Stagnant Zones Research Articles

Effects of Channelling a Peripherally Inserted Central Venous Catheter on Blood Flow

A catheter is a device that is inserted into the venous system to infuse treatment with controlled doses per unit of time. The study of its interaction with blood flow cannot be easily analysed with common analytical methods or different visualization techniques in real life. Computational Fluid Dynamics has become a very useful tool in a wide variety of fields of scientific study and has allowed access to the understanding of the anatomical and physiological functioning of the human body. In this work, Computational Fluid Dynamics is used to study the effects of inserting a catheter on blood flow and the quality of the mixture of blood with the various substances infused through this device. Results show that the insertion of the catheter not only does not worsen the blood circulation but improves it by reducing stagnant zones. Regarding mixture, a homogenization of the fluids in the venous area before their entrance to the heart was observed. Highest quality mixtures correspond to fewer infused fluids and at lower velocity.

PRINCIPLES OF SIMULATION OF ENERGY-EFFICIENT GRANULATION PROCESSES IN A FLUIDIZED BED

The principles of physical and mathematical modeling of inhomogeneous jet-pulsating fluidization in the self-oscillating mode considering the movement of solid granulated particles on the working surfaces of the gas distributing device are investigated. The research tasks include substantiating the method of interaction between the gas phase and granular solids to ensure the implementation of heterogeneous jet-pulsating fluidization in the self-oscillating mode, experimentally determining hydrodynamic parameters to minimize the risk of stagnant zones on the working surface of the gas distributing device and formulating principles for introducing flat gas jets into orthogonal planes through a gas distribution device. The physical model focuses on creating heterogeneous jet-pulsating fluidization which is based on the formation of heterogeneous porosity in the bed of solids within the apparatus chamber. The study highlights the importance of rationally organizing the interaction mode between the gas phase and solids to ensure active circulation of granular material between 3 main technological zones: humidification, active heat exchange and relaxation. This organization enables sufficient mass transfer along the height of the bed and getting a product with the desired properties. Implementing the proposed modeling principles in equipment development will allow increasing the heat utilization coefficient by more than 60 % and will facilitate the implementation of innovative technology. The research contributes to the development of fluidization technology and its application in granulation at temperatures exceeding the melting point of thermolabile components, ensuring efficient use of resources and energy, and enhancing the environmental safety of technological processes. Bibl. 22, Fig. 11.

Anatomical compatibility of a novel total artificial heart-An in-silico study.

ShuttlePump is a novel total artificial heart (TAH) recently introduced to potentially overcome the limitations associated with the current state-of-the-art mechanical circulatory support devices intended for adults. In this study, we adapted the outflow cannulation of the previously established ShuttlePump TAH and evaluated the anatomical compatibility using the virtual implantation technique. We retrospectively assessed the anatomical compatibility of the ShuttlePump using virtual implantation techniques within 3D-reconstructed anatomies of adult heart failure patients. Additionally, we examined the impact of outflow cannula modification on the hemocompatibility of the ShuttlePump through computational fluid dynamic simulations. A successful virtual implantation in 9/11 patients was achieved. However, in 2 patients, pump interaction with the thoracic cage was observed and considered unsuccessful virtual implantation. A strong correlation (r <-0.78) observed between the measured anatomical parameters and the ShuttlePump volume exceeding pericardium highlights the importance of these measurements apart from body surface area. The numerical simulation revealed that the angled outflow cannulation resulted in a maximum pressure drop of 1.8 mmHg higher than that of the straight outflow cannulation. With comparable hemolysis index, the shear stress thresholds of angled outflow differ marginally (<5%) from the established pump model. Similar washout behavior between the pump models indicate that the curvature did not introduce stagnation zone. This study demonstrates the anatomic compatibility of the ShuttlePump in patients with biventricular failure, which was achieved by optimizing the outflow cannulation without compromising hemocompatibility. Nevertheless, clinical validation is critical to ensure the clinical applicability of these findings.

Optimization of the power performance for three hybrid Darrieus-Savonius rotors based on the Taguchi method

Abstract The hybrid vertical-axis wind turbine is a unique design that overcomes the efficiency limitations of Savonius rotors and the start-up challenges of Darrieus rotors. This study uses the Taguchi optimization method to enhance the performance of a cluster of three hybrid Darrieus-Savonius vertical-axis wind turbines. The optimized parameters include distances between adjacent turbine centers, configuration angles, rotational directions, and the pitch angle. The study is the first to investigate the effect of varying the pitch angle of Darrieus airfoil blades on hybrid design performance. The optimal configuration of the three hybrid VAWTs and the isolated rotor is analyzed through flow velocity, pressure, and turbulence kinetic energy contours. The results show that the pitch angles have the greatest effect on the rated power coefficient among other studied influencing parameters. The optimal cluster configuration’s performance improvement is due to the favorable velocity gradient around the blades. Compared to the isolated rotor, the power coefficient enhancement for the optimal case is 46.545% at the rated tip speed ratio of 3.08. The hybrid rotor in the cluster can achieve almost the same power as the isolated rotor up to a tip speed ratio of 4.1 instead of 2.86 for the isolated rotor. However, the decrease in overall efficiency for some cluster configurations is due to wake flow intensity and trapping between the rotors, which causes a stagnation zone.

Effects of Mono- and Multicomponent Nonaqueous-Phase Liquid on the Migration and Retention of Pollutant-degrading Bacteria in Porous Media

The successful implementation of in-situ bioremediation of nonaqueous-phase liquid (NAPL) contamination in soil-groundwater systems is greatly influenced by the migration performance of NAPL-degrading bacteria. However, the impact and mechanisms of NAPL on the migration/retention of pollutant-degrading bacteria remain unclear. This study investigated the migration/retention performance of A. lwoffii U1091, a strain capable of degrading diesel while producing surfactants, in porous media without and with the presence of mono- and multicomponent NAPL (n-dodecane and diesel) under environmentally relevant conditions. The results showed that under all examined conditions (5 and 50 mM NaCl solution at flow rates of 4 and 8 m/d), the presence of n-dodecane/diesel in porous media could reduce the migration and enhance retention of A. lwoffii in quartz sand columns. Moreover, comparing with mutlicomponent NAPLs of n-dodecane, the monocomponent NAPLs (diesel) exhibited a greater reduction effect on the retention of A. lwoffii in porous media. Through systemically investigating the potential mechanisms via tracer experiment, visible chamber experiment, and theoretical calculation, we found that the reduction in porosity, repulsive forces and movement speeds, the presence of stagnant flow zones in porous media, particularly the biosurfactants generated by A. lwoffii contributed to the enhanced retention of bacteria in NAPL-contaminated porous media. Moreover, owing to presence of the greater amount of hydrophilic components in diesel than in n-dodecane, the available binding sites for the adsorption of bacteria were lower in diesel, resulting in the slightly decreased retention of A. lwoffii in porous media containing diesel than n-dodecane. This study demonstrated that comparing with porous media without NAPL contamination, the retention of strain capable of degrading NAPL in porous media with NAPL contamination was enhanced, beneficial for the subsequent biodegradation of NAPL.

Ventilation of large section blind headings under conditions of changing ore load size

Relevance. The need to ensure safe working conditions in the working areas of underground mines. Stagnant zones with low air velocities can be formed in large section blind heading behind the ore bulk when ore is shipped by mining machines. There is a possibility of the formation of local gas accumulations and their abrupt removal later in such stagnant zones due to the unsteadiness of accumulation and transfer of gas impurities in a blind heading. A sharp removal of gas will lead to contamination of the load-haul-dump operators’ workplace. Aim. To identify removal of exhaust gases in large section blind headings in conditions of changing ore load size. Objects. Large section blind headings with of complex geometry. Methods. Three-dimensional numerical simulation of unsteady turbulent flow of a gas-air mixture in the Ansys CFX, visualization and analysis of simulation data in the Wolfram Mathematica. Results. The paper presents the results of mathematical modeling of ventilation of large section blind headings of complex geometry under conditions of changing ore load size formed during mining operations by the load-haul-dump machines with an internal combustion engine. It is shown that either a single vortex is formed that ventilates the blind headings space, or a stagnant zone behind the bulk ore, which is characterized by a relatively low intensity of mass transfer. Vortex formation depends on the height of the ore bulk. The authors have obtained the dependences of the change in the average concentration of exhaust gases at the outlet of the blind headings space on the operating time of the machine. They determined the dependence of the correction volume coefficient on the geometric parameters of the blind headings. An analytical model of the removal of gases from the blind headings space under conditions of changing bulk ore volume is obtained. The expression of increment in gas concentration on an operator’s workplace makes it possible to derive formula to find maximum time of load-haul dump operation in a stope such that gas concentration is never higher than maximum allowable concentration.

Effects of surface roughness and Reynolds number on the solute transport through three-dimensional rough-walled rock fractures under different flow regimes

In this study, the effects of surface roughness and Reynolds number (Re) on fluid flow and solute transport are investigated based on a double rough-walled fracture model that precisely represents the natural geometries of rock fractures. The double rough-walled fracture model is composed of two three-dimensional(3D) self-affine fracture surfaces generated using the improved successive random additions (SRA). Simulation of fluid flow and solute transport through the models were conducted by directly solving the Navier-Stokes equation and advection-diffusion equation (ADE), respectively. The results indicate that as the Re increases from 0.1 to 200, the flow regime changes from linear flow to nonlinear flow accompanied with the tortuous streamlines and significant eddies. Those eddies lead to the temporary stagnant zones that delay the solute migration. The increment of Re enhances the transport heterogeneity with the transport mode changing from the diffusion-dominated to the advection-dominated behavior, which is more significant in the fracture with a larger joint roughness coefficient (JRC). All breakthrough curves (BTCs) of rough-walled fractures exhibited typical non-Fickian transport characteristics with “early arrival” and “long tailing” of BTCs. Increasing the JRC and/or Re will enhances the non-Fickian transport characteristics. The ADE model is able to accurately fit the numerical BTCs and residence time distributions (RTDs) at a low Re, but fails to capture the non-Fickian transport characteristics at a large Re. In contrast, the continuous time random walk (CTRW) model provides a better fit to the numerical simulation results over the whole range of Re. Whereas, the fitting error gradually increases with increasing Re.

Aquifer Leakage Recharge Controls on CBM Production: A Case Study in the Sanjiao Block, Eastern Ordos Basin, China.

Aquifer leakage recharge poses a prevalent challenge in coalbed methane (CBM) development, severely impeding its efficient production. This study focuses on the Sanjiao Block, located on the eastern margin of the Ordos Basin, and provides a comprehensive evaluation of the impact of aquifer leakage recharge on CBM well productivity, employing hydrochemical characteristics and numerical simulation. Fisher's discriminant analysis reveals a close association between external water sources for CBM wells in the Taiyuan Formation and the hydrodynamic environment: in the western stagnant zone, hydrochemical characteristics resemble those from the Shanxi Formation; in the eastern strong runoff zone, water from the Taiyuan Formation directly contributes to CBM well development; in the central weak runoff zone, hydrochemical characteristics suggest mixed water sources from the Shanxi Formation and Taiyuan Formation. The numerical simulation employs orthogonal experiments to quantify the sensitivity of aquifer geological parameters to CBM production, ranked from strong to weak for aquifer types, leakage channel properties, and aquifer physical properties. The fundamental reason for disparities in the efficacy of leakage recharge lies in categorizing aquifers into finite and infinite recharges based on their water supply capacity. The properties of leakage channels, including the location and scale, manifest as effects on the magnitude and shape of gas production characteristics in infinite and finite recharge aquifers, respectively. Furthermore, a discriminant flowchart of CBM production is presented, delineating the production characteristics of CBM wells under the influence of aquifer leakage recharge into six patterns and illustrating their distribution in the study area. This discriminant process provides scientific guidance for analyzing CBM production characteristics and evaluating potential under the influence of aquifer leakage recharge.

Investigating screw-agitator speed ratio impact on feeding performance in pharmaceutical manufacturing using discrete element method

In continuous powder handling processes, precise and consistent feeding is crucial for ensuring the quality of the final product. The intermixing effect caused by agitators, which alters the powder’s bulk density, flow rate, and flow patterns, plays a significant role in this process, yet it is often overlooked. This study combines discrete element method (DEM) modeling and experiments using a commercial-scale feeder to propose a Digital Twin (DT) framework. The DEM model accurately captures key flow features, such as bypass trajectories, stagnant zones, and preferential flow patterns, while providing quantitative predictions for the feed factor and zones prone to material accumulation. Scenario analysis is performed to identify the most favorable operating ranges of the screw-agitator ratio and screw speed, considering the cohesive properties of the powder. The study demonstrates that powders with poor flow characteristics require tighter operational constraints, as the screw-agitator ratio is susceptible to variations in mass feed rate. This contribution highlights the importance of selecting an appropriate screw-agitator ratio instead of maintaining a fixed value. Properly choosing this ratio helps determine an optimal operation window, which aims to achieve a minimum agitation level needed to induce unhindered flow and reduce variability in the mass flow rate.

Natural ventilation in large spaces: CFD simplified model validated with full-scale experimental data of Roman Baths

This study addresses the escalating need for energy-efficient and well-ventilated buildings by examining natural ventilation in large spaces. Validation of a CFD model was pursued through in-site experiments at the Roman Baths Museum in Chaves, Portugal. A sensitivity analysis aimed to determine the optimal number of monitoring points for model validation, crucial for establishing procedures in large-volume settings. Findings emphasized the feasibility of using a minimal number of monitored points, notably with a 3 × 3 test point arrangement, showcasing consistent temperature variations with low relative errors (0.50 %–1.75 %). Furthermore, the validated model assessed ventilation performance under diverse operational conditions, revealing slight enhancements in experimental settings, including an increase in air change rate (2.4 vs. 2.2 ACH) and a decrease in buoyancy dominance (Richardson number 197.3 vs. 241.3) compared to design conditions. Quantitative analysis highlighted similar temperature and velocity trends, with greater stratification in experimental conditions (temperature ratios 0.12 to 0.36 vs. 0.10 to 0.32). Qualitative assessments align with the quantitative analysis and enable the identification of stagnation zones and airflow distribution patterns. These findings affirm the methods' reliability in analysing ventilation in large spaces naturally ventilated, validating the model across diverse contexts, despite fewer data points.

Study of the Effect of Initial Plate Temperature in Jet Impingement Cooling Process

The microstructure characteristics and the properties of rolled steels are significantly affected by the heat transfer and boiling phenomena occurring during the jet impingement cooling on run‐out tables (ROT). In this study, experiments are conducted using a full industrial‐scale ROT facility with rectangular plates made of low‐carbon stainless steel (type 316L). The plate is heated up to a temperature ranging from to , then rapidly impinged using a single circular water jet, and the temperature drop is captured using an infrared thermal camera (FLIR A615 25°–50 Hz type). The dissipated heat flux, estimated experimentally using a 2D inverse heat conduction analysis, ranges from 6.1 to 3.4 MW m−2 across different zones along the plate surface. The impact of different initial plate temperature on the boiling behavior is studied by developing a 2D‐computational fluid dynamics (CFD) model, and the results are closely aligned with the experimental findings. The results reveal that when estimating the heat flux from CFD simulations, the best accuracy is obtained when considering fluid temperature at a point close to the plate surface (about 1 μm above the surface). Furthermore, the maximum extracted heat flux (MHF) is significantly influenced by the initial temperature of the plate. Increasing the initial plate temperature from 500 to 900 °C led to an increase of 82% in the MHF in stagnation zone, and 137% increase in the parallel‐flow region. The CFD model presented in this study and the full calculation of the boiling curves numerically will pave the road for investigating various practical parameters in jet impingement cooling.

Experimental and modeling insights into mixing-limited reactive transport in heterogeneous porous media: Role of stagnant zones

The understanding of mixing-controlled reactive dynamics in heterogeneous porous media remains limited, presenting significant challenges for modeling subsurface contaminant transport processes and for designing cost-effective environmental remedial efforts. The complexity of accurately observing, measuring, and modeling mixing-limited reactive transport has led to inadequate exploration of these critical processes. This study investigates the mixing and reaction kinetics affected by stagnant zones, which are commonly found in alluvial aquifers-aquitards and fracture-matrix systems. By conducting experiments involving conservative and bimolecular reactive transport through porous media within translucent chambers filled with two sizes of glass beads and under varying flow rates, we explored the effects of grain size and hydrodynamic conditions. Using a high-resolution camera, we monitored the concentration changes of conservative and reactive tracers, with subsequent interpretation through three-dimensional numerical simulations. The outcomes revealed the emergence of distinct mixing interfaces within both mobile and stagnant zones, culminating in a bi-peaked plume formation. Notably, the mixing and reaction times in media containing stagnant zones were found to be approximately 10 times longer than in homogeneous media. These findings, through experimental and modeling efforts, advance our understanding of mixing-limited reactive transport phenomena within heterogeneous media, underscoring the significant role of stagnant zones—a topic previously underexplored.

Developing high-flux dense Janus membrane with robust wetting and scaling resistance: A systematic comparison with Omniphobic membranes

Membrane wetting, scaling and low flux are challenging obstacles for membrane distillation (MD). However, the lack of advanced membranes capable of achieving both high flux and high wetting/scaling resistance constrains MD potential applications. Herein, a dense Janus membrane (JM) was facilely developed by co-depositing a dense PVA/PDA layer on a highly porous PTFE substrate to overcome this dilemma and systematically compared with omniphobic PTFE substrates with varied pore sizes for the first time. Results showed that, unlike flux-resistance “trade-off” observed for PTFE substrates, dense JM effectively resisted 0.4 mM SDS at a high flux of 56.8 LMH and retarded membrane scaling by 20 mM oversaturated gypsum. Robust wetting resistance was primarily attributed to the sieving effect of the sub-nanometer surface layer, which greatly protected substrate from SDS adsorption and feed intrusion, and was less affected by severe surface concentration polarization and relatively low substrate LEP than PTFE substrates. Strongly polar PVA/PDA layer provided a much more thermodynamically unfavorable continuous interface for gypsum adhesion than PTFE substrates, which played a key role in determining anti-scaling behavior. In contrast, gypsum still tended to rapidly cause membrane scaling in stagnant zones within PTFE substrates when flux was increased. This study shall provide new insights in designing high-performance membranes for robust hypersaline wastewater treatment, and highlighting dense JMs with a macroporous substrate and a highly hydrophilic dense surface layer as ideal alternatives.

Gas dynamics and heat exchange of stationary and pulsating air flows during cylinder filling process through different configurations of the cylinder head channel (applicable to piston engines)

Piston machines are used in distributed generation, are in demand as auxiliary energy sources in hybrid systems and are indispensable devices in compressor technology. The purpose of this article is to develop a method for improving the quality of the cylinder filling process based on an experimental study of the gas dynamics and heat transfer of stationary and pulsating flows in an intake system with profiled channels in a piston machine's cylinder head. Experiments were carried out on full-scale models of piston machines with thermal anemometry and thermal imaging. The article examines three cross-sectional shapes for the intake port in the cylinder head: circle (basic design), square and triangle. It is established that profiled channels in a piston machine's intake system have a significant impact on the gas-dynamic, flow and heat-exchange characteristics of both stationary and pulsating air flows. It is shown that the use of profiled channels leads to a more uniform distribution of air flow throughout the entire cylinder volume and a significant reduction in stagnation zones, which should lead to a reduction in specific fuel consumption. It is established that air flow through an intake system with square and triangular ducts increases up to 30 % compared to the basic system, which should lead to an increase in power. It is found that the use of square and triangular channels leads to an increase in the flow turbulence intensity by 3…30 % and an increase in the heat transfer coefficient to 25 % in a piston machine's intake system. On the practical side, the installation of a cylinder head with profiled channels should improve the technical, economic and environmental characteristics of piston machines.

The shoulder effect in the stagnation zone for temperature-controlled jet impingement transition boiling of submerged dielectric fluid

Two-phase jet impingement is capable of high heat transfer coefficients and high boiling critical heat flux (CHF) limits, making it a suitable technology for electronics immersion cooling applications. Previous studies have focused on the heat-flux-controlled nucleate boiling performance of an impingement jet up to the CHF. Exploration of other boiling regimes that occur under temperature-controlled surfaces is of equal fundamental importance. It has been shown for free jets that a high and consistent heat flux can be dissipated over a wide range of surface superheats in the transition boiling regime when the surface is temperature-controlled. This so-called “shoulder effect”, or heat flux shoulder, is strongest in the stagnation zone, directly beneath the jet. It has only observed using free jets of water as the cooling for interest in metals processing applications. To exploit operation in this unique boiling regime for potential applications in immersion cooling of electronics, the occurrence of this shoulder effect, as well as means for estimating the shoulder heat flux across different operating conditions, must be investigated for submerged jets and dielectric coolants. In this work, temperature-controlled submerged jet impingement is experimentally characterized using HFE-7100. A copper heater sized to be completely covered by the jet stagnation zone is increased in surface temperature via a PID controller, which allows for steady-state, temperature-controlled data to be acquired. The boiling curves, including CHF and shoulder heat flux, are measured for 0.5–3 m/s jet velocities and 5–30 K inlet subcooling. The shoulder effect is shown to exist in these conditions and high-speed imaging reveals that the shoulder heat flux effect is an enhanced film-like mode of transition boiling. It is observed that there is a proportionality between the CHF and the shoulder heat flux for the conditions investigated. The measured trends and dependencies of the shoulder heat flux on inlet subcooling and jet velocity are used to assess available predictive tools.

Simulations of design and high load operation of a model Francis turbine using bridged approach to turbulence modelling

Abstract Off-design operation of hydraulic turbines is contemporarily frequented for balance of variable energy intermittence in the electric grid. Being operationally highly flexible, these turbines allow a quick transition to off-design operation from the design point. However, such operational flexibility, and therefore the grid balancing capability is impeded by generation of flow instabilities like vortex breakdown during off-design operation. Vortex breakdown causes losses in efficiency and pressure recovery, pressure fluctuations and possibly mechanical vibrations in event of resonance between system natural and flow field fluctuation frequencies. While substantial experimental and numerical effort has already been made to study draft tube vortex breakdown, an accurate numerical flow characterization of the phenomenon is still a challenge. To this end, operation of a high head model Francis turbine under design and high load regimes using a bridged turbulence modelling approach is simulated. The approach allows a seamless transition between direct numerical simulation and Reynolds averaged Navier-Stokes equations. The highest attainable accuracy is limited by the mesh size. As such a satisfactory compromise between desired accuracy and invested computational effort is attained. The flow in the draft tube is free of anomalies under design specified operation. However, at high load an axial flow stagnation occurs centrally, and the flow is separated about the stagnated zone. The core of the vortex is enlarged with flow recirculation within it. Shear layers between the central stagnant zone and surrounding outflow kink and roll up transforming it into a spiral structure. In this work, a basic yet accurate numerical flow characterization of the aforementioned flow situations is achieved.

Mechanisms of influence of confluence containing spur-dike on microplastic transport and fate

The issue of microplastic pollution is an urgent and undeniable global ecological concern. Due to the intricate three-dimensional (3D) hydrodynamic properties, the confluence is highly susceptible to microplastic contamination, particularly in the presence of spur dike disturbance. The present research goal is to elucidate the underlying mechanism governing the impact of the spur dike on transport and retention fate of microplastic at the confluence. A 3D hydrodynamic-microplastic transport model was developed at the confluence, and the Computational Fluid Dynamics (CFD) coupled with Discrete Element Method (DEM) method was employed to conduct the simulation. The concentration distribution, residence time, and trajectory of microplastics with different sizes and materials, as well as the effect of various angles of the spur dike on them were explored. The results indicate that (i) Large quantities of polyamide and polystyrene microplastics (less than 1 mm in diameter) with a residence time greater than 70 s are present in the flow stagnation zone, flow separation zone, the vicinity of spur dike, and downstream of the flow separation. (ii) The layout of the spur dike will lead to an increase in microplastic concentrations upstream of the spur dike and downstream of the flow separation. (iii) Vorticity and mixing layer thickness play crucial roles in the retention of microplastics within the flow separation and spur dike field. (iv) The dimensionless angles of the spur dike (αN) exhibit a linear and inverse relationship with the dimensionless standard deviations (σN) within the spur dike field. This study will expand our understanding of the transport and retention mechanisms of microplastics, and provide valuable insights for accurately identifying pollution hotspots of microplastic pollution at confluences with spur dikes.

Computational Fluid Dynamics Model with Realistic Plant Structures to Study Airflow in and around a Plant Canopy on a Cultivation Shelf in a Plant Factory with Artificial Light

Airflow plays a crucial role in plant growth because it supplies CO2, O2, and energy to plants in a plant factory with artificial light (PFAL). Therefore, understanding how various factors affect airflow in and around a plant canopy is essential. In this study, we developed a computational fluid dynamics (CFD) model with realistic plant structures created using structure-from-motion imaging to investigate airflow in and around a plant canopy. The averages of the absolute percentage errors of simulated air velocity in three conditions were 6.7%, 10.1%, 12.7%, respectively. The simulated and measured air velocities agreed well, confirming the accuracy of the developed CFD model. The effects of inflow velocities and plant canopy structures on the airflow in and around the plant canopy were analysed using the validated CFD model. The inflow velocities significantly decreased stagnant zones (from 62.4% to 7.2%) and increased the airflow uniformity in and around the plant canopy. A staggered layout of the plant canopy slightly decreased stagnant zones (from 16.4% to 13.2%) and increased the airflow uniformity. The airflow in and around the plant canopy was further inhibited by a large plant structure. This CFD model provided a basis for improving the airflow status in and around a plant canopy in a PFAL.

Characterisation of discharge and flow rate predictions for asymmetric wedge-shaped hoppers

It is important to understand the flow behaviour inside wedge-shaped hoppers and accurately predict the discharge rate for the processing and handling of granular materials, regardless of whether the wedge hopper is symmetric or asymmetric. In this paper, the discrete element method (DEM) was used to reveal the flow behaviour of pellet feed in an asymmetric wedge-shaped hopper from the discharge rate, flow pattern, velocity distribution, normal contact force between particles and free-fall arch. The results showed that, with the hopper angle decreasing, the area of the active region of the particles increased, the stagnation zone decreased, and the free-fall arch became unstable. When the unilateral hopper angle was less than 45°, the discharge rate of the wedge-shaped hopper increased, and the average discharge rate reached the maximum value of 1.070 kg s−1 when the left and right hopper angles were equal to 15°. In addition, using the discharging mass proportion coefficient to represent the size of the region in which the unilateral hopper angle affected the flow of particles in the hopper, the hopper angle term in the Brown and Sellers model was corrected. The predictive errors of the corrected discharge rate model were less than 7.6% and 3.3% in the simulated and actual discharging tests respectively, which was better than that of the Brown and Sellers model. The results of the study could provide a theoretical basis for the intelligent upgrading of feed accurate handling equipment, and provide a reference basis for the design of asymmetric wedge-shaped hopper.

Effect Of Transcatheter Heart Valve Size And Deployment Height On Coronary Flow Obstruction

Coronary artery disease (CAD) is commonly found in patients with aortic stenosis; therefore, its prevalence is high in patients that are candidate for transcatheter aortic valve replacement (TAVR). As the TAVR procedure is expanding into younger and lower-risk population, the importance of early CAD monitoring and detection, as well as determination of potential impact of implant design or deployment strategy on CAD progression is of great importance. In this study, we investigate the effect of transcatheter heart valve (THV) size and deployment height on coronary flow obstruction during normotensive hemodynamic flow conditions. We employ unsteady, pulsatile flow, generated by a left heart model, and utilize clinically relevant geometry, pressure, and flow waveforms. Of particular interest is to understand the interaction between THV and anatomy regarding coronary flow obstruction. For a wide range of parameters, we examine two distinct THV deployment scenarios: nominal deployment – high coronary blockage (ND-HCB), and high deployment – low coronary blockage (HD-LCB). Additionally, we investigated the impact of the locations of coronary ostia and THV commissure alignment onto the risk of coronary flow obstruction. With the aid of 2D-2C particle image velocimetry (PIV), the distinctive flow patterns within the aortic sinus space are identified from the response of the flow to the presence of THV. Comparison between two THV deployment scenarios revealed that ND-HCB configurations lead to formation of stagnant flow zones, while the HD-LCB configuration provided an adequate washout of the entire coronary sinus. The optimal washout of the aortic root sinus is achieved when the distance between native leaflets and coronary ostia is maximized. Furthermore, results showed that up to 4% improvement in the coronary flow rate can be achieved if commissure alignment procedure is performed. As the coronary artery obstruction phenomenon is additive in its nature, a pre-existing stenotic condition in association with suboptimal THV deployment may lead to increased risk of full coronary blockage and immediate need for coronary intervention. In conclusion, this study using an experimental coronary assessment tool may provide potential insights to inform pre-procedural TAVR strategies in challenging patients’ anatomies, thereby maximizing the associated benefit.