High Temperature Region Research Articles

A Survey of Sulfur-bearing Molecular Lines toward the Dense Cores in 11 Massive Protoclusters

Sulfur-bearing molecules are commonly detected in dense cores within star-forming regions, but the total sulfur budget is significantly lower when compared to the interstellar medium value. The properties of sulfur-bearing molecules are not well understood due to the absence of large sample studies with uniform observational configurations. To deepen our understanding of this subject, we conducted a study using Atacama Large Millimeter/submillimeter Array 870 μm observations of 11 massive protoclusters. By checking the spectra of 248 dense cores in 11 massive protoclusters, a total of 10 sulfur-bearing species (CS, SO, H2CS, NS, SO2, 33SO, 34SO2, 33SO2, SO18O, and OC34S) were identified. The parameters including systemic velocities, line widths, gas temperatures, column densities, and abundances were derived. Our results indicate that SO appears to be more easily detected in a wider range of physical environments than H2CS, despite these two species showing similarities in gas distributions and abundances. Molecules 34SO2 and H2CS are good tracers of the temperature of sulfur-bearing species, in which H2CS traces the outer warm envelope and 34SO2 is associated with high-temperature central regions. High-mass star-forming feedback (outflow and other nonthermal motions) significantly elevates the sulfur-bearing molecular abundances and detection rates specifically for SO2 and SO. A positive correlation between the SO2 abundance increasing factor (F) and temperatures suggests that SO2 could serve as a sulfur reservoir on the grain mantles of dense cores and then can be desorbed from dust to gas phase as the temperature rises. This work shows the importance of a large and unbiased survey to understand the sulfur depletion in dense cores.

Unique High-Resolution Temperature Mapping of Stage 1 Turbine Vane in a Long-Term Engine Test

Abstract In this study, surface temperature maps resulting from a long-term engine test were evaluated on a stage 1 turbine vane using thermal history coatings (THCs). THCs are ceramic-type sensor coatings doped with a lanthanide ion, giving the coating photoluminescent properties. The THC's structure permanently changes when exposed to high temperatures, which in turn alters its photoluminescent properties. Therefore, historic maximum temperature maps are evaluated by optically probing the THC point-by-point across the vane's surface. The vane was exposed to a non-dedicated (multi-cycle, multi temperature-level) engine test lasting over 8 months. Two passes of THC measurements were taken, termed low resolution (LR) and high resolution (HR), each, respectively, with point pitches of 5 mm and 1 mm. The latter provided a unique insight into the historic maximum temperature profile of the vane, particularly around high-temperature gradient regions, such as those close to effusion cooling holes. The THC temperatures were compared to the engine manufacturer's (Doosan Enerbility) heat transfer code (Doosan Integrated Thermal Analysis for Cooling System (DiTACS)) for validation. The THC temperature mapping was successful with good coverage across the vane. The leading edge and pressure side trailing edge regions were typically the hottest. The HR measurements clearly show sharp thermal gradients around the effusion cooling holes on the vane's airfoil and platforms. Critically, the THC measurements were compared very well to the DiTACS measurements, validating THCs as a credible temperature measurement technique for long-term, non-dedicated engine tests for components operating in some of the most extreme environments of an engine.

Probing Krylov complexity in scalar field theory with general temperatures

Krylov complexity characterizes the operator growth in the quantum many-body systems or quantum field theories. The existing literatures have studied the Krylov complexity in the low temperature limit in the quantum field theories. In this paper, we extend and systematically study the Krylov complexity and Krylov entropy in a scalar field theory with general temperatures. To this end, we propose a new method to calculate the Wightman power spectrum which allows us to compute the Lanczos coefficients and subsequently to study the Krylov complexity (entropy) in general temperatures. We find that the Lanczos coefficients and Krylov complexity (entropy) in the high temperature limit will behave somewhat differently from those studies in the low temperature limit. We give an explanation of why the Krylov complexity does not oscillate in the high-temperature region. Moreover, we uncover the transition temperature that separates the oscillating and monotonic increasing behavior of Krylov complexity.

Physicochemical principles of creating alumina cements based on nickel and cobalt spinel

The article discusses the physicochemical principles for the production of alumina cements based on nickel and cobalt spinel. The results of tetrahedration of the CaO–Al2O3–CoO–NiO system, which undergoes changes due to solid-state exchange reactions in the high-temperature region of the CaO–Al2O3–CoO subsystem at a calculated temperature of 1439 K, as well as the decomposition of the Ca3CoAl4O10 ternary compound near 1530 K, are presented. Thermodynamic analysis establishes the stability of the conodes of the above system, allowing for its triangulation. Modifications of the subsolidus structure are combined and given for the temperature of 1530 K. All binary, ternary, and quaternary combinations thermodynamically stable in the subsolidus region of the system under study are presented. Topological graphs depicting the interconnection of elementary tetrahedrons, which allow the prediction of solid-state processes in multi-component systems, have been constructed. Based on the study of the structure of the CaO–Al2O3–CoO–NiO system, the possibility of technological forecasting of heterophase materials with high-performance characteristics is substantiated.

Numerical Simulation and Experimental Analysis for Microwave Sintering Process of Lithium Hydride (LiH).

Dense lithium hydride (LiH) is widely used in neutron shielding applications for thermonuclear reactors and space systems due to its unique properties. However, traditional sintering methods often lead to cracking in LiH products. This study investigates the densification sintering of LiH using microwave technology. A multiphysics model was established based on the measured dielectric properties of LiH at different temperatures, allowing for a detailed analysis of the electromagnetic and thermal field distributions during the microwave heating of cylindrical LiH samples. The results indicate that the electric field distribution within the LiH is relatively uniform, with resistive losses concentrated primarily in the LiH region of the microwave cavity. LiH rapidly absorbs microwave energy, reaching the sintering temperature of 520 °C in just 415 s. Additionally, the temperature difference between the low- and high-temperature regions during the sintering process remains below 5 °C, demonstrating excellent uniform heating characteristics. The microwave sintering process enhances interface migration within the LiH samples, resulting in dense metallurgical bonding between grains. In summary, this research provides valuable insights and theoretical support for the rapid densification of LiH materials, highlighting the potential of microwave technology in improving material properties.

Numerical modeling and parametric analysis of temperature distribution in soil based on water content variation under radio frequency heating for in-situ thermal remediation

Radio frequency heating (RFH) is recognized as an efficient and economical method for volatilizing organic pollutants from contaminated soils. Although some numerical simulations have been conducted to predict temperature changes during RFH, models that account for effects of water content (WC) variation on dielectric properties and temperature evolution in soil were rarely reported. To address this, a three-dimensional numerical model integrating electromagnetic-thermal conversion, heat transfer, and mass transfer was developed with coupling dynamic changes in WC and corresponding impacts on soil properties. The effects of soil types and RFH engineering parameters on temperature evolution and energy utilization were evaluated. The model's temperature prediction was validated using experimental data, indicating that temperature decreases outward from hot electrode, with high-temperature regions forming at the top and bottom regions near electrode. Water evaporation in soil causes a temperature plateau with >76.25 % of energy utilized for heating and evaporating water during 60-d RFH. Moreover, higher soil WC could increase electromagnetic-thermal conversion capability, counteracting the negative impact of increased specific heat capacity on temperature rise. Thermophysical properties of soil are crucial in RFH: sand, with lower specific heat capacity and higher thermal conductivity, results in faster heating rates. While, clay, with higher density and specific heat capacity, results in lower heating rates but greater energy utilization efficiency. Low-power RHF and wider well spacing improve the uniformity of temperature distribution but require more time to reach target temperatures. Moreover, input power influences the magnitude and timing of optimal energy utilization efficiency, while well spacing primarily affects timing. The models developed in this study provide essential guidance for RFH-based soil remediation projects.

Reinforcing the Efficiency of Plastic Upgrading through Full-Spectrum Photothermal Effect Integration of Heat Isolator.

Photoreforming of polyethylene terephthalate (PET) to H2 is practically attractive strategy for upgrading waste plastics. The major challenge is to utilize the infrared energy in the solar spectrum to improve the efficiency for photoreforming of PET to H2. Herein, through the ingenious integration of tungsten phosphide nanoparticles and tungsten single atoms (WP/W SAs) with carbon nitride (g-C3N4), the constructed hybrid inherits both the desirable properties and structural merits of the respective building blocks. Specifically, the photothermal effect of WP/W SAs couples with the "heat isolator" role of g-C3N4 due to its low thermal conductivity, thereby forming localized high-temperature regions, reducing the activation energy and improving the kinetics in the photoreforming of PET to H2. Additionally, the green pretreatment of PET using alkali-free hydrothermal strategy is reported, achieving direct separation of the ethylene glycol and terephthalic acid. This work not only provides an alkali-free hydrothermal pretreatment for PET, but also integrates the photothermal effect with the thermal insulation and opens a new avenue for harnessing solar energy into to convert plastics into H2.

Design and performance analysis of a coupled burner for the Solid Oxide Fuel Cell system

The Solid Oxide Fuel Cell (SOFC) system is characterized by high energy conversion efficiency and low emissions. The energy supply and recovery of the SOFC system are facilitated through the ignition burner and the off-gas burner, respectively. This study proposes a coupled design of the ignition burner and the off-gas burner to reduce the burner volume, thereby enhancing the power density of the SOFC system. The ignition burner employs radially opposed jet combustion with fully premixed natural gas, while the off-gas burner uses swirl diffusion combustion with the anode off gas. When the premixed gas and lean anode off gas are unable to sustain the flame, catalytic combustion is initiated. Simulation and experiment methods are utilized to analyze the performance of the coupled burner in this paper. The results indicate that uniform mixing is achieved with a high swirl number (s1 = 2.6) for the premixed gas, and the maximum excess air coefficient for stable flame combustion at 400 °C is 2.47. As the temperature of the cathode off gas increases, the flameout boundary for the premixed gas gradually increases; conversely, with increasing burner power, the flameout boundary gradually decreases. The intersection cooling effect of mixed air and circumferential high-temperature flue gas is effective, and the flame does not exceed the tolerance temperature of the catalytic carrier. The diffusion combustion of anode off gas with a swirl number (s2 = 0.5) exhibits great gas mixing uniformity without a high-temperature core region. When transitioning from flame to catalytic combustion with premixed natural gas and anode off gas, there is a temperature lag of approximately 60 s. The isotropic cylindrical cordierite catalytic carrier with a 400 mesh and a coating of 60 g/ft3 Pt0.1Pd0.5 achieves stable catalytic combustion in an environment with preheated air temperatures ranging from 400 to 600 °C and H2 concentrations of 0.25–2.91 %.

Enhancing artificial permafrost table predictions using integrated climate and ground temperature data: A case study from the Qinghai-Xizang highway

The complexities of permafrost changes, driven by climate warming and engineering activities, coupled with challenges in data acquisition, make it crucial and challenging to accurately predict the artificial permafrost table, particularly for subgrades in high-temperature unstable permafrost regions. To address this, this study developed a hybrid machine learning model (RF-LSTM-XGBoost) for permafrost table prediction. By analyzing climate change and ground temperature data from various positions and depths along the subgrade in the Tuotuo River section of the Qinghai-Xizang Highway, the Spearman correlation coefficient method was initially used to determine the important influencing factors. Random Forest (RF), Long Short-Term Memory Neural Network (LSTM), and Extreme Gradient Boosting (XGBoost) models were used to predict the artificial permafrost table, and grid search and cross-validation methods were employed to optimize the hyperparameters of each model. A linear weighted combination method based on the minimum cumulative absolute error was utilized to merge the models, and its performance was compared with the individual RF, LSTM, and XGBoost models. Subsequently, the feature importance of the variables in the machine learning model was analyzed. The results indicated a strong correlation between artificial permafrost table changes and factors such as daily average atmospheric temperature, subgrade surface ground temperature, and subgrade surface ground heat flux during the freezing-thawing cycle. The combined model highlighted daily atmospheric temperature as the most influential predictor, followed by ground heat flux, with the surface ground temperature being less impactful. The combined model demonstrated improved predictive accuracy, with MSE, MAPE, RMSE, MAE, and R2 values of 0.003, 0.052, 0.0085, 0.029, and 0.989, respectively, surpassing those of individual models. This model offers a rapid, accurate, and reliable approach for permafrost table prediction, advancing subgrade stability research in challenging permafrost environments.

CFD Investigation on Air-Staged Combustion Characteristics of Deep Peak Shaving Wall-Fired Burner Boilers

ABSTRACT In alignment with China’s ambitious goals of reaching peak carbon emissions and achieving carbon neutrality, stringent load peak regulations are being enforced for coal-fired power generation. This underlines the significance of deploying deep load peaking strategies in coal-fired units. The current research focus is on wall-fired boilers operating under ultra-low loads of 600 MWe. It delves into the flow dynamics, combustion characteristics, component concentration field, and NOx emission characteristics under varying air coefficients in the primary combustion zones (α). The findings suggest the formation of a consistently high-temperature region in the primary combustion zone, where temperatures surpass 1500 K. The middle burner exhibits superior combustion stability compared to the bottom burner. As α diminishes, several changes occur. The flow field intensity in the primary combustion zone lessens, the ignition distance contracts, and the O2 concentration in this area drops. This engenders a reducing atmosphere characterized by low O2 and high CO levels, which hampers the formation of NOx. At α = 0.95, the NO concentration peaks, with the primary generation mechanism being temperature-driven. At this juncture, the NO concentration at the furnace flue gas outlet is 287.36 mg/m3.

Optimized emamectin benzoate trunk injection: addressing temperature limitations for pine wilt disease control.

Pine wilt disease (PWD), caused by the pinewood nematode Bursaphelenchus xylophilus, poses a significant threat to global forestry, resulting in extensive economic and ecological damage. Traditional trunk injection agents (TIAs) are limited by environmental factors, such as high winter temperatures and vigorous resin flow, particularly in southern China. This study aimed to develop an ordinary temperature trunk injection agent (OTTIA) for year-round application and to evaluate its performance under high-temperature conditions in comparison to commercial TIAs. Extensive laboratory and field tests identified N,N-Dimethylformamide (DMF) and benzyl acetate as optimal solvents and Tween-40 as an effective emulsifier for the OTTIA formulation. The new agent was fully absorbed by Pinus massoniana within 3 h at temperatures exceeding 30 °C, outperforming existing commercial agents. Treated trees maintained comparable emamectin benzoate (EB) levels but achieved lower LC90 lethal concentration values (27.65 mg L-1), indicating greater efficacy. The OTTIA provided protection against PWD for ≤360 days postinjection. The development of OTTIA marks a significant advancement in PWD management, offering an effective solution for high-temperature regions and potentially transforming year-round treatment strategies. The results highlight the critical role of optimizing solvent and emulsifier combinations to enhance the efficacy and application of trunk injection agents, contributing to sustainable forest management and improved protection against PWD. © 2024 Society of Chemical Industry.

Temperature dependences of the magnetic anisotropy constants of single-crystal inclusions MnSb in an InSb matrix

The contributions of the first order K1 and second order K2 magnetic anisotropy constants to the effective constant are separated. Their competition determines the type of magnetic anisotropy «easy plane». Extrapolation of the dependences K1(T) and K2(T) to the region of high temperatures made it possible to predict the temperature TSR = 570 K, which corresponds to the spin-reorientation transition, at which the easy-axis magnetic anisotropy is formed.

Damage assessment of the CRTS III ballastless slab track in high temperature regions

Temperature-induced interfacial damage between the prefabricated slab and filling layers is a common ailment faced by slab-type ballastless tracks systems. In this study, the damage behaviour of the CRTS III ballastless track in high temperature regions is explored. To this end, a 3-dimensional finite element model of the CRTS III ballastless track is built in Abaqus, which takes into account the non-linear temperature distribution along the track depth, the non-linear cohesive relationship between the concrete to self-compacting concrete interface, and the constitutive stress-strain relation of concrete. Upon subjecting the model to various temperature and wheel loading conditions, the following main conclusions were drawn: (1) Upward warpage of the prefabricated slab undergoes an average percentage increase of 37.62 % with each 10 °C/m increase in temperature gradient, signalling a greater up-warping effect in higher temperature regions; (2) the stresses along the interface’s first and second shear directions have the greatest influence on damage initiation of the interface; (3) under the effect of equally increasing temperature gradient loads, interface nodes where damage initiation had taken place showed a steady increase with an average difference of 5.21 %; (4) applied wheel loads significantly increase the damage initiation area of the track, but the effect of varying concentrated forces typically experienced during the track’s service life does not affect the change in damage initiation area as severely.

Influence of temperature gradients on helium diffusion and clustering in tungsten: A molecular dynamics study

Tungsten and its alloys, used as plasma-facing materials in fusion reactors, endure high-flux, low-energy helium ion irradiation and temperature gradients induced by thermal load and shocks. This study utilizes molecular dynamics (MD) simulations to explore the diffusion and clustering behavior of helium (He) in tungsten (W) under temperature gradients. The migration behavior of isolated helium atoms, small helium clusters, and helium self-interstitial atom (He-SIA) clusters within tungsten is analyzed. It is revealed that both helium and He-SIA clusters tend to migrate towards higher temperature regions, exhibiting negative thermophoresis. The nucleation of helium clusters, the formation of Frenkel pairs, and the interactions between self-interstitial clusters and helium clusters are also investigated. The results indicate that helium concentration significantly impacts He nucleation behavior. Directional diffusion may lead to areas of high concentration over time, potentially promoting the formation of He clusters and bubbles. These insights enhance the understanding of tungsten's performance and durability as a plasma-facing component in fusion reactors.

Effect of transition metals (Fe, Ru and Os) on the elastic, thermodynamic, electronic, magnetic and thermoelectric properties of three Nd-filled arsenide skutterudites based on first-principles computations

Elastic, electronic, magnetic, thermodynamic, and thermoelectric properties of three neodymium-filled skutterudites NdT4As12 (T = Fe, Ru and Os) have been investigated using density functional theory. The bulk moduli increase with the atomic numbers of the transition metals. All materials are stiff, while the Os compound is the stiffest. A considerable ionic contribution is seen in their inter-atomic bonding. The Fe compound possesses the highest Debye temperature, while the Os compound has the highest melting temperature. GGA+U formalism predicts the semimetallic nature of all the compounds, but their total DOS differs near the Fermi level in both spin channels. The contributions of the Nd-f and T-d electrons differ in the three compounds and two methods. GGA+U predicts the highest magnetic moment in the Fe compound, followed by the Ru and Os compounds. The thermoelectric figure of merit shows no systematic variation with z of the transition metals and in the high temperature region it increases with temperature pretty fast. The highest value of ZT is 0.32 in the Ru compound in the spin-down channel while it is 0.24 in the spin-up channel in the Fe compound, both at 1000 K.

Continuous Casting Slab Mold: Key Role of Nozzle Immersion Depth.

Based on a physical water model with a scaling factor of 0.5 and a coupled flow-heat transfer-solidification numerical model, this study investigates the influence of the submerged entry nozzle (SEN) depth on the mold surface behavior, slag entrapment, internal flow field, temperature distribution, and initial solidification behavior in slab casting. The results indicate that when the SEN depth is too shallow (80 mm), the slag layer on the narrow face is thin, leading to slag entrapment. Within a certain range of SEN depths (less than 170 mm), increasing the SEN depth reduces the impact on the mold walls, shortening the "plateau period" of stagnated growth on the narrow face shell. This allows the upper recirculation flow to develop more fully, resulting in an increase in the surface flow velocity and an expansion in the high-temperature region near the meniscus, which promotes uniform slag melting but also heightens the risk of slag entrainment due to shear stress at the liquid surface (with 110 mm being the most stable condition). As the SEN depth continues to increase, the surface flow velocity gradually decreases, and the maximum fluctuation in the liquid surface diminishes, while the full development of the upper recirculation zone leads to a higher and more uniform meniscus temperature. This suggests that in practical production, it is advisable to avoid this critical SEN depth. Instead, the immersion depth should be controlled at a slightly shallower position (around 110 mm) or a deeper position (around 190 mm).

Thermodynamic behavior of high-power inductively coupled plasma quartz tube wall

High-power inductively coupled plasmas are commonly used in planetary entry simulations and are increasingly being used in electric propulsion applications. However, during the operation of the system, the walls of the quartz tube will crack and melt. Its thermodynamic behavior is key to ensuring the safe and reliable operation of the system, which is directly related to the distribution of thermal energy within the discharge volume. In this paper, the temperature and stress distribution of the quartz tube wall of an inductively coupled plasma generator at 27 kW–85 kW are described. A numerical simulation model was established to depict the interaction between the plasma and the quartz tube wall. In the field of experimental research, the temperature of the outer wall of the quartz tube was obtained by using a thermal imager, and a non-uniform B-spline difference method was proposed to fit the outer wall temperature of the quartz tube to eliminate the influence of the induction coil. It is found that the numerical simulation and experimental results show that the temperature is stable region, temperature rise area, temperature drop zone, and the high temperature region of the quartz tube wall is located in the coil area, and the high stress area is also located in this region. On this basis, the outer wall temperature and thermal stress of quartz tubes under different heat fluxes are studied. When the heat flux exceeds 18.6 kW/m2, the stresses in the coil area and downstream of the coil exceed the limit stress. Mechanical failures may occur in areas where the ultimate stresses are exceeded, and these results can provide theoretical data for the optimal design of high-power inductively coupled plasma generators.

Interparticle interaction effect on superparamagnetic properties of ferrimagnetic particles

Uncoated and oleic acid coated ferrimagnetic particles are synthesized. Both samples contain similar magnetite particles. Structural characterization of these particles is performed using x-ray diffraction, Fourier transform infrared spectra, dynamic light scattering, transmission electron microscopy and thermogravimetric analysis. Average crystallite size of magnetite is 7 nm. Thickness of oleic acid layer on each magnetite particle is 1 nm. The oleic acid coated sample contains 23% oleic acid. Temperature dependence of the zero field cooled and field cooled susceptibility of the uncoated magnetite particles peaks at 120 K and both the curves bifurcate at 195 K. The peak temperature and the bifurcation temperature of the system decrease due to the oleic acid coating. The inverse susceptibility does not vary linearly with temperature in high temperature region. Magnetization versus applied magnetic field data at 250 K are analyzed in three different ways to study the interparticle interaction and the particle size distribution effects on magnetization. We find that the both factors affect the magnetization process of ferrimagnetic nanoparticles.

Improved thermoelectric properties of n-type ZrNiCu0.05Sn by doping Y2O3

Half-Heusler (HH)-based alloys are promising candidates for high-temperature thermoelectric (TE) energy conversion materials due to their excellent adaptability in high-temperature regions (900 - 1100 K). However, their TE performance is greatly limited owing to the inherently high lattice thermal conductivity (κl). In this study, we introduce a synergistic strategy to reduce thermal conductivity while modifying electrical transport properties through yttrium oxide (Y2O3) dispersion. The binary NiSn compound precipitations with sub-micron dimension together with Y2O3 nanoparticles synergistically intensify the phonon scattering and enhance the seebeck coefficient (S) effectively via energy filtering effect (EFE) at hetero-interfaces, leading to a remarkable reduction in κl and a slight improvement in the power factor (PF). Consequently, upon 1.5 wt% Y2O3 introduction, the sample incorporating Y2O3 exhibits a ∼13% reduction in total thermal conductivity (κt) as compared to the HH matrix, reaching a peak ZT of 0.86 at 938 K, thereby successfully optimizing its TE performance. The presented strategy provides a feasible approach to simultaneously modulate the thermal and electrical transport behaviors to improve the TE performance of HH-based materials.

Heat transfer performance of regenerative cooling in the presence of supersonic combustion based on two-way decoupling method

As a promising active cooling method for aero engines, regenerative cooling with endothermic hydrocarbon fuel plays an important role in thermal protection systems. However, simply assuming the thermal boundary conditions for the numerical simulation of regenerative cooling as either Dirichlet or Neumann boundary conditions is often unsuitable, as the combustion process exhibits complex three-dimensional (3D) characteristics. We propose a novel multi-step iterative calculation method in this work to simulate the coupled flow and heat transfer between supersonic combustion in the combustor and regenerative cooling outside. The method captures the main features of the supersonic combustion including different shockwave structures, and generates a realistic 3D distribution of heat flux as the boundary condition for the regenerative cooling study. With improved simulation, the result shows that regenerative cooling significantly reduces the peak temperature of the combustor by 58.5% with a mass flow rate of 1 g/s. A local high-temperature region is observed on the coupled wall inside the combustor near the injector, where the flame is primarily concentrated. Increasing the mass flow rate by 100%, from 1 g/s to 2 g/s, leads to a reduction in the maximum wall temperature by up to 15.7%.