Experiment–simulation synergy on multiscale breakup dynamics in wire arc spray atomization

In the suspension high velocity oxy fuel (SHVOF) thermal spray, a suspension is injected into the combustion chamber where the jet undergoes primary and secondary breakup. Current knowledge of the primary breakup within the combustion chamber is very limited as experimental investigations are impeded due to direct observational inaccessibility. Numerical methods are also limited due to the computational costs associated with resolving the entire range of multiphase structures within SHVOF thermal spray. This paper employs a coupled volume of fluid and discrete phase model, combined with a combustion model, to simulate primary breakup at a fraction of the cost of a fully resolved simulation. A high-fidelity model is employed within this study to model the combustion chamber; the model shows a backflow region that will contribute to clogging within the nozzle. This study modifies the injector type for SHVOF thermal spray by introducing a co-flow around the liquid injection to reduce clogging within the combustion chamber. This study shows that introducing a co-flow of gas at a velocity of 200 m/s around the liquid injection reduces the backflow region by 40% within the combustion chamber. The addition of a gas co-flow results in a smaller region of backflow. Small suspension droplets with insufficient momentum are unable to overcome the backflow and will likely deposit themselves onto the wall of the combustion chamber. The deposition of the particles on the walls causes clogging of nozzles often seen in SHVOF thermal spray. The addition of a gas co-flow results in an increase in the velocity of droplets formed during primary breakup. The greater droplet velocity allows for small droplets to overcome the small backflow region near the liquid injection. The Sauter mean diameters predicted from the numerical model are compared to experimental measurements available within the literature and shows good agreement.

The computational fluid dynamics (CFD) simulation on the effect of pillar shapes on chitosan-ZnO nanoparticles flows in pillar-based microfilter was considered using ANSYS Fluent in the laminar flow condition. Three shapes of the pillar were studied: cylindrical, cuboid, and rotated cuboid pillar. The volume of fluid (VOF) method was performed under a certain set of considerations and assumptions in order to validate the microfilter design to have the same flow patterns based on the literature. The discrete phase model (DPM) was carried out in order to simulate and analyze the chitosan-ZnO nanoparticles flow behaviour and separation efficiency performance in pillar-based microfilter. The DPM was carried out in 200, 300, and 400 streams to track the position of the nanoparticles in order to analyze the separation performance for each pillar shape. The simulation involved a different number of streams that were observed on the impact of nanoparticle Reynolds number and the total number of nanoparticles. It was observed that microfilter-C (rotated cuboid pillar) has the best separation efficiency of chitosan-ZnO nanoparticles compared to microfilter-A (cylindrical pillar) and microfilter-B (cuboid pillar) based on the particle position from the outlet of microfilter which was 2.5 mm, 0.08 mm, and 2.1 mm respectively. The shape of the pillar is a critical parameter that plays a significant role in the separation performance of nanoparticles in pillar-based microfilter.

CFD simulation on performance of new type umbrella plate scrubber

This study aims to identify lower risk exterior shelter areas and building air intake locations by modeling particulate matter (PM) dispersion in a three-dimensional street canyon from a point source and comprises a wind tunnel experiment and a computational fluid dynamics (CFD) simulation. The model street canyon was a two-by-two building array of constant height with aspect ratios of 0.35, 0.70, and 1.05. A PM emission source external to the street canyon was simulated with water droplets from an ultrasonic humidifier in the wind tunnel. The CFD simulation, using the standard turbulence k-ϵ turbulence model and the Discrete Phase Model, showed that, inside the street canyon, the sidewalks had the lowest PM concentration at the breathing level of 1.5 m above the ground. Regardless of wind direction and PM source location, the roofs had the lowest PM concentration among all building surfaces with access to the internal intersection. Therefore, if an accidental point release of PM outside the street canyons occurs, pedestrians that could not enter buildings should stay on the sidewalks. For building construction and renovation, new ventilation air intakes should be installed on the roofs, and the intakes that are already installed on other building façade surfaces should be advised to be closed during such episode.

In this work, we present goodness-of-fit tests related to the Kolmogorov-Smirnov and Michael statistics and connect them to graphical methods with uncensored and censored data. The Anderson-Darling test is often empirically more powerful than the Kolmogorov-Smirnov test. However, the former one cannot be related to graphical tools by means of probability plots, as the Kolmogorov-Smirnov test does. The Michael test is, in some cases, more powerful than the Anderson-Darling and Kolmogorov-Smirnov tests and can also be related to probability plots. We consider the Kolmogorov-Smirnov and Michael tests for detecting whether any distribution is suitable or not to model censored or uncensored data. We conduct numerical studies to show the performance of these tests and the corresponding graphical tools. Some comments related to big data and lifetime analysis, under the context of this study, are provided in the conclusions of this work.

The research on oil discharge ratio (ODR) of rotary compressors used for room air conditioners is very important to improve the performance and reliability of the compressors and their systems. This paper presents a detailed computational fluid dynamics (CFD) simulation model for the refrigerant gas flow and oil droplet flow within the shell of the compressor, which is used for investigating ODR of the compressor subjected to design changes or under different operating speeds. The geometry of the rotary compressor and its oil separating burden was presented. The CFD simulation is based on the discrete phase model (DPM). The oil droplet size distribution was defined by the Rosin–Rammler diameter distribution method. The boundary conditions of the refrigerant gas and oil droplets were established. Validation of the CFD model has been made by measuring ODR of a rotary compressor used in the high efficiency air room conditioner for different design configurations and an inverter rotary compressor with R410A. The simulation ODRs of the compressor agree within 11% of the experimental-measured ODRs. The ODR of compressor could be reduced effectively by some technique.

Cyclone is often used in the Industry due to its low maintenance costs, simple design, and ease of operation. This work presents both experimental and simulation evaluation on the effect of inlet velocity and mass flow rate on the performance of a wheat conveying cyclone. According to the great importance of the pressure drop and separation efficiency on the separation phenomenon in the cyclone, a comprehensive study has been conducted in this regard. A computational fluid dynamics (CFD) simulation was realized using a Reynolds stress turbulence model, and particle-air interactions were modeled using a discrete phase model. The result showed a good agreement between the measured value and CFD simulation on the pressure drop and tangential velocity with a maximum deviation of 6.8%. It was found that the separation efficiency increased with inlet velocity up to 16 m s−1 but decreased slightly at a velocity of 20 m s−1. The pressure drop increased proportionally with inlet velocity. However, optimum performance with the highest separation efficiency (99%) and acceptable pressure drop (416 Pa) was achieved at the inlet velocity of 16 m s−1 and mass flow rate of 0.01 kg s−1.

In the present study, imperative parameters including centrifugal force, erosion, streamline, strain rate, and wall shear are evaluated in a cyclone separator. The flaw of the cyclone surface due to erosion is an acute problem in the industry. According to the great importance of the centrifugal force on the separation phenomenon, a comprehensive study is conducted. A computational fluid dynamics (CFD) simulation is realized by applying a Reynolds stress turbulence model (RSM), and particle–air interactions were modeled using a discrete phase model (DPM). The result shows a good agreement between the experimental data and CFD simulation on the tangential velocity and pressure drop. The maximum deviation of the validation process is 6.8%. It is found that the centrifugal force within the cyclone is increased with an enhancement in the inlet velocity. The separation efficiency indicates an increase–decrease treatment in various inlet velocities with inlet velocity up to 16 m⋅s−1 but decreases slightly at a velocity of 20 m⋅s−1. The pressure increases proportionally with inlet velocity. The best performance with the highest separation efficiency (99%) and pressure drop (416 Pa) obtains at the inlet velocity of 16 m⋅s−1 and mass flow rate of 0.01 kg⋅s−1. In addition, the maximum erosion rate was created in the entrance and conical part of the cyclone.

During the Coronavirus disease 2019 pandemic, short-range virus transmission has been observed to have a higher risk of causing infection than long-range virus transmission. However, the roles played by the inhalation and large droplet routes cannot be distinguished in practice. A recent analytical study revealed the predominance of short-range inhalation over the large droplet spray route as causes of respiratory infections. In the current study, short-range exposure was analyzed via computational fluid dynamics (CFD) simulations using a discrete phase model. Detailed facial membranes, including eyes, nostrils, and a mouth, were considered. In CFD simulations, there is no need for a spherical approximation of the human head for estimating deposition nor the “anisokinetic aerosol sampling” approximation for estimating inhalation in the analytical model. We considered two scenarios (with two spheres [Scenario 1] and two human manikins [Scenario 2]), source-target distances of 0.2 to 2 m, and droplet diameters of 3 to 1,500 µm. The overall CFD exposure results agree well with data previously obtained from a simple analytical model. The CFD results confirm the predominance of the short-range inhalation route beyond 0.2 m for expiratory droplets smaller than 50 µm during talking and coughing. A critical droplet size of 87.5 µm was found to differentiate droplet behaviors. The number of droplets deposited on the target head exceeded those exposed to facial membranes, which implies a risk of exposure through the immediate surface route over a short range.Electronic Supplementary Material (ESM)the Supplementary Materials are available in the online version of this article at 10.1007/s12273-022-0968-y.

Computational fluid dynamics (CFD) simulations of steel flow in an Rheinsahl–Heraeus (RH) process are realized by a discrete phase model (DPM) for the driving bubble plumes, a volume of fluid (VoF) method for the free surface in the vacuum chamber (VC), and a large eddy simulations (LES) model for the transport and mixing of steel alloys. CFD simulations are opposed to particle image velocimetry (PIV) analyses of flow pattern at the bath surface in the VC. While simple Reynolds averaged turbulence models fail to reproduce these plant observations, LES agrees fairly well. Furthermore, the steel recirculation rate is compared with empirical correlations from the literature, yielding good agreement with respect to the dependency of the recirculation rate on the gas injection rate. The absolute value of the recirculation rate increases by 15%, in case (realistic) eroded edges are considered instead of a (unrealistic) sharp‐edged geometry. Data‐assisted recurrence CFD (rCFD) is applied to accelerate conventional CFD. The rCFD simulations yield a computational speed‐up of four orders of magnitude, enabling real‐time LES at full grid resolution of three million cells. Titanium homogenization in the steel ladle is addressed by means of rCFD and compared with corresponding plant trials yielding good agreement.

This paper presents a novel segment-based Eulerian-Lagrangian transition method for predicting the primary and secondary breakup behavior of a flat nozzle spray. It combines the Volume of Fluid (VOF) method for simulating liquid sheet disintegration and primary breakup with the Discrete Phase Model (DPM) method for secondary breakup. The VOF simulation predicts the varying thickness and local velocity characteristics of the liquid sheet from the center region to the edge region near the nozzle exit. Meanwhile, the proposed segment-based linear stability analysis in this study is capable of predicting the initial droplet variation resulting from primary breakup, considering the varying behavior of the liquid sheet from different regions. The simulation results match reasonably well with experimental data at both macroscopic and microscopic levels, effectively predicting the overall spray structure, mass flow rate, and droplet size variations across different regions with good accuracy. Both experimental and numerical data show that the Sauter mean diameter (SMD) values differ between the center and edge regions, with the edge region displaying larger droplets than the center region. This indicates that the segment-based approach is crucial for successfully predicting the spatial distributions of droplet size characteristics.

In this work, a commercial distributor head is evaluated. In parallel, both numerical simulations and laboratory tests, in a bench test belonging to the National University of Rosario, are carried out. This test bench has been built to evaluate components of air drill seeder’s pneumatic transport and distribution system. Soybean (Glycine max) seeds are used in the experimental tests. In Computational Fluid Dynamics (CFD) simulations, soybean seeds are modeled as spherical, rigid, and uniform size particles. The CFD simulations of the air-seed mixture are carried out with the commercial software ANSYS Fluent, and particle trajectories are numerically computed using a Lagrangian approach. A two-way coupling method is used, named Discrete Phase Model (DPM). Results show that numerical simulations are consistent with the laboratory tests, obtained in controlled trials. In both cases, the highest flow rates of seeds are produced in frontal outlets, while rear outlets present the lowest flow.KeywordsAir drillCFDSimulationDiscrete Phase Model

Predicting accurate erosion rate due to sand particles in oil and gas production is important for maintaining safe and reliable operations while maximizing output efficiency. Computational Fluid Dynamic (CFD) is a powerful tool for erosion prediction as it provides detailed erosion pattern in complex geometry. In an effort to improve accuracy of erosion prediction, this paper proposes an algorithm to accurately represent particle shape in CFD erosion simulation through coupling with Discrete Element Method (DEM) for non-spherical shape particles. The fluid motions are predicted by CFD and the particle movements (including particle-particle and particle-wall collisions) and fluid-particle interaction are calculated using DEM. It is widely known that sand particles are of finite volume with a non-spherical shape, accurate representation of sand particles is important in CFD modelling for accurate prediction of erosion rate. Traditional CFD approach usages lagrangian tracking of sand particles through Discrete Phase Model (DPM), where a particle is assumed as a point mass for the calculation of trajectory and particle-wall interaction. Particle impact velocity and impact angle are important parameter in determining erosion. Assumption of point mass in DPM approach, will not capture particle-wall interaction accurately especially when particles are of non-spherical in shape. In additional, DPM approach ignores particle-particle interactions. This can adversary affect the accuracy of erosion predictions. Integrating non-spherical DEM collision algorithm with CFD erosion simulation, will overcome these limitations and improve erosion predictions. Benefits of this CFD-DEM erosion modelling was demonstrated for gas-solid flow in a 2" pipework which consists of out-of-plane elbows in series and blind-tees. Experimental dataset [1] for erosion pattern on each elbow was used to validate CFD predictions. Three different erosion CFD simulations were performed, traditional DPM based CFD simulation, CFD-DEM simulation for spherical shape particles and CFD-DEM simulation for non-spherical shape particles. CFD-DEM coupled simulations clearly show an improvement on erosion predictions compared to DPM based CFD simulation. Effect of non-spherical shape on rebound angle during particle-wall collision is captured accurately in CFD-DEM simulation. CFD-DEM simulation using non-spherical particle, was able to predict erosion pattern closer to experimental observations. This paper will demonstrate an increase in accuracy of sand erosion prediction by integrating DEM collision algorithm in CFD modelling. The prediction results of elbow erosion subject to a condition of dilute gas-particle flow are validated against experimental data. Improved prediction of erosion risk will increase the safety and reliability of oil & gas operations, while maximizing output efficiency.

Computational fluid dynamics simulations of snow accumulation on infrared detection sensors using discrete phase model

A three-dimensional computational fluid dynamics (CFDs) model was developed to investigate the droplet breakup mechanisms during the initial stage of gas atomization of Ag–28 wt.%Cu alloy. The model integrates the volume of fluid method, shear stress transport k–ω turbulence model, discrete phase model, and Taylor analogy breakup model. Five distinct atomization stages were identified: (i) stable jet formation, (ii) flask-like deformation by gravity, (iii) necking and detachment from aerodynamic shear, (iv) fragmentation under high-velocity gas flow, and (v) establishment of dynamic equilibrium. Three primary droplet morphologies—elongated (fibrous), spherical, and ligamentous—were observed, along with two secondary breakup mechanisms: coalescence–dissociation and direct fragmentation. Experimental results showed a strong correlation between particle size and solidification behavior. Larger particles (140–180 mesh, ∼80–109 μm) underwent surface nucleation, forming mixed divorced and coupled eutectics with pronounced Cu segregation. Smaller particles (250–300 mesh, ∼50–61 μm) solidified via homogeneous nucleation, yielding uniform, refined lamellar eutectics. To further analyze solidification behavior, a two-dimensional solidification model was employed using initial conditions from CFD simulations. The results indicated that 50 μm droplets solidified at ∼1.25 × 104 K s−1, significantly faster than 90 μm droplets at ∼8.50 × 103 K s−1, highlighting the critical influence of particle size on solidification kinetics. Overall, this study provides a comprehensive understanding of the breakup and solidification processes in gas atomization of Ag–28 wt.%Cu alloy, offering valuable guidance for optimizing powder production in additive manufacturing and powder metallurgy.