Behavior Of Bed Research Articles

Numerical Study on Combustion Behavior of Tuyere and Raceway in Blast Furnace with Oxygen-Rich Blast and Hydrogen Injection

The injection of hydrogen into a blast furnace is a promising technology to fulfill the low-carbon ironmaking purpose. A three-dimensional computational fluid dynamic (CFD) model is developed to investigate the effect of hydrogen injection rate and blast oxygen enrichment rate on the tuyere, raceway, and surrounding coke bed behaviors. It was found that hydrogen injection leads to a higher water vapor volume fraction in the raceway and a higher hydrogen fraction in the coke bed. The magnitude of velocity and temperature near the tuyere only increase slightly due to the cold inlet temperature of hydrogen, which also results in lower coke bed temperature. The volume-averaged temperature decreases from 2146 K to 2129 K when the injection rate increases from 0 to 1000 Nm3/h. Oxygen enrichment rate presents a highly positive correlation with temperature in the raceway and coke bed, water vapor and carbon dioxide volume fraction in the raceway, and pulverized coal burnout rate. Because more carbon participates in the raceway reaction with an increase in oxygen enrichment rate from 0% to 10%, the final carbon monoxide fraction in the coke bed increases from 0.29 to 0.40, and the final hydrogen fraction decreases from 0.15 to 0.13. With the increase in hydrogen injection, the temperature of the raceway and the coke bed decreased slightly. Pulverized coal burnout changes little with the hydrogen injection rate increasing from 500 Nm3/h to 1500 Nm3/h, which is because hydrogen combustion promotes pulverized coal at the front part of the raceway but inhibits it at the end due to the relative lack of oxygen. These results will help better understand the combustion behavior in the tuyere and raceway of the blast furnace with oxygen-rich blast and hydrogen injection.

Electrochemical behavior of laser powder bed fused nickel aluminum bronze: As-built and tempered alloys

Electrochemical behavior of laser powder bed fused nickel aluminum bronze: As-built and tempered alloys

Effect of scanning strategy on the thermo-structural coupling field and cracking behavior during laser powder bed fusion of Ti48Al2Cr2Nb alloys

Laser powder bed fusion (LPBF) is characterized by complicated non-equilibrium processing characteristics, involving extremely high temperature gradient and cooling rate within the mesoscopic dynamic molten pool, which brings great challenges to the forming of metal materials with high crack sensitivity (such as γ-TiAl alloy). In this paper, based on the LPBF forming process of Ti48Al2Cr2Nb alloy, a corresponding multi-track and multi-layer thermal-structure sequential coupled finite element model was constructed, and the influence of four different scanning strategies on the temperature and stress evolution behavior in the powder bed forming region was quantitatively studied, and the crack initiation criterion was also established according to the relationship between nodal flow stress and equivalent stress. It was found that island scanning strategy could induce the higher molten pool temperature and attendant larger molten pool size compared with the non-island linear scanning strategy. Besides, island scanning strategy was conducive to relieving the thermal stress inside the division region but also inducing the stress concentration in the sub-island overlap region. Specially, the strip island scanning strategy exhibited the lowest residual stress and most homogeneous stress distribution. By the experimental measurements, the strip island scanning strategy contributed to the lowest crack density of 0.33mm/mm2.

Numerical study of dynamic behavior of beryllium pebble under perturbation of electromagnetic field in fusion blanket

The fusion blanket system is a core component of fusion reactors, however the operational environment of it is notably harsh, characterized by strong magnetic fields, high heat fluxes, and intense radiation exposure. It is subjected to considerable thermal, mechanical, and electromagnetic stresses, particularly during plasma transient events. Consequently, an in-depth investigation into the safety of the blanket system under electromagnetic stress conditions is imperative. The present study focuses on a solid blanket configuration featuring a beryllium pebble bed. The study explores the dynamics of particle systems influenced by magnetic forces, formulates a comprehensive mathematical and physical model for particle systems within magnetic fields, constructs a pebble bed for particles under magnetic conditions, and scrutinizes the fundamental behavior of the beryllium pebble bed in the face of magnetic perturbations. This research contributes essential parameters and data pertinent to the design of the pebble bed in fusion devices.

24-hour movement behaviors and changes in quality of life over time among community-dwelling older adults: a compositional data analysis

BackgroundFavorable movement behavior patterns, comprising more physical activity, less sedentary behavior, and sufficient sleep, may promote the maintenance of good quality of life (QoL) with advancing age. The aim of the present study was to investigate whether movement behaviors predict future changes in QoL among community-dwelling older adults over a four-year follow-up.MethodsParticipants were 75-, 80- and 85-year-old community-dwelling older adults (n = 203) followed up for 4 years. Participants wore thigh- and trunk-mounted accelerometers for 3–7 days at baseline. Proportion of time-use in physical activity, standing and sedentary behavior were assessed based on body posture and movement intensity. Time in bed was determined using an automated algorithm. QoL was assessed during a home interview using the short Older People’s Quality of Life Questionnaire at baseline and follow-up (range 13–65, higher scores indicate higher QoL). Compositional linear regression analysis was used to study whether baseline time-use composition predicts changes in QoL.ResultsOver the 4-year follow-up, QoL scores decreased by 5% on average. Higher physical activity in relation to the other movement behaviors was associated with increase in QoL over time (βilr 0.94, p = 0.013), but this association attenuated after adding baseline physical function into the model. Sedentary behavior, standing, and time in bed were not associated with changes in QoL. Theoretical reallocation of 30 min of physical activity into sedentary behavior, standing or time in bed was estimated to decrease QoL by 0.5 (CI 95% -0.6 to -0.4), 0.6 (-0.7 to -0.5) and 0.4 (-0.5 to -0.3) points, respectively.ConclusionsTheoretical reallocation of physical activity into sedentary behavior, standing, and time in bed was found to be associated with prospective decline in QoL among older adults. Engaging more in physical activity and less in more passive activities may promote better QoL with advancing age.

Unnotched fatigue behavior of the laser powder bed fused and hot isostatic pressed Inconel 718 at 600 °C

The microstructure and mechanical properties of hot isostatically pressed (HIP) Inconel 718 additively manufactured using the laser beam powder bed fusion (LPBF) process were investigated at 600 °C, with emphasis on the high cycle fatigue behavior evaluated using the rotating bend fatigue tests, and elucidation of the role of γ” precipitate size on the fatigue resistance. Experimental results show that the unnotched fatigue strength (σf) of the peak aged alloy improves only by 7 % after HIP, as compared to that of the non-HIP peak aged alloy, despite a significant improvement in the ductility due to HIP. Over-aging the HIP alloy, however, led to a further enhancement (by ∼14 %) in σf. Fractographic analyses suggest that the fatigue crack initiation occurs from the intrusions and extrusions on the fracture surface of both versions of the aged alloy. Microstructural investigations reveal the presence of persistent slip bands (PSBs) with different morphologies in peak- and over-aged microstructures. A change in the deformation mechanism due to the size of precipitates was identified to be the reason for the formation of nano-grains (through dynamic recrystallization) within the PSBs of the alloy with a coarse γ” microstructure. In several {110} grains, ∼5 μm thick nanocrystalline grain zones formed on the specimen surface; they completely suppressed the formation of PSBs and enhanced the fatigue resistance of the HIP LPBF IN718 alloy in the over-aged condition.

Fatigue properties of a Ti–5Al–5Mo-5 V–3Cr alloy manufactured by electron beam powder bed fusion

AbstractAdditive manufacturing (AM) is a modern way of manufacturing structures, which tends to have fewer design limitations than those manufactured by conventional processes such as casting or forging. A combination of high-strength materials and small and complex structures opens up a wide range of potential applications, especially in the fields of medicine and aerospace. Titanium and its alloys show a very beneficial combination of density and mechanical properties. One of these alloys is the metastable β titanium alloy Ti– 5Al–5Mo–5 V–3Cr (Ti-5553), which is currently used mainly for large forged structures like landing gears of airplanes. In this study, for the first time the fatigue behavior of electron beam powder bed fused (PBF-EB) Ti-5553 was investigated with a focus on the defects created by the layer wise manufacturing. To understand the defect structure and its respective influence on the fatigue behavior, all specimens were scanned prior to fatigue testing using a state-of-the-art µ-focus CT. The specimens were subjected to two heat treatment procedures commonly used in technical applications, which were aiming for high strength (solution treated and aged—STA) as well as high ductility (beta annealed, slow cooled and aged—BASCA). Results indicate that the fatigue strength of PBF-EB manufactured Ti-5553 is significantly reduced compared to conventionally manufactured Ti-5553. The main reason for this are defects, which have varying critical effects depending on the heat treatment of the specimen and the defect size, shape, location and type.

Deep learning assisted characterization of bubble behavior in a gas-solid fluidized bed with binary particle mixtures

Gas-solid fluidized beds are widely applied as chemical reactors, and the fluidization quality in the bed is closely related to bubble behavior. Digital image processing is a commonly used non-invasive method for bubble behavior analysis, but it is usually constrained by experimental conditions such as lighting, making identification of bubble and emulsion phases still challenging. Herein, deep learning is applied in this study to optimize traditional digital image processing techniques. By evaluating different deep learning models (FCN, DeepLab V3, U-Net), rapid and accurate identification and segmentation of bubble images can be achieved, and the U-Net model performs best, achieving an identification accuracy of 99.05 %. Further application of U-Net to analyze bubble behavior demonstrates that deep learning methods enable efficient and accurate identification of bubbles and real-time analysis of bubble behavior, highlighting the significant potential application of deep learning in the field of complex hydrodynamics in fluidized beds.

A CFD and experimental study of hydrodynamic and heat transfer behavior in ribbed fluidized beds

Abstract The study focuses on enhancing the performance of fluidized bed systems, which are widely used in industrial processes requiring efficient heat and mass transfer. By integrating ribs at angles of 135, 150, and 165° on the riser wall, the research assesses their impact on hydrodynamic behavior and heat transfer using CFD simulations. The simulations, confirmed through experimental data, revealed that the 150° ribbed model outperforms others by improving particle mixing and achieving the highest heat transfer coefficient. The investigation also covered static pressure, solid volume fraction, and particle velocities at different bed heights (30, 60, 90, and 120 mm), showing that ribbed models significantly enhance turbulence and particle distribution, with the 150° ribs providing a balance between dynamic mixing and stable flow.

New Modeling Approaches for Ethylene Oxychlorination in Fluidized Bed Reactors: Industrial and Low Flow Rate Conditions

A simple model (Continuous Stirred-Tank Reactor) has been developed to predict the behavior of industrial ethylene oxychlorination fluidized beds operating in a turbulent regime. The approach showed good agreement both with results from industrial reactors and with those corresponding to the (Simple two phases-Plug bubble-Mixed flow emulsion approach) validated in the literature. For low flow rates, the use of the (Simple two phases - Plug bubble - Plug emulsion model) adapted to these conditions enabled us to highlight the location and extent of undesirable thermal hot spots for the process, and to propose actions to control them by acting on the temperature and/or on the feed gas flows. By comparing this model with the plug approach, the significant slowdown in ethylene conversion caused by resistance to mass transfer when feed flow rates are low is highlighted. Copyright © 2024 by Authors, Published by BCREC Publishing Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Pre- and Post-Improvement Performance of a Railway Embankment Stabilized with Ductile Inclusions

Large deflections and accumulation of permanent track geometry defects at railway soft spots cause significant operational issues including increased maintenance costs, decreased train speed, and, at an extreme, derailments and track failures. Reinforcing inclusions placed between the ties are a promising rehabilitation scheme to locally stabilize the embankment and transfer the loads to deeper, more suitable soils. In this paper we report the results of a long-term monitoring program to assess the performance of ductile inclusions, known commercially as “GeoSpike® elements”, to stabilize a rapidly deteriorating railway soft spot. Observations of track bed behavior are presented for 8 months prior to installation and 15 months after installation using a combination of LIDAR, Digital Image Correlation (DIC), and ShapeAccelArrays (SAA). Through the monitoring program, it was determined that the ductile inclusions decreased the average rate of deterioration by a factor of approximately 3, which allowed the frequency of site maintenance to be decreased from three times a year to once a year.

Modeling sorption-enhanced methane synthesis for system control and operation

To address energy transition in the immediate future, synthetic energy carriers are among the most promising options for decarbonization due to their capability to store renewable energy in the long term and rely on existing infrastructure. Methane, as a substitute for natural gas, can be produced at high purity through sorption-enhanced processes.These processes are discontinuous, they require sorbent regeneration once saturation is reached. Therefore, optimal operation of these complex systems requires the control of many time-dependent variables. In this framework, the rapid analyses that can be carried out via dynamic mathematical models could be greatly beneficial in lowering costs at the design stage.In this study, a model of a sorption-enhanced methanation system was developed and validated with experimental data. The proposed model allows the dynamic behavior of the process to be captured during production and sorbent regeneration. Insights into the process show the behavior of the sorbent bed while retaining water, demonstrating how the bed saturation occurs and how to effectively exploit it.The model potential was assessed by analyzing the alternating operation of two reactors for continuous production. The importance of bed drying was underlined to ensure the enhancement of the reaction and maximize the conversion.

Synergistic impact of corrosion pitting on the rotating bending fatigue of additively manufactured 316L stainless steel: Integrated experimental and modeling analyses

In this study, the ex-situ rotating bending corrosion fatigue behavior of laser powder bed fused stainless steel (SS) 316L has been studied incorporating experimental analyses and modeling. The findings revealed significant variations (almost 20 %) in fatigue lifetime in pre-corroded specimens relative to non-corroded (virgin) specimens because of corrosion-derived pitting phenomena on the surface. To this end, the fatigue strength of virgin (non-corroded) and pre-corroded SS 316L were recorded at 242 MPa and 203 MPa, respectively. Upon conducting the fatigue tests and extracting stress-life trends, advanced microstructural characterization and postmortem analyses were used to quantify fatigue crack behavior and fracture surface. An empirical model is also developed employing depth-sensing indentation testing, linear elastic fracture mechanics, and computer tomography scans to propose an optimum predictive trend. The analysis comparing existing models with our proposed model demonstrates reasonable agreement between experimental findings and the predicted life for the studied laser powder bed fused SS 316L material exposed to corrosion rotating bending fatigue test. The findings of this research carry important contributions to the structural integrity and longevity of marine engineering, ship construction, naval operations, and naval aviation where materials and components are exposed to cyclic loading and corrosion.

Evaluation of microstructure and mechanical properties of additively manufactured Ti–5V–5Mo-5 Al-3 Cr alloy

Ti–5V–5Mo–5Al–3Cr (Ti-5553) is a near-beta titanium alloy commonly used in aerospace applications. It is currently being explored for additive manufacturing (AM), but the fatigue behavior of this AM alloy needs to be well-understood for adoption. This paper explores the tensile and high-cycle fatigue behavior of laser powder bed (LPBF) manufactured Ti-5553 that has been post-print heat treated with a beta anneal and age (BAA), with a focus on the microstructural evolution and effects of surface roughness and print defects. Fatigue lives of as-LPBF and BAA material are nearly identical and both are far below fatigue lives of conventionally manufactured Ti-5553. As-built samples contain columnar β grains with a [001] texture in the build direction with a negligible fraction of α phase confirmed by electron backscatter diffraction (EBSD). The BAA material contains HCP alpha-phase precipitates: grain boundary α, primary α, and secondary Widmanstätten α. Fatigue samples were printed in the vertical direction and tested with an as-printed and machined surface. Both the as-LPBF and BAA samples exhibit similar fatigue strengths despite their vastly different microstructures. Machined surfaces led to an increase in tensile strength, ductility, and fatigue strength. This work emphasizes the importance of heat treatment and minimization of flaws inherent to AM processing of near-beta Ti-5553.

Influence of wind-blown sand content on the mechanical quality state of ballast bed in sandy railways

During the operation of sandy railways, the challenge posed by wind-blown sand is a persistent issue. An in-depth study on the influence of wind-blown sand content on the macroscopic and microscopic mechanical properties of the ballast bed is of great significance for understanding the potential problems of sandy railways and proposing reasonable and adequate maintenance and repair strategies. Building upon existing research, this study proposes a new assessment indicator for sand content. Utilizing the discrete element method (DEM) and fully considering the complex interactions between ballast and sand particles, three-dimensional (3D) multi-scale analysis models of sandy ballast beds with different wind-blown sand contents are established and validated through field experiments. The effects of varying wind-blown sand content on the microscopic contact distribution and macroscopic mechanical behavior (such as resistance and support stiffness) of ballast beds are carefully analyzed. The results show that with the increase in sand content, the average contact force and coordination number between ballast particles gradually decrease, and the disparity in contact forces between different layers of the ballast bed diminishes. The longitudinal and lateral resistance of the ballast bed initially decreases and then increases, with a critical point at 10% sand content. At 15% sand content, the lateral resistance is mainly shared by the ballast shoulder. The longitudinal resistance sharing ratio is always the largest on the sleeper side, followed by that at the sleeper bottom, and the smallest on the ballast shoulder. When the sand content exceeds 10%, the contribution of sand particles to stiffness significantly increases, leading to an accelerated growth rate of the overall support stiffness of the ballast bed, which is highly detrimental to the long-term service performance of the ballast bed. In conclusion, it is recommended that maintenance and repair operations should be promptly conducted when the sand content of the ballast bed reaches or exceeds 10%.

Comparative study on the compression characteristics of coal and biomass powder bed

Biomass substitution for fossil energy is desirable to achieve carbon emission reductions, and the storage and transportation process of biomass is governed by its compressibility. The compression characteristics of pulverized coal, rice husk and lignocellulose were compared under mechanical and gas pressurization, respectively. The experimental results showed that the descending order of relative packing density (RPD) was lignocellulose > rice husk > pulverized coal under mechanical pressurization, while an opposite trend was observed under gas pressurization. The cohesion properties were rationally correlated with the packing behavior of powder bed, and the differences in RPD order were discussed as the higher cohesion corresponding to a larger void fraction. For mechanical pressurization, biomass had higher void fraction, which was directly linked to larger RPD. On the contrary, gas permeated easily into the biomass powder bed, and the lower pressure drop decreased the compression capacity of gas pressurization. In addition, a model for predicting the RPD was proposed with an error of ± 5 %.

Role of heat treatment conditions in the high-temperature deformation behavior of laser-powder bed fused Fe–Cr–Ni–Al maraging stainless steel

The present research investigates the high-temperature behavior of laser powder bed fused (LPBF) Fe–Cr–Ni–Al maraging stainless steel (equivalent to PH13–8Mo). Fully dense PH13–8Mo samples are printed using an EOS M290 printer, and the effect of different heat treatments on high-temperature behavior and microstructure development is investigated. The material is studied under as-printed (AP), austenitized aged (AA, austenitized at 900 °C for 1 h followed by aging at 530 °C for 3 h), and direct-aged (DA, aged at 530 °C for 3 h) conditions. Uniaxial compression tests are conducted using a Gleeble® 3500 thermal-mechanical simulator at 400 °C and 500 °C at a quasi-static strain rate of 0.0001 s−1 to a final true strain of 0.2, while the microstructure characterization is performed using Electron Backscatter Diffraction and Transmission Electron Microscopy. At room temperature, the AA sample shows the highest hardness (strength), but at temperatures of 400 °C and 500 °C, the DA sample possesses the highest strength. Interestingly, the AP sample exhibits comparable strength to the DA sample at 500 °C, which could indicate for applications at these high temperatures, LPBF-PH13-8 Mo does not require any heat treatment.

Multi-scale study of subsurface fatigue cracking behavior of laser-powder bed fused Inconel 718 at stress ratios and temperatures

Multi-scale subsurface fatigue cracking is a significant lifetime-limiting failure mode, not yet fully understood, of additively manufactured superalloys in mechanical applications. Here, combined with some technologies of electron-backscattered diffraction, focused Ion beam, and transmission electron microscope, a series of axial fatigue tests at different stress ratios and temperatures are conducted to investigate the fatigue failure behavior of as-built superalloy manufactured by Laser-Powder Bed Fusion. The main results show that especially in the assistance of defect (e.g., pore or inclusion) and elevated temperature, the faceted cracking related to the grain feature is a typical failure mode. It is mainly controlled by shear stress and is more popular under a positive stress ratio. Based on the analysis of dislocation structure with faceted cracking, the localized plastic deformation at 25 °C is controlled by anti-phase boundary (APB) shearing, whereas that at 650 °C is caused by a combination of APB shearing, precipitation bypassing, and stacking fault shearing mechanisms. Combined with the definition of threshold value at the crack tip, a crack nucleation life prediction approach associated with the faceted cracking characteristics is proposed, and the predicted results show a good agreement with the experimental results.

Shallow beds are not plug flow reactors – Analysis of kinetic data in the presence of axial dispersion effects

Laboratory-scale shallow beds filled with catalyst particles are frequently used in catalyst screening, activity tests and kinetic measurements. Often the experimental data are interpreted with plug flow or differential reactor models. Residence time measurements have shown large deviations from ideal plug flow behavior in shallow beds, indication the presence of axial dispersion effects, i.e. is backmixing and diffusion in the bed. The behavior of laboratory-scale bed reactors was investigated by theoretical considerations of the axial dispersion model and numerical simulations in the Damköhler-Péclet space. The results revealed that large errors in kinetic parameters can appear when the dispersion model is replaced by the plug flow model. This key effect was quantified using the ratio (F) of two Damköhler numbers: the real one, and the one wrongly estimated on experimental data affected by dispersion problems and interpreted with ideal plug-flow approach. Thus, the effect of back-mixing is evaluated varying a single parameter of the kinetic model, namely the rate constant. The conclusions are valid for power-law, Langmuir-Hinshelwood and Eley-Rideal kinetics.

Experimental investigation into coal wettability changes caused by reactions with scCO2-H2O

Geological CO2 sequestration (GCS) can help mitigate global warming and enhance methane recovery from coal beds. However, few studies have linked the effects of CO2 to surface chemistry changes controlling wetting behavior in deep coal beds. Contact angles (CAs) of CO2/N2-high volatile bituminous coal-water systems were measured under different temperatures and pressures. The surface chemistry and physical structure of coals were characterized to investigate changes in physicochemical properties and their relations with wettability after reactions. For N2 treatment, the time-dependence of static and dynamic CAs were insignificant, ranging within 4°. For gaseous CO2 treatment, the static CAs and the average advancing angles increased slightly. With supercritical (sc) CO2, both the static and dynamic CAs increased significantly, and θadv changed to intermediate-wet (92°). Reactions with minerals exposed to scCO2 resulted in greater surface roughness and heterogeneity, greater contact angle hysteresis and more surface sites occupied by scCO2 rather than H2O. Increases in hydrophobic functional groups and decreases in hydrophilicity were shown by FTIR spectra, reflecting the shedding of polar oxygen-containing functional groups, reduction of hydrogen bonds, and increasing percentage of hydrocarbons. XRD patterns obtained following scCO2-treatment showed that crystallite growth and molecular polymerization were higher toward graphite-like. The calculated structural parameters of functional groups and crystallites both showed elevated coal rank. Changes in crystallite structure, notably higher carbon content and decreased negative surface charge, are unfavorable for water-wetting. This study contributes to understanding surface chemistry changes responsible for decreased wettability during CO2-enhanced coal bed methane recovery and GCS in coal reservoirs.