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Chemical vapor deposition (CVD) is a crucial technique to prepare high-quality graphene because of its controllability. In the research, we perform a systematic computational fluid dynamics numerical investigation on the effect of gas-phase reaction dynamics on the graphene growth in a horizontal tube CVD reactor. The research results indicate that the gas-phase chemical reactions in the CVD reactor are in a nonequilibrium state, as evidenced by the comparison of species mole fraction distributions during the CVD process and under chemical equilibrium conditions. The effect of gas-phase reaction dynamics on the deposition rate of graphene under different conditions is studied, and our research shows that the main causes of change in graphene growth rates under different conditions are gas-phase reaction dynamics and active species transport. The results of numerical simulation agree well with the experimental phenomena. The research results also indicate that, for methane, the main limiting factor of graphene growth is the surface kinetic reaction rate. Conversely, for active species, the main limiting factor of graphene growth is species transport. Our research suggests that the growth rate of graphene can be regulated from the perspective of the gas reaction mechanism. This method has theoretical guiding significance and can be extended to the preparation of large-area graphene. [ABSTRACT FROM AUTHOR]

The rapid development of wearable electronics highlights the urgence to develop the portable energy harvester with excellent output performance, comfortability, and sustainability. This work designs an electromagnetic walking energy harvester based on water turbine that can be embedded in shoes with good comfortability. Its working principle is that the walking generated pressure energy drives a miniature hydraulic turbine to output electricity. Experimental results show that an average power of 300 and 180 mW can be produced at heel and toe, respectively, when a man of 80 kg walks at a speed of 1.8 m s−1. This power output exceeds the piezoelectric, triboelectric, and electromagnetic walking energy harvesters reported in the past. Additionally, the simpler structure endows it better comfortability as compared with the electrostatic capacitances. Computational fluid dynamics simulations provide a further insight that the efficiency of turbine can reach 13.5% by optimizing parameters of blade number and outlet flow ratio. Finally, user real-time positioning and trajectory recording are successfully demonstrated via a wearable GPS means Global Positioning System module powered by the harvester. Due to the combination of high output performance, simple structure and low discomfort, the water turbine based walking energy harvester will provide a wide application potential in wearable devices. [ABSTRACT FROM AUTHOR]

Chirped-Pulse Fourier-Transform millimeter wave (CP-FTmmW) spectroscopy is a powerful method that enables detection of quantum state specific reactants and products in mixtures. We have successfully coupled this technique with a pulsed uniform Laval flow system to study photodissociation and reactions at low temperature, which we refer to as CPUF ("Chirped-Pulse/Uniform flow"). Detection by CPUF requires monitoring the free induction decay (FID) of the rotational coherence. However, the high collision frequency in high-density uniform supersonic flows can interfere with the FID and attenuate the signal. One way to overcome this is to sample the flow, but this can cause interference from shocks in the sampling region. This led us to develop an extended Laval nozzle that creates a uniform flow within the nozzle itself, after which the gas undergoes a shock-free secondary expansion to cold, low pressure conditions ideal for CP-FTmmW detection. Impact pressure measurements, commonly used to characterize Laval flows, cannot be used to monitor the flow within the nozzle. Therefore, we implemented a REMPI (resonance-enhanced multiphoton ionization) detection scheme that allows the interrogation of the conditions of the flow directly inside the extended nozzle, confirming the fluid dynamics simulations of the flow environment. We describe the development of the new 20 K extended flow, along with its characterization using REMPI and computational fluid dynamics. Finally, we demonstrate its application to the first low temperature measurement of the reaction kinetics of HCO with O2 and obtain a rate coefficient at 20 K of 6.66 ± 0.47 × 10−11 cm3 molec−1 s−1. [ABSTRACT FROM AUTHOR]

In this research, CrN/CrAlN multilayer coating was deposited on X12CrNiMoV12-3 stainless steel samples and compressor blades by the physical vapor deposition (PVD) method. Based on the computational fluid dynamics model, an optimized thickness of less than 10 μm with a roughness of 0.35 μm was deposited. The coating's microstructure and phase composition were characterized by XRD and SEM. Nanoindentation, adhesion, scratch, and roughness tests as well as residual stress were realized in the coated samples. A Salt spray test was also done on the samples and blades to evaluate the corrosion resistance of the coating. The CrN/CrAlN coating's elastic modulus and hardness were 371 GPa and 1745 HV, respectively. The Corrosion resistance of coated samples and compressor blades was 930 and 50 h, respectively. The induced residual tensile stress of 176.23 MPa due to the required machining process of the compressor blade before the coating was the reason for the lower corrosion resistance of coated blades. to eliminate the residual stresses and improve the corrosion performance of the coating, the blades were subjected to the tumbling process before coating. By optimizing the tumbling process for 3 h, the residual tensile stress converted to a compressive stress of −129.11 MPa, and accordingly corrosion resistance of the coated blades increased to 950 h. [ABSTRACT FROM AUTHOR]

Bioprocess scale-up and technology transfer can be challenging due to multiple variables that need to be optimized during process development from laboratory scale to commercial manufacturing. Cell cultures are highly sensitive to key factors during process transfer across scales, including geometric variability in bioreactors, shear stress from impeller and sparging activity, and nutrient gradients that occur due to increasing blend times. To improve the scale-up and scale-down of these processes, it is important to fully characterize bioreactors to better understand the differences that will occur within the culture environment, especially the hydrodynamic profiles that will vary in vessel designs across scales. In this study, a comprehensive hydrodynamic characterization of the Ambr® 250 mammalian single-use bioreactor was performed using time-accurate computational fluid dynamics simulations conducted with M-Star computational fluid dynamics software, which employs lattice-Boltzmann techniques to solve the Navier-Stokes transport equations at a mesoscopic scale. The single-phase and two-phase fluid properties within this small-scale vessel were analyzed in the context of agitation hydrodynamics and mass transfer (both within the bulk fluid and the free surface) to effectively characterize and understand the differences that scale-down models possess when compared to their large-scale counterparts. The model results validate the use of computational fluid dynamics as an in-silico tool to characterize bioreactor hydrodynamics and additionally identify important free-surface transfer mechanics that need to be considered during the qualification of a scale-down model in the development of mammalian bioprocesses. • Multiphase hydrodynamic characterization of Ambr250 mammalian vessel using CFD. • Key scale-up parameters (mixing time, bubble size, and kLa) assessed. • Validated CFD characterization of small-scale model using experimental results. • During scale-up, free surface mass transfer is important in small-scale vessels. • CFD assessment of small-scale bioreactor helps to understand cell damage. [ABSTRACT FROM AUTHOR]

This document introduces a novel concept involving an Omni-Directional Guided Vane (ODGV) encompassing a vertical axis wind turbine (VAWT) with the goal of improving its overall performance. Extensive three-dimensional computational analysis of the airfoils used in this novel ODGV structure is conducted to investigate the impact of various geometric parameters. Diverse geometric configurations of the ODGV are explored to analyze wind flow behavior across the turbine utilizing a well-validated computational fluid dynamics (CFD) model. The numerical investigations employ the Reynolds Averaged Navier–Stokes (RANS) modeling approach with the k-epsilon turbulence model. The steady state governing equations are solved using the validated CFD solver STAR CCM+. The study considers three distinct inlet velocities: 3, 6, and 9 m/s, with the aim of improving flow behavior and velocity through the ODGV. Four different modifications of the ODGV are examined, and the accuracy of the CFD model is affirmed through comparison with NACA airfoil data. Integration of the ODGV results in an enhanced self-starting behavior of the VAWT, leading to a reduction in the cut-in speed. Validation results demonstrate a strong agreement with the data obtained from CFD simulations. These results suggest that most shape ratios, except for 0.3 and 0.4 at Tip Speed Ratio (TSR) of 1.3 and 3, contribute to enhancing power and torque coefficients. Furthermore, the findings indicate that with a Sharpe ratio of 0.56, both torque and power coefficients could be improved by up to 48% and 58%, respectively. [ABSTRACT FROM AUTHOR]

The steam condenser is a crucial component in power plants, playing a vital role in influencing the overall performance of steam power plants. This paper delves into a detailed assessment of the thermal aspects and evaluation of steam surface condensers. To conduct this rigorous evaluation, we meticulously crafted a three-dimensional (3D) model of a multi-tube single-pass counter-flow heat exchanger using ANSYS Design-Modeller. Within this model, a multiphase mixture model was harnessed to replicate the condensation process that takes place within the condenser. After the model's development, a series of computational fluid dynamics (CFD) simulations were expertly executed utilizing ANSYS Fluent Workbench. The simulations encompassed diverse cooling water flow rates and steam inlet velocities. Notably, two sets of CFD simulations were carried out: the initial set featured a velocity inlet in the condenser, while the second set involved CFD simulations with a pressure steam inlet. The findings derived from these simulations unveiled a noteworthy correlation between the condensation rate within the shell and both the rate of circulating water flow and the operational pressure of the condenser. Additionally, it was discerned that the condensation rate could be further influenced by the specific geometry of the condenser. In sum, this study concludes that optimizing the geometrical configuration and baffle arrangements holds promise for increasing the condensation rate and overall performance of steam condensers employed within steam power plants. [ABSTRACT FROM AUTHOR]

Tidal turbine arrays have undergone extensive research to determine the optimal spacing for efficient performance and reduced wake generation. Small-scale laboratory tests are typically conducted to analyze wake structures prior to deployment. These tests often result in conditions of extreme blockage due to channel narrowing in comparison to turbine size. The primary objective of this study is to investigate flow behavior around turbines under blockage conditions and their performance close to the free surface, both in current-only and wave-and-current scenarios. The methodology employed a combination of blade element momentum theory and computational fluid dynamics (CFD) integrating a virtual blade model (VBM) code. The findings of this study indicate potential enhancements in tidal turbine array performance of up to 7% in lateral arrangements and 11% in streamwise arrangements under blockage conditions. The wake is significantly influenced by surface waves, which also contribute to increased downstream turbine performance. [ABSTRACT FROM AUTHOR]

The dissociation of the hydrogen molecule is rarely explored in the high-temperature flow of modern and historic nuclear thermal propulsion (NTP) engines. This study investigates the impact of absorption on highly-enriched and low-enriched uranium NTP reactors due to hydrogen dissociation surface reactions. Results show that with increasing temperature, dissociated hydrogen has a decreasing wall coverage but a significant crossflow velocity, as high as 81 mm/s, near the outlet due to absorption. This absorption changes the turbulent velocity profile while only having a small effect on the local Stanton number. Changing velocity profiles and mass loss to the wall can change mass flow rates, altering engine performance. Calculation and modeling via analytical solutions are unlikely as similar studies show non-uniqueness and existence issues at this study's R e w = 1.43. Follow-on computational fluid dynamic modeling is needed to fully capture the performance changes to the NTP engine. [Display omitted] • Notable hydrogen absorption into cladding begins at surface temperatures of 1500 K. • Highest temperatures cause the highest hydrogen absorption velocity near 81 mm/s. • Comparison to similar data shows the local Stanton Number is not largely impacted. • Axial increase in temperature may cause thermal gradients and flow circulation. • Others show R e w = 1.43 has multiple solutions and potential backflow at the wall. [ABSTRACT FROM AUTHOR]

Adsorption is a promising technology for reducing CO2 emissions from combustion gases. However, some issues must be considered when designing large-scale units with low environmental impact and cost. In this contribution, some of these issues are addressed. Firstly, sugarcane bagasse is selected as a meaningful model system. 13XBF Kostrolith zeolite is used as the adsorbent, and adsorption equilibrium data are determined using a magnetic suspension balance from Rubotherm. 13XBF showed a high CO2 capacity and CO2/N2 selectivity under post-combustion scenario conditions. Secondly, the fluidized bed process was optimized using a 3-stage adsorber and a 3-stage desorber, with heat exchangers that can be used in each stage. The constrained variable in the adsorption column is the solid-to-gas mass feed ratios. It was found that substantial CO2 recovery with 98% purity can be achieved and that the heat load in the desorption column accounts for the highest energy-optimized cost in the process. Thirdly, a detailed CFD model for the fluid dynamics and heat transfer of fluidization for one stage is presented. Bubbles were defined using a hyperbolic filter as predicted by the model, which was consistent with the semi-empirical model and emphasized the significance of bubble size in gas–solid heat transfer, which is essential to the effectiveness of adsorption/desorption. The bubble portion and its effects on the temperature are estimated. Finally, a semi-empirical approach is applied to understanding the controlling factors in a fluidized bed adsorption stage. Results show that the mass transfer from the bubbles to the emulsion is likely the most important resistance to the fluidized adsorber. [ABSTRACT FROM AUTHOR]

Intracranial aneurysms are nowadays treated with endovascular flow diverter devices to avoid sac rupture. This study explores how different linear and quadratic hydrodynamic resistance parameters reduce the flow in the sac for five patient-specific sidewall aneurysms.The 125 performed blood flow simulations included the stents using a Darcy-Forcheimer porous layer approach based on real-life stent characteristics. Time- and space-averaged velocity magnitudes were strongly affected by the linear coefficient with a power-law relationship. Quadratic coefficients alter the flow in a minor way due to the low-velocity levels in the aneurysm sac and neck region. [ABSTRACT FROM AUTHOR]

CFD‐based compartment (CPT) models offer a promising modeling method and trade‐off between computational effort and required accuracy. The models combine the relevant fluid dynamics from the computational expensive CFD and the incorporation of complex reaction mechanisms usually used in basic reactor models. However, one criticism is their reliance on specific operating points, rendering them invalid when boundary conditions change. This study explores using a CFD‐based CPT model for static mixing elements across multiple operating points by making use of the creeping flow. The mean age theory facilitates a comprehensive comparison between CFD and CPT models. Results indicate that within this flow region, the CPT model can be extrapolated to other operating points via linear scaling. [ABSTRACT FROM AUTHOR]

Several methods are available for evaluating nasal breathing and nasal airflow, as this evaluation may be made from several different perspectives. Physiologic methods for nasal airway evaluation directly measure nasal airflow or nasal airway resistance, while anatomical methods measure nasal airway dimensions. Subjective methods evaluate nasal breathing through several validated patient-reported scales assessing nasal breathing. Computational fluid dynamics evaluates nasal airflow through the analysis of several physics' variables of the nasal airway. Being familiar to these methods is of utmost importance for the nasal surgeon to be able to understand data provided by the different methods and to be able to choose the combination of evaluation methods that will provide the information most relevant to each clinical situation. [ABSTRACT FROM AUTHOR]

This article is an examination of computational fluid dynamics in the field of otolaryngology, specifically rhinology. The historical development and subsequent application of computational fluid dynamics continues to enhance our understanding of various sinonasal conditions and surgical planning in the field today. This article aims to provide a description of computational fluid dynamics, the methods for its application, and the clinical relevance of its results. Consideration of recent research and data in computational fluid dynamics demonstrates its use in nonhistological disease pathology exploration, accompanied by a large potential for surgical guidance applications. Additionally, this article defines in lay terms the variables analyzed in the computational fluid dynamic process, including velocity, wall shear stress, area, resistance, and heat flux. [ABSTRACT FROM AUTHOR]

An objective assessment of nasal breathing is currently insufficiently achievable. The application of computational fluid dynamics for this purpose is increasingly gaining attention. However, the suggested specific frameworks can differ considerably. To the best of our knowledge, there is not yet a widely accepted clinical usage of computational fluid dynamics. In this article, selected aspects are addressed that might be crucial for future development and possible implementation of computational fluid dynamics in rhinology. [ABSTRACT FROM AUTHOR]

Measuring nasal obstruction should be mandatory before every nasal surgery to determine the necessary surgical steps and to separate mucosal congestion from skeletal deformity. Rhinomanometry is considered the "golden standard" for measuring nasal airway resistance. An extension of the diagnostic power was achieved by the introduction of the four-phase rhinomanometry (4PR), which provides additional information about the influence of the elasticity of the nasal wall. Also, a high correlation to the subjective sensing of obstruction could be achieved by the introduction of logarithmic parameters. The parameters of 4PR could be classified by evaluating 36,500 measurements. The International Standardization Committee on the Objective Assessment of the Upper Airway (ISCOANA) determined it as the new standard. Adding a visual analog scale (VAS) to every measurement is a documentation of the feeling of obstruction at the moment of measurement. Practical hints for 4PR are given. The determination of obstruction for both nasal sides or the calculation of the total nasal resistance should be followed by a second analysis of the detailed obstruction anatomy. In the future, pressure losses or temperature gradients can be determined by computational fluid dynamics (CFD). A reliable way to simulate the success of single surgical steps with a high didactical meaning is the three-dimensional (3D) print of sliced nose models and to measure the effect of stepwise mechanical corrections. [ABSTRACT FROM AUTHOR]

Objectives: Ecogeographic variation in human nasal anatomy has historically been analyzed on skeletal morphology and interpreted in the context of climatic adaptations to respiratory air‐conditioning. Only a few studies have analyzed nasal soft tissue morphology, actively involved in air‐conditioning physiology. Materials and Methods: We used in vivo computer tomographic scans of (N = 146) adult individuals from Cambodia, Chile, Russia, and Spain. We conducted (N = 438) airflow simulations during inspiration using computational fluid dynamics to analyze the air‐conditioning capacities of the nasal soft tissue in the inflow, functional, and outflow tract, under three different environmental conditions: cold–dry; hot–dry; and hot–humid. We performed statistical comparisons between populations and sexes. Results: Subjects from hot–humid regions showed significantly lower air‐conditioning capacities than subjects from colder regions in all the three conditions, specifically within the isthmus region in the inflow tract, and the anterior part of the internal functional tract. Posterior to the functional tract, no differences were detected. No differences between sexes were found in any of the tracts and under any of the conditions. Discussion: Our statistical analyses support models of climatic adaptations of anterior nasal soft tissue morphology that fit with, and complement, previous research on dry skulls. However, our results challenge a morpho‐functional model that attributes air‐conditioning capacities exclusively to the functional tract located within the nasal cavity. Instead, our findings support studies that have suggested that both, the external nose and the intra‐facial soft tissue airways contribute to efficiently warming and humidifying air during inspiration. This supports functional interpretations in modern midfacial variation and evolution. [ABSTRACT FROM AUTHOR]

Heat generated from the bulb of an automotive lamp is transferred to the lamp reflector and lens through a heat-transfer mechanism. If the heat transferred to the reflector and lens exceeds the heat resistance limit of the materials used in their production, the materials deform. Therefore, lamp designers must design lamps within a limited range. If the lamp fails the heat resistance test after the design and pilot model production, the design process must be restarted. Redesigning requires significant time and costs. Therefore, a temperature-prediction algorithm for a single-function lamp during the initial design stage was developed in a previous study. In this study, a multifunction temperature-prediction algorithm with two or more heat sources was developed to predict the temperature of lamps of various shapes. The focus length based on the parabolic shape of the bulb installation surface and corner slope values near the lens were used to reflect the actual shape of the lamp. The introduction of the effective area improved the accuracy of the temperature prediction for the upper surface, which was strongly influenced by convection. The performance of the developed algorithm was evaluated by comparison with the computational fluid dynamics (CFD) results of an actual lamp model. Consequently, it was confirmed that the newly developed best prediction algorithm can be effectively applied to new automotive lamp designs. [ABSTRACT FROM AUTHOR]

A flow field analysis of a realistic, integrated, multidisk boundary layer pump as is necessary for investigating the reasons for typically quoted low efficiencies in such pumps is described. The study focuses on the three-dimensional RANS solutions of a water boundary layer pump model created to replicate a design by Morris, 1973, which consists of 170 disks and a volute channel. A baseline study is performed to investigate the rotor-only performance after which a volute alone is separately simulated to identify the performance and losses in each as separate systems. Thereafter, an integrated model is characterized across mass flow rates and rotational speeds. The flow fields of all three models are discussed and the results of the integrated model are compared to the experimental data. The results from the model with the rotor only confirm the typically made claim that the efficiency of the rotor in a boundary layer pump possesses relatively high values which in this case is ~87% at the design point, reinforcing results from previous studies that the rotor assembly is not the cause of inefficiency. The volute on its own indicated a hydraulic efficiency of around 97%. However, the integrated model yielded a rotor efficiency of around 74\% and an overall pump efficiency of 51% at the design point, clearly outlining the fact that the effect of the volute integrated with the rotor is the reason for both the rotor and pump efficiency degradation. The reason for this drop in efficiency is discussed in detail by highlighting the change in the flow topologies. The insights into the flow field and the identification of the reason for inefficiencies using a separated component analysis approach provide directions for avenues in which design improvements would need to be attempted. [ABSTRACT FROM AUTHOR]

The safety and serviceability of long-span bridges can be significantly impacted by wind effects and therefore it is crucial to estimate them accurately during bridge design. This study develops full-scale three-dimensional computational fluid dynamics (CFD) simulation models to replicate wind conditions at the Rose Fitzgerald Kennedy Bridge in Ireland. The neglect of bridge geometries and the use of small scales in previous studies are significant limitations, and both the bridge geometry and surrounding terrain are included here at full scale. Input values for wind conditions are mapped from weather simulations that apply the weather research and forecasting model. Wind velocities at four different points calculated by CFD simulations are compared with corresponding data collected from structural health monitoring field measurements. The calculated time-averaged wind velocities at four different locations on the bridge are shown to have relative differences of less than 10% from the wind velocities measured by anemometers 90% of the time. The maximum relative difference among all comparisons was only 15%, shown to be partially due to the inclusion of the full bridge and terrain geometry. [ABSTRACT FROM AUTHOR]

In order to predict the spiral bevel gear churning power loss, based on the Computational Fluid Dynamics (CFD) method, the computational model for the splash lubrication of the spiral bevel gear pair is established and validated by experiments. The churning power loss of spiral bevel gears is obtained and the corresponding flow field distribution in the gearbox with a pair of spiral bevel gears is analysed under a standard operating condition. For the churning power loss of spiral bevel gears, the loss of teeth surface is mainly caused by pressure while the loss of gear side is mainly generated by the viscous force. The effects of the gear rotational speed, oil level, oil temperature and oil shroud on the churning loss are also investigated and analysed. Ultimately, an optimisation method is proposed for the original spiral bevel geared transmission. [ABSTRACT FROM AUTHOR]

The conventional sonic boom propagation prediction method widely adopted in supersonic aircraft design involves a two-step procedure. In the first step, a compressible viscous or inviscid Computational Fluid Dynamics analysis is applied to the aircraft geometry at flight conditions to produce a flow field solution near the aircraft. Then in the second step, a one dimensional nonlinear Burgers' equation model is used to propagate sonic boom signature traces from the near field solution at flight altitude to the ground along a ray path. For an accurate ground signature prediction the near field signature must be accurately modeled at a sufficient distance from the aircraft flight path in order to minimize errors in the one dimensional propagation model. This is a very challenging task for general purpose CFD tools in a design environment because the cost of maintaining highly accurate off-body solutions increases dramatically as the radial distance is enlarged in the computational domain. It is also particularly difficult to apply these tools for wave propagation because the algorithms are normally lower order and numerically dissipative and dispersive. In this work a space marching procedure based on an optimized higher order finite difference method is developed and applied in conjunction with a CFD solution concentrated in the close vicinity of the aircraft. This new approach is much more efficient, compared to previous methods, in providing highly accurate near field signatures for full carpet ground predictions. Results indicate that near field signatures retain more waveform shape information farther from the aircraft geometry while reducing the CFD cost significantly. The predicted ground signature is also shown to converge in shape as the radial distance of the near field signature grows, which is indicative of a more ideal initial condition being supplied to the one dimensional wave propagation to ground. This feature is very difficult to replicate in a tractable manner with common CFD approaches used in design. [ABSTRACT FROM AUTHOR]

The service life and irrigation efficiency of drip irrigation systems are largely determined by the anti-clogging performance of the emitters. The degree and speed of clogging of the emitters are governed by the motion state of the particles in the flow channel. Computational fluid dynamics coupled discrete element method (CFD-DEM) and experiments were used to analyse anti-clogging performance and particles transport characteristics of a stellate irrigation emitter. With the angle of repose of sediment particles as the optimization objective, the key parameters of physical properties of sediment particles and container were obtained in the discrete phase model using a Plackett-Burman test, steepest climb test and Box-Behnken test. A novel evaluation method for assessing anti-clogging performance based on particles mass passing rate is proposed and its accuracy experimentally verified. Using three particles groups with different particle size distributions, the anti-clogging performance of stellate emitter was found to better than the widely used toothed emitter. In particular, the anti-clogging performance of the stellate emitter was found to be superior with the sensitive particle size of 0.03 mm. It was shown that sediment particles demonstrated retention, bonding and deposition in the inlet far away from the flow channel, the backwater area at the vertical vertex of the stellate structure and the backwater area at the joint of the stellate emitter flow channel structure units. • The parameters of physical properties of sediment particles and emitter are obtained. • A novel evaluation method for anti-clogging performance is proposed. • Anti-clogging performance of the stellate emitter is better than toothed emitter. • The transport characteristics of particle groups are analysed. [ABSTRACT FROM AUTHOR]

A model-based investigation of the interplay between furnace setup and spatio-temporal evolution of particles' state variables is also presented. The effect of feed size distribution and processing of ultrafine ore are discussed. The process is controlled primarily by the wall temperature and secondarily the air feeding rate; an increase of furnace wall temperature from 900 to 1200°C reduced the final density to 484, 979, and 1262 kg/m3 for feed size of 150 μm, 250 μm, and 350 μm. Model predictions are in good agreement with the experimental measurements possessing differences below 10% in most cases. [ABSTRACT FROM AUTHOR]

This paper presents a solution verification and validation study for an overset mesh based numerical wave tank in OPENFOAM, which considers the coupling between a free-surface hydrodynamic flow model, a rigid body motion model, and an overset mesh. The coupling between the rigid body motion solver and the free-surface flow solver was achieved in a segregated manner. Free decay of roll motion of a barge was modeled using the numerical wave tank, and the damping coefficient was selected as the target quantity for solution verification. The least-square based solution verification procedure was adopted, where one of the four types of error estimators was fit to the data in the least-square sense. Both structured and unstructured mesh were tested, and their effects on the convergence order, numerical uncertainty, and error were carefully investigated. From the numerical tests, it is found that the numerical wave tank exhibits a very good convergence property for the floating body problems with structured mesh, i.e., nearly second order in space and first order in time. However, when switching the body-fitted mesh to unstructured mesh, the grid convergence is reduced to first order. Unstructured mesh does not significantly affect the convergence order in time domain, but results in a larger uncertainty due to data scattering. [ABSTRACT FROM AUTHOR]

Most models employed for fluid forces in drill-string dynamics are of reduced order. The simplified nature of these models often fails to describe the complex behavior of the fluid force, in particular, when the drill-string movement is non-trivial or even when non-Newtonian behavior is predominant. In this work, the fluid forces are estimated by modeling the dynamic of the drilling fluid for both Newtonian and non-Newtonian fluids, and compared with reduced-order models. To achieve it, the lattice-Boltzmann method is implemented to solve the fluid model, while prescribed movements are set for the tool-joint. With the obtained fields, the forces are calculated and compared with recurrent models. Finally, it is observed that some models are capable of describing the interaction as long as the dynamic of the tool-joint is simple. In the presence of other trajectories--e.g., bouncing and chaotic--the models fail to describe the details of the dynamic. [ABSTRACT FROM AUTHOR]

In general, submarines are designed to optimize operation below the water surface because they spend most of their time underwater. On the other hand, the performance in the free surface condition is also important because submarines face a variety of scenarios to complete operational missions, and the free surface condition is unavoidable for port departure and arrival. In the case of a submarine, the numerical accuracy of the potential theory for seakeeping analysis is excellent in submerged conditions, but it is poor in free surface conditions because of nonlinear effects near the free surface area. In this study, STAR-CCM+ was used as a Reynolds-averaged Navier-Stokes (RANS) solver to estimate the seakeeping performance of a Canadian Victoria Class submarine in irregular waves. The results were compared with those of model tests from a published paper. In addition, the potential theory code was also used to assess the seakeeping performance and compare it with computational fluid dynamics (CFD) results. From the calculation results, the motion responses in irregular waves using CFD showed similar trends to the experimental results. In contrast, motion responses from potential code showed significantly larger values than the experimental results. In conclusion, CFD simulations with irregular waves can be a good solution to predict the seakeeping performance of submarines in free surface conditions. [ABSTRACT FROM AUTHOR]

This article uses scaled physical and numerical modeling to investigate an idealized but complicated problem in which green water impacts a circular cylindrical structure located on top of a fixed box representative of a vessel. A focused wave group was used to overtop the box and generate the green water event, which resembled a plunging wave with air entrainment. The plunger collapsed and ran across the deck before impacting and then scattering from the cylinder. To test the adequacy of the physical modeling, nominally identical experiments were conducted in two different laboratories, in different countries. The numerical modeling comprised computational fluid dynamics (CFD) simulations performed using openfoam. The flow features, the force on the cylinder, and the surface elevation on top of the box are compared in detail across the two physical models and the CFD. Consistent load measurements were obtained from the two physical model tests, with force impulse results differing by less than 10%, underscoring the validity of the results, even accounting for the complexity of flow-structure interactions. A comparison with numerical model results reveals some sensitivity to experimental precision in the flow measurements on top of the box and the green water load. Nonetheless, the overall force impulse discrepancy between experiments and numerical models is within 15%, highlighting that the robustness of the methods was used despite these sensitivities. The sensitivity to CFD mesh and iterating the incident wave to match CFD and experiment are also explored. The agreement between experiment and CFD serves as an example of the utility of CFD for modeling green water loads. [ABSTRACT FROM AUTHOR]

Microcombustors are microscale combustion devices that can be used to power microelectromechanical systems. Many combustor configurations are reported in the literature and, among them, combustion in a microscale recirculating heat exchanger is a feasible option. In this work, a simple, double‐channel, recirculating heat exchanger is considered. The novelty of the present work lies in the heat transfer analysis approach to design a microcombustor. A combustor is designed using thermal resistance networks for a premixed fuel containing a methane–air mixture in stoichiometric ratio. The length of the combustor is designed based on the position of the combustion flame. Computational fluid dynamics is utilized to validate the theoretical results. The analysis is carried out for adiabatic and nonadiabatic conditions. The combustor lengths for adiabatic and nonadiabatic (ceramic) combustors vary from 39 to 242 mm and 49 to 276 mm, respectively, for variations in the mass flow rate of the premixed gases from 6 to 10 mg/s. A minimum limiting flow rate of 6 mg/s was identified. The average error in the maximum combustion gas temperatures between the theoretical and CFD results obtained in this work is 4.2%. The theoretical approach presented can be suitably applied to more complex geometries involving multichannels and variations in geometrical properties. [ABSTRACT FROM AUTHOR]

Reducing friction using lubricant is of great significance to reducing energy consumption and extending the life of machinery. Surface texturing is effective to enhance the lubrication condition, and it is crucial to properly design the texture’s morphology. In this study, a sector-shaped surface texture is designed and demonstrated using both numerical and experimental methods. A computational fluid dynamic method based on Navier–Stokes equations and a two-phase cavitation model is performed to evaluate the effect of the texture in the hydrodynamic lift and to optimize the geometrical parameters of the texture. The mechanism associated with the additional hydrodynamic pressure generation is also revealed according to the results of the simulation. Then, pin-on-disk rotary friction experiments are performed on steel disks textured by a femtosecond laser to verify the lubricant effect of the proposed texture. The results of the experiment suggest that the sector-shaped textures reduce friction more than conventional circle-shaped textures, which coincides well with the results of the simulation. [ABSTRACT FROM AUTHOR]

A foreseen feature of the Molten Salt Fast Reactor is the adoption of a bubbling system for the removal of gaseous and metallic fission products (FPs). This mechanism injects helium bubbles into the core to remove FPs from the salt through floating and mass transfer mechanisms for metallic and gaseous FPs, respectively. The present work is aimed at analyzing this helium bubbling system, focusing on gaseous FPs. We investigate both operational and safety-related features in order to get information useful for the design and to assess the convenience of its adoption. Accordingly, our investigations split into two strands: (1) analyzing the characteristics of the bubbling system itself and (2) assessing the safety features of the reactor in its presence. In order to perform the above analyses, we add the capability to simulate production, transport, and mass transfer of an arbitrary number of gaseous FPs to a preexisting multiphysics solver, built with the OpenFOAM suite. In terms of operational characterization, our analyses quantify the removal efficiency through a characteristic removal time and estimate the poisoning effect of gaseous FPs. In addition, we evaluate the activity and decay heat of the removed gas, which is an aspect crucial for the design of the off-gas unit, and the effect of the bubbling system on the power versus the fuel mass flow rate curve, which is a possible control mechanism. Among our safety-related studies, we first evaluate the void coefficient, determining upper bounds on the helium flow rate in order to avoid prompt supercriticality in case of prompt loss of helium injection. The latter accidental scenario is also analyzed considering the thermal-hydraulic dynamics of the system. We also discuss another accident: complete loss of helium removal. [ABSTRACT FROM AUTHOR]

This paper considers the steel reheating process, in which cold slabs are reheated to a temperature suitable for hot rolling operations. Temperature uniformity within the slab is very important during reheating, as non-uniformities often lead to quality concerns in the later stages of the production process. Attaining slab temperature uniformity is quite challenging, therefore, a thorough understanding of the reheating process becomes very important. Due to the extreme conditions inside the furnace, numerical tools like computational fluid dynamics are necessary for such situations. However, when applied to these complex installations, it often leads to very lengthy computational times. This paper develops a computationally efficient transient model to simulate the environment around a slab. This Truncated Transient Slab Model is a coupled model: it uses the temperature and flow profiles from a full-scale steady-state simulation and imposes those on a smaller domain that represents the immediate environment around the slab. The efficiency of the model is compared to the state of the art. With the simulations available in the literature, it was found that the proposed model can simulate a furnace seven times larger (grid size), with much higher grid and time resolutions, using only a third of the computational resources. [ABSTRACT FROM AUTHOR]

The heat recovery steam generator (HRSG) can be regarded as a heat exchanger, which uses the heat rejected from the gas cycle to supply steam for the vapor cycle. HRSGs are consisted of many tube bundles (or harps). Supplying a duct burner in the upstream of an HRSG necessitates constructing the first bundle using different finned-tube materials with dissimilar fin configurations including unequal fin-pitch sizes. The computational fluid dynamics (CFD) has been widely used to study the flow through tube bundles; however, considering a fixed fin-pitch size for all rows of the finned-tubes. There is no trace of numerical analyses to treat tube bundles with unequal fin pitch sizes, apparently, because there are major challenges for the classical strategies, say unified-domain approach, to simulate tube bundles constructed from tubes with different fin configurations. This work introduces the splitted-domain approach as an innovative strategy to pass over the challenges with using the unified-domain approach. Then, these two approaches are used to model the superheater module of a real HRSG with available online measured data. The calculated Nusselt numbers and pressure drops indicate that the splitted-domain approach provides more accurate results than the unified one in simulating tube bundles constructed from tubes with dissimilar fin configurations. [ABSTRACT FROM AUTHOR]

Advanced reactors are characterized by passive safety systems to be activated in case of an accident. Molten salt reactors are equipped with a passive emergency draining system. In case of an accident, the reactor shuts itself down, the freeze plug melts due to decay heat, and fuel salt is discharged into the draining tank. The behavior of the freeze plug during liquid-to-solid transition and reactor operation, as well as in the event of an accident was investigated taking two important safety criteria into consideration i.e. the plug shall not melt during normal operation (unwilling opening) and shall passively melt in case of an accident. To evaluate the effectiveness of the freeze plug, computational fluid dynamics method was used. The results showed that draining pipe blocking time is 900 s and 70% of the interior of the freeze plug solidifies in 2700 s. Furthermore, it was concluded that the freeze plug did not cause any unwilling opening. In addition, the freeze plug opening time was calculated as 400 s. Since this value is less than the limiting time of 1100 s which depends on material strength temperature, the freeze plug can be utilized as a passive safety system component. [ABSTRACT FROM AUTHOR]

Open-channel junctions pose a risk associated with flooding and erosion. However, despite the numerous studies concerning the channel junctions, the bed and flow field evolutions at junctions for flood conditions have yet to be investigated. To address this research gap, this paper investigates the evolutions of the bed and flow field during a flood event at a right-angled open-channel junction utilizing three-dimensional (3D) computational fluid dynamics (CFD) modeling. The transient Reynolds-averaged Navier–Stokes (RANS) equations with the renormalized group (RNG) k–ϵ as the turbulence closure for the flow field, the Meyer-Peter and Muller equation for bed-load sediment transport rate, the convection–diffusion equation for the sediment concentration distribution, and the sediment continuity equation for the bed evolution are used in the numerical model. The model simulates the characteristics bed morphology at the junction with reasonable accuracy compared with the available laboratory data. Three scenarios (Scenarios 1, 2, and 3) were considered by applying the triangular flood wave at the inlet of the tributary channel, main channel, and both channels, respectively. The quasi-equilibrium deformed bed channel junction with steady inflow conditions of the validation case was considered as the initial condition for the flood flow simulations. The simulated results show that the junction bed is deformed considerably due to the significant increase in bed shear stress during a flood event. The deepest scour area gradually grows wider during the passage of the flood wave. The maximum value of the scour increased by 24.4%, 14.6%, and 31.2% in Scenarios 1, 2, and 3, respectively. The findings of the study improve the understanding of the junction hydrodynamics and bed morphological features for flood conditions. [ABSTRACT FROM AUTHOR]