Radial Temperature Difference Research Articles

Multi-physics coupled numerical simulation study to optimize process parameters for electromagnetic stirring of semi-solid A356 aluminum alloy under the influence of skin effect

The electromagnetic stirring (EMS) method stands as a widely used technique in creating semi-solid aluminum alloy slurry due to its convenience and precision in parameter control compared to other methods. In this study, a comprehensive model that combines electromagnetics, flow, heat transfer and solidification was formed. By analyzing the influence of input current and frequency on the electromagnetic force, the behavior of various process parameters in velocity field and temperature field under influence of the skin effect is investigated. The aim is to find the optimal process parameters for production of slurry using the low-frequency EMS. The results show that within the investigated range, by adjusting the input current and frequency to 150 A and 15 Hz, higher fluid velocities and appropriate distribution of vortex zones can be observed, while achieving a uniform temperature field, the highest cooling rate and the minimum radial temperature difference. In addition, the sample prepared under the optimal process parameters shows that the melt edge is least affected by the skin effect, which leads to a higher stirring strength and a smaller overall grain size, which is consistent with the theoretical skin effect research found within the simulation section.

Research on the characteristics of hydrogen production by methanol steam reforming in a Fresnel lens concentrated tubular reactor

The methanol steam reforming process involves variable heat absorption along the flow direction, resulting in a non-uniform temperature within the reactor. To improve the hydrogen production performance, this paper introduces an innovative solar-driven reactor, the Fresnel Lens Concentrated Collector Tubular Reactor (FLCCTR), which matches solar energy collection with the endothermic reforming process through optimized design. The heat flux density on the reactor's inner wall was determined using the Monte Carlo method. Subsequently, a 3D model was developed that integrates flow, heat and mass transfer, along with reforming kinetics. This model assessed the effects of inlet flow rate, temperature, steam-to-methanol ratio, and heat flux density type on hydrogen production performance. Results indicate that the inlet flow rate significantly affects performance, with the reactor maintaining a minimal radial temperature difference of 3.554K. It also indicated that non-uniform heat flux reduces the temperature increase and CO output by 36.84% at the outlet.

COMPUTATIONAL AND EXPERIMENTAL STUDY OF THE STRESS-STRAIN STATE OF A PIPE UNDER EXTERNAL RADIAL LOAD, INTERNAL PRESSURE AND TEMPERATURE DIFFERENCE

Oil and gas pipelines are subjected to complex of loads and impacts during operation. The purpose of this article is an experimental assessment of the stress-strain state of a pipe under the action of external radial force on a laboratory bench by the strain gauge method, as well as a computational and experimental assessment of the stress-strain state under the combined action of radial force, internal pressure and temperature difference. Accounting for internal pressure and temperature difference (other factors affecting the pipeline) is carried out using well-known theoretical formulas which are confirmed by practice. The total stresses from the effects of several factors of influence are determined due to the principle of superposition.Experimental and computational studies of the stress-strain state of the pipe cross section under the influence of external radial force corresponding to the pipe deflection from 0 to 8 mm; internal pressure from 0 to 14 MPa; temperature difference from minus 60 C to 60 C have been carried out. Graphs of the dependence of maximum stresses on the factors of influence are constructed. Empirical formulas have been obtained for calculating the maximum equivalent von Mises stress of the cross-section of the pipe with a diameter of 325 mm under various loading options, they are necessary to assess the strength of the pipeline structure.

Study on temperature field in the process of induction heat treatment with current assisted weld double side method

At present, in the process of weld induction heat treatment, the common method is to carry out centralized induction heating in the weld area, which will lead to large radial temperature difference of the weld, poor controllability of temperature distribution and easy to cause the defects of residual stress concentration in the weld area. To solve the above problems, this paper adopts the two-sided method to conduct induction heating on both sides of the weld, and at the same time, the auxiliary pulse current is passed into the weld to improve the quality of the weld. ANSYS finite element software is used to establish a multi-field coupling prediction model of electric-magnetic-thermal structure, and explore the distribution law of the auxiliary pulse current and the temperature field of the weld. Finally, an experimental study of pulsed current assisted two-sided induction heating is carried out. Temperature test and metallographic test were carried out respectively to verify the effectiveness of pulsed current assisted induction heating technology.

Temperature Field Characteristics of Limited Slip Clutch under Various Condition Parameters

The temperature field of limited slip clutch (LSC) seriously interferes with torque transmission. In this paper, the attribute of dynamic partition of slip heat flux is considered. A calculation model of temperature field is also established by combining the proposed new method of fluid-solid equivalent convective heat transfer. The simulation and experiment of different relative speed, lubricant flow, and temperature are carried out. Furthermore, the comprehensive evaluation index of average temperature growth ratio and maximum radial temperature difference is proposed. The results show that the deviations of temperature rising rate and average temperature are not more than 0.2 °C/s and 6 °C, respectively. Heat flux partition value of separator plate increases approximately proportionally with relative speed. Changing relative speed from 40 r/min to 80 r/min, average temperature growth rate and maximum radial temperature difference of separator plate increase by 0.35 °C/s and 2.08 °C, respectively. On the contrary, increasing lubricant flow or reducing lubricant temperature weakens actual heat flux input of clutch. From 3 L/min to 10.5 L/min about lubricant flow, the average temperature growth rate and maximum radial temperature difference caused by higher relative speed are reduced by 0.32 and 2.71 °C, respectively. However, when lubricant temperature is adjusted from 65 °C to 30 °C, average temperature growth rate is reduced by 0.51 and the variation of maximum radial temperature difference does not exceed 0.32 °C. The research can accurately simulate actual energy flow at friction pair interface and assist in exploring the influence of condition parameters on temperature field.

Analysis of Cavity Disk Heat Transfer by Solving Inverse Heat Transfer Problem

Abstract The flow and heat transfer within compressor rotor cavities of aero-engines is a conjugate problem. The operating conditions buoyancy forces, caused by radial temperature difference between the cold throughflow and the hotter shroud, can influence the amount of entrained air significantly. By this, the heat transfer depends on the radial temperature gradient of the cavity walls, and in turn, the disk temperatures are dependent on the heat transfer. In this article, disk Nusselt numbers are calculated in reference to the air inlet temperature and in comparison to a modeled local air temperature inside the cavity. The local disk heat flux is determined from measured steady-state surface temperatures by solving the inverse heat transfer problem in an iterative procedure. The conduction equation is solved on a 2D mesh using a validated finite element approach, and the heat flux confidence intervals are calculated with a stratified Monte Carlo approach. An estimate for the amount of air entering into the cavity is calculated by a simplified heat balance. The major influences on the Nusselt number were found to be the mass flowrate entering the cavity and the density of the fluid inside the cavity.

Feasibility study on cooling scheme design of the concrete shielding for swimming pool-type low-temperature heating reactor

Elevating the operational parameters of Swimming Pool-type Low-Temperature Heating Reactors to augment heating capacity raises concerns about heightened water temperatures within the pool. Elevated water temperatures pose a significant challenge to the integrity and durability of the concrete shielding, necessitating innovative solutions for effective thermal insulation. Existing approaches, such as insulation coatings and static insulation water layers, have shown limitations in maintaining prolonged cooling efficiency under reactor operating conditions. In response to this challenge, our research introduced a novel approach: the implementation of a flowing water layer within the concrete structure. A specialized insulation water layer is integrated within the reactor to efficiently isolate high-temperature pool water from the surrounding concrete shielding. A comprehensive experimental setup is established to assess the insulation effectiveness, yielding insights into the water layer’s insulation performance. Results demonstrate a significant radial temperature difference of up to 14.31 °C between the cold and hot walls of the water layer within the experimental parameters. Investigation into critical experimental variables indicates that inlet positioning minimally affects insulation efficiency. This study not only verifies the viability of the insulation water layer approach but also furnishes crucial experimental data for future research endeavors about the cooling scheme of the Swimming Pool-type Low-Temperature Heating Reactor.

Simulated and experimental study on the relationship between coefficient of friction and temperature of aluminum-based brake disc

PurposeThis study aims to clarify the relationship between the coefficient of friction (COF) and temperature of aluminum-based brake discs.Design/methodology/approachThree friction blocks with different COFs are examined by a TM-I-type reduced-scale inertial braking dynamometer. On this basis, the thermo-mechanically coupled model of friction pairs is established to study the evolution of brake disc temperature under different COFs using ADINA software.FindingsResults indicate that the calculated disc temperature field matches the experimental well. The effect of COF on the peak temperature is magnified by the braking speed. With the COF increasing, the rise rate of instantaneous peak temperature is accelerated, and the dynamic equilibrium period and cooling-down period are observed in advance. The increase in COF promotes the area ratio of the high-temperature zone and the maximum radial temperature difference. When the COF is increased from 0.245 to 0.359 and 0.434 at 140 km/h, the area ratio of high-temperature zone increases from 12% to 44% and 49% and the maximum radial temperature difference increases from 56°C to 75°C and 83°C. The sensitiveness of the axial temperature difference to the COF is related to the braking time. The maximum axial temperature difference increases with COF in the early stages of braking, while it is hardly sensitive to the COF in the later stages of braking.Originality/valueThe effect of COF on the aluminum-based brake disc temperature is revealed, providing a theoretical reference for the popularization of aluminum-based brake discs and the selection of matching brake pads.

Thermal Analysis on Heat Pipe Receiver in Advanced Solar Dynamic System

In this paper, unit heat pipe receiver in advanced solar dynamic system was numerically simulated. Accordingly, mathematical model was set up, numerical calculation method was offered, numerical results were compared with the experimental results concerned. The temperature field of PCM (Phase Change material) was shown, the thermal performance of heat pipe receiver was analyzed. Analysis results show the axial and radial temperature difference of heat pipe are small; the thermal performance of heat pipe receiver is stable and reliable. The existence of void cavity influences the process of phase change; the temperature gradient of PCM zone is very significant because of the effect of void cavity.

Numerical study of reaction enhancement in hydrogen oxidation reactor with supercritical water medium by twisted oval structure

The oxidation of hydrogen in supercritical water supplies heat for the supercritical water gasification technology and is an essential part of the system. The mild release of heat in a limited space is a significant challenge. In the present study, a twisted oval structure was used to enhance the mixing inside the reactor, avoiding excessive local temperature and promoting heat transfer to the outside. A numerical model was developed to investigate hydrogen oxidation in supercritical H2O / CO2 mixtures. The effects of different inlet and structure parameters, including temperature, velocity, components, twisted pitch length, and aspect ratio, were evaluated. The steady-state simulation found that the circular structure allowed high-temperature fluids to cluster significantly around the nozzle and axis, resulting in excessive local temperatures. In contrast, the twisted oval structure stabilized the axial temperature faster while enabling more uniform temperature distribution in the radial direction. The maximum radial temperature difference and radial temperature variance were reduced by an average of 52.18% and 81.31%, respectively. Furthermore, the unreacted hydrogen escaping from the reactor at high flow rates was also avoided due to the enhanced radial mixing by the secondary flow in the twisted oval structure. The transient-state simulation showed that the twisted oval structure could stabilize the temperature distribution rapidly during reactor start-up, which might support further scale-up for the reactor.

Optimization of the thermal field of 8-inch SiC crystal growth by PVT method with “3 separation heater method”

Silicon carbide (SiC) has important application prospects in power and radio frequency (RF) devices. However, preparing large-diameter, high-quality SiC crystals is challenging. The major technique for growing large-diameter SiC crystals is the physical vapor transport (PVT) method and the key point for adjusting conditions is to find an optimal thermal field. In this study, we propose a resistance heating method called the “3 separation heater method” with 3 heaters separated by the graphite foam insulations so that 3 important parts (the SiC source powder area, SiC seed area, and seed holder) of the growth cell can be heated independently through thermal radiation from each separated heater. Further, the insulation separators play an important role as a switch of the heat flux. The numerical studies of the thermal field design for this model are conducted with the help of the numerical simulation software COMSOL Multiphysics and its appropriate parameters are explored. At last, the relationship between the parameters and crystal growth conditions, such as the radial temperature difference (RTD) and edge temperature gradient (ETG), is expressed by the back-propagation (BP) neural network and the optimal parameter values for crystal growth conditions have been confirmed using the non-dominated sorting genetic algorithm (NSGA-II).

Study on Dynamic Line Rating of Overhead Transmission Line Based on Large-Scale New Energy Power Grid Connection

With increasing new energy power grid connections and increasingly complex user loads, higher ampacity is required during peak power demand. Construction of new transmission lines can cost a lot and is limited by the environment and the shortage of land resources. Considering the intermittency of new energy power generation, dynamic line rating can increase the power transmission capacity of existing lines by exploiting their potential capacity. In this paper, the ampacity of transmission lines is calculated accurately, and influencing factors of ampacity are studied. Additionally, temperature change patterns and field distribution of the lines are studied. The results show that wind speed, ambient temperature, and sunshine intensity are the three main factors affecting the ampacity. Wind speed is proportional to ampacity, while ambient temperature and sunshine intensity are opposite. Then, it is found that the thermal inertia effect of transmission lines that temperature change lags behind current change can be utilized for ampacity enhancement. Furthermore, the radial temperature difference is found in the lines, and excessive temperature differences may accompany the risk of strand breakage. It is of great significance to study the temperature field of the lines for dynamic line rating based on large-scale new energy power grid connections.

Environmental Stability Design of the Aerial Mapping Camera Based on Multi-Dimensional Compound Structure.

Environmental stability technology plays an important role in improving the adaptive range, image resolution and ensuring the stability of geometric parameters of aerial mapping camera. Traditional environmental stability methods directly implement active and passive thermal design to optical systems, which is easy to lead to radial temperature difference of optical components, and cannot eliminate the influence of pressure change. To solve the above problem, a method of environment stability design based on multi-dimensional structure is proposed. Firstly, the aerial mapping camera is designed as imaging system component (core) and sealing cylinder (periphery), and a sealed air insulation sandwich is formed between the two parts to realize the sealing design. A thermal interface is reserved outside the seal to avoid the radial thermal stress caused by direct heating of the optical parts, and a multi-dimensional Environmental stability structure is formed. Secondly, the core and the external thermal environment of aerial mapping camera in complex aviation environment are modeled and theoretically analyzed. Finally, the effectiveness and stability of the multi-dimensional structure method is verified by the thermal simulation and the flight. The results show that the thermal control power is 240 W, the thermal gradient of the optical system is less than 5 °C, the radial temperature difference is less than 0.5 °C. High quality image and ground measurement accuracy are obtained. Compared with tradition thermal control methods, the proposed method has the advantages of accuracy and low power consumption, which can effectively reduce the power consumption and difficulty of the thermal control.

Elastohydrodynamic lubrication model and failure test for micro-contact thermodynamic characteristics of friction interface

A micro-contact thermodynamic model is proposed to study the interfacial characteristics in wet friction pair based on Elastohydrodynamic Lubrication (EHL) theory. The study takes into account the asperity elastic-plastic deformation, establishing an improved model with high accuracy in verifications with experimental data and existing model. With this optimized micro-contact thermodynamic model, we systematically discussed the influence of sliding speed, oil temperature, and average surface pressure on thermodynamic behaviors such as rough contact area, pressure distribution, and temperature distribution. Additionally, experimental investigations revealed the complex failure mechanism of the friction disc. Specifically, during the failure process, the friction coefficient and the radial temperature difference gradually increase. The metal oxides form on the surface, and the graphite distribution is gradually dispersed.

Design and Optimization of Thermal Field for PVT Method 8-Inch SiC Crystal Growth.

As a wide bandgap semiconductor material, silicon carbide has promising prospects for application. However, its commercial production size is currently 6 inches, and the difficulty in preparing larger single crystals increases exponentially with size increasing. Large-size single crystal growth is faced with the enormous problem of radial growth conditions deteriorating. Based on simulation tools, the physical field of 8-inch crystal growth is modeled and studied. By introducing the design of the seed cavity, the radial temperature difference in the seed crystal surface is reduced by 88% from 93 K of a basic scheme to 11 K, and the thermal field conditions with uniform radial temperature and moderate temperature gradient are obtained. Meanwhile, the effects of different processing conditions and relative positions of key structures on the surface temperature and axial temperature gradients of the seed crystals are analyzed in terms of new thermal field design, including induction power, frequency, diameter and height of coils, the distance between raw materials and the seed crystal. Meanwhiles, better process conditions and relative positions under experimental conditions are obtained. Based on the optimized conditions, the thermal field verification under seedless conditions is carried out, discovering that the single crystal deposition rate is 90% of that of polycrystalline deposition under the experimental conditions. Meanwhile, an 8-inch polycrystalline with 9.6 mm uniform deposition was successfully obtained after 120 h crystal growth, whose convexity is reduced from 13 mm to 6.4 mm compared with the original scheme. The results indicate that the optimized conditions can be used for single-crystal growth.

Numerical analysis of the thermal-elastic-plastic state of electrical contact gasket made from dispersion-reinforced composite materials using the fusioned deposition modeling method

The article presents the results of a theoretical study on determining the suitability of using electrical contact gaskets (ECG) in industrial conditions (Castner direct graphitization furnaces), made of coke-pitch composite using additive technologies based on the Fused Deposition Modeling (FDM) method.
 Numerical analysis of the physical state of ECG under the conditions of industrial application was performed on the basis of the mathematical statement of the thermo-elastic-plasticity problem and the algorithm of implicit inverse mapping of its solution based on the finite element method in the Mathcad programming environment. To construct the geometry and tetraid mesh of the ECG model, a freely open program code was used - the Gmsh CAD system for grid generation, and for the visualization of the results of physical field calculations, the free open program code ParaView was used.
 The study of the thermo-elastic-plastic state of ECG under the conditions of the graphitization process in Castner furnaces was carried out in the temperature range up to 900 °С, at which the thermoplastic properties of the material are manifested. At the same time, such physical fields of ECG were analyzed as temperature distribution, resulting displacements, equivalent elastic stresses according to Mises, equivalent total, elastic and plastic deformations according to Mises, and the volume fraction of ECG material in a plastic state, depending on the temperature level and radial gradient temperatures (radial temperature difference) of electrical contact gaskets.
 Numerical simulation of the thermo-elastic-plastic state of the ECG was carried out under the conditions of force loading by external pressure on the lateral surface of the gasket of 2.5 MPa and different values ​​of the radial temperature difference in the range of 15–90 °C in the temperature range up to 900 °C. It was established that: at the stages of formation of semi-coke and coke in the material of the coke-pitch composite ECG under the thermomechanical conditions of operation of the Kastner furnace, a margin of strength of not less than unity was obtained; with the subsequent increase in the temperature level in the Castner furnace to 3000 °C and above, the raw material of ECG, as a result of thermal destruction, has already turned into coke and, therefore, its mechanical properties have become close to the mechanical properties of electrode blanks in columns that are subjected to graphitization. This gives reason to assert that the ECGs will not be mechanically destroyed during the entire graphitization campaign of the Castner furnace.
 On the basis of the analysis of the results of numerical simulation, the possibility of using ECGs made from dispersion-reinforced composite materials (coke-pitch mixtures) by the FDM method in the technology of graphitizing electrode products according to the Сastner method is substantiated.

CFD investigation on thermal hydraulics of the double-wall bayonet tube heat exchanger in CLEAR-S facility

The double-wall bayonet tube type heat exchanger design can monitor and mitigate the occurrence of Steam Generator Tube Rupture (SGTR) accidents, which is one of the most important accidents of GEN-Ⅳ lead-cooled Fast Reactor (LFR). The lead-based reactor engineering validation facility CLEAR-S will be used for the integrated testing and verification of the megawatt-level double-wall bayonet tube heat exchanger. In this study, the Shear Stress Transport turbulence model (SSTk-ω) was used to pre-simulate the thermal characteristics of the CLEAR-S double-wall bayonet tube heat exchanger before the experiment. The verification shows that the numerical simulation results of the single bayonet tube structure are in good agreement with the RELAP5 simulation results and experimental data from CLEAR-S. CFD analysis reveals that the non-effective heat exchange area will preheat the liquid water on the side of the tube, so that the overall heat exchange performance decreases by about 4%. The heat conduction of the powder interlayer is the largest heat transfer resistance, which weakened the influence of the lead-bismuth eutectic (LBE) side flow and temperature inhomogeneity on the heat transfer of the tube bundle and significantly reduced the wall radial temperature difference of each bayonet tube. The conclusions of this study can provide a reference for the experiment and design of double-wall bayonet tube heat exchangers.

Influences of the Contact State between Friction Pairs on the Thermodynamic Characteristics of a Multi-Disc Clutch.

The relationship between clutch thermodynamic characteristics and contact states of friction components is explored numerically and experimentally. The clutch thermodynamic numerical model is developed with consideration of the contact state and oil film between friction pairs. The clutch bench test is conducted to verify the variation of the clutch thermodynamic characteristics from the uniform contact (UCS) to the intermittent contact (ICS). The results show that the oil film decreases gradually with increasing temperature; the lubrication state finally changes from hydrodynamic lubrication to dry friction, where the friction coefficient shows an increasing trend before a decrease. Thus, the friction torque in UCS gradually increases after the applied pressure stabilizes. When the contact state changes to ICS, the contact pressure increases suddenly and the oil film decreases rapidly in the local contact area, bringing about a sharp increase in friction torque; subsequently, the circumferential and radial temperature differences of friction components expand dramatically. However, if the contact zone is already in the dry friction state, friction torque declines directly, resulting in clutch failure. The conclusions can potentially be used for online monitoring and fault diagnosis of the clutch.

Calculation and analysis of ampacity and stress of overhead transmission line

To ensure the safe operation of a transmission line, it is necessary to study the radial temperature rise and the stress and strain distribution of the transmission line under on-load state. A three-dimensional solid finite element model of reinforced aluminum conductor steel was established, and the temperature and stress distribution of the conductor were calculated. The effects of operating tension, wind speed, and radial temperature difference on the temperature and stress distribution were analyzed. The radial temperature difference increases about 1.40–3.16 °C with the rise of the mean temperature of the conductor. When the ambient temperature decreases from 20 to −40 °C, the mean temperature of the conductor decreases from 50.34 to −9.31 °C, and the external layer stress increases from 44.59 to 60.19 MPa. At the same time, the external layer stress of the conductor increases with the increase in wind speed and operating tension. The stress of the outermost aluminum conductor of the conductor under the radial temperature difference load increases with the rise in the temperature difference, and the stress of the inner aluminum conductor and the inner steel core decreases with the rise in the temperature difference.

Axisymmetric flow structure of thin liquid film under radial temperature difference

Axisymmetric flow structure of thin liquid film under radial temperature difference