High Temperature Duration Research Articles

Spatial and Temporal Variations’ Characteristics of Extreme Precipitation and Temperature in Jialing River Basin—Implications of Atmospheric Large-Scale Circulation Patterns

In recent years, extreme climate events have shown to be occurring more frequently. As a highly populated area in central China, the Jialing River Basin (JRB) should be more deeply explored for its patterns and associations with climatic factors. In this study, based on the daily precipitation and atmospheric temperature datasets from 29 meteorological stations in JRB and its vicinity from 1960 to 2020, 10 extreme indices (6 extreme precipitation indices and 4 extreme temperature indices) were calculated. The spatial and temporal variations of extreme precipitation and atmospheric temperature were analyzed using Mann–Kendall analysis, to explore the correlation between the atmospheric circulation patterns and extreme indices from linear and nonlinear perspectives via Pearson correlation analysis and wavelet coherence analysis (WTC), respectively. Results revealed that among the six selected extreme precipitation indices, the Continuous Dry Days (CDD) and Continuous Wetness Days (CWD) showed a decreasing trend, and the extreme precipitation tended to be shorter in calendar time, while the other four extreme precipitation indices showed an increasing trend, and the intensity of precipitation and rainfall in the JRB were frequent. As for the four extreme temperature indices, except for TN10p, which showed a significant decreasing trend, the other three indices showed a significant increasing trend, and the number of low-temperature days in JRB decreased significantly, the duration of high temperature increased, and the basin was warming continuously. Spatially, the spatial variation of extreme precipitation indices is more obvious, with decreasing stations mostly located in the western and northern regions, and increasing stations mostly located in the southern and northeastern regions, which makes the precipitation more regionalized. Linearly, most of the stations in the extreme atmospheric temperature index, except TN10p, show an increasing trend and the significance is more obvious. Except for the Southern Oscillation Index (SOI), other atmospheric circulation patterns have linear correlations with the extreme indices, and the Arctic Oscillation (AO) has the strongest significance with the CDD. Nonlinearly, NINO3.4, Pacific Decadal Oscillation (PDO), and SOI are not the main circulation patterns dominating the changes of TN90p, and average daily precipitation intensity (SDII), maximum daily precipitation amount (RX1day), and maximum precipitation in 5 days (Rx5day) were most clearly associated with atmospheric circulation patterns. This also confirms that atmospheric circulation patterns and climate tend not to have a single linear relationship, but are governed by more complex response mechanisms. This study aims to help the relevant decision-making authorities to cope with the more frequent extreme climate events in JRB, and also provides a reference for predicting flood, drought and waterlogging risks.

Influence of ammonia and Brown gas injection on the iron ore sintering characteristics under biochar substitution

The influence of ammonia and Brown gas injection on the iron ore sintering characteristics was explored through sintering pot experiments based on biochar substitution to increase biochar substitution proportion and reduce fossil energy consumption. By dividing the high-temperature stage of the sintering bed, the heating rate and cooling rate were calculated, and the reasons for poor sintering quality under a high biochar substitution ratio were explored. The results showed that under the 40% biochar substitution ratio, the cooling rate of the sintering bed significantly increased, the high-temperature duration time was short, and the sintering quality deteriorated severely. Additional injection of 0.5–1% vol ammonia or 1–2% vol Brown gas can reduce the cooling rate, prolong the high-temperature duration, and optimize the sintering quality. Based on 1% vol ammonia or 2% vol Brown gas injection, reducing the proportion of biochar with equal calorific value further increases the sintering comprehensive index, which means that using 1% vol ammonia or 2% vol Brown gas injection to assist sintering can reduce the proportion of coke usage to 60%, while the proportion of biochar substitution is 33.76% and 32.47%, respectively. The research results provide an effective solution for low-carbon sintering.

The synergistic effect of high temperature and relative humidity on non-accidental deaths at different urbanization levels

Numerous studies have examined the impact of temperature on mortality, yet research on the combined effect of temperature and humidity on non-accidental deaths remains limited. This study investigates the synergistic impact of high temperature and humidity on non-accidental deaths in China, assessing the influence of urban development and urbanization level. Utilizing the distributed lag nonlinear model (DLNM) of quasi-Poisson regression, we analyzed the relationship between Wet Bulb Globe Temperature (WBGT) and non-accidental deaths in 30 Chinese cities from 2010 to 2016, including Guangzhou during 2012–2016. We stratified temperature and humidity across these cities to evaluate the influence of varying humidity levels on deaths under high temperatures. Then, we graded the duration of heat and humidity in these cities to assess the impact of deaths with different durations. Additionally, the cities were categorized based on gross domestic product (GDP), and a vulnerability index was calculated to examine the impact of urban development and urbanization level on non-accidental deaths. Our findings reveal a pronounced synergistic effect of high temperature and humidity on non-accidental deaths, particularly at elevated humidity levels. The synergies of high temperature and humidity are extremely complex. Moreover, the longer the duration of high temperature and humidity, the higher the risk of non-accidental death. Furthermore, areas with higher urbanization exhibited lower relative risks (RR) associated with the synergistic effects of heat and humidity. Consequently, it is imperative to focus on damp-heat related mortality among vulnerable populations in less developed regions.

Performance and Interfacial Microstructure of Al/Steel Joints Welded by Resistance Element Welding.

In this study, an upper sheet of an A6061 aluminum alloy and a lower sheet of Q235 steel were welded by resistance element welding with a steel rivet. The temperature field during welding was calculated using ABAQUS numerical simulation software, and the interfacial microstructure was observed. A nugget was formed between the rivet shank and the lower sheet. With increases in welding current and welding time, the tensile shear load of the joint increased first and then decreased slightly. When the welding current was 14 kA and the welding time was 300 ms, the tensile shear load of the joint reached a maximum of 7.93 kN. The smaller the distance from the position to the lower sheet along the interface between the rivet shank and upper sheet, the longer the high-temperature duration and the higher the peak temperature during welding. At the junction of the rivet shank, upper sheet, and lower sheet in the joint, the high-temperature duration was the longest, at about 392 ms, and the peak temperature was the highest, at about 1237 °C. The results show that the smaller the distance from the position to the lower sheet along the interface between the rivet shank and the upper sheet in the joint, the thicker the reaction layer generated there, and that the thickness of the reaction layer was about 2.0 μm at the junction of the rivet shank, upper sheet, and lower sheet in the joint.

Thermal radiation hazards of the external flow field for vented hydrogen–air explosion: Effect of nitrogen fraction

An experimental investigation is conducted to examine the impact of nitrogen fraction on vented explosions of hydrogen–air–nitrogen mixtures in a 1-m-long cylindrical duct at 1 bar and 281 K. The study employs high-speed shadowgraph imaging, a pressure testing system, and infrared thermal imaging to record the venting process. The results showed that as the nitrogen fraction increases, the rupture time of the vent cover gradually increases. However, the internal peak overpressure exhibits an opposite trend, with P2 (caused by the ignition of unburned gas outside the tube by the escaping flame) near the vent consistently dominating. The frequency of Helmholtz oscillations initially decreases and then increases with increasing nitrogen fraction. Higher nitrogen fractions are associated with a greater likelihood of lower external peak overpressure but a decreasing trend in maximum external impulse. The maximum temperature shows an initial decrease followed by an increase with the addition of nitrogen fraction. This trend is also observed for flame length, flame width, high-temperature duration (>500 °C), and heat energy. Furthermore, the study determined safety zones that are free from thermal radiation damage.

Electrothermal power cycling of 15 kV SiC PiN diodes

Through extensive experimental measurements for the static and dynamic characteristics, the commercially available 15 kV Silicon Carbide (SiC) PiN diode are evaluated by power cycling. The forward voltage of diodes is used to indirectly measure the junction temperature. The SiC PiN diodes feature smaller die size, less reverse recovery charge and less on-resistance when compared to the commercially available closely rated Silicon PiN diodes. Nevertheless, during the power cycling experiments, the bipolar degradation and the degradation of contact metallization in SiC PiN diode gives rise to the increase of on-resistance even though its on-state losses is not as high as in the Silicon device. Such degradations are not observed from the Silicon PiN diode for the same junction temperature and the same high-temperature duration.

Process Control of a Compost-Reactor Turning Operation Based on a Composting Kinetics Model

Composting is a biochemical as well as a heterogeneous process, and the turning operation is important to maintain aerobic conditions and improve the efficiency of the composting process. Therefore, the turning frequency is an important factor for the precise control of the composting reactor. It is necessary to determine the changes in the physical and chemical parameters of the composting process and to simulate them. Pretreated vinegar residue and wool washing sludge were mixed at a mass ratio of 6:4 for the composting process. The composting reactor’s temperature, CO2, CH4, and organic matter content were collected during the composting process. According to the principles of composting, a kinetic model of composting based on the change in CO2 gas concentration and heat balance in the composting reactor is developed, which provides a theoretical basis for the subsequent control of the composting reactor. The comparison of the model predictions to the measured results of the composting reactor shows that the SSE, R2, and RMSE for the organic matter content simulation are 8.122, 0.943, and 1.274 g/kg, respectively, and the SSE, R2, and RMSE for the temperature simulation are 29.54, 0.959, and 2.71 °C, respectively. Based on the prediction of the temperature in the reactor based on the composting kinetics model, the process control for the turning operation is proposed to achieve precise control of the composting process. The results show that the duration of high temperature in a composting reactor is prolonged for 2 days, the degradation rate of organic matter occurs at a more rapid speed, and the operation efficiency of the production line can be improved by more than 10%. This indicates that the decision-making method based on the composting kinetics model can improve the composting efficiency.

Experimental research on axial mechanical properties of circular CFSST columns after exposure to temperature and sliding

This paper presents experimental investigations on axial mechanical properties of circular concrete-filled stainless steel tube (CFSST) columns after exposure to temperature and sliding. A total of 117 CFSST specimens were tested under axial compression loading with four factors (i.e., tube thickness, temperature, duration, and concrete compressive strength) considered. Test results indicated that the initial stiffness of circular CFSST short columns was degenerated due to high-temperature sliding. Circular CFSST specimens exhibited a 50.9% lowest residual strength at 1000 ℃. The influence of high-temperature duration on the residual strength of circular CFSST short columns was limited. The residual strength of specimens was positively correlated with the thickness and concrete compressive strength. All circular CFSST columns after exposure to temperature and sliding experienced an outward local buckling under axial compression. In addition, the parameters formulae of residual strength for circular CFSST columns after exposure to temperature and sliding are proposed, which achieve sufficient accuracy. The research could offer valuable references for strengthening circular CFSST columns after fire.

Behavior of square concrete-filled stainless steel tube columns after high-temperature sliding

This paper presents herein pertains the experimental and numerical investigations on axial compressive behavior of square concrete-filled stainless steel tube (CFSST) columns after high-temperature sliding. A total of 117 CFSST specimens were tested under axial compression loading. The design variables included tube thickness, temperature, duration, and concrete compressive strength. Test results indicated that the initial stiffness of square CFSST short columns was degenerated due to high-temperature sliding. CFSST specimens exhibited a 62.7% lowest residual strength at 1000 °C. The influence of high-temperature duration on the residual strength of square CFSST short columns after high-temperature sliding was limited. The residual strength of specimens was positively correlated with the thickness and concrete strength. All square CFSST columns after high-temperature sliding experienced an outward local buckling under axial compression. Finite element models of square CFSST columns after high-temperature sliding are established and validated against the experimental results. In addition, the parameter formulae of residual strength for CFSST columns after high-temperature sliding were proposed, which achieved high accuracy. This research results could provide strengthening reference for the application of CFSST columns after high-temperature sliding.

Development and Evaluation of Cow Dung Composting Equipment with Ventilation and Heating

Traditional cow manure composting equipment often lacks ventilation, heating, and real-time monitoring and adjustment capabilities, hindering manure maturation and proper utilization of compost, moisture reduction, and optimal environmental conditions for microbial activity. To address these limitations, we optimized and redesigned the structure and control elements of conventional composting equipment. In doing so, we developed a novel cow manure composting apparatus based on the target composting quantity method. The new design features a refined ventilation and heating structure, as well as an enhanced control system using PLC and MCGS. This equipment provides improved composting effects while offering real-time monitoring of composting data, effectively promoting the composting process. Further evaluation of the modified equipment was conducted using fermented cow dung, demonstrating its feasibility. The experiment yielded positive results, indicating that the composted cow manure satisfied all necessary standards across all evaluation parameters. These parameters included the moisture content of the compost, the duration of high temperature, the pH, and the seed germination index. The seed germination rate reaches 85%, and the water content of manure is 9.3%, which is much higher than the industry standard.

Impacts of Reservoir Operation on Hydrodynamic and Thermal Conditions in a Large Deep Reservoir and the Potential Ecological Impacts

Many large-deep reservoirs have been built, are under construction, or are planned in southwestern China, to meet increasingly high energy demands. The construction of dams can significantly alter the natural hydrodynamic and thermal conditions of rivers, thereby, threatening aquatic ecosystems, e.g., fish and algae communities. However, the impacts of large-deep reservoir operations on the hydrodynamic and thermal conditions and their potential influence on aquatic ecosystems have seldom been addressed. In this study, a quasi-3D hydrodynamic model is developed to describe the hydrodynamic and thermal conditions of a large deep reservoir, Nuozhadu, the largest reservoir along the Lancang River. The water temperature and flow velocity after the impoundment of the reservoir are examined. To explore how reservoir operation changes the hydrodynamic and thermal conditions, five groups of reservoir operational scenarios based on different water levels and discharge rates are conducted. Our results indicate that a lower water level combined with a higher discharge rate can increase the flow velocity and decrease the surface water temperature in the reservoir, which may contribute to diminishing the growth of Cyanobacteria. Meanwhile low water levels can also increase the outflow water temperature to protect the downstream fish. Further, the LowLevel and MaxPower schemes were designed to provide ecologically favorable hydrodynamic conditions, and to maximize power generation, respectively. The LowLevel scheme was found to reduce the duration of high surface water temperature (>25°C) by 18 days annually and reduce the outflow temperature by 0.8°C in the fish spawning period, at the expense of a 10% reduction in power generation. This study contributes to a better knowledge of the linkage among hydrodynamic, thermal conditions, and ecological impacts due to reservoir operation, and provides a novel perspective regarding the ecological safety of a large deep reservoir operation.

The overpressure and temperature characteristics of hydrogen-air mixtures during a vented explosion in a large L/D ratio duct: Effect of burst pressure

Explosion venting is an effective way to reduce the hazards of gases and dust fuel explosion in a confined space. Since there is little attention paid to the thermal radiant damage produced by the vented flame, the surface temperature distribution for hydrogen-air mixtures with different burst pressures (Pv) is investigated in a large L/D ratio duct. The high-speed shadowgraph imaging system, pressure testing system and infrared thermal imager are used to record the explosion venting process. The Pv and the thickness (δ) of the polyester vent cover are in the direct ratio, while the vent failure time shows a nonlinear relationship with the δ. Five internal overpressure peaks (P1, P2, P3, PRef, Pneg) are distinguished. With the addition of Pv, P1 increases gradually, while P2 disappears in some higher Pv. The external flow field is obtained and discussed in detail. The cases of lower Pv with the unburned gas escaping from the vessel can sustain a high flame speed, whereas other cases only involve a flame jetting process with a relatively low speed. The high-temperature (>500 ℃) duration shows an ‘M’ shape with the Pv. Besides, the safety distances to prevent humans from suffering thermal radiant damage have been determined.

Effect of thermal condition on isothermal-pressing joined strength of silanized Al alloy/carbon fiber-reinforced polyamide-6

Carbon fiber-reinforced thermoplastics (CFRTPs) and lightweight metals are widely used in multi-material structures owing to their high strength and excellent corrosion resistance, thus stimulating research on various heat-assisted techniques to join them. Currently, the isothermal-pressing process has been developed to realize sound interface joining between CFRTP and Al alloy under relatively uniform thermal conditions. However, a quantitative investigation of the interaction between thermal conditions, chemistry reactions, and joining strength is still lacking. This current investigation analyzed chemical reaction state and resultant bonded strength of isothermal-pressing joined interface of silanized 5052 Al alloy and carbon fiber-reinforced polyamide-6 (CF/PA6) under various thermal conditions. X-ray photoelectron spectroscopy and Raman scattering analysis showed the increasing consumption of epoxy groups on silanized 5052 Al alloy side with the increase in joining temperature and residence time. This suggested higher temperatures and sufficient high-temperature duration times could efficiently promote the interface chemical reaction, increasing interface bonding strength. As the joining temperature or residence time increased, the fracture location gradually shifted from the silane coupling layer/re-solidified resin interface to the re-solidified resin close to interface, and even it directly passed through CF/PA6 along the thickness direction. Under the current adopted conditions, a critical high-temperature duration time of ∼6.0 s at least was recommended by optimizing the joining time to achieve high-strength joining between 5052 Al alloy and CF/PA6. The findings will guide optimizing the joining conditions in heat-assisted joining processes of Al/CFRTP hybrid structures.

Preliminary discussion on the ignition mechanism of exploding foil initiators igniting boron potassium nitrate

Exploding foil initiator (EFI) is a kind of advanced device for initiating explosives, but its function is unstable when it comes to directly igniting pyrotechnics. To solve the problem, this research aims to reveal the ignition mechanism of EFIs directly igniting pyrotechnics. An oscilloscope, a photon Doppler velocimetry, and a plasma spectrum measurement system were employed to obtain information of electric characteristics, impact pressure, and plasma temperature. The results of the electric characteristics and the impact pressure were inconsistent with ignition results. The only thing that the ignition success tests had in common was that their plasma all had a relatively long period of high-temperature duration (HTD). It eventually concludes that the ignition mechanism in this research is the micro-convection heat transfer rather than the shock initiation, which differs from that of exploding foil initiators detonating explosives. Furthermore, the methods for evaluating the ignition success of semiconductor bridge initiators are not entirely applicable to the tests mentioned in this paper. The HTD is the critical parameter for judging the ignition success, and it is influenced by two factors: the late time discharge and the energy of the electric explosion. The longer time of the late time discharge and the more energy of the electric explosion, the easier it is to expand the HTD, which improves the probability of the ignition success.

Active electrode materials for lithium-ion battery

Nanoproducts spherical spinel lithium manganese oxide (LiMnO) with about 20 nm in diameter was synthesized by explosive method. The growth of lithium manganate via detonation reaction was investigated with respect to the presence of an energetic precursor, such as the metallic nitrate and the degree of confinement of the explosive charge. The detonation products were characterized by scanning electron microscopy. Powder X-ray diffraction and transmission electron microscopy were used to characterize the products. Lithium manganate with spherical morphology and more uniform secondary particles, with smaller primary particles of diameters from 10 to 30 nm and a variety of morphologies were found. Lithium manganate with a fine spherical morphology different from that of the normal spinel is formed after detonation wave treatment due to the very high quenching rate. It might also provide a cheap large-scale synthesis method. Explosive detonation is strongly nonequilibrium processes, generating a short duration of high pressure and high temperature. Free metal atoms are first released with the decomposition of explosives, and then theses metal and oxygen atoms are rearranged, coagulated and finally crystallized into lithium manganate during the expansion of detonation process.

Bonding properties between steel-basalt hybrid fibers reinforced cementitious composites and existing concrete at high temperatures

Steel-basalt hybrid fibers reinforced cementitious composite (SBFRCC) is a potential reinforcement and repair material for engineering structures with fire risk due to its excellent mechanical properties exposed to ambient and high temperatures. However, the bonding properties between SBFRCC and existing concrete are still unclear, especially at high temperatures. To fill this gap, the bonding properties between SBFRCC and existing concrete at high temperatures were investigated based on two situations by using the slant shear and splitting tensile tests. First, the existing concrete was heated at high temperatures and then bonded with SBFRCC and strengthening concrete to form combined systems, respectively. The effects of the interface roughness, high temperature duration, and post-fire-curing on their bonding properties were investigated. Second, the existing concrete was bonded with SBFRCC and then heated at high temperatures, and the effects of fly ash substation rates on the bonding properties were studied. Besides, the backscattered-electron (BSE) was used to observe the interface between the exiting concrete and SBFRCC exposed to various temperatures. Results show that the first bonded and then heated specimens are slide-failed and separated at the bonding interface from room temperature to 600 °C, while the damage is generated within the existing concrete at 800 °C. SBFRCC has better high temperature resistance than the existing concrete. The slant shear and splitting tensile strengths between PC-A and SBFRCC are 9%–33.3% higher than that of PC-A and strengthening concrete at all temperatures. The appropriate roughness at the interface by polishing can significantly improve the bonding properties between the existing concrete and SBFRCC. The bonding strength is recovered by more than 18.2% and 29.8% after the post-fire curing of 28 and 90 d, respectively. The increase of fly ash substitution rates has a certain contribution to the bonding properties above 600 °C.

Post-fire performance of axially-loaded elliptical concrete-filled steel tubular stub columns

This paper investigates the post-fire performance of elliptical concrete-filled steel tubular (CFST) columns by a series of post-fire axially-loaded stub column tests and numerical analysis. The test parameters included target temperature, high temperature duration time, section type and section size. A post-fire stress-strain relationship model of core concrete applicable to the elliptical CFST column was proposed according to the test data, and finite element analysis (FEA) model of the elliptical CFST column was established. Based on the FEA model, the temperature and deformation developments, failure mode, stress and load distributions of elliptical CFST columns were analyzed and discussed, and parametric analysis was further conducted to identify the key influencing factors on the post-fire ultimate bearing capacity and residual bearing capacity index of elliptical CFST columns. Finally, a simplified formula was proposed to calculate the post-fire residual bearing capacity index of elliptical CFST columns.

Enhanced high-temperature stability of indium tin oxide - Indium oxide thermocouples by two-step annealing

The complex internal structure of the aero-engine and the high-temperature, high-pressure, and high-speed airflow make it difficult to measure the internal temperature. Indium tin oxide (ITO) and In2O3 films have been studied for their application in high-temperature thermocouples and strain gauges. Due to their large Seebeck coefficient and high-temperature stability, ceramic thin-film thermocouples are expected to be used at high-temperature measure. In this paper, ITO-In2O3 thermocouples were fabricated by magnetron sputtering. Besides, the electrical properties of the air-annealed and two-step nitrogen-annealed thermocouples were compared, including the repeatability of thermoelectric response after multiple thermal cycles and the drift rate during the high-temperature duration. The microstructure and electrical conductivity of both the as-deposited and post-annealed ceramic thin films were tested respectively. The result shows that the resitivity and Seebeck coefficient of the thin films annealed in nitrogen is reduced, but the stability at high temperature is greatly improved.

Enhanced mechanical and anticorrosion properties in cryogenic friction stir processed duplex stainless steel

In the present work, duplex stainless steels (DSSs) SAF2507 were friction stir processed with flowing cryogenic medium mixed with liquid nitrogen and industrial ethanol. Homogeneous ultrafine grained (UFG) dual-phase structure with ferrite (α) and austenite (γ) grains with average size of around 1 μm was obtained due to the significantly lower peak temperature and shorter high-temperature duration. The developed UFG dual-phase structure enabled a dramatic enhancement of yield strength by about 22 %, while maintaining a high elongation of 55 % owing to the excellent strain hardening capacity. The grain refinement and increased number of α/γ interfaces were dominantly responsible for the significantly improved YS, while the massive development of geometrically necessary dislocations around the deformation incompatible α/γ interfaces primarily contributed to improving the strain hardening capacity. As a result, the enhanced strength-ductility synergy was achieved by cryogenic friction stir processing. Also, the obtained UFG dual-phase structure helps with enhancing corrosion resistance. This work provides a new strategy for preparing uniform UFG DSSs with outstanding mechanical properties and anticorrosion.

Post-fire bond behaviour in elliptical concrete filled steel tubes: Experiment and simulation

The post-fire bond behaviour between the steel tube and core concrete in elliptical concrete filled steel tubes (ECFST) is studied in this paper. A total of 15 post-fire push-out test specimens, including 9 elliptical, 3 circular and 3 square CFSTs, were designed and tested. The testing parameters included: (a) target temperatures (Ttar = 20 °C, 600 °C and 800 °C); (b) high temperature duration time (td = 30 min, 60 min, 180 min and 300 min); (c) length of long axis of elliptical section (2a = 200 mm and 300 mm); (d) section type (elliptical, circular and square). The test results indicated that the target temperature and high temperature duration time affected the post-fire bond strength of ECFSTs significantly, and the post-fire bond strength of ECFSTs could be increased with the increasing values of the two parameters. Based on the test data, a two-linear stage bond stress versus slip constitutive model considering the influence of both the temperature and fire-exposed surface area was proposed and verified to capture the post-fire bond behaviour in ECFSTs, which could be used in the refined bond behaviour numerical analysis of ECFSTs.