Changes In Temperature Field Research Articles

Gas Temperature Distribution and Fluctuation in a Lab-Scale Fire Whirl

Fire whirls cause an increase in fire damage. This study clarified the unsteady behavior of fire whirls, considering that instantaneous changes in the temperature and flame shape of fire whirls can affect the damage to the surrounding area. Numerical simulations of a lab-scale flame that simulates a fire whirl were performed to investigate the changes in gas temperature and velocity fields under various fuel inflow velocities. The flow field was obtained by solving a continuity equation and a three-dimensional Navier-Stokes equation, and the turbulence was resolved using a large eddy simulation. A chemical equilibrium partially premixed combustion model was used, and radiation effects were considered. The time-averaged gas temperature distribution along the burner central axis revealed that the gas temperature decreased monotonically from upstream to downstream. The time-averaged velocity distribution along the burner central axis showed that the velocity decreased as one moved downstream, but the decrease was uneven. The time variation of the gas temperature demonstrated that the higher the fuel inflow velocity, especially near the burner, the greater the gas temperature flutter. Furthermore, the larger the fuel inflow velocity, the larger the flame swell and wobble. The results showed that the fuel inflow velocity affected temperature fluctuation and flame undulating movement.

Mathematical modeling of the temperature field of the arc of a conductive channel taking into account the temperature dependence of thermal conductivity

The article is devoted to mathematical modelling of the plasma temperature field taking into account the temperature dependence of thermal conductivity. The channel model was taken as a basis. Neglecting a very small fraction of the energy received by the ions during their acceleration in the longitudinal field, it can be assumed that all the energy taken by the arc discharge from an external source in the arc column passes directly to the plasma electrons. To find the temperature field by the integration method, the equation of thermal conductivity was solved. At the same time, the arc column is considered as a cylindrical continuous conductive rod in which all the supplied electrical energy is diverted due to thermal conductivity to the cooled walls of the discharge tube. The arc itself is represented by two regions: conductive and non-conductive. Based on mathematical modelling, the law of temperature field change in the arc cross-section was obtained. A formula was also derived to determine the effective radius of an electrically conductive channel.

Research and Application of Temperature Load of Switchgear

Abnormal changes in the temperature and load current of the high-current switchgear will directly affect the reliable operation of the equipment. In order to effectively monitor the temperature of the switchgear and ensure the reasonable arrangement of temperature measurement sensors, this paper realizes the optimal arrangement of sensors and the temperature prediction of the switchgear through simulation and test of the switchgear. Firstly, Ansoft electro thermal simulation module is used for joint simulation, the change of temperature field and the heating of current carrying bus are analyzed, the test data of temperature change under different environmental conditions are obtained, and the relationship between the temperature sensor and the distance between the hot spot is mastered. Then the temperature load curves under different currents are obtained through the test, and the accuracy of the research results is verified by the combination of theoretical simulation and field test. The test results can not only provide guidance for the temperature sensor installation scheme of substation field operation and maintenance personnel, but also improve the stability of equipment operation.

Simulation research on thermal protection performance of firefighting robots and design of protection system

In response to manufacturing strategy demand, fire accidents in petroleum, chemical, forestry, and high-rise buildings are on the rise. Although the firefighting robot can replace fire rescue workers who come into the dangerous rescue site, electronic devices’ thermal failure problem caused by high temperatures in the whole electronic equipment problem is bigger. The proportion of electronic device thermal failure has a significant impact on the normal operation of electronic equipment. How to dissipate heat quickly and avoid local high temperatures becomes a key problem. Most domestic and foreign scholars only study the influence of thermal protection materials themselves on robot protection systems, and few study the influence of heat insulation materials and heat dissipation materials on robot protection systems through appropriate structure combinations. Therefore, the establishment of comprehensive high-temperature fire situations on the fire protection robot automatic detection of smoke concentration and temperature of heat insulation material and heat dissipation material composition of folded tensile structure and liquid nitrogen cooling system thermal protection model of robot thermal protection performance research is of great significance, at the same time through COMSOL Multiphysics software to simulate the proposed model, Select the best heat dissipation materials and heat insulation materials, protect the internal electronic components in the fire accident sustained high temperature, can adjust the temperature as soon as possible, make it adapt to the change of temperature field, for the rescue process to gain 2~15 minutes time duration.

Numerical Investigation on the Effect of Thermal Gate Moving Rate on Directional Solidification Process

The temperature field distribution during the growth of crystalline silicon by the directional solidification (DS) method is an important factor affecting the growth rate, the shape of the melt-crystal (m-c) interface, and thermal stress. To solve the problem of m-c interface convexity at the early stage of crystal growth caused by supercooling at the bottom center of silicon ingot during DS. In this paper, a two dimensional (2D) global transient numerical model based on a large-size ALD-G7 (G7) crystalline silicon ingot furnace is established and experimentally verified. Based on the model, the influence of different bottom thermal gate moving process curves on the convexity of the m-c interface at the early stage was studied, with emphasis on the changes in temperature field, m-c interface, and thermal stress at the early stage of crystal growth. We have designed three cases, case 1 uses the original moving process curve of bottom thermal gate, case 2 and case 3 adjust the process curve to 0.95 and 0.9 of the original ratio, respectively. The numerical simulation results show that compared with case 1, the average heat dissipation at the bottom of the silicon ingot in case 2 and case 3 is reduced by 2.7 kW·m−2 and 4 kW·m−2, and the maximum thermal stress is also reduced by 3 MPa and 4 MPa, separately. The maximum convexity of the interface is reduced by 25 mm and 20 mm, and the convexity is reduced by 55% and 44% on average, respectively.

Numerical simulation and experimental analysis of machining morphology with pulsed laser

In this study, simulation and experimental studies are used to evaluate the temperature field distribution and process law for the pulsed laser processing of stainless steel. The numerical simulation is based on the theory of heat transfer. The temperature field distribution and change process of the stainless steel surface under the influence of laser is explained subjectively, and the morphology evolution law of stainless steel during the entire process is studied. The influence of insufficient laser spot overlap ratio and the variation of laser power on the machining quality is analyzed by comparing with the experimental results. The evolution law of machining morphology and size with the laser incident angle, scanning speed, repetition frequency, and laser power are evaluated. The results provide theoretical support for determining the high-quality processing of stainless steel by a pulsed laser, which can be used for the parameter optimization of laser processing, such as metal material cutting, surface microstructure preparation, and two-dimensional code marking.

Soot combustion characteristics of oxygen concentration and regeneration temperature effect on continuous pulsation regeneration in diesel particulate filter for heavy-duty truck

The effects of oxygen concentration and regeneration temperature on continuous pulsation regeneration of DPF (diesel particulate filter) for heavy-duty truck are crucial. The regeneration performance characteristics of the oxygen concentration of 7.2%, 8.2% and 9.4% and regeneration temperature of 823 K, 873 K and 923 K are investigated in this paper. The pressure trend, temperature field change, regeneration reaction rate and the dynamic regeneration oxygen concentration are analyzed. The complete soot regeneration can be achieved of all the simulation cases with different oxygen concentration and regeneration temperature. Under the same oxygen concentration conditions, the higher the regeneration temperature has the wider range of high-pressure pressure region. The highest and the lowest pressure appear at the regeneration temperature/oxygen concentration condition of 923 K/7.2% and 823 K/9.4%. The maximum temperature is 1792.5 K under the condition of 923 K/9.4%. The dynamic reaction rates of the 9 simulation cases are diverse significantly in the inlet and outlet sections of the DPF. The difference between the maximum and minimum reaction rates is less than 0.001. The study results is able to determine the regeneration oxygen concentration and regeneration temperature for achieving complete regeneration of DPF.

Research on numerical simulation of temperature field in directional solidification process controlled by finite element method

As an emerging metal heat treatment process, directional solidification technology has excellent properties exhibited by non-destructive materials at room temperature. It has become one of the current research hotspots and frontier topics in the field of engineering at home and abroad. In the industrial field, when the metal to be welded is welded, its own structural characteristics need to bear a large thermal load. In order to ensure the normal operation of the welding process and obtain good benefits, a finite element model must be established to simulate the temperature field changes in the process and corresponding compensation measures. Firstly, this paper analyzes the finite element discretization and numerical calculation method of the radiative heat transfer boundary, and establishes a directional solidification simulation model by using the finite element method, and then it establishes a directional solidification simulation model according to the mathematical change process of the temperature field; Secondly, this paper simulates the key technology of the temperature field in the directional solidification process with finite element method. Finally, the finite element method is used to analyze the mathematical model of the temperature field in the directional solidification process, and the calculation results are compared with the actual situation. It can be seen from the conclusion that the system simulation and theoretical prediction method established in this paper is correct, reasonable and accurate.

Improving the crystal quality of AlN films by nanosecond laser annealing

Aluminum nitride (AlN) thin film of thickness 300 nm grown on sapphire substrate was annealed by a nanosecond laser at a wavelength of 532 nm. The laser energy values were 2 J, 3 J, 4 J, and 4.5 J, respectively. In order to increase the absorption of laser energy by the sample, 50 nm thick tungsten films were deposited on the left half of the sample. Surface morphology and Raman spectrum of AlN films were characterized before and after annealing using scanning electron microscope (SEM) and Raman spectrometer, respectively. The SEM micrographs have shown that the surface of AlN film had a large number of voids before annealing. After annealing, the size of the voids becomes smaller and their number decreases with the increase of laser energy density. The full width at half maximum (FWHM) of AlN film was roughly 6-10 cm−1 before annealing and 4-8 cm−1 after annealing. The results showed that the surface morphology and FWHM of the AlN films were improved after laser annealing compared with those before annealing. Finally, COMSOL Multiphysics simulated the temperature field change of AlN film after laser irradiation and the evolution of its surface.

Thermally induced structural response of a solar sail spacecraft in Earth orbit

The solar sail spacecraft for earth missions experience shadow region in Earth orbit, the resulting temperature field changes will induce the structural response on the sail films and the booms of the solar sail, thus disturb the attitude control of the spacecraft. Therefore, it is valuable to study the thermally induced structural response of solar sails caused by abrupt temperature filed. In this paper, the solar sail with square films and booms is studied. A sequential-coupled analysis method is proposed. Based on this method, the thermal analysis model of the solar sail is established, then the temperature variation law of the solar sail during orbiting the earth is obtained through simulation. Based on the structural analysis model of the solar sail, the structural response caused by temperature change is calculated, and the influence of material parameters on such response is analyzed. The results show that, the sudden change of temperature field will not only cause the shrinkage and expansion of the film, but also lead to obvious vibration on the boom. This vibration can be reduced by using thermal control coating or increasing the boom thickness. The results of this paper have important referential value for the design of thermal control system of solar sails.

Structural Response Analysis of FPSO under Pool Fire

There is a large proportion of pool fire occurrence on the upper part of offshore platforms. In order to reduce the occurrence of fire disasters, the fire risk assessment of FPSOs should be carried out. According to the temperature characteristics of offshore platform fires based on computational fluid dynamics, the temperature field of the superstructure of the offshore platform under pool fire has been analyzed, the regularities of the distribution of the wall temperature of the platform of FPSO under different wind speeds are studied, and research on the distribution of heat radiation flux of different fire is made. Based on the finite element method, the structural response of the platform structure in different fire scenarios has been made. In consideration of the pool fires caused by liquid leakage of the upper part of the platform structure, with the basis of the changes of temperature field and radiation field being obtained by CFD, a structural response analysis of the offshore platform structure using the finite element method and a risk assessment method based on quantitative analysis for pool fires caused by liquid leakage is proposed.

Solving the heat transfer boundary condition of billet in reheating furnace by combining “black box” test with mathematic model

Comprehensive radiant heat transfer coefficient, convective heat transfer coefficient and furnace temperature are the key parameters constituting the boundary conditions of the billet heat transfer model. This paper presents a novel method to obtain these parameters by combining "black box" test with mathematical model. Average relative errors of the calculated surface temperature and centre temperature of the case reheating furnace compared with the measured values are 2.34% and 3.51%, which verifies the method's feasibility. Influence law of furnace temperature characteristic parameters on billet temperature is analyzed. When the intercept, slope and amplitude change, the regions where the billet temperature field changes significantly is in or near the HEⅠsection, which are the key section to adjust the billet temperature field through single characteristic parameter. The longer the period is, the smoother the change of billet temperature in the same spatial region is, which is conducive to the uniform heating of billet. However, if only increasing the period, there may be a situation that the billet discharging temperature exceeds the target. Change of single characteristic parameter has its limitations. In order to achieve the accurate control of billet temperature, the collaborative change of each characteristic parameter is required.

Inclined magnetic structures and magnetic phase diagrams for the Pb2Fe2−xMnxGe2O9 (x = 0.16) single crystal

Single crystals of the Pb2Fe2−xMnxGe2O9 (x = 0.16) antiferromagnet have been grown. Using the specific heat measurements, a Néel temperature of TN = (42.0 ± 0.5) K for the synthesized crystals has been found. It has been shown using the magnetic measurements that, due to the competition between the magnetoanisotropic contributions of the iron and manganese subsystems in the crystals, near a temperature of Tc = 22 K, a spontaneous spin-reorientation transition occurs, the temperature of which in an applied magnetic field changes with the field value and orientation relative to the rhombic axes of the crystal. Based on the analysis of the temperature and field dependences of the magnetization obtained at different orientations of the magnetic field, it has been established that, below Tc, an inclined magnetic structure is formed in the crystal. The antiferromagnetic vector of the inclined structure rotates smoothly in the rhombic bc plane with increasing temperature from a direction close to the b axis at T = 4.2 K and tends to the rhombic c axis at T = Tc. The rotation of the antiferromagnetic vector occurs also at fixed temperatures T < Tc with increasing magnetic field. In the temperature range of Tc < T < TN, the antiferromagnetic vector is oriented along the rhombic c axis.Magnetic phase diagrams of states have been built for different magnetic field orientations relative to the rhombic axes of the crystal. The richest phase diagram is shown to correspond to the orientation H||c and contains, along with the above-listed states, one more inclined phase, in which the antiferromagnetic vector rotates toward the rhombic a axis direction with a change in temperature or magnetic field.

Atomic-scale insight into the tetragonal platelets correlated with the antiferroelectricity in Na0.5Bi0.5TiO3-based materials

The structural origin of antiferroelectric (AFE)-like double P–E loops near the depolarization temperature in lead-free Na0.5Bi0.5TiO3 (NBT)-based materials remains elusive despite decades of study. Here, temperature-dependent ferroelectric properties, Raman spectra, and advanced electron microscopy reveal that the AFE-like behavior in Mn: NBT single crystals is strongly related to the tetragonal phase. The tetragonal platelets oriented along three principle directions of the pseudo-cubic cell with the typical thickness of 1–2-unit cells were visualized at the atomic scale. Special AFE-like dipoles were formed by two antiparallel-polarized tetragonal platelets with a thickness of 2-unit cells, which are separated by a thin non-polar and tilt-free transition layer. Such locally structural components vary in both volume and/or size to a certain extent as changing temperature, chemical composition, and external electric field, phenomenologically showing AFE characteristics. Our study provides the decisive atomic-scale information of tetragonal platelets and establishes a hitherto unobserved AFE-like structure existing in the NBT-based materials.

Microstructure evolution, mechanical properties of FeCrNiMnAl high entropy alloy coatings fabricated by laser cladding

In this work, FeCrNiMnAl high entropy alloy (HEA) coatings under different laser energy density (Led, 50–92 J/mm2) were fabricated on 17-4PH stainless steel by laser cladding (LC). The influence of different laser energy density on the geometric morphology, microstructure, microhardness and tribological properties of HEA coating was investigated. To obtain the specific solidification parameters (temperature gradient and solidification rate), the finite element model was established to express the transient change of molten pool temperature field. The columnar-to-equiaxed transition (CET) corresponding to different zones of HEA coating was revealed. The result showed that the geometric parameters increased with the rise of Led because of the Marangoni convection. Equiaxed crystals and columnar crystals were distributed on the top and bottom zones of HEA coatings respectively, and the CET behavior was observed. Higher temperature gradient and lower solidification rate were conducive to the growth of columnar-crystals. Furthermore, at the Led of 92 J/mm2, HEA coatings showed relatively high crack sensitivity. HEA coatings significantly improved the tribological properties owing to metal oxide particles generated by oxidation. In the mechanical properties test, the maximum microhardness of prepared HEA coating (1800 W) was 587.83 HV0.2, which was 1.63 times that of 17–4PH substrate. Metal oxide particles generated a flat wear-resistant enamel layer which protected the coating surface. The tribological properties was optimal at the Led of 64 J/mm2, the average friction coefficient and wear rate were 0.4654 and 7.026 × 10−8 mm2/N, respectively.

Modeling of the Natural Objects’ Temperature Field Distribution Using a Supercomputer

There are some regions where the unique type of mineral water mining is compounded by the complex structure conditions of the field. Due to the high emergency risks, the automation of this type of mineral water fields’ exploitation process is a necessity. Kislovodskoe mineral water field was chosen as the experimental object, because it has a number of features that make it barely possible to use the conventional methods of mineral water extraction. In the process of extraction, the random vector impacts the mineral water pumping systems. This is mainly due to the complex hydrogeological structure. For the experiment, the laboratory installation and mathematical model were presented by the temperature field changing, due to the similitude of the mathematical apparatus and the hydrodynamic processes behavior,. The main object of this article is the analysis of the reservoir’s temperature field behavior using a hybrid supercomputer, and the differences between the supercomputer and a conventional personal computer modeling quality and implementation costs are also given..

Numerical simulation of DC casting of large-size rare earth magnesium alloy ingot under low-frequency electromagnetic field

For studying the changes of macro-physical field in the casting process of large-scale rare earth magnesium alloy, through the numerical simulation method, a two-dimensional axisymmetric multi-physical field coupling model was established by using the multi-physical simulation software COMSOL Multiphysics. The changes of temperature field, flow field, Lorentz force, and liquid fraction of large-size rare earth magnesium alloy with diameter of 750 mm under different electromagnetic parameters (magnetic field frequency and current intensity) in steady state of direct-chill (DC) casting were studied. The results reveal that using a magnetic field can reduce the temperature gradient and greatly accelerate the melt flow, the depth of the sump is reduced by about 50 mm. As the current intensity rises, the flow rate in the melt becomes accelerated, the sump depth becomes shallower, while the melt area with a liquid fraction of 0.5 to 0.63 increases. The Lorentz force rises as the magnetic field frequency increases, but the skin depth of the magnetic field decreases from 64.9 to 36.4 mm.

Study on Sustainable Well Water Pumping Technology to Melt Ice in Winter for the Middle Route of the South-to-North Water Diversion Project

In order to improve the water delivery capacity of the middle route of the South-to-North Water Diversion Project in winter, the technology of pumping well water to melt ice was previously adopted to improve the water temperature of the channel. In order to protect the local ecology and channel water quality during the process of pumping and recharging, this paper has analyzed the optimal limit to the range of groundwater level fluctuations and groundwater temperature fluctuations. The Baiquan Underground Reservoir was considered as the research object, and a three-dimensional numerical model of hydrothermal coupling was established. Correlation analyses of pumping and recharge capacity with various factors, and between temperature changes after recharging and various factors, were carried out with a view to protecting local water quality. The single well pumping and recharging scheme was optimized by genetic algorithm. The quantitative estimation formula of pumping and recharge water capacity, and the well depth, permeability coefficient, initial water level, and duration of continuous pumping and recharge, as well as the recovery water level variation formula, were established under the limitation of water level fluctuation. The quantitative relationship between horizontal maximum diameter, L, and the recharge flow rate, the continuous recharge duration, vertical maximum depth, H; and the well depth, temperature change rate, K, and the recharge water temperature, were obtained. The results showed that the permeability coefficient and soil thermal conductivity had little effect on the temperature field change. Additionally, recharge should be carried out in summer, when the temperature of recharge water is above 14.8 °C. When the number of pumping or recharging times, n, is two, the total amount of pumping or recharging during the operation period reaches its maximum. Compared with continuous operation during the operating period, this report found that the total amount of pumped water would increase by 1.1 × 106 m3, and the total amount of recharge would increase by 7 × 105 m3.

Study on the Effect of Bridge Deck Spacing on Characteristics of Smoke Temperature Field in a Bridge Fire

The numerical simulation method is used to simulate the distribution characteristics of the smoke temperature field of a double-deck bridge smoke temperature field during tanker fire under natural ventilation. The influence of the distance between double decks on the truss and ceiling temperature field change in the double-deck bridge is investigated. The results show that the range of high-temperature area gradually decreases with the increase in bridge deck spacing. The maximum excess temperature function of the tunnel ceiling is also applicable to the bridge, but the coefficient is smaller than that of the tunnel experimental formula. An equation is proposed to predict the maximum excess temperature of the truss under different bridge deck spacings. As the bridge deck spacing increases, the maximum excess temperature decreases. The excess temperature of the truss increases along the truss, and the maximum excess temperature appears at the top of the truss. Based on the energy equation, an equation for the excess temperature of the truss is established. As the vertical height increases, the excess temperature of the truss above the fire source exponentially increases. The research results will contribute to the fire hazard evaluation and safety design of bridges.

Enhanced corrosion resistance in accident-tolerant FeCrAl alloy by water-assisted laser surface modification

FeCrAl alloys have been widely developed as an alternative accident-tolerant cladding material in light water reactors since the Fukushima nuclear accident in 2011. A large thermal neutron cross-section is the most severe challenge for FeCrAl alloys in the final commercial use, and a thinner cladding was necessary to overcome this, which led to higher corrosion resistance requirements. To address this issue, a surface treatment process is described here to enhance the corrosion resistance of the FeCrAl alloy via a water-assisted laser modification. By varying the laser power and laser scanning speed, the relationship between corrosion and processing parameters was investigated to better understand the mechanism with various characterizations. A heat-transfer model with boiling heat transfer boundary conditions was built and simulated using a finite element method to reveal the change in temperature field during processing. A corrosion test was performed with a simulated light water reactor (LWR) hydro-thermal environment for 120 h. The corrosion rate and oxide film thickness of the water-assisted laser modified FeCrAl alloy sample decreased by 83 % and 50 %, respectively, compared to the as-received one, and this was ascribed to the formation of protective oxide film during laser processing, along with grain refinement and elimination of holes and scratches.