Search Results (642)

Micro-combustion-powered thermoelectric generators (μ-CPTEGs) combine the high energy density of hydrocarbons with solid-state conversion, offering compact and refuelable power for long-endurance electronics. Such characteristics make μ-CPTEGs particularly promising for aerospace systems, where conventional batteries face serious limitations. Their achievable performance hinges on how a swirl-stabilized flame transfers heat into the hot ends of thermoelectric modules. This study uses a conjugate CFD framework coupled with a lumped parameter model to examine how input power and equivalence ratio shape the flame/flow structure, temperature fields, and hot-end heating in a swirl combustor-powered TEG. Three-dimensional numerical simulations were performed for the swirl combustor-powered TEG, varying the input power from 1269 to 1854 W and the equivalence ratio from φ = 0.6 to 1.1. Results indicate that the combustor exit forms a robust “annular jet with central recirculation” structure that organizes a V-shaped region of high modeled heat release responsible for flame stabilization and preheating. At φ = 1.0, increasing Q_in from 1269 to 1854 W strengthens the V-shaped hot band and warms the wall-attached recirculation. Heating penetrates deeper into the finned cavity, and the central-plane peak temperature rises from 2281 to 2339 K (≈2.5%). Consistent with these field changes, the lower TEM pair near the outlet heats more strongly than the upper module (517 K to 629 K vs. 451 K to 543 K); the inter-row gap widens from 66 K to 86 K, and the incremental temperature gains taper at the highest power, while the axial organization of the field remains essentially unchanged. At fixed Q_in = 1854 W, raising φ from 0.6 to 1.0 compacts and retracts the reaction band toward the exit and weakens axial penetration; the main-zone temperature increases up to φ = 0.9 and then declines for richer mixtures (peak 2482 K at φ = 0.9 to 2289 K at φ = 1.1), cooling the fin section due to reduced transport, thereby identifying φ = 0.9 as the operating point that best balances axial penetration against dilution/convective-cooling losses and maximizes the TEM hot-end temperature at the fixed power. Full article

This study reports the initial thermal and thermochemical performance of a novel solarized Auger-type reactor for Pyrolysis (SARP), specifically developed for the valorization of organic solid waste into solar-derived fuels. A key innovation of this system lies in its integration with a high-flux, point-focus solar concentrator that enables controlled delivery of concentrated solar radiation to drive endothermic processes. At the front of the reactor, the thermal evaluation under solar irradiation shows that surface temperatures reached up to approximately 750 °C on the exterior, while the hottest section of the interior briefly reached approximately 700 °C, in the pyrolysis zone. In contrast, the preheating zone inside the reactor exhibits temperatures ranging from 160 °C to 306 °C, indicating a non-uniform thermal profile for the incoming feedstock. The campaign focused on thermochemical pyrolysis, in which pecan walnut tree pruning residue biomass was processed under controlled semicontinuous operation. Batches of 600 g were pyrolyzed, yielding approximately 390 g of biochar and achieving a peak hydrogen concentration of 14.5% vol in the product gases. These findings demonstrate the reactor’s potential for solar-driven waste-to-fuel conversion. Full article

Methane pyrolysis produces hydrogen (H₂) with solid carbon black as a co-product, eliminating direct CO₂ emissions and enabling a low-carbon supply when combined with renewable or low-carbon heat sources. In this study, we propose a hybrid geothermal pyrolysis configuration in which an enhanced geothermal system (EGS) provides base-load preheating and isothermal holding, while either electrical or solar–thermal input supplies the final temperature rise to the catalytic set-point. The work addresses four main objectives: (i) integrating field-scale geothermal operating envelopes to define heat-integration targets and duty splits; (ii) assessing scalability through high-pressure reactor design, thermal management, and carbon separation strategies that preserve co-product value; (iii) developing a techno-economic analysis (TEA) framework that lists CAPEX and OPEX, incorporates carbon pricing and credits, and evaluates dual-product economics for hydrogen and carbon black; and (iv) reorganizing state-of-the-art advances chronologically, linking molten media demonstrations, catalyst development, and integration studies. The process synthesis shows that allocating geothermal heat to the largest heat-capacity streams (feed, recycle, and melt/salt hold) reduces electric top-up demand and stabilizes reactor operation, thereby mitigating coking, sintering, and broad particle size distributions. High-pressure operation improves the hydrogen yield and equipment compactness, but it also requires corrosion-resistant materials and careful thermal-stress management. The TEA indicates that the levelized cost of hydrogen is primarily influenced by two factors: (a) electric duty and the carbon intensity of power, and (b) the achievable price and specifications of the carbon co-product. Secondary drivers include the methane price, geothermal capacity factor, and overall conversion and selectivity. Overall, geothermal-assisted methane pyrolysis emerges as a practical pathway to turquoise hydrogen, if the carbon quality is maintained and heat integration is optimized. The study offers design principles and reporting guidelines intended to accelerate pilot-scale deployment. Full article

Coke is an essential raw material in the blast furnace (BF) ironmaking process. Its moisture content significantly impacts BF ironmaking production. This study employs a coupled Computational Fluid Dynamics–Discrete Element Method (CFD-DEM) approach to simulate the drying process of wet coke within a coke silo (CS) dryer. Initially, the model was validated by comparing numerical results with experimental data from the literature. Subsequently, it investigated the gas flow dynamics, heat and mass transfer characteristics, and differences in drying behaviour across distinct dryer zones. Finally, the effects of inlet gas velocity and inlet gas temperature on the drying process were systematically quantified. Simulation results reveal that the bottom of the CS dryer exhibits a low-velocity laminar state, while the middle and upper regions display intense gas flow motion. Consequently, the bottom region exhibits insufficient particle drying in comparison to other zones, with the average particle moisture content decreasing by less than 20%. Under the continuous heat exchange between the hot gas and the particles, the moisture content of the particles decreases rapidly. Based on the drying rate behaviour, the drying process exhibits the following three different stages: the pre-heating period, the constant-rate period, and the falling-rate period. Compared to zones 1 and 3, zone 2 exhibits higher temperatures due to its high heat transfer efficiency, which significantly promotes a reduction in particle moisture content. An increase in inlet gas velocity enhances the particle drying rate and heat flux, accelerates moisture reduction, and raises the temperature. The impact of inlet gas velocity is most pronounced after the constant-rate period, with particle drying uniformity decreasing as the inlet gas velocity increases, consequently leading to a decline in drying quality. Increasing inlet gas temperature significantly increases particle temperature and heat flux throughout the drying period and accelerates the high-rate drying stage. These findings provide fundamental insights for further understanding and studying the coke drying process. Full article

With the low-carbon transformation of the steel industry, using low-carbon raw materials is one of the important ways to achieve the “dual carbon” goals. Pellets have great physical and chemical properties as low-carbon furnace materials, which can significantly reduce blast furnace carbon emissions, exhibiting favorable overall environmental benefits. Increasing their proportion in the furnace is one of the important measures the steel industry can take to reduce carbon emissions. Binders play a critical role in the pelletizing process, and their properties directly influence pellet quality, thereby affecting the subsequent blast furnace smelting process. Compared with traditional bentonite, organic binders have become a potential alternative material due to their environmental friendliness, renewability, and ability to significantly reduce silica and alumina impurities in pellets while improving the iron grade. This work systematically elucidates the mechanism of organic binders, which primarily rely on the chemical adsorption of carboxyl groups and the hydrogen bonding of hydroxyl groups to enhance pellet strength, and then provides three typical examples of organic binders: lignosulfonate, carboxymethyl cellulose (CMC), and carboxymethyl starch (CMS). The common characteristic of these organic binders is that they are derived from renewable biomass through chemical modification, which is a derivative of biomass with renewable and abundant resources. However, the main problem with organic binders is that they burn and decompose at high temperatures. Current research has achieved technological breakthroughs in pellet quality by combining LD sludge, low-iron oxides, and nano-CaCO₃, including improved iron grade, reduced reduction swelling index (RSI), and enhanced preheating/roasting strength. Future studies should focus on optimizing the molecular structure of organic binders by increasing the degree of substitution of functional groups and the overall degree of polymerization. This approach aims to replace traditional bentonite while exploring applications of composite industrial solid wastes, effectively addressing the high-temperature strength loss issues in organic binders and providing strong support for the steel industry to achieve the green and low-carbon goals. Full article

The efficient recovery of waste heat is essential for improving sustainability in industrial and urban energy systems. This study presents the experimental evaluation of a passive heat recovery unit composed of finned thermosyphons and Bismuth Telluride (Bi₂Te₃) thermoelectric generators (TEGs). The primary objective was to characterize its simultaneous thermal recovery and electrical generation capabilities under airflow and temperature conditions simulating low-grade industrial exhaust streams. The system was tested in an open-loop wind tunnel simulating exhaust gases under air velocities of 0.6, 1.1, and 1.7 m/s. Heat was transferred to the TEGs through finned thermosyphons, enabling power generation via the Seebeck effect. The passive heat exchange mechanism successfully recovered up to 250.9 W of thermal power, preheating the inlet air by a maximum of 9.5 °C with a peak thermal effectiveness of 44.4%. Simultaneously, the system achieved a maximum temperature difference of 30.0 °C across the thermoelectric modules, generating a total electrical power of 163.7 mW (81.8 mW per TEG). This dual-purpose operation resulted in a maximum overall first-law efficiency of 9.38% and an electrical power density of 52.20 W/m² from the low-grade thermal stream. These results confirm the technical feasibility of this compact, passive, and maintenance-free design, highlighting its potential for integration into applications like district heating or industrial ventilation, where balancing thermal and electrical outputs is crucial. Full article

To reduce the impact of renewable energy generation on power grid stability, preheating combustion technology is introduced to maintain coal-fired boiler efficiency at low loads. A 330 MW coal-fired boiler is retrofitted with preheating combustion devices to improve combustion performance and lower NO_x emissions. The device is installed in the reduction zone between the furnace burnout zone and the burner zone. The combustion characteristics of the boiler with and without these devices are examined at 50% rated load. Numerical simulations are conducted to analyze the effects of preheating coal input and burner arrangement on temperature and species distribution within the boiler. Results show that increasing preheating coal input from 0 to 30 t/h enhances NO_x reduction due to a higher flow rate of preheated products. At a preheating coal input of 20 t/h, the combustion efficiency reaches 96.9%. The NO_x concentration at the furnace exit rises from 122.4 to 171.3 mg/Nm³ as the height of the burner arrangement increases. The middle three-layer burner arrangement achieves a uniform temperature distribution and a peak combustion efficiency of 97.6%. The bottom and middle three-layer burner arrangements are recommended for efficient and clean combustion. Compared to the original boiler, the retrofitted boiler’s combustion efficiency increases from 96.3% to a maximum of 97.6%, while the NO_x concentration at the furnace outlet drops from 168.1 to 93.2 mg/Nm³, showing that installing preheating combustion devices promotes efficient and clean combustion. Full article

While laser-assisted turning (LAT) improves the machinability of GH 4169 through heating-induced thermal softening, revealing the influence of the laser processing parameters on its thermal field and machining efficiency is crucial. In this study, the influence of different laser processing parameters on the thermal field during the preheating process of LAT is systematically investigated by combining finite element (FE) simulation and experimentation, from which the optimal processing parameters of the LAT of GH 4169 are obtained. Firstly, the experimental platform of LAT is established, and a 2D FE model of the LAT of GH 4169 is constructed. Secondly, the absorption coefficient of GH 4169 with a 1064 nm wavelength laser is calibrated through experimentation and FE simulation, which lay an accurate foundation for the subsequent thermal field analysis. Furthermore, the FE simulation of the preheating process of the LAT of GH 4169 is carried out, focusing on the influence of laser power, laser spot diameter, laser spot movement speed and laser spot–tool edge distance on the thermal field, in terms of the peak and final preheating temperatures. The results show that laser power, laser spot movement speed and laser spot diameter have a significant influence on both of the two temperatures, while laser spot–tool edge distance only affects the final preheating temperature. In addition, the regression equations of the peak and final preheating temperatures are obtained based on the FE simulation results, and the optimal processing parameters are determined by combining the boundary conditions (peak temperature of 650–950 °C and initial preheating temperature of ≤190 °C). Comparison experiments with conventional turning (CT) show that under the optimal processing parameters, LAT can effectively reduce the cutting force, surface roughness and tool flank wear, which indicates that a rational selection of laser processing parameters is crucial for improving the capability of LAT of GH 4169. Full article

The behavior of S and Cs during the alternate adsorption of each adsorbate on the Ni(100) surface is studied at room and elevated temperatures by means of low-energy electron diffraction (LEED), Auger electron spectroscopy (AES), thermal desorption spectroscopy (TDS) and work function (WF) measurements. For Cs deposition on the S-covered Ni(100) surface, the presence of sulfur increases the binding energy and the maximum amount of adsorbed cesium, as happens with other alkalis too. The first Cs overlayer is disordered, while the second strongly interacts with S with a tendency toward a Cs_xS_y surface compound formation. This interaction causes the gradual demetallization of the Cs overlayer with the increasing S coverage in the underlayer. When the Cs_xS_y stoicheometry is complete, however, subsequent Cs deposition forms an independent rather metallic overlayer. When the sulfated covers the surface, S(0.5ML)/Ni(100) is preheated to 1100 K, the S-Ni bond strengthens and S-Cs interaction correspondingly weakens to a degree that the S underlayer retains a periodic structure on the Ni substrate. This behavior indicates that the preheated S/Ni(100) surface is passivated to a degree against Cs with reduced mobility of sulfur adatoms. Differently, when S is adsorbed on the Cs-covered Ni(100) surface at room temperature, sulfur adatoms diffuse underneath the Cs overlayer to interact with the nickel substrate and form the same structural phases as on a clean surface. During that process, the sticking coefficient of sulfur remains constant regardless of the amount of pre-deposited cesium. The presence of Cs, however, increases the amount of S that can be deposited on the Ni substrate, probably in favor of the Cs_xS_y compound formation, which demetallizes the surface independent of the sequence of adsorption. Full article

At present, the characteristics of supercritical hydrothermal combustion for heavy oils remain unclear, which severely limits the application of this process. In this work, the effect of key parameters on the characteristics of supercritical hydrothermal combustion of heavy oil are studied. The heat value at a heavy oil concentration of 30 wt.% is 12.21 MJ·kg⁻¹, significantly higher than that of an alcohol–water mixture with an equivalent mass fraction. Thus, the minimum ignition temperature of heavy oil can reach the subcritical temperature of 300 °C. Appropriately increasing pressure and the oxidation coefficient can enhance burnout efficiency, but an excessively high oxidation coefficient will produce adverse effects. The optimized parameters for heavy oil supercritical hydrothermal combustion are a preheating temperature of 350 °C, a fuel concentration of 30 wt.%, an oxidation coefficient of 1.5, and a reaction pressure of 25 MPa, resulting in a burnout rate of 99.15%. Full article

Efficient utilization of low-calorific-value gases reduces emissions but remains challenging. Self-heat-maintained combustion uses fuel’s exothermic heat to sustain stability without external heat, yet the feed gas typically requires preheating (typically 573–673 K). This study innovatively proposes a compact regenerative catalytic reactor featuring an integrated helical heat-recovery structure and replaces empirical preheating with a user-defined function (UDF) programmed heat transfer efficiency model. This dual innovation enables self-sustained combustion at 0.16 vol.% methane, the lowest reported concentration for autonomous operation. Numerical results confirm stable operation under ultra-lean conditions, with significantly reduced preheating energy demand and accelerated thermal response. Transient analysis shows lower space velocities enable self-maintained combustion across a broader range of methane concentrations. However, higher methane concentrations require higher inlet temperatures for self-heat maintenance. This study provides significant insights for recovering energy from low-calorific-value gases and alleviating global energy pressures. Full article

In recent decades, pollutant emissions from the combustion of fossil fuels have become increasingly serious for the environment. The present paper reports experimental results for research carried out under laboratory conditions for a Selective Catalytic Reduction (SCR) system, implemented in different configurations on an ISUZU 4JB1 diesel engine. The obtained results allow for a comparative analysis of NOx formation as a function of diesel engine load (χ = 25–100%), at 1350, 2100, 2850, and 3600 rpm, with the engine operating under either cold (T < 343 K) or warm (T > 343 K) regimes. A preheating system for AdBlue droplets, in the form of a metal honeycomb that uses electromagnetic induction and incorporates a high-frequency generator, was introduced in the flow path of the combustion gases and tested to compare the experimental results. This system enabled temperatures of up to 643 K. A magneto-strictive system was also introduced in the SCR structure to atomize the AdBlue droplets to a minimum diameter of 3.5 μm. Using this principle, combined with preheating, the effect of calefaction was compared with the classical case of the internal heating of the SCR catalyst. For experimental purposes, piezoelectric cells dedicated to the transformation of the AdBlue solution into micro- or nano-droplets, which were entrained into the SCR by an ejector, were also used. Experimental results are presented in graphical form and reveal that the use of preheating, heating, or piezoelectric cells leads to improved NOx conversion. The tested solutions showed reductions in NOx emissions of up to eight times depending on the diesel engine load, demonstrating their strong impact on NOx reduction. Full article

Waste heat recovery using Organic Rankine Cycle (ORC) systems shows significant potential for reducing CO₂ emissions from ships. This study designs and analyzes ORC systems for recovering multi-grade waste heat from the exhaust gas, jacket water, and scavenging air of a marine two-stroke diesel engine. A thermodynamic model is developed to investigate the effects of working fluid preheating temperature, evaporation pressure, and heat source conditions on system performance. Results show that appropriately increasing the preheating temperature of the working fluid can enhance power output. For hydrocarbons with higher critical temperatures, power output exhibits an extremum as preheating temperature increases, while for fluids with lower critical temperatures, power output increases continuously until the evaporation pressure limit is reached. Increasing evaporation pressure decreases power output but improves thermal efficiency, with a corresponding increase in heat transfer and exergy loss rates in the exhaust gas preheater. Additionally, the temperature of the heat source has an important effect on the energy and exergy balance distribution and power output of the ORC. For every 10 K rise in exhaust temperature, the bottoming cycle power output of cyclohexane increases by approximately 12.3%. This study provides theoretical support for efficient marine waste heat recovery and working fluid selection. Full article

Dust explosion prevention and mitigation of the consequences thereof require measurement of dust explosion parameters. Testing methods are defined by European and American standards, producing results in explosion chambers of a 1 m³ standard volume and, alternatively, 20 L. However, the results are influenced by some processes that are neglected by the standards, perhaps because it is believed that their effect is small in a 1 m³ chamber. But their effect becomes significant in a smaller 20 L chamber. Preconditioning of the system caused by dust dispersion itself, as well as the ignitor flame, is one such problem. The aim of this work is to further investigate the physical and chemical processes caused by dust preheating after an ignitor’s action. Analytical methods, such as STA, GC/MS and FTIR, were used to analyse the composition of the atmosphere after exposure of lycopodium dust, a natural material, to certain temperatures up to 550 °C in air and nitrogen. In the second step, gas samples were taken from the 20 L chamber after dispersion of lycopodium and ignition by two 5 kJ pyrotechnical ignitors. Depending on the temperature and atmosphere, various concentrations of CO, CO₂, H₂O, NO_x and organic compounds were measured. It was observed that the dispersed dust decomposed into mostly CO and CO₂ in the area near the ignitors, even in an atmosphere in which the oxygen concentration was lower than 2% by volume. The concentrations of other organic compounds were very low and included mostly methane, ethylene and acetaldehyde. However, when incorporating CO, the overall concentration of flammables was high enough to generate a hybrid mixture. Full article

This study investigates the influence of temperature measurement accuracy on tool failure mechanisms in industrial hot forging processes. Challenges related to extreme operational conditions, including high temperatures, limited access to measurement surfaces, and optical interferences, significantly hinder reliable data acquisition. Thermal imaging, pyrometry, thermocouples, and finite element modeling were employed to characterize temperature distributions in forging tools and billets. Analysis of multi-stage forging of stainless steel valve forgings revealed significant discrepancies between induction heater settings and actual billet surface temperatures, measured by thermal imaging. This thermal non-uniformity led to localized underheating and insufficient dissolution of hard inclusions, confirmed by dilatometric tests, resulting in billet jamming and premature tool failure. In slender bolt-type forgings, excessive or improperly controlled billet temperatures increased adhesion between the forging and tool surface, causing process resistance, billet sticking, and accelerated tool degradation. Additional challenges were noted in tool preheating, where non-uniform heating and inaccurate temperature assessment compromised early tool performance. Measurement errors associated with thermal imaging, particularly due to thermal reflections in robotic gripper monitoring, led to overestimated temperatures and overheating of gripping elements, impairing forging manipulation accuracy. The results emphasize that effective temperature measurement management, including cross-validation of methods, is crucial for assessing tool condition, enhancing process reliability, and preventing premature failures in hot forging operations. Full article