Temperature Gradient Distribution Research Articles

The study of core and particle model of Fushun oil shale based on microwave field

As an unconventional oil and gas resource, oil shale can alleviate the shortage of oil and gas resources. As a new heating process for oil shale retorting and in-situ mining, microwave can effectively exploit and utilize oil shale. In this paper, the Fushun oil shale and particle model under microwave field are studied by means of experiment and numerical simulation. Based on the measurement of the basic physical properties of oil shale, the effects of microwave power and absorbent (semi-coke and graphite) on the pyrolysis of oil shale were investigated. The experimental results show that the heating rate is the fastest when the maximum microwave power is 700 W without adding absorbent or adding the same absorbent. At the same power, the effect of graphite is slightly better than that of semi-coke. In the aspect of numerical simulation, COMSOL simulation software is used to simulate the oil shale core and particles based on the three-dimensional electromagnetic thermal model. The experimental conclusion is verified. At the same time, it is found in the simulation results that microwave heating has better temperature distribution gradient and electric field distribution. Furthermore, the microwave port is extended to the underground for the simulation of microwave in-situ mining. It is found that the reservoir temperature reaches 450 °C after 1000 days of reservoir heating.

A two-dimensional semi-analytic thermal model for global temperature distribution predicting and hot spot monitoring in interior permanent magnet synchronous motor

A two-dimensional semi-analytical thermal model (SATM) is presented, aiming to quickly and accurately achieve global temperature distribution predicting and hot spot monitoring for interior permanent magnet synchronous motor (IPMSM). Thereby, it provides a reliable analysis tool for thermal behavior evaluation and prevents undesired consequences induced by excessive temperature rise, which is of great worth and significance in promoting the flourishing of IPMSM. SATM combines the analytical method, lumped parameter thermal network, and finite element analysis to obtain an analytical solution for thermal behavior through mathematical derivation by considering the complicated configuration, heat source distribution, heat dissipation condition, and material thermal dependence. Through SATM, it is possible to observe the global temperature distribution as well as the location and size of hot spots in each element. The temperature distribution gradient on the static is more pronounced than that on the dynamic; secondly, the area with the most severe heating is mainly found on the winding; furthermore, the hot spot on the winding is mainly located a little bit inside the center. Moreover, the thermal behavior of IPMSM at rated load is investigated by numerical analysis and experiments. A comprehensive comparison with SATM is done. The computational deviations between SATM and numerical analysis regarding the hot spot, minimum, and average temperatures on each element are all within 4.06%. However, SATM consumes only 20.92% of the time and 68.29% of the storage of the numerical analysis. The measured data also fully prove the reliability and validity of the comparison. It is certain that SATM can well break through the limitation of the existing non-numerical technique to quickly and accurately achieve global temperature distribution predicting and hot spot monitoring of IPMSM. It provides researchers and engineers engaged in thermal behavior evaluation with good analysis means, design guidance, and optimization direction.

Study on the ablative characteristics of steel target irradiated by nanosecond pulsed pseudo spark electron beams: Experiment and molecular dynamics simulation

A combination of simulation and experimentation is employed to explore the influence of the non-uniformity of energy distribution in nanosecond PSEB on the target ablation. Firstly, A spatiotemporally distributed heat source model is built using Monte Carlo computational method and an ablation phase transition model is established using molecular dynamics method. The results reveal the time evolution of multiple cavities in the sub-surface region, as well as the temperature and stress field distributions with electron beam irradiation. Phase explosion formation and lattice structure changes in the steel target during the ablation process is found for the first time. The PSEB modified AISI1045 steel samples is experimentally conducted. The characterization results show the changes in the crystal structure within AISI1045 steel, which is attributed to the formation of an amorphous layer resulting from grain refinement and structural defects, as well as the combined effects of thermal elastic stress waves, shock thermal stress waves and temperature gradient distribution. The experimentally obtained crystal phase changes are consistent with the simulation results, confirming the accuracy and validity of the modelling. The findings of this study provide a molecular-scale explanation for the formation of unique morphology and micro-structures during the PSEB ablated metal target.

Refined Analysis of Spatial Three-Curved Steel Box Girder Bridge and Temperature Stress Prediction Based on WOA-BPNN

Bridges often improve the visual appeal of urban landscapes by incorporating curve elements to create iconic forms. However, it is noteworthy that curved bridges have unique mechanical properties under loads compared to straight bridges. This study analyzes a spatial three-curved steel box girder bridge based on an actual engineering case with a complex configuration. Initially, the finite element software Midas/Civil 2021 is utilized to establish a beam element model and a plate element model to examine the structural responses under dead loads in detail. Then, two different temperature gradient distribution models are employed for the temperature effect analysis. The backpropagation neural network (BPNN) optimized by the WOA algorithm is trained as a surrogate model for finite element models based on the results of temperature stress simulation. The results reveal that the bending–torsion coupling effect in the second span of the spatial three-curved steel box girder bridge is pronounced, with the maximum torque reaching 40% of the bending moment. The uneven distribution of cross-section stress is particularly significant at the vertices, where the shear lag coefficient exceeds 3. Under the action of temperature gradients, the bridge displays a warped stress state; the stress results obtained from the exponential model exhibit a 21% increase compared to BS-5400. Optimization of the weights by the WOA algorithm results in a significant improvement in prediction accuracy, and the convergence speed is improved by 30%. The coefficient of determination (R2) for predicting temperature stress can reach as high as 0.99.

Study on the mechanism of fiber-optic hot-wire sensing based on DFB-FL thermally induced chirp effect

In this paper, we propose an intensity demodulated fiber-optic hot-wire sensing method based on the thermally induced chirp effect of distributed feedback fiber lasers. The cobalt-doped fiber is fused at the rear end of the erbium-doped distributed feedback fiber laser to constitute a hot fiber wire with a gradient temperature distribution. The cobalt-doped fiber is heated up under the excitation of the residual pump light. Then the thermally chirp of the erbium-doped phase-shifted fiber grating brings out the change of the lasing threshold condition of the distributed feedback cavity and a significant reduction of the output power. When this structure is further altered by thermal induced chirp under external thermal field, the lasing output power will be further changed. The experimental results of the dynamic fluid thermal field and the static thermal field shows that, the fiber-optic hot-wire structure can sensitively detect the weak airflow and the thermal field of the environment by monitoring the laser power.

Research on discharge process of Bi2Te3 module under different thermal stimulation conditions

In the actual working process, the working environment temperature of the thermoelectric device is constantly changing, and rarely remains stable, a thermoelectric device is composed of more than one thermoelectric module monomer (PN junction), each of which can be used as an independent research object. To address this issue, the thermoelectric properties of thermoelectric modules (p, n-type Bi2Te3) are measured under different temperature environments. A self-constructed thermoelectric performance test platform, an infrared thermal imager, and a voltage acquisition system are used to monitor different temperature difference conditions in real-time. A transient discharge evaluation model was established to calculate the real-time discharge amplitude of the thermoelectric module based on its temperature gradient distribution. The results show that the error of the transient discharge evaluation model is about 5%, which is reliable. For large-sized thermoelectric modules, the maximum discharge amplitude under open circuit voltage can be obtained solely based on the overall temperature gradient of the thermoelectric module; the amplitude of the electrical output signals increases uniformly when the temperature difference between the two ends of the module is increasing uniformly; and the stable electrical output signals are also produced at both ends of the module when the temperature difference is stabilized. After stabilization, when the temperature drops uniformly, the amplitude of the electrical output signal decreases uniformly. In the range of T = 298–573 K, the greater the temperature difference between the two ends of the thermoelectric module is, the greater the amplitude of the stabilized electrical output signal is; and vice versa. The greater the rate of thermal loading, the faster the increase in the amplitude of the electrical output signal at both ends of the thermoelectric module. This also reduces the time needed to reach steady state equilibrium, enabling the thermoelectric module to produce a stable electrical output earlier than individual p and n-type Bi2Te3 modules.

Macro-ordered porous carbon nanocomposites for efficient microwave absorption

Tunable and efficient porous carbon-based microwave absorbers are essential in electromagnetic compatibility and protection due to their pronounced dielectric losses and ultralow density. However, it is still challenging to achieve satisfactory impedance matching and attenuation ability owing to the difficulty of realizing custom-designed porous structures. Herein, we propose a material-structure collaborative approach which includes multi-scaling, component modulation and systematic investigation of macroscopic structures. Macro-ordered porous carbon nanocomposites (MOPCN) assembled with MWCNTs and chitosan (CHI) were fabricated via freeze casting and MWCNTs/CHI ratio regulation. By simply varying the freezing temperature gradient distribution from radial (R) to axial (A), radial-centrosymmetric and honeycomb-like pore arrays were realized respectively. Compared with the honeycomb-like pore array, the radial-centrosymmetric pore array imparts much stronger microwave attenuation capability due to enhanced phase contiguity and optimized spatial arrangement. Such configuration also enabled one to optimize impedance matching and absorption, alleviating the over-dependence of microwave absorption performance on material composition. Optimum absorption of up to −70.6 dB at 9.3 GHz and −72.9 dB at 8.8 GHz were achieved for the MOPCN-1/4-R and MOPCN-1/2-A composites, respectively, with effective absorption band covering the entire X-band at a low filler loading of 1 wt%. Overall, this study provides a further understanding of the structure-property relationship and paves the way for future exploration of plainified microwave absorbers based on optimized macropore structures while preserving low filler loading.

A linear chirp fiber Bragg grating with tunable bandwidth enabled by MXene's photothermal effect

An efficient method for tunable spectra of the fiber Bragg grating (FBG) using a gradient temperature field is proposed theoretically and experimentally. The temperature field modulation in the core region of the FBG is achieved by utilizing the photothermal conversion properties of MXene Ti3C2Tx, which guarantees a flexible adjustment of temperature gradients in the FBG axis. The spectra of FBG under different gradients of temperature fields are simulated by the transfer matrix method. The simulation results show that the gradient temperature distribution in the FBG axis can induce spectral chirps of FBG. The increase in the bandwidth of the spectrum and the decrease in the reflection intensity are caused by the rise of the temperature gradient. In the experiments, Ti3C2Tx films are coated onto the sidewall of FBG, and the non-uniform temperature gradient field in the FBG axis is formed and tuned by varying the intensity and spatial distribution of the pump laser on the Ti3C2Tx film. The spectral bandwidth measured at 10 dB can be broadened by 4.6 times from 0.57 to 2.63 nm with excellent linear tunability as a function of the pump power. This method provides an effective scheme for the spectral tuning of linear chirp FBGs in all-optical control.

Thermo-electro-elastic coupled modeling and simulation of functionally graded piezoelectric structures

Compared with the composite materials, the functionally graded materials can not only provide better specific stiffness but also reduce the risk of layered damage. Therefore, the graded distribution forms have become the development trend of advanced structures. An efficient finite element (FE) modeling method and numerical simulation of plate and shell with nonlinear temperature gradient coupling are developed based on the FOSD hypothesis for thermo-electro-elastic coupled functionally graded piezoelectric material (FGPM) integrated with smart structures in this paper. The constitutive model for thermo-electro-elastic coupled FGPM is derived. Assuming that the temperature gradient distribution changes secondarily through the thickness, two nonlinear physical models for temperature change are constructed. Based on the FOSD hypothesis, the multi-field coupled FE equation of plate and shell is derived. The accuracy of the present FE model is verified by the commercial calculation structures. The parametric simulation of FGPM shells is carried out based on the FE model.

Experimental Analysis of Third Harmonic on Zero Line Heating Influence Based on COMSOL

In the study of zero-line heating fire hazard caused by the third harmonic, the harmonic content in a high harmonic incidence place is measured, and an indoor physical experiment platform is built as well. Based on the experimental platform, the third harmonic heating experiment on zero lines is carried out with different wire diameters. The heating pattern of zero lines under different working conditions is obtained, which could provide a certain experimental basis for electrical fire prevention in public places. Based on the COMSOL multi-physical field coupling simulation software, the third harmonic heating model of zero line is established, and the curve of temperature distribution gradient and zero line temperature is obtained. The comparison between simulation results and experimental results verifies the accuracy of the simulation model. It provides a theoretical method for a reasonable selection of zero-line diameter, arrangement of zero line layout, and prevention of electrical fire.

Heat behavior and axial temperature distribution of a Ti-6Al-4V alloy in a superconducting induction heater with a controllable magnet structure

Ti-6Al-4V (TC4) metal billets can usually be preheated by gases, resistance furnaces, and conventional induction heater powered by alternating current. However, the disadvantages of these heating methods are long heating time and small skin depths. The novel superconducting induction heater has several advantages in terms of heating quality, heating efficiency, heating time and axial temperature control. It has gained successful commercial application in the large aluminum extrusion industry in 2021. However, no studies on TC4 heating behavior using a superconducting induction heater have been reported, and no studies on uniform and gradient temperature characteristics of TC4 in superconducting induction heater. The uniform temperature distribution of TC4 is helpful to reduce the heating residual stress of forgings. The gradient temperature distribution of TC4 billet can obtain different properties in different parts of the same TC4 billet, which is suitable for manufacturing functionally graded materials. In this study, a high-temperature superconducting (HTS) direct-current (DC) induction furnace was firstly used to perform heating experiments for TC4 metal billets of 1250 mm length and 220 mm diameter. The application of the superconducting magnet for induction heating allows for high-power and fast heating of the TC4 billet at an extremely low frequency (4 Hz). The HTS induction heater technology has the advantages of high penetration depth, high energy efficiency (>82%), high heating uniformity, and controllable temperature distribution. Additionally, it improves the metal heating quality and reduces the heating cost. The 10 identical iron pieces of superconducting magnet on both sides of the iron core can be adjusted independently. The gradient and uniform temperature distributions of the thermally optimized TC4 billets were experimentally determined using adjustable electromagnetic heating power. Subsequently, the heating behavior of TC4 billets was modeled and compared using the numerical multiphysical finite element method; the results obtained using this method are in agreement with the experimental results. An expert database has been established for the heating strategy of TC4 billets. The optimized axial temperature distribution was analyzed for three different TC4 billet diameters (Φ220, Φ300, and Φ446 mm). The obtained gradient and uniform axial temperature distributions had an error of less than ±3 °C, and the adjustable difference at two-ends temperature of TC4 billets was in the range 10–100 °C/m. Finally, the maximum thermal stress on the TC4 billet during heating also was analyzed. The results of this study will be useful of the novel HTS induction heater application for TC4 billet heating, and axial temperature control. The uniform temperature distribution control will reduce the heating residual stress of forgings. The gradient temperature distribution of TC4 billet is suitable for manufacturing functionally graded materials.

Numerical simulation of the heat transfer process of separation column in thermal cycling absorption process

Thermal cycling absorption process with a typical structure composed of separation column and plug flow reverser is an efficient method for hydrogen isotope separation. The temperature variation on separation column is the driving force for the isotope separation process, and the distribution of temperature gradient in the separation column affects the efficiency of the separation. Considering the actual heat transfer process by the equipment, there is an axial temperature gradient on the separation column, which can affect the separation efficiency. Numerical simulations can make a great help in the analysis and optimization of the temperature distribution in the separation column. In this work, a simplified two-dimensional axisymmetric model of the oil bath structure has been built, and the heat transfer process between the heat conduction oil, structural materials and packing materials in separation column has been calculated, coupling with the fluid field. The simulation results show the detailed temperature distribution on the separation column and indicates that the temperature gradient is affected by the flow rate of the heat conducting oil. The minimum flow rate under different cooling efficiency and temperature uniformity requirements are derived from the simulation. Furthermore, the specific temperature gradient distribution on the separation column can provide design guidance to optimize the separation process.

Non-uniform thermal characteristics investigation of three-dimensional electrochemical-thermal coupled model for pouch lithium-ion battery

Recently, lithium-ion batteries have been preferred as an approach for energy infrastructures. However, its uneven performance directly affects battery modeling, parameter estimation and thermal management. To understand the non-uniform thermal characteristics of pouch battery, a three-dimensional multiphysics model that combines an electrochemical model and a thermal model is developed in this study. Here, three models with lumped and non-uniform heat source as well as temperature are comprehensively compared and evaluated under different discharge rates. Results indicate that the dimensionality and lumped-source of model have negligible effects on predicting heat generation and maximum temperature, but the temperature gradient distribution shows deviation of 64.0/62.1% at 5 C discharge. Due to the uneven heat generation, an overheating region appears along the battery center to positive tab, especially at high discharge rates. What's more, it is found that more heat is generated at a high discharge rate and low-temperature, which leads to higher temperature rise and temperature gradient. In addition, the critical heat transfer coefficient that represents the critical heat dissipation capacity of thermal management system is estimated. These findings can provide insights into the selection of battery models and the design of thermal management systems in accordance with different scenarios.

Study on the morphology of liquid–gas interface inside inertial confinement fusion target under the condition of temperature gradient based on Young–Laplace equation

This study investigates the morphology of the liquid–gas interface inside inertial confinement fusion targets with temperature gradients from the perspective of force balance. The effects of contact angle, liquid volume, temperature gradient, and target size on the interface morphology are discussed. The filling of the fuel and the preparation of the ice layer inside the target are carried out near the deuterium–deuterium triple point at 18.71 K, accompanied by temperature gradient distributions of different magnitudes. The morphology of the liquid–gas interface has a significant impact on the subsequent laser experiments. The differential equation for calculating the morphology of the liquid–gas interface under non-uniform temperature field is derived based on the Young–Laplace equation. In order to verify the accuracy and applicability of the model as well as to provide guidance for practical applications such as process optimization, experimental data within a temperature gradient range of 0.69–1.38 K/cm during the fuel filling process were selected. Image processing techniques, including denoising and edge detection, were applied to the experimental images. The obtained structured data were compared with the numerical solutions of the equation for the liquid–gas interface morphology. The accuracy of the equation was verified by the results. Based on this, the morphology of the liquid–gas interface of deuterium–deuterium inside targets under different experimental conditions was calculated. It was found that a smaller target radius, higher filling temperature, smaller contact angle, and larger temperature gradient are more conducive to subsequent experiments.

2.85-kW cryogenic Nd:YAG slab laser operating at 946 nm

A several-kilowatt level laser at 946 nm is demonstrated in a cryogenically cooled diode-pumped Nd:YAG slab system. The oscillator realizes the record of the output power of 2.85 kW in a compact cavity with the homemade cryogenically cooled Nd:YAG crystal slab. The pulse repetition rate and pulse width of the laser are 400 Hz and 200 µs, respectively, and the center wavelength under full power is 946.2 nm with a bandwidth of about 0.5 nm. The absorption linewidth at 808 nm is a little narrowed and blue shifts at the cryogenic temperature, while the cooling temperature decreases from 300 to 77 K. The measured thermal conductivity increases from 10 to 70 W/mˑK, and the thermal expansion coefficient decreases from 7.5*10−6 to 1.5*10−6/K. These results could guide us in simulating the temperature gradient and thermal-induced stress distributions in the crystal slab.

Simulation study on erosion of barrel under thermal-mechanical-chemical coupling environment

Artillery is known as the “God of War”. When the ballistic performance of the barrel is reduced to the allowable value specified by the index due to erosion and wear, the life of the barrel is terminated, and the artillery equipment completely loses its combat effectiveness. The erosion and wear of the barrel involves many factors such as temperature, mechanics, chemistry. In this paper, based on the theory of internal ballistics and heat conduction, the temperature gradient distribution law of the inner wall of the barrel during the firing process of large-caliber artillery is simulated and calculated. Combined with Fick’s second law and the theory of metal phase transition, The relationship between the [C] content in the thermochemically affected layer of the barrel and the number of firing, the relationship between the thickness of the thermally affected layer and the explosion temperature of the propellant and the temperature of the inner wall were quantitatively analyzed. On this basis, the anatomical analysis of different parts of the barrel after firing verified the accuracy of the erosion model, quantitatively revealed the barrel erosion mechanism, and clarified the direction for the life improvement of large-caliber artillery barrels.

Hot‐air drying of corn kernels: Drying kinetics and quality improvement

AbstractBackground and ObjectivesDuring the hot‐air drying process of corn kernels, excessive stress can cause cracks to develop. For this reason, it's essential to identify the optimum parameters that can minimize stress during hot‐air drying.FindingsIn this study, a three‐dimensional fitness model was established based on the average geometric size of corn kernels. Additionally, a hot‐air drying model was constructed on the basis of heat and mass transfer, stress‐strain theory, and conservation law of heat and mass transfer. Simulated calculations of heat and mass transfer were performed to obtain the temperature and moisture gradient distribution. This distribution was then coupled with a stress model to reveal the variation of drying stress. Verification experiments were conducted on the drying model. The results indicated that the temperature and moisture gradient were symmetrically distributed about the geometric center of corn kernels. At symmetrical positions about the geometric center, their sizes were almost equal but their directions are opposite. The thermal stress and moisture gradient stress showed the fact of larger surface but smaller interior of corn kernels. Furthermore, they both increased rapidly in the initial stage and then slowly decreased. The maximum value of thermal stress was 4.57 kPa, and the maximum value of moisture gradient stress was 0.49 MPa.ConclusionsMass transfer plays a significant role in the hot‐air drying process, and cracks can develop as a result of excessive moisture gradient stress. To mitigate these issues, it's important to increase the air humidity in a controlled manner to significantly reduce the total stress. The maximum error in temperature between simulated and experimental results was 8.5%. This suggests that our drying model can be effectively utilized to explore temperature gradient, moisture gradient, and stress distribution of corn kernels.Significance and NoveltyThis study provides insights into the mechanism of stress generation that occurs during the hot‐air drying process of corn kernels. Our analysis indicates that properly increasing the air humidity can significantly reduce drying stress and consequently prevent the formation of cracks. This ultimately leads to improved product quality and economic value.

Temperature, Velocity and Pressure Gradient Distribution of Oil Production in South West Cameroon using a Mixed Convection Heat Transfer in a Horizontal Tube

Temperature, Velocity and Pressure Gradient Distribution of Oil Production in South West Cameroon using a Mixed Convection Heat Transfer in a Horizontal Tube

Influence of the liquid plug on the heat transfer performance of the ultra-thin flat heat pipe

Under extreme size, the ultra-thin flat heat pipe will form a liquid plug connecting the upper and lower surfaces due to the size effect and surface tension, and the liquid plug occupies and separates the vapor flow path. To study the influence of the liquid plug on the heat and mass transfer performance of the ultra-thin flat heat pipe, the ultra-thin flat heat pipe with a thickness of 1 mm and a filling rate of 30% is theoretically analyzed and visualization research. The results show that the liquid plug divides the vapor flow path into two separate sections, obstructing the continuous vapor flow. And the two sections are evaporated and condensed, respectively. The liquid plug will affect the temperature gradient distribution. In the hot end bubble, the temperature gradient decreases in the region where the condensing phase change occurs and increases in the region adjacent to this. The liquid plug needs to be pushed from the evaporator to the condenser during the heating process, resulting in an increased start-up time for the ultra-thin flat heat pipe. At low heating power of 4 W and 8 W, the liquid plug leads to the wick of the evaporator being completely covered by the liquid plug or liquid film, and the thermal resistance is higher than that without the liquid plug. When the heating power rises to 12 W and 16 W, the evaporator enters the nucleated boiling stage, and the liquid plug will replenish the working fluid reflux in the wick, and the thermal resistance decreases compared to the case without the liquid plug.

Three-Dimensional Temperature Field Simulation and Analysis of a Concrete Bridge Tower Considering the Influence of Sunshine Shadow

This paper forms a set of three-dimensional temperature field simulation methods considering the influence of sunshine shadow based on the DFLUX subroutine and FILM subroutine interface provided by the Abaqus platform to simulate the three-dimensional temperature field of concrete bridge towers and study its distribution law. The results show that the method has high accuracy for shadow recognition and temperature field calculation. The maximum difference between the shadow recognition results and the theoretical calculation value was only 19.1 mm, and the maximum difference between the simulated temperature and the measured temperature was 3.3 °C. The results of analyzing the temperature field of the concrete bridge tower using this algorithm show that the temperature difference between the opposite external surface of the tower column can reach 11.6 °C, which is significantly greater than the recommended temperature difference value of 5 °C in the specifications. For the concrete bridge tower, in the thickness direction of the tower wall, the temperature change was obvious only at a range of 0.3 m from the external surface of the tower wall, and the temperature change in the remaining range was small. In addition, the temperature gradient distribution of the sunshine temperature field in the direction of wall thickness conformed to the exponential function T(x) = T0e−αx + C. Additionally, the data fitting results indicate that using the temperature data at a distance of 0.8 m from the external surface as the calculation parameter in the function can achieve the ideal fitting result.