High Flow Rates Research Articles

Biocomposite materials from natural rubber/polylactic acid blends reinforced rubberwood sawdust for producing children's toys

Biocomposite materials are prepared by blending natural rubber (NR) and polylactic acid (PLA) reinforced with rubberwood sawdust (RWS). This study aimed to investigate the effects of PLA grade, NR/PLA blend ratio, and RWS content on flexure, tension, hardness, and water absorption characteristics, including thermal stability. The RWS content significantly affected the physical and mechanical properties of the biocomposite materials. The increasing additions of RWS from 30 to 50 wt% increased the mechanical modulus, hardness, and water absorption but decreased the thermal stability of the biocomposites. Polymer blended with an NR/PLA ratio of 30/70 reinforced with 30 wt% RWS exhibited the highest mechanical strength, whereas a blend ratio of 40/60 was found to be reinforced with 40 wt% RWS. The polymer matrix blended with a higher PLA content resulted in superior biocomposite properties. Thus, the biocomposites with an NR/PLA ratio of 30/70 had better properties than those with a ratio of 40/60. Further, biocomposites with PLA grade of low melt flow rate (6 g/10 min) improved their properties more than that of a high melt flow rate (80 g/10 min). Therefore, the appropriate formulation of biocomposites for producing children's toys is a blend ratio of 30/70 with 2003D PLA grade of low melt flow rate and reinforcement with 30 wt% RWS. The tensile, flexural, and compressive forces of a toy boat prototype were 70.08, 104.9, and 124.8 N, respectively, while the specified standard is 69.0, 69.0, and 113.5 N, respectively, thus meeting the requirements of the American Society for Testing and Materials F963.

Assessing the Potential of Environmental DNA for Monitoring Nature‐Like Bypasses: Erroneous Surveillance Owing to DNA Flow‐Through

ABSTRACTNature‐like bypasses refer to fishways that simulate natural streams. Apart from facilitating fish migrations, bypasses possess the capacity to enhance biodiversity in dammed rivers. Feasibility of environmental DNA (eDNA) as a tool for bypass assessments is unknown. This study investigated fish eDNA in 10 bypasses and their main channels. Initially, the relative DNA flow‐through was estimated in bypasses. Subsequently, the impact of environmental factors and bypasses on fish assemblages was evaluated, and the robustness of the eDNA and electrofishing methods was assessed pertaining to bypass monitoring. The eDNA flow‐through was computed using an equation to estimate the residual DNA at specified distances downstream of the source site. The relative DNA flow‐through was lowest in the longest bypass with low flow rate and highest in the shortest bypass with higher flow rate and was dependent on the DNA decay rate coefficient used. The redundancy analysis revealed significant effects of spatial location, agriculture, catchment area, and bypass length on the species composition. The within‐river analyses indicated significant and nonsignificant bypass effects on species composition and total species richness, respectively. Higher richness and DNA abundance of migratory and threatened species were observed in the bypasses than in the main channels. The eDNA samples displayed higher species richness compared to electrofishing. The species composition of the bypass eDNA samples was intermediate between that of the main channel eDNA and bypass electrofishing samples, which further corroborated performance of eDNA flow‐through in bypasses. Therefore, bypass eDNA samples represented variable mixtures of local and main channel assemblages, indicating relatively low robustness of eDNA for quantitative and spatially accurate bypass assessments. Nevertheless, these results demonstrate practical applicability of eDNA in surveying the presence of desired species and evidence of the benefits of bypasses in supporting biodiversity and species threatened by damming.

Study on the Destruction Law and Main Controlling Factors of Corrosion Product Film in H2S-CO2 Coexistence System

Abstract The failure law and main controlling factors of corrosion product film in this corrosion environment were studied according to the characteristics of H2S-CO2 coexistence in a gas field pipeline, so as to provide guidance for corrosion prevention and control of gas field pipeline. Sediment effects of sand particles in the pipeline on corrosion, the influence of flow rate, dissolved oxygen and sediment on corrosion products were analyzed by conducting corrosion experiments at 0.5m/s, 1m/s and 2m/s, corrosion experiments without oxygen and aerobic conditions. The destruction law of corrosion product film in pipeline and the main controlling factors of corrosion product film in single well pipeline and gathering and transportation line were determined. The results show that high flow rate will cause local damage of corrosion product film and promote pitting corrosion, dissolved oxygen will destroy the integrity of corrosion product film, and sediment is one of the factors causing local corrosion and perforation of pipeline inner wall. The corrosion product film structure of the gas field pipeline will be destroyed and pitting corrosion under the condition of high flow rate, oxygen and sand deposition. Meanwhile, the main control factor affecting the corrosion product film destruction of the gas field single well pipeline is dissolved oxygen, and the main control factor affecting the corrosion product film destruction of the gas field gathering and transportation main line is sediment.

Efficacy of balloon-expandable extreme-low-temperature ventricular epicardial cryoablation: A preclinical proof of concept evaluation

BackgroundCurrent epicardial ablation technologies are limited by the inability to create adequate depth lesions and risk of collateral injury to extracardiac structures. ObjectiveThe purpose of this study was to evaluate the feasibility and efficacy of ventricular epicardial ablation with a novel balloon-expandable extreme-low-temperature (XLT) cryoablation catheter with an embedded insulation pontoon for protection of extracardiac structures, which has been specifically designed for epicardial ablation. MethodsTen healthy swine underwent surgical (n = 6) and subxiphoid percutaneous (n = 4) epicardial access. A total of 3–6 sites were targeted in the right and left ventricular wall for different exposure durations. Ablation was performed with a large footprint (surgical) and smaller footprint (percutaneous) version of the HeartPad (Corfigo Inc., Montclair, NJ) XLT system. The system consists of the balloon-expandable cryoablation catheter and a console. The console vaporizes liquid helium (–269°C) and controls continuous delivery of extremely cold helium gas at high flow rates through a high-efficiency ablation element mounted on an expandable insulation pontoon to protect extracardiac structures. Ablation lesions were assessed by gross pathology and histologic examination. ResultsA total of 42 epicardial lesions were created. Mean lesion depth increased progressively with ablation time (surgical catheter: 11 ± 2 mm at ≤30 seconds, 13 ± 4 mm at 60 seconds, 15 ± 3 mm at ≥120 seconds, P = .001; percutaneous catheter: 10 ± 2 mm at 30 seconds, 14 ± 2 mm at 60 seconds, 16 ± 2 mm at 120 seconds, P = .001). Lesion geometry seemed unaffected by presence and thickness of epicardial fat. One episode of ventricular fibrillation occurred after ablation over the atrioventricular groove and 2 adjacent obtuse marginal arteries. ConclusionSurgical or percutaneous epicardial ablation using the HeartPad XLT cryoablation system is feasible and can efficiently produce deep ventricular lesions in different epicardial locations.

Characterising the discharge of hillslope karstic aquifers from hydrodynamic and physicochemical data (Sierra Seca, SE Spain)

Groundwater flow has been investigated in the Sierra Seca, Spain. Maximum recharge to the central core of the mountain occurs at high elevations, which provides recharge to two overlapping karst aquifers constituting a groundwater storage zone at a lower elevation break in slope. Both karst aquifers are associated with three springs arising from the upper part of the permeable formations. The climate is characterized by long and intense periods of drought and short periods of rainfall, which trigger discharges from the springs. Spring flow recession curve analysis, cross-correlation and monitoring of groundwater temperature and electrical conductivity have demonstrated contrasts observed in the hydrodynamic and physicochemical response of the three springs during flood events. One spring records floods with narrow and short peaks of high discharge accompanied by sharp drops in temperature and electrical conductivity. Another spring records floods with somewhat wider peaks and sharp increases in temperature and electrical conductivity (piston effect), whereas the third spring shows great consistency in all monitored characteristics. It is concluded that the absence of a piston effect in the spring with the highest flow rates is due to the contribution of rapidly circulating water that is expelled by semi-active karst networks (overflow) before reaching the saturated zone, which does not occur in the other springs due to the absence of overflow hydrological pathways. The most regular spring owes its functioning to the contribution of infiltrated water in the bed of an upstream riverbed, which explains this regularity.

Microstructure and mechanical property of high-density 7075 Al alloy by compression molding of POM-based feedstock

Metal injection molding of aluminium alloy (MIM-Al) attracts attention, owing to the lightweight, corrosion resistance and good thermal conductivity. However, it is hard to fabricate high-quality MIM-Al due to the hard-to-sinter powder and poor mechanical properties. Here, we report a facile compression molding process for fabricating high-density 7075Al alloy parts using polyformaldehyde (POM)-based feedstock. Pressureless sintering with a high nitrogen flow rate was adopted to promote sintering densification process. The wetting behavior, rheological properties, and morphology of the feedstock were characterized, showcasing the shear-thinning behavior and suitable viscosity for POM-PP-SA binder. Through controlling the compact pressure, mold temperature and holding time, green gear part with good shape retention and dense microstructure was achieved. Influence of process factors and sintering temperature on the microstructure and mechanical properties of 7075Al alloy are investigated. Remarkably, the aluminum alloy components sintered at 610 °C exhibited excellent performance, with a relative density reaching 97.6 % and a tensile strength of 214.8 MPa. This achievement provides a foundation for the industrial application of complex-shaped aluminum alloy components through the compression molding process.

Machine learning assisted mechanism modeling for gas phase electrohydrodynamic system

In this paper, a hybrid physics-data driven model for electrohydrodynamic gas system (EHDGS) was developed by combining artificial neural network (ANN) with mechanism modeling method. ANN was used to correlate the relationship between the variables (electrode distance, diameter of grounding cylinder, applied voltage, electric field gradient, etc.) in a needle-cylinder EHDGS and the initial space charge density. The results showed that the ANN model of nine neurons can well predict the initial space charge density. The coefficient of determination (R2) reaches 0.9874, and the mean absolute error is as low as 0.0067. Subsequently, a hybrid mechanism model where the initial space charge density was predicted from the ANN model was constructed to simulate the needle-cylinder EHDGS. The experiment with the needle-cylinder EHDGS was carried out. The simulation results were in good agreement with the experimental data, demonstrating the reliability of the proposed hybrid model. The electric field distribution, space charge distribution, and flow field distribution behavior of the EHDGS were then analyzed in detail. The effects of key parameters on the flow characteristics of EHDGS were systematically studied, showing that higher voltage and shorter distance give higher flow rate up to 2.5 m/s. The diameter of the cylinder also significantly influences the breakdown voltage. Three dimensionless groups were defined and their effects on spatial charge density distribution were investigated. This study provides both insights and an efficient tool for the design and optimization of EHDGS.

Analyzing the design and performance of a high flow rate digital flow control unit: Structural insights and simulation findings

Analyzing the design and performance of a high flow rate digital flow control unit: Structural insights and simulation findings

A simple guideline for designing droplet microfluidic chips to achieve an improved single (bio)particle encapsulation rate using a stratified flow-assisted particle ordering method

Encapsulation of a single (bio)particle into individual droplets (referred to as single encapsulation) presents tremendous potential for precise biological and chemical reactions at the single (bio)particle level. Previously demonstrated successful strategies often rely on the use of high flow rates, gel, or viscoelastic materials for initial cell ordering prior to encapsulation into droplets, which could potentially challenge the system's operation. We propose to enhance the single encapsulation rate by using a stratified flow structure to focus and pre-order the (bio)particles before encapsulation. The stratified flow structure is formed using two simple aqueous Newtonian fluids with a viscosity contrast, which together serve as the dispersed phase. The single encapsulation rate is influenced by many parameters, including fluid viscosity contrast, geometric conditions, flow conditions and flow rate ratios, and dimensionless numbers such as the capillary number. This study focuses on investigating the influences of these parameters on the focused stream of the stratified flow, which is key for single encapsulation. The results allow the proposal of a simple guideline that can be adopted to design droplet microfluidic chips with an improved single encapsulation rate demanded by a wide range of applications. The guideline was validated by performing the single encapsulation of mouse embryonic stem cells suspended in a gelatin-methacryloyl solution in individual droplets of phosphate buffer saline, achieving a single encapsulation efficiency of up to 70%.

The prospects for the use of alternative gel formers for hydraulic fracturing

The article discusses the relevance of using alternative gel-forming agents in the preparation of fracturing fluids for hydraulic fracturing (HF). Besides the obvious tasks, such as increasing the residual conductivity of the fractures created during stimulation, it also addresses the impact of alternative gelforming agents on the treatment process. The author, supported by field data, concludes that under otherwise equal conditions, replacing traditional fracturing fluids with alternative ones significantly reduces frictional pressure losses in the pipes, which is particularly important when treating deep and extensive horizontal wells with limited internal pipe diameters. Moreover, the aforementioned impact of gel-forming agents on frictional pressure losses allows for a reserve of power in the hydraulic fracturing fleet equipment. Consequently, the treatment can be performed with higher flow rates under otherwise equal conditions, without the need for additional high-pressure pumps or the deployment of more expensive, stronger, larger-diameter tubing. Another important conclusion reached by the author is that due to the specific properties of alternative fracturing fluids, their ability to transport and retain proppant is significantly increased. This property of fracturing fluids is especially important when treating low-permeability, fractured formations and during the stimulation of long horizontal wells. On the other hand, the use of alternative gel-forming agents raises the requirements for the controlled breakdown of fracturing fluids, complicating the task of selecting a rational formulation and necessitating additional research.

CaCl2-Citrate Regional Anticoagulation with Continuous Veno-Venous Haemodialysis Leads to Unwanted Chloride Loading Compared to Continuous Veno-Venous Hemofiltration with Systemic Anticoagulation

Introduction: Chloride transfers during continuous renal replacement therapy (CRRT) have not been adequately described and may differ based on CRRT technique. We aimed to measure chloride mass transfer (JS,Cl) during CRRT and identify associated determinants. Methods: We performed a two-centre, prospective, observational study in France and Australia in ICU patients with CRRT initiated for <24 h. Patients received continuous veno-venous hemofiltration (CVVH) or continuous veno-venous haemodialysis (CVVHD, with citrate-CaCl2 regional anticoagulation). Over a 24 h period, plasma and effluent chloride concentrations were measured every 4 h to compute chloride mass transfer (JS,Cl, in mmol.min-1) using a modality-specific model, with negative value indicating chloride transfer towards the patient. Secondary outcomes were the identification of CRRT settings associated with JS,Cl (using multivariate mixed effects regression). Results are presented with median (interquartile range). Results: Between February 2021 and August 2022, we enrolled 37 patients (64 [56–71] years, 67% male), for a total of 20 CVVHD and 20 CVVH sessions. Over 24 h, plasma chloride concentrations were significantly higher, and JS,Cl significantly lower during CVVHD, compared to CVVH (−0.10 [−0.33 to 0.15] vs. 0.01 [−0.10 to 0.13] mmol.min-1, p < 0.05). With both modalities, net ultrafiltration (QUFNET) and plasma chloride concentrations were the principal determinants of JS,Cl, with higher QUFNET being associated with an increase in JS,Cl during CVVHD. Also, CVVHD sessions demonstrated a concentration gradient between the plasma and the effluent chamber of −6 [−9 to −4] mmol.L-1. Finally, CaCl2 reinjection during CVVHD accounted for 35% [32–60%] of total JS,Cl in sessions with a negative JS,Cl. Conclusion: Compared to CVVH, CVVHD with regional citrate anticoagulation was associated with greater chloride mass transfer to the patient and higher plasma chloride concentrations. This was due to high dialysate chloride concentrations and CaCl2 reinjection. This effect could only be controlled by high net ultrafiltration flow rates.

Prediction of thermal efficiency of double pass solar air heater having discrete multi V and staggered ribs

AbstractThis manuscript endeavors to elucidate a comprehensive analysis for the assessment of thermal efficiency in double pass solar air collectors augmented with fabricated roughness, instrumental in the generation of heated air for applications in heating and drying. The analytical procedure delineates comparisons between a smooth and a double‐sided, roughened absorber, characterized by discrete, multi V and staggered configurations of roughness. The analysis was performed for different roughness parameters including relative roughness width (W/w) from 4 to 8 and relative staggered rib size (r/e) from 1 to 4 and relative rib pitch (p′/p) from 0.2 to 0.8 while other parameters were kept constant. The research scrutinizes the impact of a constellation of parameters: the temperature rise coefficient (ΔT/I, varying between 0.002 and 0.02 K‐m²/W), Reynolds number (Re, spanning 2000–20,000), solar irradiance (I, ranging from 600 to 1000 W/m²), and the geometric variables of the artificial roughness, on both the thermal efficiency and efficiency enhancement factor of the collector. The study revealed that the roughened collector exhibits higher thermal efficiency compared to smooth collector for a similar condition. The extreme enhancement in thermal efficiency of the collector with roughness has been found to be 56.75% more than nonroughened collector for Re = 2000. A further observation was made that thermal efficiency has increased sharply for lower flow rate (Re &lt; 10,000) whereas for higher flow rates (Re &gt; 10,000), this increase becomes nearly asymptotic. In addition, the efficiency enhancement factor has also been found to increase with an increase in ΔT/I. A peak value of 2.321 has been found to be obtained for the efficiency enhancement factor for ΔT/I = 0.02 K‐m2/W and I = 1000 W/m2 as a result of the studies conducted.

Hierarchical Pore Structure Composite Electrode by Electrospinning for Dendrite‐free Zinc‐Based Flow Battery

AbstractIn the pursuit of sustainable energy solutions, zinc‐based flow batteries stand out for their potential in large‐scale energy storage, offering a blend of cost efficiency and safety. Although the porous electrode provides an increased specific surface area for reaction, the non‐uniform deposition of zinc, attributed to uneven concentration distribution within the porous electrode, has been a pivotal issue in accelerating the formation of zinc dendrites, which hinders the enhancement of energy density. A composite electrode with a strategic hierarchical pore structure has been developed with aligned nitrogen‐doped carbon fibers and traditional carbon felt. This structure takes advantage of the large pores of the carbon felt for efficient through‐flow paths, ensuring higher flow rates, while the dual‐scale pores within the electrospun film enhance mass transfer and increase the specific surface area. At 320 mA cm−2, it achieved an ≈11.4% improvement in the battery's energy efficiency. Moreover, the nitrogen doping and the optimized reaction uniformity within the composite electrode have been instrumental in reducing the generation of zinc dendrites. The battery, integrated with the innovative composite electrode, maintained an energy efficiency of 59.2% at 320 mA cm−2 after 300 cycles, which is a substantial improvement in operational longevity.

Suppressing the Memory Effect in Al Doped 3C-SiC Grown Using Chlorinated Chemistry

The memory effect of Al doping in 3C-SiC prevents sharp interfaces between layers of different doping levels and can lead to unintentional doping of subsequent epilayers and even growth runs. Introducing HCl into the growth phase of 3C-SiC reduces the Al incorporation but has a significant impact on Al dopant decay rates and background levels within the chamber, resulting in far sharper doping profiles. The impact of relatively high flow rates of HCl is low within a chlorine-based growth system giving fine control over its influence on the growth process and memory effect.

A column study on Cu (II) adsorption from synthetic solutions using phyto-mineral hybrid adsorbents: RSM optimization, regression modeling and isotherm studies

Abstract Herein we report a novel approach to synthesize hybrid adsorbents using moringa oleifera and zeolite. Three variants were prepared using zeolite mass fractions % of 0.25 %, 0.5 % and 0.75 % respectively. The hybrid adsorbents were investigated for Cu (II) removal from synthetic wastewater using fixed bed column. The lab-scale fixed bed column was designed for Cu (II) removal and optimized using Response Surface Methodology (RSM). The variable parameters included bed height, flow rate, metallic concentration and zeolite mass fraction %. As per results, higher zeolite mass fraction resulted in higher Cu (II) removal. Similarly, the higher bed height increased the removal % of Cu (II). On the other hand, both higher flow rate and metallic concentrations resulted in a declined removal. The highest removal of Cu (II) ions was indicated by hybrid adsorbent with zeolite mass fraction of 0.75 % with 96 % at 1 mL/min flow rate, bed height of 3 cm and metallic concentration of 5 ppm respectively. The maximum adsorption capacities (Qm) indicated by hybrid adsorbents were 19 mg/g (0.25 % Mass Fraction Z), 21.5 mg/g (0.5 % Mass Faction Z) and 24.5 mg/g (0.75 % Mass Fraction Z). The adsorption data best fitted Langmuir Isotherm with R2 value of 0.99 for all variants. When the adsorption data was analyzed using isotherms, data by all three variants best fitted Langmuir isotherm with R2 values of 0.99 for all the variants. Conclusively, higher mass fraction % of zeolite enhanced the removal capacity of Phyto-mineral hybrid adsorbents for Cu (II), whereas higher flow rates and metal concentrations resulted in a declined adsorption of the respective metal ions.

Advanced visualisation of biomass charcoal combustion dynamics using MWIR hyperspectral and LWIR thermal imaging under varied airflow conditions

Biomass charcoal combustion is a complex process, significantly influenced by various operating parameters. Among these parameters, air supply emerges as a critical factor affecting combustion efficiency, gas emissions, and thermal dynamics. In this study, we explored these complex interdependencies using a novel combination of mid-wavelength infrared (MWIR) hyperspectral imaging and long-wavelength infrared (LWIR) thermal imaging, under different airflow rates. Our findings demonstrated that while increased airflow accelerated the overall combustion rate, it simultaneously decreased combustion efficiency. Specifically, the thermal profiles showed an increased surface temperature at a low flowrate (0.5 L/min) while decreasing in temperature with higher flowrates. The decreased system temperature led to a lower combustion efficiency because of the reduced conversion rate from combustible gases (CH4 and CO) into CO2 and H2O. Additionally, the results also demonstrated that cooling effects of the high flowrates primarily impeded the solid-phase combustion stage. This is further corroborated by the temporal and spatial variation in the emissions of key gas species (H2O vapor, CH4, CO, and CO2) observed through hyperspectral imaging. The emission evolution of these gases displayed the different stages of the gas-phase and solid-phase combustion. The spatial distribution of the trace gases showed a decreased distribution radius due to the enhanced diffusion to the fuel surface when the airflow increases, aligning well with the two-film model established in the literature. Furthermore, we utilised spectral radiance ratios (CO/CO2, CH4/CO2, H2O/CO2) to gain additional insights into the combustion dynamics. These ratios evidenced the decrease in combustion efficiency at high airflow rates. Finally, the increased H2O/CO2 ratio further demonstrated the impeded char combustion and a shift towards pyrolysis at higher airflow rates because of the decreased thermal equilibrium of the system. The findings from this study provide critical insights into the dynamics of biomass charcoal combustion and illuminates the path for optimising energy efficiency and assessing the environmental implications from burning biomass fuels.

Experimental study on the mechanical degradation of partially hydrolyzed polyacrylamide in pore throats

Understanding mechanical degradation is crucial for successful polymer flooding. In this study, the effects of stretching velocity, pore-throat ratio, polymer concentration, and migration distance on the mechanical degradation of HPAM were studied using a pore-throat model. Additionally, the contribution of tensile degradation at the entry point of the pore-throat model to the overall mechanical degradation was assessed through extrapolation. The experimental results indicate that tensile degradation at the entry point is the primary cause of the mechanical degradation, and its contribution is positively related to the flow rate. The mechanical degradation correlates positively with the stretching velocity (0.41 ∼ 6362s−1), pore-throat ratio (6 ∼ 60), and polymer concentration (500 ∼ 2200mg/L). Moreover, higher flow rate amplify the effects of changes in polymer concentration and pore-throat ratio on mechanical degradation. As the migration distance increases, the mechanical degradation initially increases and then stabilizes in the pore-throat model, whereas in the sand-packed model, the mechanical degradation continues to increase with increasing migration distance. This study enhances our understanding of polymer mechanical degradation and offers insights for developing strategies to reduce mechanical degradation and improve polymer-enhanced oil recovery.

Experimental and numerical studies on hydrogen leakage and dispersion in underground parking garages: Impact of leakage direction on safety considerations

Hydrogen leakage in confined spaces poses significant safety risks in hydrogen energy applications, potentially leading to fires and explosions. This paper focuses on the accident scene of hydrogen leakage and dispersion in underground parking garages. A medium-scale model (1/10) of an underground parking garage is designed and built to study the characteristics of the dispersion of hydrogen leaked from hydrogen fuel cell vehicles (HFCVs) in underground garages using experimental and numerical simulation methods. This paper focused on analyzing the dispersion characteristics of hydrogen leaked from hydrogen fuel cell vehicles (HFCVs) within these environments, with particular attention given to the influence of leakage direction—upward, horizontal, and downward—on hydrogen concentration distribution over space and time. For instance, it was observed that under equivalent flow rates, upward leakage tends to result in higher hydrogen concentrations at the leakage site. Conversely, downward leakage promotes wider hydrogen diffusion around the source, particularly evident at higher flow rates. Horizontal leakage, comparatively, exhibits lower risk due to greater air volume absorption. Complementing the experimental data, numerical simulations revealed consistent patterns in hydrogen diffusion. Specifically, the simulations illustrated a cyclic accumulation-diffusion-accumulation process. Notably, vertical upward leakage demonstrated the largest volume of regions exceeding a 4 % hydrogen volume fraction, whereas vertical downward leakage resulted in the greatest volume of regions surpassing an 18.3 % hydrogen volume fraction. This disparity arises from hydrogen accumulation beneath the vehicle in cases of vertical downward leakage. Conversely, regions of high concentration induced by horizontal leakage were the smallest. The study offers valuable insights for the design and construction of HFCVs and parking facilities, providing a theoretical framework for enhancing safety measures.

Control of Flow and Acoustic Fields Around an Axial Fan Utilizing Plasma Actuators

Abstract Small axial fans, commonly employed for cooling electronic equipment, are frequently housed within narrow ducts, where intense tonal sound with duct resonance can occur, particularly when the blade passing frequency or its harmonic frequency aligns with the duct's resonance frequency. To mitigate resonant sound, this study proposes a flow control using dielectric barrier discharge plasma actuators, which induce a flow along the generation of plasma in air. The control effects on flow field, acoustic radiation, and aerodynamic characteristics are evaluated through direct aeroacoustic simulations and experiments conducted at different flow rates. The computational results reveal that swirling flow occurs in the inflow due to fan rotations at low flow coefficients. This swirling flow is weakened by utilizing plasma actuators, which are arranged to induce flows in the circumferentially reverse direction compared to fan rotations. This control method weakens the resonant sound at low and intermediate flow coefficients, while intensifying it at high flow coefficients, all at the same rotational speed. Moreover, the static pressure coefficient decreases and increases at low and high flow coefficients, respectively, with the latter attributed to an increase in the relative inflow angle induced by the control. Experimental findings demonstrate that the acoustic resonance was reduced by the control at both low and high flow rates, achieved by adjusting the rotational speed to maintain the same flowrate and static pressure rise as in the baseline case.

Optimizing CO2 hydrate storage: Dynamics and stability of hydrate caps in submarine sediments

Addressing the escalating impacts of climate change, this study explores the potential of CO2 storage in submarine sediments, presenting a promising strategy for sustainable global warming mitigation. We examine the dynamics and stability of CO2 hydrate caps using magnetic resonance imaging to investigate their spatial-temporal distribution under varying flowrates and storage pressures. Our findings indicate that hydrate caps predominantly expand along the flow direction, influenced significantly by the state of CO2 (liquid or gas) and operational parameters (storage pressure and CO2 flowrate). Notably, higher flowrates and pressures expedite hydrate formation, thereby mitigating the risks of injection well blockages and enhancing cap stability. However, excessively rapid formation may compromise cap thickness and effectiveness. The study delineates optimal conditions that sustain hydrate cap integrity, advocating for a minimum safety pressure of 9000 kPa to prevent failure. These insights significantly advance the development of efficient CO2 storage strategies in submarine environments, offering vital guidance for policy and industry practices aimed at achieving carbon neutrality. By highlighting the technological challenges and solutions associated with deep-sea CO2 storage, this research contributes to the broader discourse on innovative approaches to climate change mitigation.