High-temperature Characteristics Research Articles

An experimental and kinetic modeling study on the high-temperature ignition and pyrolysis characteristics of cyclohexylamine

Amine compounds are an important class of nitro-containing fuels and represent as promising renewable fuels. However, the structural effect from the alkyl group on the combustion characteristics of amines remains an urgent problem to promote their usage in practical engines. To probe and replenish the combustion properties of amine fuels, this work reported an experimental and kinetic modeling study on the high-temperature ignition and pyrolysis characteristics of cyclohexylamine over a wide range of conditions. Specifically, a high-pressure shock tube is used to measure the ignition delay times under the temperature range from 1100 K to 1700 K with pressure of 2 and 5 bar and the equivalence ratios of 0.5, 1.0 and 2.0. The pyrolysis characteristics is studied using a single-pulse shock tube at fuel concentration of 0.5% diluted by argon in the temperature range 950–1400 K at 5 and 10 bar with the residence time around 1.6 microsecond. A detailed kinetic mechanism is developed to simulate the experimental results. To improve the accuracy of the detailed mechanism, primary initial reactions of cyclohexylamine including the hydrogen abstraction reactions and the CN decomposition reaction are theoretically studied at G4//M06–2X/6–311++G(d, p) level of theory with transition state theory and RRKM/mater equation. The detailed kinetic mechanism shows good prediction accuracy of the ignition delay times and pyrolysis product distributions under different temperature, pressure and equivalence ratio conditions. Sensitivity analysis results indicate that the most sensitive reaction is O2 + H = O + OH with the most negative sensitivity coefficient and the abstraction reaction of vinylamine with OH radical, C2H3NH2 + OH = C2H3NH + H2O also exhibits large sensitivity coefficients. Reaction path analysis reveals that the abstraction reactions control the initial oxidation of cyclohexylamine and cyclohexen-1-amine, cyclohexen-2-amine, and cyclohexen-3-amine are also major intermediates during the oxidation of cyclohexylamine besides small pyrolysis products.

Study on high-temperature oxidation and hot corrosion characteristics of Cr60Ni40 laser cladding layer

In order to investigate the high-temperature characteristics of Cr-based alloy, Cr60Ni40 laser cladding layer (60 wt% Cr and 40 wt% Ni) were prepared and subjected to high-temperature oxidation test and hot corrosion test. The results prove that there are Cr segregation and large particles of Cr precipitated within the raw Cr60Ni40 cladding layer. During the high-temperature test, Cr2O3 protective film was generated on the surface of the cladding layer, protecting the substrate to different degrees. However, the particles precipitation of Cr caused uneven growth of Cr-rich oxide, and the Cr segregation brought about internal corrosion with Cr2O3 as the main products.

Novel SAW Temperature Sensor with Pt/Ti/AlN/Mo/AlN/Si Structure for High Temperature Application

In this paper, a surface acoustic wave (SAW) temperature sensor with a Pt/Ti/AlN/Mo/AlN/Si structure was prepared, and the high temperature characteristics of the sensors at 20–600 °C under different electrode metallization rates (ղ) were measured. It was found that frequent device mutation occurred in the first high-temperature test, and that the mutation point decreased with the increase in the electrode metallization rate (ղ). In the subsequent test, the data became stable, the sensor’s center frequency increased, the return loss (S11) decreased and the factor of merit (Q) increased. After annealing the same sensors at 600 °C for 30 min, they could achieve performance improvement in the first test, meaning that proper annealing can improve sensor performance. In addition, the annealed SAW sensor was tested in the temperature range of 20–1000 °C, which met the requirement of a temperature range of 20–900 °C, its f–T curve was linear, the factor of merit (Q) was 34.5 and the sensitivity was 46.6 KHz/K.

Engineering mycelium fungi into an effective char-forming thermal protection material via alkaline deacetylation

The char yield from mycelium fungi can be improved via alkaline deacetylation wherein chitin polymer segments are converted to chitosan moieties. The influence of alkaline deacetylation conditions (e.g., temperature, incubation time and alkali concentration) on the biochemical composition, microstructural and physicochemical characteristics and thermal properties of mycelium fungi is poorly understood. In this paper, we investigated the influence of different alkaline deacetylation conditions on the degree of deacetylation and thermal properties of non-pathogenic Basidiomycota phylum, mycelium fungi, grown in molasses. Particularly, we determined the relationship between the degree of deacetylation and high-temperature char-forming characteristics of deacetylated mycelium. Further, the effect of an oxidizing agent, KMnO4, on the thermal stability and char-forming characteristics of alkaline-treated mycelium was investigated. This paper presents a comprehensive investigation of the relationship between the degree of deacetylation and char yields at high temperatures (e.g., >300°C) as well as an in-depth interrogation of the thermal degradation mechanisms governing the thermal stability of alkaline (and KMnO4) treated mycelium. Research findings from this study have advanced knowledge of the development and design of bio-derived thermal protection materials for fire-threatened infrastructure.

Experimental Investigation on Failure Mechanism of Hot Dry Rock under Microwave Irradiation

Hot dry rock (HDR) geothermal energy is clean energy that can meet people’s demand for low carbon. The traditional hydraulic fracturing method is challenging to break HDR dominated by granite, mainly because of HDR’s high temperature and hard characteristics. Microwave irradiation is considered a proven approach to breaking granite. This study investigates the failure mechanism of HDR at 500°C–800°C under microwave irradiation. The experiments cover preheating, uniaxial compression, granulometric analysis, binocular vision monitoring (BVM) technique, and X-ray powder diffraction. The result shows that the uniaxial compression strength of granite decreases the most at 500°C–600°C, which is 62.77% on average. The failure form is from the brittle failure (untreated) to ductile failure (800 °C) with the rise of the microwave irradiation temperature. The microwave makes a particle size in the range of 0.6–2.36 mm the most apparent particle size of granite after uniaxial compression. The BVM technique reconstructs the surface deformation with a 0.7% error. Microwaves cause heat accumulation near the rock near the magnetron, resulting in the formation of crack networks and a molten cavity. The possibility of microwave-assisted fracturing of HDR is discussed at the end of the article.

Fire resistance of low alloy Q420d high-strength steel column under high-temperature creep.

The high-temperature mechanical and creep characteristics of Q420D steel are investigated in this essay. To determine the steel's high-temperature yield strength, the high-temperature tensile test of Q420D steel was first performed. In the temperature range of 400°C-800°C, the high-temperature creep test under various pressures was conducted, and the creep strain curve over time was produced. Finite element analysis and comparison were done to examine the impact of creep strain on the Q420D steel column's bearing capacity under high-temperature conditions. The findings demonstrated that: Using Abaqus, a finite element fire resistance analysis of a Q420D steel column, was conducted while taking initial geometrical flaws, residual stress, and creep effect into account. As a result, the critical temperature of a Q420D steel column under various load ratios was determined. The largest deviation from the critical temperature in the standard GB51249-2017 was 2.9% when the creep effect was taken into account under the load ratio R = 0.3. The highest reduction in fire resistance limit time under low load ratio conditions, taking into account the creeping impact of Q420D steel columns, is 35%. The findings demonstrate that the high-temperature creep energy greatly lowers the steel column's fire resistance.

Strength Reduction of Concrete Subjected to High Temperatures: Effects of Various Aggregates

Previous studies on the strength degradation of concrete subjected to high temperatures were analyzed. To analyze the effect of the coarse-aggregate type on strength degradation, data from previous studies were collected, and the coarse aggregate used, physical properties of the aggregate, and heating conditions were analyzed. The concrete types were classified into normal, heavyweight, and lightweight concrete. Their high-temperature characteristics were analyzed and evaluated according to the mixed coarse aggregate. Finally, the correlations derived from the analysis results were compared with the CEB Code. The analysis results were different for different concrete and coarse-aggregate types, and different tendencies from the CEB Code were observed.

Deformation Prediction Theory of Thermal Barrier Coatings near Cooling Holes under Thermal Cycling.

Thermal barrier coating (TBC) systems are widely adopted in gas turbine blades to improve the thermal efficiency of gas turbine engines. However, TBC failure will happen due to the thermal stress between the different layers of the TBC systems. The traditional two-layer theoretical model only considers TGO (thermally grown oxide) and a substrate in the inner cooling hole with the surface uncoated, which results in poor prediction of the deformations of the TBC systems. It should be mentioned that the effect of TBC is very important because the thickness of TBC is much larger than the TGO thickness. In this study, a new three-layer theoretical model was derived, which is composed of the cylindrical TGO and TBC mounted in the substrate with a circular hole, and the stress and strain of TGO near the cooling hole under the condition of the thermal cycles were calculated. The high temperature characteristics of TGO and the substrate including the high temperature strength and growth ratio were from the experiments. The results show that the strain of the developed three-layer model is irrelevant with increasing number of cycles, which indicates that TBC in the cooling hole significantly inhibits the deformation of TGO near the cooling hole. Therefore, aimed at confirming the feasibility of the three-layer theoretical model, the finite element analysis with coating in the cooling hole and on the surface was carried out with a three-layer axisymmetric model, which proves that the 3-layer theoretical model can predict the deformation trend near the cooling hole.

Effect of ore types on high temperature sintering characteristics of iron ore fines and concentrate

Sinter quality (strength and reducibility) plays an important role in reducing the GHG emissions from the blast furnace ironmaking process and is significantly influenced by the reactions occurring in the sintering bed. Formation and fluidity of the initial sinter melt from adhering fines and its interactions with coarse nucleus particles are the key sintering reactions. Hence understanding of these high temperature characteristics of iron ore is urgently needed in order to produce strong and reducible sinter and optimise resource utilisation. In the present study, laboratory scale sintering tests were carried out to examine the effect of adhering fines and nucleus particles from various ores on the characteristics of initial sinter melt formation, fluidity, as well as penetration and assimilation. The formation ability and fluidity of the initial melts from various adhering fines were quite different, and various iron ore fines required distinct CaO contents to form the melt and spread out. The ore type of adhering fines and substrates affected the penetration and assimilation ability of the initial melt, but a good formation ability and fluidity of initial melt was the basis of good penetration and assimilation ability. Based on the micro and macro sinter structure, the high temperature characteristics were further related to the sinter quality and sintering performance. This information is expected to provide excellent tools in formulating and optimising future low cost and low emission sinter blends.

Manufacturing of Ti–Nb–Cr–V–Ni high entropy alloy using directed energy deposition and evaluation of materials properties

High entropy alloy (HEA) is a new material that can overcome the limitations of the physical properties of conventional materials, exhibit excellent mechanical properties, and be employed in various extreme environments. In particular, refractory HEA composed of refractory materials such as Ti and Ni are expected to exhibit desirable high-temperature properties. Metal additive manufacturing has a shorter manufacturing time than the conventional casting method and is suitable for HEA manufacturing using various metal materials. Specifically, directed energy deposition (DED) has a high solidification rate that is advantageous for grain refining, prevents intermetallic compounds, and averts shrinkage that occurs in the casting method, thereby reducing cracks and deformations and resulting in fewer defects and superior production quality. In this study, a HEA with desirable high-temperature characteristics that are composed of Ti–Nb–Cr–V–Ni was designed by optimizing thermodynamic parameters and deposited using DED. The deposited Ti–Nb–Cr–V–Ni exhibited a body-centered cubic structure. Tensile strength, hardness, differential scanning calorimetry (DSC), and thermal conductivity analyses were performed to analyze its mechanical and thermal properties. Ti–Nb–Cr–V–Ni exhibited a fine structure and high tensile strength at high temperatures due to the characteristics of the DED process, but low elongation at room temperature. These strength characteristics are attributed to the microstructure of Ti–Nb–Cr–V–Ni, which mainly forms the BCC phase. And Ti–Nb–Cr–V–Ni exhibited high hardness and high thermal stability enough to be used in extreme environments with high temperatures.

Influence of Water Immersion Time on Re-Ignition Characteristics of High Temperature Oxidized Coal

ABSTRACT After a coal seam is mined, the oxidized coal left in its goaf is prone to water immersion, and spontaneous combustion accidents involving water-immersed coal may easily occur when mining the underlying coal seam. Using scanning electron microscopy and nitrogen adsorption experimental methods, the physical structure of high-temperature pre-oxidized water-immersed coal samples was characterized. By means of infrared spectroscopy, electron spin resonance (ESR) and simultaneous thermal analysis, the microscopic characteristics of the coal samples and the endothermic and exothermic characteristics of the oxidative combustion process were studied. The results showed that a specific pre-oxidation soaking time generated more oxidation pores in the coal sample, causing more water to become trapped in the pores and increasing the secondary oxidation heat absorption. High-temperature oxidation promoted the conversion of coal sample functional groups (FG) and free radical active sites, Water immersion led to the formation and loss of FG, and the longer the water immersion time was, the greater the loss. The larger average pore size of the pre-oxidized water-immersed coal sample provided more coal-oxygen contact sites, and the breaking of chemical bonds in the FG during the secondary oxidation process accelerated the heat release and promoted the oxidative re-ignition of the coal sample. The spontaneous combustion of water-immersed coal in the goaf can be prevented by controlling the high oxidation temperature and water immersion time.

Study on high-temperature and high-voltage insulation characteristics of polypropylene blend with highly packed elastomeric domains for power cable applications

In this paper, we report the high-temperature and high-voltage (HV) insulation characteristics of the polypropylene (PP) blend with highly packed elastomeric domains that showed excellent mechanical toughness in our previous study to find its suitability as insulation material for power cable applications. The main focus lies on tensile properties with thermal aging, thermomechanical behavior corresponding to the thermal transition, high-temperature volume resistivity and DC dielectric strength, and space charge accumulation behavior of the PP blend in comparison to the crosslinked polyethylene (XLPE). Our PP blend having low elastic modulus of approximately 266.9 MPa exhibited high tensile strength and elongation at break, and high-temperature stability as well. Using this PP blend, not only good HV insulating performances in volume resistivity and DC breakdown strength (BDS) were obtained similar to XLPE, but also adequate values were obtained at high temperature, even at 110 °C, which was not possible with XLPE. However, there was space charge accumulation and electric field distortion in the PP blend like XLPE, which needs to be suppressed. Therefore, our PP blend is expected to have the potential to replace existing XLPE as insulation materials for future HV power cables.

Experimental investigation of performance properties of asphalt binder and stone matrix asphalt mixture using waste material and warm mix additive

Many distresses occur in the pavement due to the increase in traffic and changes in weather conditions through the year (hot to cold). Asphalt binder modification is the best way to control these stresses. On the other hand, utilization of warm mix asphalt additives has significant environmental benefits. This research investigates the influence of simultaneous usage of two waste material (ground tire rubber (5%, 10% 15%, and 20% by weight of asphalt binder) and natural bitumen (10%, 20%, 30%, and 40% by weight of asphalt binder)) on performance behavior of asphalt binders and mixtures containing warm mix asphalt additive. Performance behavior of binders and mixtures were evaluated by several tests such as; conventional asphalt binder tests, linear Amplitude Sweep (LAS), Multiple Stress Creep Recovery (MSCR), Bending Beam Rheometer (BBR), Dynamic Shear Rheometer (DSR), storage stability, resilient modulus, indirect tensile strength, dynamic creep, hamburg wheel track, and four point beam fatigue (FPB) tests. The statistical analysis was performed to investigate the additives have significant effect or not. Results revealed that fatigue and rutting performance of samples were improved by combination of waste materials. Addition of waste natural bitumen led to decreases the low-temperature behavior of asphalt binder, while addition of waste ground tire rubber improves the resistance against low-temperature cracking. Addition of natural bitumen up to 10% has positive impact on storage stability of binder and by adding more content of additive, phase separation occurred. Warm mix additives improve the fatigue and rutting resistance of mixtures containing waste materials. Adding 20% CR to 30% Gilsonite -modified binder causes an enhanced the high temperature characteristics of about 34%. Based on outcomes, waste ground tire rubber enhances the fatigue resistance of mixtures containing natural bitumen. In general, utilization of waste materials in combination with warm mix additives improve the performance properties of asphalt binder and mixture. Mr of mixtures, containing 40% Gilsonite, was 52% greater compared to base mixture. Nonetheless, 30% Gilsonite as well as 5% CR had Mr values nearly 44% higher compared to base mixture. Also, based on statistical analysis, addition of mentioned additives has significant effect on improving the performance of specimens.

Effect of High-Sintering-Temperature Reduction Behavior on Coke Solution Loss Reaction with Different Thermal Properties

With the shortage of high-quality coking coal resources and the pursuit of low-cost smelting, the types and sources of coal have changed. Therefore, it is difficult to establish an effective correlation between the existing evaluation indexes of coke thermal performance and the production indexes of the blast furnace. The dissolution deterioration of coke directly affects the production benefits of the blast furnace, and the dissolution deterioration of blast furnace coke is the result of ore–coke coupling. To better understand the mechanism of the coupling reaction relative to the thermal properties of coke, this paper experimentally studies ore–coke coupling between two kinds of coke and one kind of blast furnace standing sinter which have different reactivities but are used in practical applications. This method adopts a matched thermogravimetric device. By analyzing and calculating the high-temperature reduction behavior and characteristics of the sinter and the dissolution loss behavior and characteristics of coke in the gas–solid coupling reaction test of coke and sinter, and comparing and fitting the coupling reaction factors of the coupling reaction and the thermal properties of coke, it was revealed that the real degradation behavior of coke was affected by the reduction reaction of the sinter. The results show that the temperature range with the best matching degree between the reduction reaction of oxygen supply from sinter and the gasification reaction of oxygen consumption from coke is at a position where the coupling factor is closest to 1. In the gas–solid coupling reaction between low-reactivity coke and sinter, the strongest dissolution rate, RCSL, is approximately 1200 °C, while in the gas–solid coupling reaction between high-reactivity coke and sinter, the RCSL is approximately 1100 °C. The minimum strength, CSCSL, of high-active coke and sinter after dissolution is approximately 1100 °C, while that of low-active coke and sinter after dissolution is approximately 1200 °C. It is shown that there is a good linear relationship between the RCSL of high- and low-reactive coke and strength after dissolution loss CSCSL.

High-temperature deformation characteristics of 3D printing of nano-ceramic materials

In order to improve the application effect of three-dimensional printing of nano ceramic materials, the high-temperature deformation characteristics of three-dimensional printing of nano ceramic materials were studied. First, the main raw materials and experimental instruments for preparing nano ceramic materials were selected. Then, high-temperature nano ceramic materials were prepared by using 8%, 12%, and 15% polyester modified silicone resins respectively; And put it into the storage box of the direct writing 3D printer to print the 3D ceramic sample with the 3D printer. At last, the high temperature deformation characteristics under different high temperature environments are analysed. The results show that the adhesive force and salt spray resistance of 12% polyester modified silicone resin 3D ceramic specimens are good, and the bending strength of 12% polyester modified silicone resin 3D ceramic specimen is high, its structural stability is good, and the deformation value is small under the same high temperature environment.

A new method of parameter identification for proton exchange membrane fuel cell based on hybrid particle swarm optimization with differential evolution algorithm

With the characteristics of high energy conversion efficiency, high energy den?sity and low operating temperature, the proton exchange membrane fuel cells (PEMFC) have become one of the green energy sources with broad prospects. The establishment of accurate mathematical model of the PEMFC is the basis of simulation and control strategy. At present, some intelligent algorithms have certain drawbacks, and can hardly find the balanced point between precision and computational time. In this study, a novel parameter identification approach com?bining the hybrid particle swarm optimization (PSO) algorithm with differential evolution, i.e. hybrid DEPSO, is proposed to obtain the unknown parameters in the PEMFC mathematical model and solve the problems of premature convergence of PSO and poor global search ability of differential evolution. Six benchmark functions are applied to verify the performance of the algorithm. The results prove that the hybrid DEPSO can evade local optimum preferably while having swifter convergence rate. Two PEMFC stacks are investigated and modeled. In order to evaluate the accuracy of model, the sum of squared errors between the measured voltage and the estimated output voltage are examined. Numerical results show higher accuracy of the hybrid DEPSO-based model comparing with other recently published optimization approaches. Furthermore, the simulation results indicate that the accuracy of the PEMFC model optimized by the hybrid DEPSO algorithm improves 0.19-1.86%, which can provide a new solution the multi-objective opti?mization problem and promote the practical application of the PEMFC.

Spatial and Temporal Characteristics of Extreme High Temperature in Altay Prefecture of Xinjiang in Recent 40 Years

Spatial and Temporal Characteristics of Extreme High Temperature in Altay Prefecture of Xinjiang in Recent 40 Years

Evaluation of the Applicability of Three Methods for Climatic Spatial Interpolation in the Hengduan Mountains Region

Abstract An ideal spatial interpolation approach is indispensable for obtaining high-quality gridded climatic data in mountainous regions with scarce observations, particularly for the Hengduan Mountains Region (HMR) with dense longitudinal ranges and gorges. However, there is much controversy about the applicability of thin plate smooth spline (TPSS), cokriging, and inverse distance weighting (IDW) in mountainous regions. Here, we use the daily observations of temperature and precipitation at 125 stations in HMR and its surroundings from 1961 to 2018 and adopt three interpolation methods to map the annual average temperature and precipitation at a resolution of 500 m in HMR. Then, we assess the applicability of three interpolation methods in HMR from the perspectives of interpolation accuracy and effects. The evaluation implies a satisfactory interpolation accuracy of TPSS with the highest correlation and lowest error, whether for temperature (R2 = 0.92, RMSE = 1.2°C) or precipitation (R2 = 0.54, RMSE = 165.9 mm). In addition, the TPSS could better display the temperature (precipitation) gradient along elevation and depict dry valleys’ high-temperature and low-precipitation characteristics. Moreover, the satisfactory interpolation performance of TPSS mainly benefits from the screening of optimal TPSS model that varied primarily with the regional topography feature and meteorological observation density. The uncertainty of gridded climate datasets has become an urgent problem to solve in the complex terrain. This research illustrates the satisfactory applicability of TPSS for climatic spatial interpolation in HMR, providing theoretical support for high-precision interpolation in complex terrain, hopefully improving the regional weather forecasts and disaster warnings.

Resource utilization of High-Ti vanadium titanomagnetite: Preparation and properties of sinter

In order to achieve the goal of resource utilization of High-Ti vanadium titanomagnetite (High-Ti VTM), the high-temperature sintering characteristics of High-Ti VTM were investigated by micro-sintering experiments, while the effects of different ordinary iron ore dosage and basicity on the sintering process parameters and sinter quality were investigated by sintering pot experiments. The results showed that the TiO2 and SiO2 contents increased gradually with increasing dosage of High-Ti VTM, and the liquid phase fluidity index and binder phase strength increased gradually, while the assimilation temperature and intergranular consolidation strength showed a decreasing trend. With the increase of the dosage of ordinary iron ore, the vertical sintering speed was reduced, while the sinter yield and tumble index gradually increased. As the basicity of the sinter gradually increased, the sintering time and the pulverization degree of the sinter gradually increased and the sinter yield gradually decreased, while the vertical sintering speed and the tumble index both showed a trend of first increasing and then decreasing. The results of the study provide data to support the preparation of sinter with High-Ti VTM.

Numerical Study of High-Temperature Gas Transport Characteristics During the Continuous Welding Process

Numerical Study of High-Temperature Gas Transport Characteristics During the Continuous Welding Process