absent or displaced hilum, irregular outlines, necrosis, multiple confluent lymph nodes, the presence of microcalcifications, and peripheral or mixed flow pattern on colour Doppler imaging.Conclusion - US is the first line imaging method in palpable masses in children, first to confirm the presence of lymph nodes, and second to better delineate the lymph node’s characteristics, which guides further diagnostic decisions and treatment.

Unravelling groundwater and surface water sources in the Esteros del Iberá Wetland Area: An isotopic approach

In the Esteros del Iberá Wetland Area (EIWA, NE Argentina), the southern sector of the transboundary Guarani Aquifer System (SAG) is overlain by the Ramsar listed Iberá Wetlands and several rivers, that combined extend across 37,930 km2 and represent one of the largest freshwater systems on the South American continent. Previous hydrogeological studies encompassing the entire SAG proposed preferential discharge of groundwater of various origins and ages to the EIWA. In this study, a multi-tracer study using major ionic species, δ18O, δ2H and 222Rn was conducted in lagoons, rivers, wells, and boreholes in the EIWA to confirm if discharge from the transboundary SAG is contributing to the surface water system. End-member Mixing Analysis (EMMA) determined the existence of four main end-members: groundwater from the SAG, more saline groundwater from the deeper Pre-SAG, and two poorly mineralised end-members from shallow, Post-SAG. EMMA calculations clearly illustrated complex binary and ternary mixing patterns involving the four end-members and highlighted the role of geological structures, specifically regional steep faults, in controlling the mixing patterns. 222Rn activities allowed in-situ identification of preferential deep groundwater discharge into both surface waters and shallow groundwaters. These findings provide strong evidence for the widespread existence of upward flows along major faults in this sector of the SAG, inducing complex mixing flow patterns and explaining the presence of old groundwater in shallow aquifers. Mapping the sources of water and the hydrological interactions are relevant for improving water balance estimates and develop management policies towards the preservation of these wetlands.

Regional Characteristics and Control Method of the Mixing Flow Pattern for Water-Lubricated Tilting Pad Thrust Bearings

The water-lubricated tilting pad thrust bearings (WTTBs) of the reactor coolant main pump and high-power RDT operate at a large linear velocity, heavy load, and low viscosity. On the basis of the performance prediction of WTTBs in the mixing flow pattern, a hypothesis of the regional flow pattern is proposed. To compare the lubrication performance under four kinds of flow pattern modes, a thermo-elasto-hydrodynamic lubrication model of the WTTB considering the flow pattern is established, and a partition iteration algorithm for the mixing flow pattern is provided. Moreover, a method for controlling the flow pattern by changing the pad surface morphology is proposed. A simulation is used to indicate that the bearing performance under the mixing flow pattern calculated by the regional flow pattern mode is between that of the laminar and turbulent flows. The regional mixing flow pattern mode can automatically retrogress to the single flow pattern mode by changing the operation conditions. Both the circumferential bulge and radial concave pad surfaces are beneficial for increasing the turbulent area and thereby improving the load-carrying capacity of the WTTB.

Digital Microfluidic Mixing via Reciprocating Motions of Droplets Driven by Contact Charge Electrophoresis.

Contact charge electrophoresis (CCEP) is an electrically controllable manipulation technique of conductive droplets and particles by charging and discharging when in contact with the electrode. Given its straightforward operation mechanism, low cost, and ease of system construction, it has gained traction as a versatile and potential strategy for the realistic establishment of lab-on-a-chip (LOC) in various engineering applications. We present a CCEP-based digital microfluidics (DMF) platform with two parallel electrode modules comprising assembled conventional pin header sockets, allowing for efficient mixing through horizontal and vertical shaking via droplet reciprocating motions. The temporal chromic change caused by the chemical reaction between the pH indicator and base solutions within the shaking droplets is quantitatively analyzed under various CCEP actuation conditions to evaluate the mixing performance in shaking droplets by vertical and horizontal reciprocating motions on the DMF platform. Furthermore, mixing flow patterns within shaking droplets are successfully visualized by a high-speed camera system. The suggested techniques can mix samples and reagents rapidly and efficiently in droplet-based microreactors for DMF applications, such as biochemical analysis and medical diagnostics.

Study on Flow Characteristics and Mass Transfer Mechanism of Kettle Taylor Flow Reactor

A scheme of a gas–liquid mixed jet is designed by installing gas distributor at the bottom of a stirred tank reactor to generate Taylor vortex. The eddy flow characteristics and mass transfer mechanism in the reactor are analyzed by numerical simulation and experiment. The results show that the evolution law of Taylor vortex in a stirred tank reactor with a rotating Reynolds number is similar to that in a conventional Taylor reactor. The Taylor vortex generated in the stirred tank reactor creates a partial plug flow region in the original complete mixing flow pattern, which reduces back mixing, the plug flow area expands with the increase of rotating Reynolds number. Under the condition of a critical rotating Reynolds number (Recr), the gas phase homogeneity of the reactor is increased by 28% and the dissolved oxygen rate is increased by about 5 times, which effectively improves the flow condition in the reactor and strengthens the mass transfer efficiency between the gas and liquid. The research results provide a theoretical basis for breaking through the limitation of small reaction space of conventional Taylor flow reactor and expanding production scale. The refit of kettle reactor is universal and easy to operate.

Effective Analysis of Different Gas Diffusers on Bubble Hydrodynamics in Bubble Column and Airlift Reactors towards Mass Transfer Enhancement

Even bubble column reactors (BCR) and airlift reactors (ALR) have been developed in terms of various related aspects towards mass transfer enhancement, the effective analysis of gas diffuser types on mass transfer and gas–liquid hydrodynamic characteristics is still limited. Therefore, the present study aims to analyze the relative effect of different types of air diffusers on bubble hydrodynamics and mass transfer performance to understand their behaviors and define the best type. The experiments were conducted by varying different diffuser types, reactor types (BCR and ALR), and superficial gas velocity (Vg) (0.12 to 1.00 cm/s). Five air diffusers including commercial fine sand (F-sand) and coarse sand (C-sand) diffusers, and acrylic perforated diffusers with orifice sizes of 0.3 mm (H-0.3), 0.6 mm (H-0.6), and 1.2 mm (H-1.2), were used in this study. For every condition, it was analyzed in terms of bubble hydrodynamics and oxygen mass transfer coefficient (KLa). Lastly, the selected diffusers that provided the highest KLa coefficient were evaluated with a solid media addition case. The results of both reactor classes showed that F-sand, the smallest orifice diffuser, showed the smallest air bubbles (3.14–4.90 mm) compared to other diffusers, followed by C-sand, which larger about 22–28% on average than F-sand. ALR exhibited a better ability to maintain smaller bubbles than BCR. Moreover, F-sand and C-sand diffusers showed a slower rising velocity through their smaller bubbles and the tiny bubble recirculation in ALR. Using F-sand in ALR, the rising velocity is about 1.60–2.58 dm/s, which is slower than that in BCR about 39–54%. F-sand and C-sand were also found as the significant diffusers in terms of interfacial area and gas hold-up. Then, the KLa coefficient was estimated in every diffuser and reactor under the varying of Vg. Up to 270% higher KLa value was achieved from the use of F-sand and C-sand compared to other types due to their smaller bubbles generated/maintained and longer bubble retention time through slower rising velocity. After adding 10% ring shape plastic media into the reactors with F-sand and C-sand diffusers, a better performance was achieved in terms of KLa coefficient (up to 39%) as well as gas hold-up and liquid mixing. Lastly, ALR also had a larger portion of mixed flow pattern than BCR. This eventually promoted mass transfer by enhancing the mixed flow regime.

An improved meshless artificial viscosity technology combined with local radial point interpolation method for 2D shallow water equations

The two-dimensional shallow water equations (SWEs) are a hyperbolic system of first-order nonlinear partial differential equations which have a characteristic of strong gradient. In this study, a newly-developed numerical model, based on local radial point interpolation method (LRPIM), is adopted to simulate discontinuity in shallow water flows. In order to accurately capture the information of wave propagation, the LRPIM is combined with the split-coefficient matrix (SCM) method to transform the SWEs into a characteristic form and the selection of the direction of local support domain is introduced into the LRPIM. An improved meshless artificial viscosity (MAV) technique is developed to minimize the non-physical oscillations near the discontinuities. Then, the LRPIM and the second-order Runge–Kutta method are adopted for spatial and temporal discretization of the SWEs, respectively. The feasibility and validity of the proposed numerical model are verified by the classical dam-break problem and the mixed flow pattern problem. The comparison of the obtained results with the analytical solution and other numerical results showed that the MAV method combined with LRPIM can accurately capture the shocks and has high accuracy in dealing with discontinuous flow by adding appropriate viscosity to the equations in the discontinuous region.

Effects of Scale-Up and Impeller Types on Spherical Agglomeration of Dimethyl Fumarate

Spherical agglomeration (SA) allows for intensifying a crystallization process through simultaneous particle size enlargement and process efficiency enhancement, without a compromise between bioavailability and processability of active pharmaceutical ingredients (APIs). Inefficient collision intensity may encounter during scale-up of an SA process, while mixing intensity and flow patterns do play critical roles especially in a batchwise stirred tank. In the present study, the scalability of an SA process by operating at all the same configurations of different scales, 0.5, 2, and 10 L, using a common one-layered impeller with four pitched blades was examined through the use of dimethyl fumarate as a model API. Insights into the guidelines for scaling up of the SA process are also given. Furthermore, the effects of impeller types, including the one-layered impeller, the two-layered impeller with four pitched blades, and the maxblend impeller, on the size, size distribution, and roundness of dimethyl fumarate agglomerates were investigated carefully.

Parametric study of the progressive freeze concentration for desalination

A progressive freeze concentration (PFC) process was applied to treat several waters where clean ice was generated one-dimensionally, and salt and impurities concentrate into the liquid phase. The impact of eight process parameters on salt percent removal and ice percent recovery were investigated. They were coolant temperature, stirring rate, advance speed of crystallizer, feed solution concentration, feed solution temperature, ice seeding, crystallizer material, and mixing flow pattern. The significant process parameters found were stirring rate, coolant temperature, and feed solution concentration. Temperature difference between feed solution temperature and coolant temperature is important in minimizing supercooling which has a negative effect on treatment. For example, our results showed a temperature difference of 10 °C for a feed solution temperature of 2.5 °C were needed to minimize supercooling. Salt percent removal was found to be directly related to while ice percent recovery was inversely related to the stirring rate. Treatment of an artificial seawater (salinity 35.67 g/L) and a RO brine concentrate (salinity 2600 mg/L) resulted in 51% and 70% ice percent recovery and 74% and 97.7% salt percent removal, respectively. An application of the PFC process includes brine concentrate treatment for inland desalination plants.

Numerical Study of Effects of Backpressure on Self-Pulsation of a Liquid-Centred Swirl Coaxial Injector

This study investigated the effects of backpressure and operating conditions on the self-pulsation characteristics of a liquid-centred swirl coaxial (LCSC) injector. To this end, a three-dimensional numerical simulation via octree adaptive mesh refinement as well as coupled level-set and volume of fluid method were employed. Self-pulsation is suppressed by backpressure for a constant gas–liquid momentum flux ratio (MFR). When backpressure is constant, the strength of self-pulsation varies with the mass flow rate of the gas (m˙g), which is constant with experimental data due to the variation in the flow patterns in the recess chambers. The self-pulsation frequency increases with backpressure and m˙g. The trends of the spray angle and intensity of self-pulsation are consistent. As backpressure increases, the radial distribution of the mass flow rate of the liquid changes from a double- to single-peak. The central mass flow rate increases with backpressure and m˙g, which also affect the pressure oscillations inside and outside the liquid film in the injector. We proposed a self-pulsation mechanism, in which self-pulsation is closely related to the dominant surface wave and Kelvin–Helmholtz (K–H) instability. Self-pulsation under the critical mixing flow pattern is stronger than that under inner or outer mixing flow patterns. Under the critical mixing flow pattern, the K–H vortex is relatively strong, and the spray oscillation is not restricted by the wall of the recess chamber.

Numerical investigation on spray self-pulsation characteristics of a liquid-centered swirl coaxial injector

Self-pulsation characteristics of a liquid-centered swirl coaxial (LCSC) injector are investigated numerically based on the coupled volume of fluid VOF and Level Set (CLSVOF) model. Good agreements of simulation results and experiment data, in aspect for self-pulsation frequency and spray angle, are generally achieved. On the basis of the flow dynamics of the injector, mechanism of spay self-pulsation in recessed LCSC injector is proposed. The self-pulsation arises from the periodic blocking of annular gas by the liquid sheet. Self-pulsated “Christmas tree” spray patterns result from the periodic vortex rings generating and shedding around the liquid sheet. Theoretical analysis demonstrates that the self-pulsation frequency is almost the same as the frequency of the liquid sheet impacting the recess chamber wall, and the model may be able to predict the self-pulsation frequency. Pressure oscillation inside the air-core is closely related to the primary breakup of the liquid sheet, and the frequency is consistent with the self-pulsation frequency. Effects of the gas-liquid mass flow rate ratio (GLR) on the self-pulsation frequency and pressure oscillation frequency inside the air-core are negligible. The self-pulsation intensity peaks under conditions with the critical mixing flow pattern, while, the pressure oscillation intensity inside the air-core increases with the elevating of GLR. It seems that the spray self-pulsation could improve the spray angle.

A Traffic Flow Evolution Process toward Mixed Equilibrium with Multicriteria of Route Choice Behaviour

Based on the price-quantity adjustment behaviour principle of disequilibrium theory, the route choices of travellers are also affected by a quantity signal known as traffic flow, while the route cost is considered as a price signal in economics. Considering the quantity signal’s effect among travellers, a new route comfort choice behaviour criterion and its corresponding equilibrium condition are established. The network travellers are classified into three groups according to their route choice behaviour: travellers in the first group choose the shortest route following the route rapidity behaviour criterion with complete information forming the UE (user equilibrium) pattern, travellers in the second group choose the most comfortable route following the route comfort behaviour criterion with complete information forming the QUE (quantity adjustment user equilibrium) pattern, and travellers in the third group choose a route according to their perceived travel time with incomplete information forming the SUE (stochastic user equilibrium) pattern. The traffic flows of all three groups converge to a new UE-QUE-SUE mixed equilibrium flow pattern after interaction. To depict the traveller-diversified choice behaviour and the traffic flow interaction process, a mixed equilibrium traffic flow evolution model is formulated. After defining the route comfort indicator and the corresponding user equilibrium state, the equilibrium conditions of the three group flows are given under a mixed equilibrium pattern. In addition, an equivalent mathematical programming of the mixed equilibrium traffic flow evolution model is proposed to demonstrate that the developed model converges to the mixed equilibrium state. Finally, numerical examples are examined to evaluate the effect of route comfort proportions on the traffic network flow evolution and analyse the performance of the proposed model.

Thermographic studies of cocurrent and mixed flow spray drying of heat sensitive bioactive compounds

Production of powders of heat sensitive bioactive compounds in a bench scale spray drier was studied under cocurrent and mixed flow pattern conditions using two inlet air temperatures of 200 and 120 °C. Two natural colorants (riboflavin-5-phosphate and red beet) and an enzyme (alpha-amylase), were selected for experimentation. Thermographic studies showed interesting asymmetric profiles of temperatures outside and inside of the drying chamber, because turbulent air flow conditions and thermal trajectories of atomized drops during its drying process were dependent on flow patterns. Powders of natural colorants maintained its color strength, and alpha-amylase powders retain more than 82.9% of its enzyme activity even at the highest air temperature of 200 °C and using mixed flow. This work concludes that spray drying under cocurrent and mixed-flow patterns of heat labile bioactive compounds is feasible, influencing drying yields and the properties of powders obtained.

Mixing assessment of non-cohesive particles in a paddle mixer through experiments and discrete element method (DEM)

In this study the mixing kinetics and flow patterns of non-cohesive, monodisperse, spherical particles in a horizontal paddle blender were investigated using experiments, statistical analysis and discrete element method (DEM). EDEM 2.7 commercial software was used as the DEM solver. The experiment and simulation results were found to be in a good agreement. The calibrated DEM model was then utilized to examine the effects of the impeller rotational speed, vessel fill level and particle loading arrangement on the overall mixing quality quantified by the relative standard deviation (RSD) mixing index. The simulation results revealed as the impeller rotational speed was increased from 10 RPM to 40 RPM, generally a better degree of mixing was reached for all particle loading arrangements and vessel fill levels. As the impeller rotational speed was increased further from 40 RPM to 70 RPM the mixing quality was affected, for a vessel fill level of 60% and irrespective of the particle loading arrangement. Increasing the vessel fill level from 40% to 60% enhanced the mixing performance when impeller rotational speed of 40 RPM and 70 RPM were used. However, the mixing quality was independent of vessel fill level for almost all simulation cases when 10 RPM was applied, regardless of the particle loading arrangement. Furthermore, it was concluded that the particle loading arrangement did not have a considerable effect on the mixing index. ANOVA showed that impeller rotational speed had the strongest influence on the mixing quality, followed by the quadratic effect of impeller rotational speed, and lastly the vessel fill level. The granular temperature data indicated that increasing the impeller rotational speed from 10 RPM to 70 RPM resulted in higher granular temperature values. By evaluating the diffusivity coefficient and Peclet number, it was concluded that the dominant mixing mechanism in the current mixing system was diffusion.

Optical determination of oxygen mass transfer in a helically-coiled pipe compared to a straight horizontal tube

The gas-liquid mass transfer of oxygen has been examined experimentally in a helically-coiled pipe using an optical colorimetric method. Two tracer redox-reactions have been used for this purpose: (i) methylene blue and (ii) resazurin. The gas hold-up has been varied from 0.1 to 0.6, and liquid flow rate from 0.37 to 0.68 l/min, both leading to plug-flow conditions in the helix for all parameter combinations. A progress variable has been defined to measure the advancement of the reaction and thus, oxygen transfer to the liquid. The resazurin reaction turned out to be more appropriate for mass transfer studies, due to the bigger time constant difference of oxidation and reduction. Therefore, it can be adapted more easily to the specific conditions of the set-up. It also possesses more intense colours and higher fluorescence intensity, which might be useful for other mass transfer studies. As expected, the oxygen mass transfer increases with gas hold up, but liquid flow rate has little influence. A comparison with a horizontal tube of the same diameter shows the drastically increased mass transfer in the helix, due to better radial mixing and different flow pattern. Depending on the experimental conditions, oxygen concentration in the helix was up to twice that of the horizontal tube. This can be explained by the much higher liquid side mass transfer velocity, which is determined in this study from the experimental kla-values and specific bubble surface per turn of the helix. For this purpose, bubble dimensions and gas-liquid cell volumes have been determined from the experimental images. The paper thus presents a locally resolved characterization of gas-liquid mass transfer in a helically coiled reactor. The high mass transfer especially during the first turns of the helix shows its advantages compared to a straight tube.

Effect of hydrodynamic mixing conditions on wet oxidation reactions in a stirred vessel reactor

The aim of this study was to investigate the impact of mixing intensity and mixing flow patterns on solid waste degradation, and production of valuable intermediate by-products such as acetic acid. Total suspended solids generally decreased, soluble chemical oxygen demand, dissolved organic carbon, and acetic acid concentration generally increased with the progress of the reaction and increase in the mixing intensity. The results showed that axial-radial flow pattern (using pitch blade impeller) and medium impeller speed (500 rpm) resulted in a higher degree of solid degradation and production of acetic acid.