Search Results (99)

Due to their low environmental impact, various mineral or cellulose-based natural fibres have recently attracted attention in the construction industry. Hence, the current study focused on basalt fibres and explored the changes in the physical, mechanical, and micro-structural properties of geopolymer concrete reinforced with such fibres. The current study used self-compacting geopolymer concrete, an eco-friendly concrete composed of fly ash, ground granulated blast furnace slag, and an alkali activator, in addition to the regular components of normal concrete. The self-compacting geopolymer concrete compacts under its own weight, so extra compaction is not required. The present study investigated the effect of the fibre content and length. Two different fibre lengths were considered: 12 mm and 30 mm. Three different percentages (1%, 2%, and 3% of the weight of the total mix) of the basalt fibres were considered to determine the optimum fibre content. The mix design was carried out for all the mixes with different fibre contents and fibre lengths, and the workability properties in the slump flow, T-500, and J-ring tests are presented. The effects of the fibre length and content were evaluated in terms of compressive strength (28 and 56 days) and split tensile strength. The results indicated that a higher fibre content effectively increased the compressive strength of 12 mm long fibres. In contrast, a lower fibre content was ideal for the 30 mm long fibres. In addition, the short fibres were more effective in enhancing the geopolymer concrete’s tensile strength than the long fibres. Furthermore, a detailed microscopic analysis was carried out, which revealed that fibre clustering, voids, etc., changed the strength of the selected fibre-reinforced self-compacting geopolymer concrete. Moreover, the analytical method’s predicted tensile strength agreed with the experimental results. Full article

This study presents a theoretical analysis of the solar flux distribution within the receiver of the high-flux solar furnace at IER-UNAM. The furnace comprises an array of 409 first-surface spherical facets, each hexagonal in shape with a side length of 20 cm, and all mounted on a spherical framework. Each facet is carefully adjusted to focus sunlight onto a single focal point. Initially, the distribution of solar radiation is evaluated based on measurements obtained in Temixco, Morelos, Mexico (18°50′21″ N, 99°14′7.5″ W). Using these data, an analytical model is proposed to describe the solar radiation distribution using a Gaussian approximation. An additional analytical model is then developed to estimate the concentration distribution and its geometric shape at the furnace’s focal point, considering the solar width’s root mean square (RMS) value along with the optical errors associated with the heliostat and the reflective facets. Ultimately, by applying the concept of the effective solar source, an analysis of the solar flux distribution within the furnace receiver is conducted. This results in an analytical equation that characterizes the two-dimensional and three-dimensional distribution of the concentrated solar flux. Calculations reveal that the system captures approximately 30 kW of power, with peak concentrations reaching around 10,000 suns. Full article

Reducing the large amounts of carbon dioxide emitted during cement processing is crucial to control the adverse effects of greenhouse gases. This study provides a promising alternative technology to reduce such carbon dioxide emissions and investigate physical and mechanical characteristics of alkali-activated materials with rice husk ash (RHA). To this end, compressive strength, drying shrinkage, and water penetration resistance of mortar made with RHA, blast furnace slag (BFS), and alkaline activator (sodium carbonate, NC) are investigated. Two RHA particle sizes of 45 and 150 µm types are used, thereby varying the RHA replacement ratio of 0, 7.5, 15.0 wt.%. Based on adiabatic hydration temperature, Archimedes porosity, pH, ignition loss, scanning electron microscopy, and energy-dispersive X-ray spectroscopy and X-ray diffraction results of paste, the effect of RHA on mechanical characteristics is examined. Experimental investigation reveals that compressive strengths of mortar sample made with the RHA replacement ratio of 15 wt.% to BFS were recorded between 48 and 51 MPa. When the RHA replacement ratio of 15 wt.% 150 µm was used, the length change was 1147 × 10⁻⁶ and the moisture penetration depth was less than 11 mm. Notably, water penetration resistance significantly improves with increasing RHA content; however, at high replacement ratios, the particle-size effect is not prominent. Furthermore, increasing the RHA replacement ratio decreases the porosity but increases the ignition loss and produces C-S-H gel. Full article

The study is the first to examine the combined use of blast-furnace sludge as a source of microelements and converter slag as a soil-deoxidizing agent in oat (Avena sativa L.) cultivation in sod-podzolic soils. It has been established that blast-furnace sludge is a highly dispersed waste, which contains about 50% iron, 7% zinc, and a small amount of calcium, silicon, magnesium, aluminum, and sulfur. Hazardous components such as lead, arsenic, etc., are not detected. Converter slag comprises porous granules up to 3 mm in size, consisting mainly of calcium compounds (CaO, Ca(CO)₃, CaSiO₃, CaFe₂O₄) and a small amount of Mn, Al, and Mg trace elements. In a laboratory experiment, blast-furnace sludge increased the germination of oats by 5–10%, regardless of the addition of a deoxidizer (slag), but at the same time suppressed the growth of stem length by a maximum of 18% at 1 g∙kg⁻¹. The addition of slag raised substrate pH and increased the index by 8% at a sludge concentration of 0.1 g∙kg⁻¹. Root length in deoxidizer-free variants increased by 50–60% and with the addition of slag by 27–47%. Root dry mass also increased under the addition of sludge by 85–98%; however, the addition of slag reduced the indicator to the control level. In a field experiment with the combined application of waste, an increase in yield by more than 30% was shown. When soil was treated with slag and sludge, the height of plants increased by an average of 18%. It should be noted that the introduction of waste did not affect the quality of the grain. The use of slag increased the lead content in the soil, which is probably due to the sorption properties of calcium compounds in the slag, since lead was not found in the analyzed waste. Presumably, lead is sorbed by slag from the lower soil horizons, concentrating and immobilizing it in the upper layer. This version is supported by the absence of lead accumulation in straw and oat grain. The zinc-containing sludge increased the content of this element by 33% in the soil, as well as by 6% in straw and by 14% in grain. Thus, we found that the studied metallurgical wastes can be used as nutrients for agriculture, both individually and jointly. Overall, the proposed approach will contribute both to reducing the amount of accumulated waste and to improving the efficiency and sustainability of agricultural production and CO₂ sequestration. However, the features of the accumulation of heavy metals in soil and plants under the influence of the analyzed types of waste require more in-depth study, including within the framework of long-term field experiments. Full article

Injecting hydrogen-rich fuel into blast furnaces is an effective strategy to reduce carbon dioxide (CO₂) emissions. The present study established a three-dimensional (3D) model based on a coherent jet of hydrogen-rich fuel. The combustion characteristics and the flow, heat, and mass transfer behaviors in the reaction region were simulated by the Computational Fluid Dynamics (CFD) method. The effects of fuel jet velocity on the distributions of gas velocity, temperature, and species in the reaction region were systematically analyzed. The results show that hydrogen-rich fuel burned around the main jet, generating a high-temperature, low-density flame. As flame length increased, the main jet experienced less decay. The outward expansion of the jet caused continuous diffusion of gas temperature and its components. As the fuel jet velocity increased, the temperature along the main jet centerline rose sharply, while the length of the high-concentration gas region extended. Doubling the jet velocity increased its centerline velocity by 11% and raised the average reaction region temperature by 4.12%. The obtained highlighted results are of paramount importance for optimizing hydrogen-rich smelting in blast furnaces. Full article

Electric Arc Furnaces (EAFs) are widely used in the steel manufacturing industry to melt scrap steel by employing a large number of electric arcs. EAFs play an important role in ensuring the efficient production of steel. However, their nonlinear and variable load characteristics have a significant impact on power quality. Because the active power of an electric arc depends on its length, a system for controlling the electrode positions is necessary. This paper presents a control system based on a fuzzy logic controller for the active power control of an electric arc furnace. Individual simulation scenarios were chosen with both reference values and the process taken into consideration. The reference, constant value, step variation, and the sequence of step variation were investigated, as well as step disturbances and the sequence of step disturbances from the viewpoint of the process. Furthermore, the procedure of changing the tap on a transformer was investigated. The proposed solution minimizes the time required for charge elaboration, but the main benefit is that there are no additional costs in the implementation process because the installation remains identical, with the only changes being improvements to soft control management. Full article

To accommodate the integration of renewable energy, coal-fired power plants must take on the task of peak regulation, making the low-load operation of boilers increasingly routine. Under low-load conditions, the phase transition point (PTP) of the working fluid fluctuates, leading to potential flow instability, which can compromise boiler safety. In this paper, a one-dimensional coupled dynamic model of the combustion and hydrodynamics of a supercritical boiler is developed on the Modelica/Dymola 2022 platform. The spatial distribution of key thermal parameters in the furnace and the PTP position in the water-cooled wall (WCW) are analyzed in a 660 MW supercritical boiler when parameters on the combustion side change under full-load and low-load conditions. The dynamic response characteristics of the temperature, mass flow rate, and the PTP position are investigated. The results show that the over-fire air (OFA) ratio significantly influences the flue gas temperature distribution. A lower OFA ratio increases the flue gas temperature in the burner zone but reduces it at the furnace exit. The lower OFA ratio leads to a higher fluid temperature and shortens the length of the evaporation section. The temperature difference in the WCW outlet fluid between the 20% and 60% OFA ratios is 11.7 °C under BMCR conditions and 7.4 °C under 50% THA conditions. Under the BMCR and 50% THA conditions, a 5% increase in the coal caloric value raises the flue gas outlet temperature by 32.7 °C and 35.4 °C and the fluid outlet temperature by 6.5 °C and 9.9 °C, respectively. An increase in the coal calorific value reduces the length of the evaporation section. The changes in the length of the evaporation section are −2.95 m, 2.95 m, −2.62 m, and 0.54 m when the coal feeding rate, feedwater flow rate, feedwater temperature, and air supply rate are increased by 5%, respectively. Full article

The present study focuses on the mechanical performance of steel and polyvinyl alcohol fibers embedded in the geopolymer matrix. A high-strength geopolymer concrete with fly ash, slag and silica fume as precursors and sodium hydroxide and sodium silicate solutions as activators has been tested for its strength in compression and flexure. The influence of fibers on flowability, long-term shrinkage and sulphuric acid attack on the geopolymer concrete has also been studied. The dosage of fibers was maintained at 1%, 2% and 3% by volume, and fibers of length 13 mm have been used in the study. Results indicate that slag with 3% steel fibers by volume had a predominant influence on the strength development of steel fiber-reinforced geopolymer concrete, yielding a compressive strength of 107 MPa after 28 days. Blast furnace slag resulted in increasing the shrinkage of concrete due to rapid gel formation owing to the presence of calcium ions, although the fibers helped reduce the shrinkage to some extent. The strength of steel fiber geopolymer concrete was superior to PVA fiber geopolymer concrete; however, after an acid attack, the strength of steel fiber geopolymer concrete was reduced more than PVA fiber geopolymer concrete due to the enhanced corrosion resistance of PVA fibers. Full article

The basic national condition that is dominated by coal will not alter in the foreseeable future. Coal-fired boiler is the main equipment for coal utilization, and cyclone burner is a practical type of burner. There is a cyclone formation, a primary air duct inside the center air duct, and a secondary air duct. Introducing a small stream of pulverized coal gas or oil mist stream or gas directly into the reflux zone in the center duct ignites first a stable combustion and a small fluctuation of ignition pressure. In this paper, the variation of furnace temperature for cyclone pulverized coal burner corresponding to different excess air factors and the composition of gases such as O₂, CO, CO₂, and NO_X produced by combustion were investigated using fluent software. A single cyclone pulverized coal burner from an actual coal-fired boiler is used, and a combustion zone applicable to the study of a single pulverized coal burner is established to study the actual operation of a single pulverized coal burner at different excess air coefficients. The findings indicate that the ignition position of pulverized coal combustion advances with decreasing α (Excess Air Factors); however, the length of the produced high-temperature flame gets shorter. As the value of α decreases, the burnout in the furnace decreases and the CO emission concentration increases, with a maximum CO mole fraction of 0.38% at α = 1.2 and a maximum CO mole fraction of 3.13% at the axial position when α decreases to 0.8. The furnace’s concentration of NO_X, the NO_X emission level decreases significantly with decreasing α. The NO_X mole mass increases gradually with increasing α, and in the bottom portion of the primary combustion zone, more NO_X is produced. The concentration of NO_X in the chamber changes significantly after α exceeds 1.0, and the NO_X at the outlet surges from 417.25 ppm to 801.07 ppm, which is attributed to the increase in the average temperature of the chamber, which promotes the generation of thermophilic NO_X. The distribution pattern of O₂ mole fraction along the furnace height cross-section at different excess air factors is basically the same, with a maximum at the burner inlet and a gradual decrease in the O₂ content as it enters the combustion chamber to react with the pulverized coal in a combustion reaction. The value of α = 0.8 when the air supply is obviously insufficient, the fuel cannot be fully combusted, and only a small amount of CO₂ is produced. Full article

Neutron diffraction instruments offer a platform for materials science and engineering studies at extended temperature ranges far from ambient. As one of the widely used neutron sample environment types, cryogenic furnaces are usually bulky and complex, and they may need hours of beamtime overhead for installation, configuration, cooling, and sample change, etc. To reduce the overhead time and expedite experiments at the state-of-the-art high-flux neutron source, we developed a low-cost, miniature, and easy-to-use cryogenic environment (77–473 K) for in situ neutron diffraction. A travel-size mug serves for the environment where the samples sit inside. Immediate cooling and an isothermal dwell at 77 K are realized on the sample by direct contact with liquid N₂ in the mug. The designed Al inserts serve as the holder of samples and heating elements, alleviate the thermal gradient, and clear neutron pathways. Both a single-sample continuous measurement and multi-sample high-throughput measurements are demonstrated in this environment. High-quality and refinable in situ neutron diffraction patterns are acquired on model materials. The results quantify the orthorhombic-to-cubic phase transformation process in LiMn₂O₄ and differentiate the anisotropic lattice thermal expansions and bond length evolutions between rhombohedral perovskite oxides with composition variation. Full article

X80 pipeline steel has played a vital role in oil and gas transportation in recent years. However, hydrogen-related issues frequently lead to pipeline failures during service, resulting in significant losses of properties and lives. Three heat treatment processes (furnace cooling (FC), air cooling (AC), and water cooling (WC)) were carried out to investigate the effect of different microstructures on hydrogen-induced cracking (HIC) susceptibility of X80 pipeline steel. The WC sample demonstrated the highest hydrogen embrittlement index, registering at 21.9%, while the AC and FC samples exhibited progressively lower values of 15.45% and 10.98%, respectively. Under equivalent hydrogen charging durations, crack dimensions with a maximum length exceeding 30 μm in the WC sample generally exceed those in the FC sample and AC sample. The variation is attributed to the difference in microstructures of the samples, predominantly lath bainite (LB) in water-cooled samples, granular bainite (GB) in air-cooled samples, and ferrite/pearlite (F/P) in FC samples. The research results demonstrate that the sensitivity of lath bainite (LB) to HIC is significantly higher than that of pearlite, ferrite, and granular bainite (GB). The presence of a large amount of martensite/austenite (M/A) constituents within bainite results in a multitude of hydrogen trap sites. HIC cracks in bainite generally propagate along the profiles of M/A constituents, showing both intergranular and transgranular cracking modes. Full article

Temperature has a great influence on the mechanical properties of ductile cast iron or nodular cast iron. A thermomechanical treatment was carried out at various elevated temperatures of 450 °C, 750 °C and 850 °C using a universal testing machine with a tub furnace. Specimens were held at these temperatures for 20 min to ensure a homogeneous temperature distribution along the entire length of the specimen, before a tensile load was applied. Specimens were deformed to various levels of uniform strain (0%, 25%, 50%, 75%, and 100%). These degrees of deformation were measured with a dial gauge attached to a movable cross plate. Three strain rates were used for each specimen and temperature: $1.8\times {10}^{-4} {\mathrm{s}}^{-1}$, $9\times {10}^{-4} {\mathrm{s}}^{-1}$ and $4.5\times {10}^{-3} {\mathrm{s}}^{-1}$. A simple analytical model was extracted based on the CT tensile test geometry and yield stress and a 0.2% offset strain to measure the fracture toughness (J_IC). To validate the analytical model, an extended finite element method (XFEM) was implemented for specimens tested at different temperatures, with a strain rate of $1.8\times {10}^{-4} {\mathrm{s}}^{-1}$. The model was then extended to include the tested specimens at other strain rates. The results show that increasing strain rates and temperature, especially at 850 °C, increased the ductility of the cast iron and thus its formability. The largest percentage strains were 1 and 1.5 at a temperature of 750 °C and a strain rate of $1.8\times {10}^{-4} {\mathrm{s}}^{-1}$ and $9\times {10}^{-4} {\mathrm{s}}^{-1},$ respectively, and reached their maximum value of 1.7 and 2.2% at 850 °C and a strain rate of $9\times {10}^{-4} {\mathrm{s}}^{-1}$ and $4.5\times {10}^{-3} {\mathrm{s}}^{-1},$ respectively. In addition, the simple and fast analytical model is useful in selecting materials for determining the fracture toughness (J_IC) at various elevated temperatures and different strain rates. Full article

Achieving the thermal conductivity required for efficient heat management in semiconductors and other devices requires the integration of thermally conductive ceramic fillers at concentrations of 60 vol% or higher. However, an increased filler content often negatively affects the mechanical properties of the composite matrix, limiting its practical applicability. To address this issue, in this paper, we present a new strategy to reduce the required ceramic filler content: the use of a thermally conductive ceramic composite filler with carbon nanotubes (CNTs) grown on aluminum nitride (AlN). We combined catalyst coating technology with vacuum filtration to ensure that the catalyst was uniformly applied to micrometer-sized AlN particles, followed by the efficient and uniform synthesis of CNTs using a water-assisted process in a vertical furnace. By carefully controlling the number of vacuum filtration cycles and the growth time of the CNTs, we achieved precise control over the number and length of the CNT layers, thereby adjusting the properties of the composite to the intended specifications. When AlN/CNT hybrid fillers are incorporated into silicone rubber, while maintaining the mechanical properties of rubber, the thermal diffusivity achieved at reduced filler levels exceeds that of composites using AlN-only or simultaneous AlN and CNTs formulations. This demonstrates the critical influence of CNTs on AlN surfaces. Our study represents a significant advancement in the design of thermally conductive materials, with potential implications for a wide range of applications. Full article

This study systematically investigates the formation of NO_x in the thermal decomposition of N₂O, focusing on the impact of Kelvin–Helmholtz (K-H) instability in combustion environments. Using premixed CH₄ co-flow flames and an electric furnace as distinct heat sources, we explored NO_x emission dynamics under varying conditions, including reaction temperature, residence time, and N₂O dilution rates (X_N2O). Our findings demonstrate that diluting N₂O around a premixed flame increases flame length and decreases flame propagation velocity, inducing K-H instability. This instability was quantitatively characterized using Richardson and Strouhal numbers, highlighting N₂O’s role in augmenting oxygen supply within the flame and significantly altering flame dynamics. The study reveals that higher X_N2O consistently led to increased NO formation independently of nozzle exit velocity (u_jet) or co-flow rate, emphasizing the influence of N₂O concentration on NO production. In scenarios without K-H instability, particularly at lower u_jet, an exponential rise in NO₂ formation rates was observed, due to the reduced residence time of N₂O near the flame surface, limiting pyrolysis effectiveness. Conversely, at higher u_jet where K-H instability occurs, the formation rate of NO₂ drastically decreased. This suggests that K-H instability is crucial in optimizing N₂O decomposition for minimal NO_x production. Full article

Steelmaking is one of the most energy-intensive industries, so improving control efficiency helps to reduce the energy used to produce a tonne of steel. Mutual influences between the phases of an electric arc furnace in available electrode movement control systems cause unproductive electrode movements as a reaction to the redistribution of currents among the phases of a three-phase power supply system due to changes in arc length in one of the phases. The nonlinearity of the characteristics of an electric arc furnace significantly complicates the ability to provide autonomous electrode movement control. The approach proposed in this paper, based on the formation of a matrix of mutual influences with variable coefficients, significantly improves the per-phase autonomy of the electrode movement control system. Nonlinear dependences of the mutual influence coefficients as a function of the current increment in the phase in which the disturbance occurred are obtained. Thus, it is possible to practically eliminate unproductive electrode movements in existing control systems by avoiding the traditional use of a dead zone, which reduces the control quality in the zone of small disturbances. The complex of experiments performed using the mathematical model demonstrate that the mutual influence improves the dynamic properties of the electrode movement system in certain operating modes. Full article