Flow Patterns Research Articles

Comprehensive CFD Analysis of Base Pressure Control Using Quarter Ribs in Sudden Expansion Duct at Sonic Mach Numbers

This study aims to assess the effect of rib size, shape, and location in a suddenly expanded flow at sonic Mach number. Flow from a converging nozzle is exhausted into a larger area of duct diameter of 18 mm. The geometric parameters considered are the area ratio, duct length, rib radius, and inertia parameters, which are considered the level of expansion at critical Mach number. In the present study, duct lengths were from 1D to 6D, rib radii considered were 1 mm to 3 mm, and rib locations were 0.5D, 1D, 1.5D, 2D, and 3D. Results show that when the ribs are placed near the reattachment point with a 3 mm radius, they are efficient and capable of reducing the suction in the recirculation zone and the base pressure, which was lower than the ambient pressure in the absence of ribs, is assorted larger than the back pressure. If the requirement is to equate the pressure at the base to ambient pressure, then a 2 mm radius is the right choice. Furthermore, the 1 mm rib cannot reduce the suction in the base region, and base pressure remains sub-atmospheric for the entire range of rib locations, as well as the NPRs of the present study. When the orientation of the ribs is changed, and the flow interacts with the flat surface instead of the curved surface, there is a marginal change in the flow pattern, and there is no significant change in the base pressure values.

Experimental Study of Airfoil Aerodynamic Behavior under Oscillating Motion in Ground Effect

When a flying vehicle approaches a water or land surface, it induces changes in the fluid flow field pattern known as the "ground effect." This research analyzes the ground effect phenomenon, exploring its impact on aerodynamic coefficients and flow patterns around the NACA0012 airfoil in an incompressible subsonic regime under static and dynamic conditions with pitch movements. Numerical simulations and experimental testing in an incompressible subsonic wind tunnel were deployed. The flow field solution is derived from the Navier-Stokes equations, incorporating the Transition SST turbulence model. Initially, the impact of the ground effect phenomenon was investigated at varying distances from the surface in the static state. Subsequently, the airfoil underwent a sinusoidal pitching oscillation at each distance with a specified frequency and amplitude. This allowed for examining its aerodynamic characteristics over time. The static analysis results reveal alterations in the curve's behavior and pressure distribution on the airfoil surface at close distances to the surface. This is attributed to the ground effect phenomenon, which reduces lift force to a certain height and then increases. Dynamic analysis further demonstrates changes in lift coefficient oscillation amplitude. It also exhibits a minimum and maximum lift point phase difference as the airfoil approaches the surface.

Rheology and Processing of High-Strength Liquid Crystal Polymer Reinforced Thermoplastic Composite Materials

Liquid crystal polymer (LCP) composites are presented as lightweight, high-strength, thermoplastic composites. Fumed silica (FS), carbon black (CB), carbon nanostructures (CNS), and boron nitride (BN) added to the polyphenylene sulfide (PPS) increased the viscosity ratio of the PPS to the LCP. PPS filled with 5 wt.% FS was used to optimize injection molding conditions and had a viscosity ratio ranging from 2 to 13. Increasing fill time to 5 s brought about the highest tensile strength of 99 MPa and modulus of 12.5 GPa, while the tool and melt temperatures imparted no significant effect. Mechanical and thermal properties of select LCP materials processed using molding conditions optimized for the experimental materials are presented. Mechanical properties in the crossflow direction were lower than in the flow direction, which could be overcome with tool design and placement of valve gates to tailor the flow patterns. BN filled composites increased the thermal conductivity to a value of 0.26 W/mK at 16 wt.% loading.

Effect of Induced Wheel and Impeller Inlet Diameter on the Hydrodynamic Performance of High-speed Centrifugal Pumps

The high-speed centrifugal pump plays a crucial role in fields such as aerospace and petrochemical industries, owing to its characteristics of elevated rotational speed and high head. During high-speed operation, the centrifugal pump is prone to cavitation, which alters the fluid flow state within the pump, leading to vibrations, noise, and a sudden decrease in pump head and efficiency. Simultaneously, the collapse of cavitation bubbles generates impact pressure that can damage the pump's internal flow components, significantly reducing its operational lifespan and causing severe consequences. Moreover, under constant-flow conditions, the absolute and relative velocities of the fluid at the impeller inlet are functions of the suction pipe diameter. Therefore, there exists an optimal value for the impeller inlet diameter to enhance the centrifugal pump's resistance to cavitation. Similarly, the different geometric and structural parameters of the inducer also influence the hydraulic performance of the centrifugal pump. The focus of this study is on the external characteristics and internal flow patterns of an optimized high-speed centrifugal pump. In this paper, the entire flow field of the model pump is numerically simulated using ANSYS CFX software. The performance and overall flow field state of the high-speed centrifugal pump under different impeller configurations and inlet diameters are explored. The influence of blade wrap angle and inlet diameter on the high-speed centrifugal pump is revealed, providing a theoretical basis for subsequent optimal design.

Liquid and gas permeabilities of nanostructured layers: Three-dimensional lattice Boltzmann simulation

Liquid water and gas permeabilities in nanostructured catalyst layers (CLs) (pore size ∼10–150 nm) and microporous layers (MPLs) (pore size ∼50 nm-5 μm) are crucial to reduce the mass transport loss in proton exchange membrane fuel cells (PEMFCs). Experimental measurement of their permeabilities poses great challenges due to their brittle and thin characteristics. Presently, considerable discrepancy exists in the reported permeability values for CLs and MPLs in the literature with variation spanning several orders of magnitude. This study digitally reconstructed various nanostructures of similar pore size as CLs and MPLs to calculate their permeabilities using the Lattice Boltzmann Method (LBM) based on no-slip (e.g. for liquid water flow in MPL and CL's secondary pores) or slip condition (e.g. for gas flow in MPL). Analysis was performed to evaluate the range of pore size in nanostructures for the two boundary conditions. A comprehensive investigation was conducted under various parameters such as the Reynolds number (Re), sphere diameter, porosity, and pore structure. The results revealed that permeability exhibits an increasing trend with the diameter and porosity. The predicted permeability of randomly arranged spheres agrees well with established correlations. The random sphere structure demonstrates higher permeability than their body-centered cubic (BCC) and face-centered cubic (FCC) counterparts. Under slip boundary condition, the permeability was enhanced, compared to the no-slip condition. This study's novelty lies in using distinct boundary conditions to assess the permeabilities of liquid and air, based on flow pattern analysis in the CL and MPL pore structures. A new empirical correlation describing the influence of the Knudsen number (Kn) on the slip permeability was developed, exhibiting consistency with simulation across the entire porosity spectrum.

Reliability of Uroflowmetry Pattern Interpretation in Adult Women.

Uroflowmetry is often used to assess lower urinary tract symptoms (LUTS). Criteria for characterization of flow patterns are not well established, and subjective interpretation is the most common approach for flow curve classification. We assessed the reliability of uroflowmetry curve interpretation in adult women. Uroflowmetry studies were obtained in 296 women who participated in an observational cohort study. Four investigators with expertise in female LUTS and urodynamics reviewed and categorized each tracing for interrater reliability. A random subset of 50 tracings was re-reviewed by each investigator for intrarater reliability. The uroflowmetry tracings were rated using categories of continuous, continuous fluctuating, interrupted, and prolonged. Other parameters included flow rate, voided volume, time to maximum flow, and voiding time. Agreement between raters is summarized with kappa (k) statistics and percentage where at least three raters agreed. The mean age of participants was 44.8 ± 18.3 years. Participant age categories were 18-24 years: 20%; 25-34 years: 17%; 35-64 years: 42%; 65+ years: 18%. Nine percent described their race as Asian, 31% Black, 62% White, and 89% were of non-Hispanic ethnicity. The interrater reliability was highest for the continuous flow category (k = 0.65), 0.47 for prolonged, 0.41 for continuous fluctuating, and 0.39 for interrupted flow curves. Agreement among at least three raters occurred in 74.3% of uroflow curves (69% for continuous, 33% for continuous fluctuating, 23% for interrupted, and 25% for prolonged). For intrarater reliability, the mean k was 0.72 with a range of 0.57-0.85. Currently accepted uroflowmetry pattern categories have fair to moderate interrater reliability, which is lower for flow curves that do not meet "continuous" criteria. Given the subjective nature of interpreting uroflowmetry data, more consistent and clear parameters may enhance reliability for use in research and as a screening tool for LUTS and voiding dysfunction. Parent trial: Validation of Bladder Health Instrument for Evaluation in Women (VIEW); ClinicalTrials.gov ID: NCT04016298.

Process Intensification in Distillation using HiGee Rotating Packed Bed

For decades, improving the gas-side mass transfer coefficient in rotating packed beds has been a formidable challenge. Distillation, often limited by gas-phase resistance, requires substantial innovation to enhance these coefficients. Rotating packed beds offer a distinct advantage over conventional columns, primarily due to the intense micro-mixing within fluid channels. This micro-mixing significantly boosts mass transfer between phases and facilitates rapid attainment of steady-state conditions, making them a superior choice for processes where gas-side resistance is the bottleneck. The current study emphasis on the mass transfer performance of rotating packed for acetone water system with two different packing materials viz., wire mesh and ceramic beads. Working principle of HiGee, typical flow pattern, modeling equations have been discussed in this paper. The effects of rotational speed, gas flow rates and radial thickness of the packing on mass transfer performance were also investigated. The mass transfer coefficients of the rotating packed bed HiGee were increased with increasing the rotational speed. The Height Equivalent to Theoretical Plates (HETP) of the rotating packed bed used in this study was 5-6 times less than the conventional packed columns. This study contributes to significantly advancing the industrial applications of rotating packed beds.

Comparative Study on the Application Efficacy of Small Disturbance Equation versus One-Dimensional Euler Equation in Nozzle Flow Analysis

This paper presents a numerical simulation study of subsonic and supersonic nozzle flow regimes utilizing the Small Disturbance Equation (SDE), implemented through Python to analyze flow stability under various boundary conditions. The SDE, extensively applied in aerospace, meteorology, and fluid mechanics, offers a critical framework for examining aircraft stability and maneuverability, essential for ensuring flight safety. Additionally, its application extends to spacecraft stability and control in aerospace science. The findings from this study reveal that subsonic flows, characterized by their stability and smoothness, respond more predictably under varying boundary conditions compared to their supersonic counterparts. Conversely, supersonic flows demonstrate increased sensitivity to changes in boundary conditions, resulting in more complex flow patterns. This sensitivity underscores the need for precise control mechanisms in supersonic applications to maintain flow stability and ensure the safety and efficiency of aerospace operations. The simulations underscore the practical importance of the SDE in advancing the understanding of dynamic flow problems across different scientific and engineering disciplines.

Normalization of Oscillating Flow Pattern on Transcranial Duplex Colour-coded Doppler.

Normalization of Oscillating Flow Pattern on Transcranial Duplex Colour-coded Doppler.

4.K. Scientific session: The realm of the information ecosystem and its public health impact

Abstract Workshop background As a field of science, study, practice, and policy, infodemic management has emerged during the Covid-19 pandemic but has since been emancipated and can be translated to any topic where information ecosystems play a vital role. In particular relevant to public health, infodemic managers have grown in the ranks of institutes of public health, academic institutions, UN agencies and civil society organizations, tackling outbreaks and public health issues as wide as mpox, Marburg, teen mental health, chronic diseases, seasonal influenza, Ebola and routine immunization. Aiming at improving public health strategies, they are responsible for exploring and investigating personal and organizational (health) information ecosystem, generating evidence, identifying patterns of communication and information flow, tackling the onset and distribution of circulating mis- and disinformation, better understanding information voids, and respond to citizen needs concerning information demands around emergencies. In this workshop, we will focus on several common challenges associated with implementing whole-of-society interventions and strategies for resilience to health misinformation. Solving these challenges, which often are too big just for the health system to solve, will sometimes require creativity, out-of-the-box thinking as well as cross-disciplinary perspectives and new partnerships. Infodemics are also a global challenge that can easily cross borders, which is why country-to-country discussions of experiences by participants is encouraged-while no previous infodemic management experience is required. Workshop objectives The workshop will be organized as a research symposium with five speakers from infodemic management, health information, and health literacy. They will provide a solid introduction to infodemic management from different perspectives and angles. (i) The first presentation will introduce a study on health information seeking and health literacy in midwife-led care and the modern information environment. (ii) The second presentation will discuss how fact-checking organizations can partner within public health for a healthier internet. (iii) The third presentation will focus on unravelling misinformation by investigating the associations between health literacy and resilience. (iv) The fourth presentation will present a novel web-platform for credible health information and tackling misinformation. (v) The fifth presentation focuses on the impact of misinformation on social media in the context of natural disasters. The format of this workshop will be 5x8-minute presentations, including Q&A with the audiences, followed by a 20-minute panel discussion, reflecting the relevance of the results to public health research, practice and policy. Key messages • Infodemic management seeks to quickly understand the public’s information and health needs improve future public health responses, especially during emergencies. • Whole-of-society approaches are needed to address and mitigate harms caused by infodemics by developing closer partnerships and understanding between health systems and the public.

Calculation of intraprocedural hemodynamics with computational functional dynamic in mitral valve edge-to-edge repair

Abstract Background Hemodynamic outcomes in patients undergoing transcatheter edge-to-edge-repair of the mitral valve (M-TEER) are difficult to predict. Computational functional dynamic (CFD) is frequently used in biomedical engineering to simulate blood flow patterns under various conditions. The authors developed a standardized workflow for individualized analyses and investigated the hemodynamic of mitral regurgitation volumes and gradients by using CFD. Methods 20 patients from two high volume centers who suffered from severe mitral regurgitation (MR) and underwent full cycle cardiac computed tomography (CT) prior procedure were enrolled. Baseline computed tomography and intraprocedural data were analyzed. Based on the specific valve morphology, individualized CFD-simulations were performed to calculate MR volumes prior to intervention and estimate hemodynamics after M-TEER. Results CFD-analyses of 20 patients (mean age 80±4 years, 60% male) showed excellent correlation between baseline PISA method-based MR volumes (45±23ml) measured in transesophageal echocardiography (TEE) and CFD-based calculation (45±26ml; R=0.917; P<0.001) as well as between TEE-measured mean baseline effective regurgitant orifice area (EROA; 27±16mm²) and CFD-measured EROA (24±18mm²; R=0.869; P<0.001)). After device implantation, correlation between intraprocedural TEE-measured and CFD-estimated correlation for residual MR volumes (R=0.949; P<0.001) and EROA (R=0.841; P<0.001) remained robust. Post-interventional mean diastolic pressure gradient (TEE) was 3.6±2.8mmHg which was in close correlation with the CFD estimated gradient (3.0±1.8mmHg, R=0.905; P<0.001). Conclusions This is the first study to use a CFD-standardized workflow for predicting hemodynamic changes in patients undergoing M-TEER using data from two different centers. In the future, CFD-based analyses might serve as a key-diagnostic tool for predicting residual MR volumes and gradients for M-TEER-procedures.Comparison of TEE and CFD flow patternBland-Altman-Blots

Associations of different definitions of iron deficiency with cardiac structure and function, congestion, exercise capacity and prognosis in heart failure

Abstract Background It is uncertain how best to diagnose iron deficiency (ID) in patients with heart failure (HF) as different ID definitions have been proposed with discordant results. Objectives To assess the relationship of different ID definitions with cardiac structure and function, congestion, exercise capacity, and prognosis in outpatients with HF. Methods ID was defined according to guidelines (G-ID: ferritin <100 ng/mL or ferritin 100-299 ng/mL with transferrin saturation [TSAT] <20%) or as TSAT <20%. Alternative definitions (iron <13 ¼mol/L, ferritin <100 and <300 ng/mL) were explored. Relationship with rest and exercise ultrasound findings, cardiopulmonary exercise testing and a composite endpoint of cardiovascular hospitalisations or all-cause mortality were assessed. Results Of 1502 patients (72% with left ventricular ejection fraction [LVEF] ≥50%), 471 (31%) had TSAT <20%, while 728 (48%) had G-ID. Compared to those without ID, patients with TSAT <20% or G-ID showed impaired cardiac structure and function at rest and peak exercise and lower peak oxygen consumption; they were also more likely to display a discontinuous renal venous flow pattern and more lung B-lines. Only TSAT <20% was associated with significant inferior vena cava dilatation. Lower TSAT, iron and haemoglobin were associated with more severe effort intolerance and ultrasound signs of congestion, while ferritin and LVEF were not (Picture 1). During a median follow-up of 16 months, 62 (4%) patients died, and 244 (16%) were hospitalised for cardiovascular reasons. No patients were hospitalised immediately after the enrolment visit because of clinical findings. At Kaplan-Meier analyses, TSAT <20% was associated with a greater risk of adverse events, as were iron ≤13 ¼mol/L, ferritin ≥300 ng/mL and <100 ng/mL (p <0.01 vs ferritin 100-299 ng/mL) and G-ID (Picture 2). After adjusting for age, sex, diabetes, haemoglobin, estimated glomerular filtration rate (eGFR), NT-proBNP, rest LVEF and peak VO2 <16 mL/kg/min, TSAT <20% and iron ≤13 ¼mol/L were associated with worse outcomes (hazard ratio 2.41, 95% confidence interval 1.85-3.14 and 1.90, 1.46-2.47), while G-ID or ferritin <100 or <300 ng/mL were not (Picture 1). Conclusions In outpatients with HF, TSAT <20% is more consistently associated with echocardiographic signs of poorer functional capacity and multi-organ congestion than other ID definitions. TSAT <20% and iron ≤13 ¼mol/L, but not G-ID or ferritin-based ID, seem to predict a worse prognosis.Picture 1Picture 2

Ultrasonographic and functional evaluation of forearm circulation with occluded radial artery

Abstract Introduction The transradial approach (TRA) has gained popularity in cardiology procedures. This study aims to evaluate forearm and hand arterial circulation in radial artery (RA) occlusion (RAO) patients after coronary angiography (CAG) and percutaneous coronary interventions (PCI). The ulnar (UA) and anterior interosseous artery (AIA) can compensate for RAO. Methods A prospective, observational study was conducted on 40 RAO patients after CAG/PCI. Ultrasonographic and functional evaluation (Barbeau test) of collateral circulation through AIA or UA were performed. Statistical analyses were applied to evaluate various Doppler ultrasound parameters and the anatomical characteristics of the RAO. Results The RAO group mean age was 71.22 ± 9.99 years, and 45% were male. RA, UA, and AIA showed significant differences in peak systolic velocity, end-diastolic velocity, arterial diameter, total flow volume, and stroke volume (p < 0.01). Pulse quality over RA and UA also differed significantly (p < 0.0001). Blood flow direction in the distal RA segment divided patients into an antegrade flow group (50%) from AIA and a retrograde flow group (50%) from UA. The Barbeau test results varied among RAO patients, with type D being the most common. Anatomical locations of RAO included the anatomical snuffbox (10%), wrist (60%), and forearm (30%). The logistic regression model revealed that the Barbeau test results on Finger 2 (p=0.0006, OR=0.1398) and Finger 4 (p=0.004, OR 0.2843) were significant predictors for the occurrence of antegrade or retrograde blood flow in the distal RA when RAO occurred. Furthermore, when the RA was occluded, the study revealed that a palpable pulse over the RA was still possible in 15% of cases. Conclusion Ultrasonographic evaluation and the Barbeau test can assess collateral circulation and predict blood flow patterns in RAO patients. Further research is needed to validate these findings, explore additional factors influencing collateral circulation and access route selection, and investigate the clinical implications of different RAO anatomical locations in cardiology procedures.Radial Artery OcclusionThe pulse quality over RA/UA with RAO

Physics-based modeling of debris flows and assessing the performance of effective mitigation measures

BackgroundClimate change-induced geohazards are increasingly posing a critical threat to the sustained functionality and resilience of constructed infrastructures. Among these hazards, debris flows represent significant natural disasters, particularly in mountainous terrains, causing widespread property damage and loss of life globally. These phenomena involve complex interactions between solid and fluid forces, resulting in long run-out distances and high-speed flows. Predicting and monitoring debris flows is challenging due to the intricate interplay of these forces.ObjectiveThe objective of this study is to evaluate the structural damage caused by debris flows and assess the efficacy of rigid barrier structures with passages/apertures.MethodEmploying Smoothed Particle Hydrodynamics, a Lagrange-based mesh-free computational technique, the researchers simulated the impact of debris on a stiff structure. The focus was on the Rishiganga river valley in the Indian state of Uttarakhand, a region recently devastated by a debris flow that severely compromised essential infrastructure, including a hydroelectric power station. The research entailed modeling the debris flow in this specific locale and analyzing its effects on an assumed downstream rigid structure. Additionally, the study explored the outcomes of introducing a rigid barrier upstream.Results and ConclusionResults indicated a substantial reduction in the impact on the downstream structure with the presence of an upstream rigid structure. Moreover, as the number of apertures in the upstream barrier was increased, the impact of flow on the downstream structure further diminished, because of a more streamlined flow pattern.

Non-equilibrium solute transport in a fractured rock matrix system under a radial flow pattern

Non-equilibrium solute transport in a fractured rock matrix system under a radial flow pattern

Effects of veno-arterial extracorporeal membrane oxygenation return cannula side hole structure on aortic hemodynamic features under different perfusion levels.

The interaction between primary left ventricular output and Veno-arterial extracorporeal membrane pulmonary oxygenation (VA ECMO) flow may impede the perfusion of aortic vessels with hyperoxic blood, leading to differential oxygenation. ECMO return cannula design significantly influences the perfusion level of blood supplied via ECMO. This study aimed to investigate the impact of various cannula designs (side hole number) on intravascular flow patterns under different blood perfusion conditions. Six return cannula models with different side hole number and three cardiac output waveforms were designed based on clinical data for comparative analysis. The position of the blood mixing zone (MZ) was influenced by the flow-volume ratio of the heart output (CO/(CO+Qec)) and cannula design. As the CO/(CO+Qec) and the number of side holes in the cannula increased, the MZ shifted from the ascending aorta to the descending aorta. Concurrently, aortic wall and scalar shear stress on the impact side of ECMO cannulation reduced progressively. Return cannula with side holes effectively mitigated discrepancies in the perfusion of the renal artery and inadequate perfusion of the lower limb vessels on the cannula side while simultaneously reducing damage to the vessel walls and blood. However, increasing the number of side holes in the return cannulas resulted in diminished perfusion of the aortic arch bifurcation vessels by hyperoxic blood supplied via ECMO. Increasing the number of return cannula side holes for VA ECMO femoral artery cannulation improves hypoxic perfusion in the lower limb and reduces vascular endothelial injury, but may also lead to inadequate hypoxic perfusion in the upper body.

Water flow pattern recognition and fracture characterization in near-surface chalks using time-lapse ground-penetrating radar: An experiment

Predicting subsurface water flow is inherently complex due to the heterogeneity of geological formations. Water infiltration occurs through various pathways, such as pore throats, fractures, or faults, depending on the sediment type. In an effort to enhance our understanding of water flow within heterogeneous, fractured chalks formations, we integrate ground penetrating radar (GPR), acoustic measurements, and photogrammetric surveys to examine the flow patterns. We first conduct a field experiment of injecting water into chalks and monitor the water flow through a time-lapse GPR reflection survey. Then we identify the water-affected zone by analyzing the GPR data, and correlate the water-affected zone with the identified fractures on the exposed strata. Finally, we verify the water effect through measured acoustic velocities of acquired samples. Our analysis of the GPR data encompasses direct subtraction, traveltime delay, electromagnetic (EM) velocity changes, and water saturation variations. These analyses consistently indicate a predominant southeastward flow direction. This finding is corroborated by the fractures identified through photogrammetry, which closely match the water-affected zone, suggesting that water flow is indeed fracture-driven. The measured acoustic velocities are utilized to estimate water saturation using an iso-frame rock physics model, which shows consistency with the saturation estimated through EM velocity, further validating the monitoring results. These findings advance the understanding of fluid flow and its interaction with fracture system in heterogeneous chalks, and provide a reference for future studies by demonstrating the efficacy of integrating photogrammetry-identified fractures, EM velocity, and acoustic velocity to verify monitoring outcomes.

Visualization Study on Oil Return Characteristics of Vapor Compression Heat Pump System

Vapor compression heat pump technology is a widely utilized method for energy conversion. Lubricating oil plays a crucial role in the heat pump system cycle by effectively reducing wear on the compressor’s moving parts and preventing refrigerant leakage. However, it can also create an oil film in the heat exchange equipment, which increases thermal resistance and diminishes heat transfer efficiency. This study utilizes a vapor compression heat pump system test bench to investigate factors influencing the system’s oil circulation rate, the two-phase flow patterns of refrigerant and lubricating oil, and the impact of oil circulation on system performance. The findings reveal that as the compressor speed increases, the oil circulation rate initially decreases before increasing again. Additionally, a decrease in the evaporator’s heat load leads to a reduction in oil circulation at high temperatures, while it increases at low temperatures. Furthermore, increasing the opening of the electronic expansion valve results in a gradual decrease in the oil circulation rate, whereas an increase in the refrigerant charge correlates with a rise in the oil circulation rate. The oil return flow pattern can primarily be categorized into three states: slow oil return, oil film flow, and high-speed oil return. These patterns are closely related to the degree of superheat, with lower superheat levels intensifying oil return.

Definition of Critical Metrics for Performance Evaluation and Multiphase Flow Modeling in an Alkaline Electrolyzer Using CFD

Gas evolution and flow patterns inside an alkaline electrolyzer cell strongly affect efficiency, although such effects have not been explored in detail to date. The present study aims to critically analyze the dependence of cell performance on the multiphase flow phenomena, defining some key metrics for its assessment using CFD. Six performance indicators, involving gas accumulation, bubble coverage, and flow uniformity, are applied to a 3D CFD model of an alkaline cathodic cell, and possible optimizations of the cell geometry are evaluated. The results demonstrate the complexity of defining the optimal indicator, which strictly depends on the case study and on the analysis at hand. For the cell analyzed herein, the parameters linked to the electrode volume fraction were indicated as the most influential on the cell efficiency, allowing us to define the best geometry case during the optimization. Furthermore, a sensitivity analysis was conducted, which showed that higher mass flow rates are generally preferable as they are linked to higher bubble removal. Higher current densities, allowing enhanced gas production, are instead associated with slightly lower efficiencies and stronger nonuniformity of the electrolyte flow inside the cell.

Flow regimes in a melting system composed of binary fluid: transition from penetrative convection to diffusion

In a horizontally heated melting system, where a solid substance is subject to melting by a warmer liquid beneath, the presence of solute in the liquid introduces a complex interplay between temperature and concentration dynamics. Employing a recently developed sharp interface method (Xue et al., J. Comput. Phys., vol. 491, 2023), we conduct direct numerical simulations to investigate the transient behaviour of the system across a broad range of Rayleigh numbers and solute concentrations. Our observations reveal distinct flow regimes: at low concentrations, the system resembles a temperature-driven melting problem, characterized by vortex rolls beneath the melting interface. As the solute concentration increases, a stably stratified layer emerges beneath the interface, leading to the transition from thermal convection to penetrative convection, which resembles those flow characteristics observed in the double-diffusive convection. This shift results from the competition between the stabilizing effect induced by solute concentration gradient and the destabilizing effect caused by temperature gradient. Otherwise in the diffusion regime, characterized by very high solute concentrations, the flow becomes static due to the complete suppression of convection by the stably stratified layer. This regime further exhibits two distinct patterns: ‘melting’ and ‘dissolution’. Beyond characterizing diverse flow patterns, our study conducts a quantitative analysis, examining heat/mass transfer, melting rates, and the evolution of temperature and concentration at the interface. These insights contribute to a better understanding of the intricate interplay between temperature and solute concentration during phase change, with implications for accurately estimating melting rates in binary fluid systems.