Equivalent Thermal Stress Research Articles

Analysis and verification of electrodynamic force, thermal stress and current sharing for CRAFT converter structure design

In the design realm of fusion power supplies, structural components play a pivotal role in ensuring the safety of fusion devices. To verify the reliability of the converter structure design at the Comprehensive Research Facility for Fusion Technology (CRAFT), meticulous analysis of the converter's dynamic impact is carefully performed based on the worst fault current (400 kA), firstly. Subsequently, the thermal stress analysis based on the maximum allowable steady-state temperature is finished, and the equivalent thermal stress, thermal deformation, maximum shear stress of a single bridge arm and the whole converter are studied. Furthermore, a simple research method involving the current-sharing characteristics of a bridge arm with multi-thyristor parallel connection is proposed using a combination of Simplorer with Q3D in ANSYS. The results show that the current-sharing characteristics are excellent. Finally, the structural design has been meticulously tailored to meet the established requirements.

Study of thermal properties and stresses in a 1.05 MW molten salt furnace for recovering and storing blast furnace gas waste heat

Utilizing a molten salt furnace to recover waste heat from blast furnace gas and storing it in high-temperature molten salt represents an innovative solution for steel waste heat recovery systems. In this study, a 1.05 MW spiral coil vertical molten salt furnace thermal energy storage system was constructed. During the thermal storage experiment under a 75 % heating load, the system achieved a heating efficiency of 74.57 % and a molten salt temperature of 560.3 °C. To analyze the thermal performance and thermal stress of the molten salt furnace, a three-dimensional transient numerical computational model using ANSYS Fluent and Matlab software was developed. A two-dimensional thermoelastic model was employed to assess the thermal stress of the spiral coil. The deviations between the experiment and simulation for the molten salt outlet and coil temperature were 1.40 % and 1.66 %, respectively. Furthermore, the three-dimensional temperature and thermal stress distributions under the benchmark case were simulated, finding that the maximum coil temperature reached 574.20 °C, while the maximum coil stress was 446.30 MPa. Increasing the heating load, molten salt inlet temperature, and time all lead to increased equivalent thermal stress. However, the location of the coil radius at 16 mm showed a minor sensitivity to heat flow density. Additionally, increasing the molten salt inlet mass flow rate by 0.1 kg/s resulted in a 2.99 MPa reduction in equivalent thermal stress. This paper provided valuable insights into the thermal properties and evolution of thermal stresses during the heating process in molten salt furnaces, offering a promising approach for recycling blast furnace gas in steel plants.

Numerical study on cooling performance and thermal stress characteristic of an f-class gas turbine stator blade

In this study, a coupled numerical computation approach integrating aerothermal and thermomechanical effects was employed to investigate the cooling efficiency and thermal stress characteristics of gas turbine stator blades. A comprehensive analysis was conducted considering varying turbulence intensities in the coolant flow (spanning from 0.05 to 0.15) and different coolant media configurations, including pure air, dual-medium mixture of air and steam, and pure steam. The distributional traits of cooling efficiency and thermal stress on the stator blade surface under these conditions were meticulously examined. Furthermore, quantitative assessments were performed to determine the extentto which coolant turbulence intensity and coolant type affect the average cooling efficiency and maximum equivalent thermal stress of turbine stator blades, thereby revealing the influence laws. The results reveal that the minimum cooling efficiency on the stator blade surface predominantly occurs at the position of channel 4 on the pressure surface, while the highest cooling efficiency is generally found near the leading edge of the suction surface. Regions of elevated thermal stress were consistently concentrated around the stator blade tip and root areas. When the coolant turbulence intensity increased from 0.05 to 0.15, the average cooling efficiency on the stator blade surface improved by 2.06%, accompanied by a reduction of 1.12% in the maximum thermal stress. In comparison to pure air cooling, dual-medium (air and steam) cooling and pure steam cooling lead to respective enhancements in the average cooling efficiency of approximately 3.3% and 13.2%, with corresponding decreases in the maximum thermal stress of 2.18% and 10.2%.

Numerical and experimental study on thermal performance and thermal stress of molten salt receiver during preheating

Due to the high thermal stress, the evacuated molten salt tower receiver is prone to safety problems during the daily preheating, but there is relatively little research on it, especially on on-site receivers. In this study, the preheating performance of a lab-scale receiver is experimentally investigated first, and the influence of several operating or environmental factors on its thermal performance is obtained. The experimental results indicate that the tube front side always reaches the wall temperature requirement of salt circulation before the tube back side. Then, the numerical model of the receiver tube based on the finite volume method and 2D thermoelastic method is established and verified. Finally, by applying the numerical model to an on-site receiver, the influence of extreme environmental conditions on the preheating performance of the on-site receiver are obtained. It is found that the minimum and maximum thermal stresses occur at 90° and 180° of the outer wall, respectively, and the thermal stress is determined by the circumferential temperature gradient. The equivalent thermal stress first increases and then decreases during preheating, and the maximum equivalent thermal stress reaches within the first few minutes. Compared with the windless condition, the maximum equivalent thermal stress under strong wind (10 m/s) is reduced by 20.5%. The maximum equivalent thermal stress is linearly related to the ambient temperature, and it decreases by 6 MPa for every 10 °C increase in ambient temperature.

Numerical study on thermal performance and thermal stress of molten salt receiver tube based on induction heating

Induction heating is an emerging research method that can recreate half-perimeter heating of a receiver tube in a tower-concentrating solar power plant. In this study, a three-dimensional (3D) field numerical model that couples electromagnetic induction, heat transfer, and turbulence, is developed to study the thermal performance of a receiver tube during the preheating process and under salt circulation conditions. The effects of the coil-to-tube distance, coil power, molten salt inlet temperature, molten salt inlet velocity, and ambient temperature were investigated. Furthermore, the thermal stress distribution and evolution in the tube were calculated. The heat generation was fund to be concentrated on the outer surface of the tube front. The increase in coil power significantly accelerated the preheating process. With increase in the coil power from 200 to 500 W, the time required for the maximum tube temperature to reach 350 °C reduced by 55.67 %. The heating efficiency increased with increasing coil power, molten salt inlet velocity, and ambient temperature decreased with increasing coil-to-tube distance and molten salt inlet temperature. Among them, the molten salt inlet temperature had a more significant effect. As it increased from 250 to 400 °C, the heating efficiency decreased from 47.17 to 18.82 %. The maximum and minimum equivalent thermal stresses at preheat stabilization were reached at θ = 0° and θ = 45°, respectively. Furthermore, the equivalent thermal stress at preheat stabilization differed from that with salt circulation by only 4.46 %.

Czochralski (CZ) process modification with cooling tube in the response to market Global silicon shortage

Recently, the silicon wafer producers, affected by Covid-19 and USA-China competition, looks for new production processes to increase the production. On the other hand, the common parts of CZ puller such as heater, crucible and thermal shield are optimized over time and now the common CZ process is reached to limitation for further improvement. Here, we propose a modified CZ method by adding a cooling tube into the growth zone. The new proposed Cz method is applied to the 8″ crystal growth process. A fully 3D transition model including energy equation, Navier–Stokes equation, surface-to-surface radiation heat transfer, moving mesh and thermal stress equations is implemented. The simulation is performed for both original and new CZ method. It was proved that the new CZ method increases the pulling speed up to 25 %. To ensure about the crystal quality, the thermal stress is compared between original and new proposed CZ method. Although it was found that the thermal stress increases about twice but still the maximum von Mises stress never exceeds the critical value 25 MPa. Additionally, the power consumption is also found to enhance maximum 2 kW under new conditions. To evaluate the model the interface and heater power for the original CZ puller is compared with industrial CZ process and it shows acceptable accuracy.

Effects of Annular-finned Tube Deformation on Thermal Stresses in a Heat Exchanger

Nowadays, along with the developments in the industry, many machines and structures are exposed to very high-temperature environments, which has caused various types of thermal load in them. These conditions have led to focused studies on thermal stresses in structures. Heat exchangers are among the structures in which the temperature difference causes thermal stress. In this paper, “finite volume” and “finite element” methods are used to solve flow equations and thermal stress equations in solids, respectively. In addition, the effect of changes in the shape of the annular finned pipe on the thermal stresses in the heat exchanger is investigated. The study results on changing the pipe shape from circular to elliptical show that by changing the pipe shape, the thermal stress in the fin can be significantly reduced; for instance, in the cases reviewed in this paper, the thermal stress has decreased by 9%. Furthermore, the results of thermal stress show that the Maximum Effective Stress point, both before and after changing the shape, is still located at the fin’s base. So, according to the results of this study, examining the effect of pipe shape changing on thermal stress is an imperative measure when designing heat exchangers.

Design of a Morphing Skin with Shape Memory Alloy Based on Equivalent Thermal Stress Approach.

Shape memory alloy (SMA) is one of the potential driving devices for morphing aircraft due to its advantages of pseudoelasticity, superelasticity, and shape memory effect. Precise and fast analysis of SMA has simultaneously become a key requirement for industrial applications. In this study, a user-defined material subroutine (UMAT) was implemented and successfully applied in a three-dimensional numerical simulation in ABAQUS based on the extended Boyd–Lagoudas model. In addition to the conventional detwinned martensite (Md) and austenite (A), twinned martensite (Mt) was also considered to model the practical transformation accurately. Then, the equivalent thermal strain approach was adopted to simplify the simulation complexity with UMAT. By resetting the thermal expansion coefficient, the thermal strain equivalent to the original phase transformation strain was generated. The approach was validated in two cases, showing consistent results with the extended Boyd–Lagoudas model and reduction in time consumption by 89.1%. Lastly, an active morphing skin integrating the single-range SMA and a stainless-steel plate was designed to realize two-way morphing. The calculated arc height variation of the skin was 3.74 mm with a relative error of 1.84% compared to the experimental result of 3.81 mm. The coupled use of UMAT and the equivalent thermal stress approach helped to reduce the challenge in modeling SMA.

Numerical investigation on fatigue life of aluminum brazing structure with fin-plate-side bar under the low temperature thermal-structure cyclic stress

A stress analysis model was established to analyze the thermal and structural stress of aluminum brazing structure with fin-plate-side bar (ABS) in the LNG plate-fin heat exchanger. The fatigue life of ABS was evaluated based on the above stress analysis results by the different standard. The result shows that the thermal and structural stress concentration is generated at the brazed joint of ABS. Under the common action of thermal and structural stress, the equivalent stress is influenced mainly by the equivalent thermal stress. The equivalent alternating stress was calculated to be 153.5 MPa based on thermal and structural stress. The permissible cycle numbers at the brazed joint of ABS, which is calculated by the fatigue assessment procedure of ASME and JB4732, are 3311 and 2953, respectively. The fatigue assessment results based on the third strength theory is more conservative for the ABS. The influence of operation parameters is also analyzed for the fatigue life of ABS. The temperature difference between NG and MR, MR temperature and NG pressure will be the main factors to impact the fatigue life of that. And a method is proposed to predict the fatigue life of ABS according to the main factors. The error will be less than 10% between the prediction results and the simulation results.

Effects of TVSR process on the dimensional stability and residual stress of 7075 aluminum alloy parts

Abstract Residual stress generated during the blank forming and machining process significantly influences the dimensional stability of the mechanical parts. The equivalent bending stiffness and thermal vibration stress relief (TVSR) are two factors that affect the deformation of thin-walled workpiece. To increase the machining accuracy, on the one hand, increase the equivalent bending stiffness in manufacturing, and on the other hand, usually conduct the stress relief process to reduce the residual stress in manufacturing. In the present study, morphology optimization and TVSR process are conducted on a thin-walled part Specimen B of 7075 aluminum alloy to control the residual stress and machining deformation before finish machining. As a contrast, Specimen A is machined in one step. The deformations vary with time of Specimen A and B are measured. The corresponding finite element model is built to further study the stress and distortion during the machining process. Results showed that (1) deformation decreased with the increase of equivalent bending stiffness, compared with Specimen A, the maximum deformation of Specimen B decreased by 58.28%. (2) The final maximum deformation of Specimen B can be reduced by 38.33% by topology reinforcement to improve the equivalent stiffness and TVSR to reduce the residual stress.

Optimization and simulation of furnace temperature curve based on heat

The welding quality of reflow welding is closely related to the setting of furnace temperature curve. Based on the law of heat transfer between heat transfer conduction and heat ionization in the process of reflow welding, the mathematical model of PCB plate heat transfer process is established based on the relationship between conveyor belt transfer speed, temperature of each temperature zone and minimum equivalent heat stress in the process of reflow welding, and the optimization model of furnace temperature curve is established with the minimum heating factor and minimum equivalent thermal stress as the optimization target. At the same time, the simulation analysis of stress strain before and after optimization is carried out by finite meta-method, and the results show that the iso-effect force after optimization is reduced by 6.5%, the warp deformation degree of the corner is also reduced to a certain extent, and the maximum iso-effect variable is reduced by 5%. The results provide reference and basis for the improvement of reflow welding process.

Improving thermomechanical properties of cracked brittle honeycombs by negative Poisson’s ratio effect

This work investigates the effects of cracking on the overall properties of brittle auxetic/non-auxetic honeycombs. The micro numerical model and macro theoretical model are established simultaneously. The analytical expressions of crack opening displacement (COD) are derived and the results agree well with numerical simulations. The fracture toughness of honeycombs is calculated by combining the stress in the numerical model and the stress intensity factor (SIF) in the theoretical model. The reductions in the equivalent stiffness and equivalent thermal stress coefficient (TSC) of the cracked honeycombs are predicted. The negative Poisson’s ratio (NPR) effects on those fracture mechanics parameters and equivalent thermomechanical properties are studied. And considering the orthogonal anisotropic properties of honeycombs, the cracking along two orthogonal directions is examined. It reveals that the significant NPR effects can only be detected in a single direction and the effects in another direction are inconspicuous. In addition, the effects of crack length, medium dimensions, and cell-wall angle of honeycomb cells on the overall performance of the cracked medium are also evaluated by parametric studies and the results are displayed graphically.

Numerical investigation of thermo-mechanical properties for disc brake using light commercial vehicle

A brake is a device using which frictional resistance is applied for stopping a moving vehicle. In disc brakes, the component on which the pads are squeezed when the brake pedal is applied. Disc brakes are subjected to both mechanical and thermal stresses. The cyclic thermal stress is more significant than mechanical stress. In this study, three-disc brakes with different profiles are selected to investigate the thermo-mechanical behavior analytically and numerically. This analysis develops a three-dimensional (3D) thermo-structural coupling model, implements transient thermal Analysis and transient structural Analysis of disc brake profiles with a frictional heat. The thermo-structural problem is solved by the finite element method to get the transient temperature and thermal stress fields of the disc brake under emergency braking. Comparison between the three profiles has been made using different parameters, including the maximum temperature on the surface, equivalent thermal stress (Von-Mises), and thermal deformation. The result has shown that the having grooved profile on its surface exhibited 34Mpa of equivalent stress, whereas the solid type and the drilled type have shown 80Mpa and 57Mpa. It also shows that the grooved type brake is efficient by far more magnitude than the other two profiles. In general, the thermal stress developed and thermal deformation on the would significantly decrease when it has a profile that allows for better heat dissipation to the surrounding.

Thermal characteristics and thermal stress analysis of a superheated water/steam solar cavity receiver under non-uniform concentrated solar irradiation

Solar cavity receiver is a vital component in a solar power tower (SPT) system, where concentrated solar irradiation is absorbed, converted into heat and carried away by a kind of heat transfer fluid. The cavity receiver usually suffers from the high-flux and non-uniform concentrated solar irradiation, which would cause local overheating, large temperature gradient and even thermal stress fracture of the receiver and bring challenges for the safety of its daily operation. Therefore, it is necessary to investigate the thermal and mechanical performance of the solar cavity receiver. In the present study, a superheated water/steam solar cavity receiver with three boiling panels and a superheater was chosen as the physical model. An integrated simulation method, which couples the Monte-Carlo ray tracing (MCRT) method, the appropriate heat transfer correlations, the finite volume method (FVM) and the finite element method (FEM), was employed to simulate the complicated heat transfer process inside the receiver and conduct the thermal stress analysis for the absorber panels. With this method, the three-dimensional wall temperature and thermal stress distributions were gained both on the boiling panels and the superheater, and the causes of thermal stress induced by different temperature gradients were analyzed in detail. The following results were obtained: 1) The heat flux, wall temperature and equivalent thermal stress distributions all appear highly non-uniform on the absorber panels; 2) The hot spots can be found on the membrane wall between the elbows of the boiling panels, which can easily generate the high thermal stress due to the large temperature gradient with their surroundings; 3) The bi-axial stress at the outer and inner radius of the boiling tubes can be created by the large radial temperature gradient, and the thermal stress varies as a cosine distribution across the circumference of the superheated tubes, which is induced by the large temperature gradient in the circumferential direction. Besides, the spot-like areas with high thermal stress can also be found on the superheated tubes due to the considerable nonlinear axial temperature gradient. Moreover, the thermal stress on the membrane wall connected with both the boiling and the superheated tubes has the definite directionality, which shows parallel to the tubes or perpendicular to the tubes; 4) The thermal stress concentration always occurs at the high-temperature and structural discontinuity locations. Here, the thermal stress of the superheater is 360 MPa higher than that of the boiling panels. In general, the superheater has both the higher wall temperature and thermal stress, which is more crucial for the safe operation of the superheated water/steam solar cavity receiver.

Dynamic heating and thermal destruction conditions of quartz particles in polydisperse plasma flow of RF-ICP torch system

Numerical simulation of turbulent mixing process of polydisperse quartz particle (particle size distribution in the range of 0.1–0.4 mm) flow with Ar and Ar-H2 plasma generated by radio frequency inductively coupled plasma (RF-ICP) torch has been made. An approximate two-stage approach has been proposed to calculate the spatial–temporal distributions of temperature and resulting thermal stress in quartz particles during dynamic heating in polydisperse plasma flow. The influence of working gas compositions, particle size distributions, injection angle and flow rate of carrier gas on the thermal destruction conditions of quartz particles has been determined under different particle feed rates. It is found that all the solid quartz particles (0.1–0.4 mm) could be thermal destructed without overheating in RF-ICP torch system, when the hydrogen volume fraction in working gases is more than 1.5%–2% and particle feed rate is in a certain range. The values of the maximum and minimum feed rates have been determined under different hydrogen volume fractions. An optimal particle injection angle and flow rate of carrier gas is found around 50°–60° and 160–220 slpm, under which the value of maximum equivalent thermal stress in quartz particles is highest.

Thermo-structural fatigue and lifetime analysis of a heat exchanger as a feedwater heater in power plant

Today, the use of shell and tube heat exchangers has become widespread and they are used in various industries under very diverse operating conditions. Specific operating conditions make it possible to consider and simulate the operating terms and failure conditions of these converters. In this study, the design of a shell-and-tube counter-flow heat exchanger in AutoCAD software is first considered, and the system is then meshed and simulated in ANSYS 2019 software. Simulation results of temperature, pressure, heat flux and fluid velocity within the system are reported in order to understand the system performance. Failure conditions are evaluated according to the ASME VIII Boiler and Pressure Vessel Code, and the results of equivalent thermal stress analysis and system lifetime under two extreme loading conditions are reported. The highest equivalent thermal stresses under these extreme load conditions occur at the joints of the tubes and tubes sheet and is equal to 641 and 931 MPa, respectively. Also, the lifetimes of tubes and tube sheets are 105 and 104 cycles respectively for the valley and peak load conditions.

Numerical analysis of thermal stresses and strains of annular finned tube bundle in turbulent flow regime

In this paper, the effect of turbulent flow on the thermal stresses and strains created in an annular finned-tube bundle is studied. The finite volume method and the transition SST model, along with the SIMPLE algorithm, are used to solve the flow equations, and the finite element method is used to solve the thermal stress equations in solid. The results obtained from the effective stress and strain in the annular fins bundle show that despite the temperature difference of less than 1 degree between the base and the edge of the fin, the amount of thermal stresses cannot be ignored and the asymmetric distribution of temperature in the fins leads to the shear stresses which play a key role in determining the maximum position of the effective stresses in some rows. The results show that the amount of effective stress and strain in the third and fourth rows are significantly smaller than the first and second rows. The results also show that the highest amount of the effective stress occurs in the first row and the fin base at zero-degree angle, the value of which is 0.6 MPa. The predominance of the tangential stresses at the fin base in this row is the cause of this issue. However, in the second fins onwards, although the tangential stresses are still higher, the greater asymmetry of the temperature around the fins in these rows leads to comparability of the shear stresses with tangential stresses and creates the maximum effective stress at angles other than zero degree. Therefore, according to the results of this paper, the analysis of the flow around the annular fins is necessary to calculate thermal stress and strains and it determines the vulnerable points in each tube row. It is natural that with increasing temperature difference between the base and the edge of the fin and with increasing fin hight, the importance of these studies increases.

Investigations on the thermal behavior and associated thermal stresses for short pulse laser heating

The fractional type Cattaneo heat conduction equation and the associated thermal stress equation are established for studying the thermal and related stress behavior of the short pulse laser heating. With the Laplace transform method, the analytical solution of the temperature distribution and thermal stress field are derived. Compared to the classical Fourier heat transfer model and the standard C-V one, the results of the present model show the thermal diffusion feature as well as the thermal wave behaviour, which is more realistic. Furthermore, the influences of the fractional order parameter on the thermal and related stress behavior are discussed. The thermal velocity, thermal variation rate and the peak value of the temperature and the thermal stress depend on the fractional order parameter. The fractional type Cattaneo heat model and associated thermal stress exhibit the non-local nature.

Probing Slip Differential Heat of Magnetorheological Fluids Subjected to Shear Mode Operation and Its Effect on the Structure.

The paper probes slip differential heat of magnetorheological fluids (MRFs) subjected to shear mode operation and its effect on the structure. To begin, we present a novel model for measurement of slip differential heat to describe temperature rise of MRFs mainly caused by friction between magnetorheological particles. It includes two stages: (1) The micro-macro analysis of slip differential heat of MRFs including force, movement and heat between neighboring particles based on magnetic dipole and Hertzian contact theories, and (2) the further application to two basic disc-type and cylinder-type magnetorheological clutches combined with finite element simulations involving electromagnetic field and thermal analysis. The model takes into account the effect of each of the main influencing factors, such as the input current of excitation coil, the rotational speed difference of the clutches, the size and volume fraction of particles, the saturation magnetization of particles, and the structural size of the clutches, etc., on the slip differential heat of MRFs. Then the thermal structure analysis of MRFs comprising thermal deformation and equivalent thermal stress is carried out. Moreover, the effect of typical governing parameters on the slip power of MRFs and the influence of slip differential heat on the structure of MRFs are investigated individually. We show that such a model is effective in reflecting the temperature-slip time relation of MRFs. It is shown that the input current and the rotational speed difference have great effect on the slip power, and the slip differential heat has a certain influence on the micro-structure of MRFs.

Influence of parameters of a laser cleaning soil rust layer on the surface of ceramic artifacts.

The laser cleaning effect can be affected by many parameters, including laser power, scanning speed, laser repetition rate, and pulse duration, and the cleaning effect with these parameters is investigated. It is found that the cleaning effect is negligible for an infrared high-repetition nanosecond-pulsed laser with repetition rate from 100 to 400 kHz and pulse duration from 58 to 240 ns and is significantly related to the laser power and scanning speed. Moreover, the cleaning thresholds related to laser power and scanning speed for a soil rust layer on ceramic artifacts are measured under the step distance of 281.3 μm. The heat conduction equation and thermal stress equation are used to simulate the cleaning effect with the influence of these parameters, which is in good agreement with the experimental data.