Maximum Thermal Stress Research Articles

Thermal performance and thermal stress analysis of a supercritical CO2 solar conical receiver under different flow directions

To ensure the safe and efficient operation of the receiver in the concentrated solar power system, it is necessary to study its performance characteristics. Different from considering the thermal performance alone, this study comprehensively analyzed the thermal and mechanical performance of the solar receiver by using a coupled thermal-mechanical model. The critical factors including geometric parameters (aspect ratio H/D and angle ratio φ/φmax), operation parameters (mass flow rate, inlet temperature and direct normal irradiance (DNI)) and flow directions (up-flow and down-flow) were investigated. The results demonstrated that the optimum thermal efficiency achieved 85.67% when H/D = 1.5 and φ/φmax = 0.25, and the maximal thermal stress was 87.61 MPa. Increasing the flow rate from 0.01 kg/s to 0.06 kg/s improved the thermal performance, but increased the thermal stress. An opposite trend was observed when the inlet temperature increased from 573 K to 773 K. As the DNI increased from 200 W/m2 to 1000 W/m2, the maximal thermal stress increased by approximately 3 times, when the DNI >800 W/m2, the thermal performance would be deteriorated. Although the thermal performance under up-flow was better, the thermal stress was greater, the receiver should adopt an up-flow flow direction.

Adjustable multifocus laser separation scheme for thick glass with flexibly controllable thermal stress distribution

As a high-quality thick glass separation method, multifocus technology has proven its superiority. For a certain thickness of glass, there must be an optimal multifocus distance. But, the positions of the foci cannot be adjusted flexibly in current multifocus schemes without changing the energy proportions; the influence of thermal stress distribution on the quality of thick glass separation has not been systematically studied. An adjustable multifocus laser scheme has been proposed in this paper and proved by optical design, ray tracing, and experiment. First, finite element simulations have been performed to analyze the thermal stress distribution inside 20 mm glass. The simulation results show that thermal tensile stress exceeds the fracture threshold only at the upper and lower sides of the glass but not in the middle; the maximum thermal tensile stress reduces inside the glass when the symmetrical focal distance increases. Then, a series of separation experiments of 20, 22, and 25 mm thick soda lime glass have been carried out, which have adjusted foci positions to control the thermal stress distribution. The experimental results show that the deviation length decreases with an increase of the foci distances, and the optimal symmetrical foci distances reduce as the glass thickness increases.

Study on thermal-mechanical coupling of the ceramic layer in diesel engine piston with thermal barrier coating

Piston performance has an important on vehicle reliability, efficiency, and exhaust emissions. Application of the thermal barrier coating is an effective method for preventing heat transfer from combustion chamber to the substrate. The numerical model of thermal barrier coating piston is established by using finite element method, and a comprehensive thermal-mechanical result is given to determine the influence of ceramic thickness on ceramic layer and substrate. Compared with uncoated piston, the maximum temperature of substrate decreased by 3.34%, 4.09%, 5.19%, 5.95%, and 6.69%, corresponding to ceramic thicknesses of 0.15 mm, 0.2 mm, 0.25 mm, 0.3 mm, and 0.35 mm. The maximum thermal stress decreases from 78 MPa to 73 MPa. For ceramic layer of the thermal barrier coating piston, the maximum temperature appears at the top surface of the ceramic layer, while the maximum thermal stress occurs at the bottom of the ceramic layer. As the ceramics thickness increases from 0.15 mm to 0.35 mm, the maximum temperature of the ceramic layer increases from 322 ?C to 377 ?C, while the maximum thermal stress decreases from 95 MPa to 89 MPa. Thermal-mechanical coupled stress analysis shows that the maximum coupling stress occurs at the pinhole and its value does not change significantly. The thickness of the ceramic layer has little effect on the pinhole, but has a great influence on the ceramic layer.

マルチスケール構造体の熱応力問題に対する形状最適設計

This study proposes a shape optimization method to minimize the maximum thermal stress of the microstructures in a multiscale structure caused by thermal loading. Using the homogenization method, the homogenized elastic tensors and the homogenized thermal expansion coefficient tensors for the microstructures are calculated to link the microstructures to the macrostructure. The KS function is used to avoid discontinuities and singularities in the maximum thermal stress. Based on the problem formulation, the shape gradient functions are derived for shape optimization.

Обобщенные модельные представления теории теплового удара для локально-неравновесных процессов теплообмена

An open problem of the theory of thermal shock in terms of a generalized model of dynamic thermoelasticity under conditions of a locally nonequilibrium heat transfer process was considered. The model simultaneously includes three coordinate systems: Cartesian coordinates - a massive body bounded by a flat surface; spherical coordinates - a massive body with an internal spherical cavity; cylindrical coordinates - a massive body with an internal cylindrical cavity. Three types of intensive heating and cooling are considered: temperature, thermal, medium. The task is set: to obtain an analytical solution, to carry out numerical experiments and to give their physical analysis. As a result, generalized model representations of thermal shock in terms of dynamic thermoelasticity have been developed for locally nonequilibrium heat transfer processes simultaneously in three coordinate systems: Cartesian, spherical, and cylindrical. The presence of curvature of the boundary surface of the thermal shock area substantiates the initial statement of the dynamic problem in displacements using the proposed corresponding "compatibility" equation. The latter made it possible to propose a generalized dynamic model of the thermal reaction of massive bodies with internal cavities simultaneously in Cartesian, spherical and cylindrical coordinate systems under conditions of intense thermal heating and cooling, thermal heating and cooling, heating and cooling by the medium. The model is considered in displacements on the basis of local non-equilibrium heat transfer. An analytical solution for stresses is obtained, a numerical experiment is carried out; the wave nature of the propagation of a thermoelastic wave is described. A comparison with the classical solution is made without taking into account local non-equilibrium. On the basis of the operational solution of the problem, design engineering relations important in practical terms for the upper estimate of the maximum thermal stresses are proposed.

Laser Effect on a Pathologically Altered Capsule of the Lens of the Eye

One of the current areas of application of lasers in ophthalmology is cataract surgery and reducing the number of negative reactions to surgical intervention. In the postoperative period, clouding of the lens capsular bag and the risk of contraction capsular syndrome associated with changes in the biomechanical properties of the lens and capsular bag system are often observed. In the work, the biomechanics of such system were studied. Lenses that were placed in a 10% formalin solution to create cataract-simulating opacity for various amounts of time were studied by optical-coherent tomography, speckle-interferometry method and with fiber-optics setup for scattering dynamics registration. It was shown that speckle interferometry technique is sensitive to structural changes of lenses due to formalin exposure, which makes tissue more elastic and less transparent. OCT shows the same result and is more sensitive to the changes of laser wavelength. In addition, theoretical studies were carried out and have shown that changing laser wavelength can be dangerous for the integrity of the capsule film during medical intervention due to increase of maximum thermal stress.

The influence of initial shaft resistance mobilisation in the response of seasonally, thermally-activated pile foundations in granular media

The thermal-activation of pile foundations for use within shallow geothermal energy systems has received much attention and the results from various studies have allowed the development of a broad understanding of the thermo-mechanical behaviour of thermally-activated (TA) pile foundations. One area that requires further attention is the clarification of the foundation response under seasonal cyclic thermal loading. This study systematically assesses the impact of balanced cyclic thermal loading in relation to the initial mechanical loading, for isolated floating piles and pile groups in a frictional soil medium. The pile thermal response was evaluated for differing levels of mobilisation of the shaft resistance with respect to the initial mechanical loading and for piles at varying spacing based on a unit cell approach. Isolated piles with high shaft mobilisation were found to develop significant irrecoverable settlement during thermal cycling however the maximum thermal stress was similar irrespective of the initial shaft mobilisation. These results are remarkably similar to those reported in small scale tests of TA piles in sand, confirming that the behaviour reported in these is likely to be due to the result of low shaft restraint, rather than thermally-induced loss of resistance on the pile–soil interface. On the other hand, piles in close proximity were found to behave quasi thermo-elastically at the same initial mechanical load, which is attributed to an alteration in mobilised pile resistance due to pile–soil–pile interference under the initial mechanical loading and, to a lesser extent, thermal activation of the ground between the piles both of which reduce the relative movement between the pile and the soil. This pile group thermal effect has major beneficial implications for the geotechnical and structural design of TA pile foundations.

Design and Fabrication of Leadless Package Structure for Pressure Sensors

Abstract Silicon piezoresistive pressure sensors can only operate below 125 °C due to the leakage current of the PN junction. However, silicon-on-insulator (SOI) high-temperature pressure sensors use SiO2 for total dielectric isolation to solve this problem. At present, SOI high-temperature pressure sensors mostly use lead bonding package structure, with gold wire to lead the electrical signal and silicone oil as the protection medium, but the working temperature of silicone oil is limited to about 150 °C. In this paper, the leadless package structure is designed using pressure conduction on the backside of the chip and replacing the gold wire with sintered silver paste. The materials and dimensions of the leadless package structure are determined and then obtained a complete package structure through manufacturing. The reliability of the leadless package structure after silver paste sintering was verified by finite element analysis, and the results showed that the thermal stress caused by high and low-temperature cycles in the leadless package is minimal and does not affect the sensitivity of the pressure-sensitive chip. The size of the leadless package structure was optimized by Taguchi orthogonal method, and the maximum thermal stress was effectively reduced. Also, the key factors affecting the thermal stress of the leadless package in the package structure were identified by the variance number analysis method. The optimized leadless package structure size was remanufactured, and the sintered package structure was tested. The data show that the sensitivity of the pressure sensor is 30.82 mV/MPa with a nonlinearity of less than 0.4% full-scale (FS).

Fe3O4 Nanoparticles with Carboxylic Acid Functionality for Improving the Structural Integrity of Whole Vitrified Rat Kidneys

The successful rewarming of cryopreserved organs has always been a big challenge for the cryopreservation technology aimed at improving the shortage of available organs for transplantation. The traditional water bath rewarming produces more obvious devitrification and thermal stress damages, resulting in negative effects on the organ structure and physiological function. Nanowarming technology via induction heating of iron oxide nanoparticles for rewarming large-volume frozen biosamples is a promising strategy to overcome related problems. In this study, Fe3O4 nanoparticles modified with carboxylic acid are used for nanowarming to rewarm the whole frozen kidney. The key steps including loading and elution of the cryoprotectant and magnetic nanoparticles (mNPs), vitrification of large-volume samples, and nanowarming of the whole kidney are explored in detail to achieve whole kidneys with a more integrated structure. Compared with water bath thawing, the nanowarming method could reduce the maximum thermal stress of the whole kidney by 2 orders of magnitude and has enough rewarming rate to avoid the devitrification phenomenon, so as to obtain a lower cell apoptosis rate, a more integrated vascular network, and a lower residual amount of mNPs inside the kidneys after elution. The optimization of the nanowarming method for the whole kidney could provide effective guidance for the large organ cryopreservation in clinical transplantation.

Constructal design for the layout of multi-chip module based on thermal-flow-stress coupling calculation

The thermal-flow-stress coupling model of multi-chip module with uniform heat generation under natural convection condition is established. Taking the chip aspect ratio and edge distance as design variables, a comprehensive performance indicator considering the maximum temperature, maximum thermal stress and maximum deformation is constructed to optimize the layout of chips with the constraints of the total occupied areas of printed circuit board and chips according to constructal theory. The results show that the comprehensive performance indicator decreases monotonically with the increase of the chip aspect ratio under the constraints of equal spacing, hence the chips should be designed as thin as possible according to the design requirements. Releasing the constraint of equal spacing, the comprehensive performance indicator increases monotonically with the increase of the edge distance when the chip aspect ratio is constant; the comprehensive performance indicator first decreases and then increases with the increase of chip aspect ratio when the edge distance is constant. The comprehensive performance indicator of the multi-chip module can be reduced by 0.65, the maximum temperature, the maximum thermal stress and the maximum deformation can be reduced by 6.28%, 9.44% and 9.66%, respectively. The methods and results herein could provide theoretical guidance for the thermal design of layout of multi-chip module.

Effect of actual frequency features generated in machining process on the temperature and thermal stress of potassium dihydrogen phosphate crystal

Temperature and thermal stress can affect the laser-induced damage threshold of Potassium Dihydrogen Phosphate (KDP) crystals. In this work, actual frequency features in the machined surface of KDP crystal are extracted and reconstructed by power spectral density and continuous wavelet transform methods. Wave optics theory is used to calculate the effect of surface frequencies on the temperature and thermal stress of KDP crystals exposed to laser irradiation at a wavelength of 1.064 µm and the power of 200 MW/μm2 in 1 ns. According to the results, the temperature and thermal stress increase once the wavelength of surface frequency approaches the incident laser wavelength. With a further increase in the wavelength (1.064–20 µm), maximum temperature and thermal stress exhibit a tendency to decline. When the wavelength of surface frequency exceeds 60 µm, maximum temperature and thermal stress keep constant with changing surface frequency. Maximum temperature and thermal stress are found to be proportional to the amplitudes of frequency features at the same wavelength. Furthermore, temperature affected by actual frequency is 4–12 K higher than that in the case of ideal frequency at the same wavelengths and amplitudes. With increasing wavelength, the positions of maximum temperature and thermal stress extend to the interior of KDP crystal.

Performance improvement of variable-angle annular thermoelectric generators considering different boundary conditions

Practical applications of thermoelectric generators are impeded by their low thermoelectric conversion efficiency, and improving the efficiency is vital for the advancements of thermoelectric technology. In this paper, a novel method is proposed for the performance analysis and improvement of the annular thermoelectric generators with variable-angle PN legs (VATEGs). The influence of the PN leg angle on the output performance of the VATEG is investigated by introducing an angle function. Given the volume of the PN legs, the relationship of output performance between the VATEG and traditional constant-angle ATEG (CATEG) is established under different boundary conditions based on a proposed generic model of VATEG. The results are verified numerically using the finite element method. Using the model, it is shown that the output performance of the VATEG is significantly affected by the shape of the PN leg. Finally, the thermal stress on the PN leg is next investigated using a high-fidelity 3D model of the variable-angle PN legs implemented in COMSOL, and it is found that the shape difference has a considerable influence on the thermal stability of VATEG. Under the condition of constant heat flux on the hot side and constant temperature on the cold side of the thermoelectric modules, it shows that when the radius factor is 2, the output performance can be improved by 35% with the designed VATEG, at the expense of 30% higher maximum thermal stress on the PN legs.

Thermoelastic Analysis of Annular Sector Plate Under Restricted Boundaries Amidst Elastic Reaction

An analytical framework is developed for the thermoelastic analysis of annular sector plate whose boundaries are subjected to elastic reactions. The exact expression for transient heat conduction with internal heat sources is obtained using a classical method. The fourth-order differential equation for the thermally induced deflection is obtained by developing a new integral transformation in accordance with the simply supported elastic supports that are subjected to elastic reactions. Here it is supposed that the movement of the boundaries is limited by an elastic reaction, that is, (a) shearing stress is proportional to the displacement, and (b) the reaction moment is proportional to the rate of change of displacement with respect to the radius. Finally, the maximum thermal stresses distributed linearly over the thickness of the plate are obtained in terms of resultant bending momentum per unit width. The calculation is obtained for the steel, aluminium and copper material plates using Bessel's function can be expressed in infinite series form, and the results are depicted using a few graphs.

Thermal stress reduction strategy for high-temperature power electronics with Ag sintering

Thermal stress caused by the coefficients of thermal expansion (CTE) mismatch of materials is the main failure mechanism in power electronic packaging. High junction temperature (Tj) would induce larger thermal stress and accelerate failing process. In this paper, two packaging strategies to reduce thermal stress of power module for high-temperature operation were presented based on organic-free sintered Ag bonding and wireless packaging structuring: reduce elastic modulus of sintered Ag layer by changing sintering parameters; and reduce the CTE mismatch by changing the ribbon material. Finite-element analysis (FEA) simulations confirmed that these strategies can effectively reduce the maximum and average thermal stress in power electronics packaging. Furthermore, by combining these two strategies, high-temperature power cycling test indicated that the wireless packaging with Cu30Mo70 ribbon and 5 MPa sintering pressure exhibited excellent durability and reliability in the temperature swing at the junction (ΔTj∆Tj) over 150 K.

Design a New Type of Laser Cladding Nozzle and Thermal Fluid Solid Multi-Field Simulation Analysis.

Coaxial powder feeding technology in the field of metal additive manufacturing is booming. In this paper, a new laser cladding nozzle with powder feeding channels of inner and outer rings is designed. The nozzle works with a new kind of laser, which is a new heat source with an inner beam and outer beams. The water-cooling channels are simulated in Ansys Workbench. The simulation results present the temperature distribution of the working nozzle and the velocity of the cooling water. The thermal dilation of the nozzle in the working environment is also simulated. The results show that the loop water cooling channel could effectively reduce the high temperature of the nozzle down to about 200 °C. In addition, it could well restrain the thermal deformation of the nozzle lower to 0.35 mm. The equivalent stress of most parts is controlled under 360 MPa. Then, the powder flows of the inner and outer rings of the multiple powder feeding channels are simulated in Ansys Fluent. The convergence effect of the powder flow could be assumed and some significant parameters, such as the velocity, are acquired. The results present that these multiple powder feeding channels could realize the generation and removal of removable supports of workpieces with highly complex shapes and achieve a large processing range and good processing efficiency. The velocity of the powder flow at the outlet is elevated to about 5 mm/s. Then, the thermal cladding states under the new laser heat source of the powder are simulated in Workbench. The temperature of the melting process and the thermal deformation and the equivalent stress/strain of the additive parts are obtained in the emulation. The results emerge that the powder melting range and the ascending temperature of the melting pool are improved with this effect. The greatest temperature of the melting pool is about 2900 °C in the machining process, and the maximum thermal equivalent stress is 1.1407 × 1010 Pa.

Analysis of crack on the labyrinth part of the gas turbine engine

The main objective of this study is to analyze the crack developed in the Labyrinth seal of a gas turbine engine and to determine the number of cycles required for the crack to grow to various lengths. Here, ANSYS Mechanical APDL is the tool to carry out the crack analysis. The crack is modelled and analyzed according to the principles of Linear Elastic Fracture Mechanics (LEFM) theory by Griffith and Paris law because of the negligible plasticity found at the crack tip. Here, the model is analyzed with and without the crack for the temperature and stress profile. The stress intensity factor is obtained using the ANSYS software. The information is derived from the graph of crack propagation rate as a function of stress intensity factor of Haynes 25 material which was used to analytically determine the number of cycles the labyrinth seal could sustain. The maximum and minimum temperatures were 1132 °C and 250 °C over a span of 10 mm length, which was the region of interest. The maximum thermal stress generated was around 1430 MPa at crack tip region for full crack model. The stress intensity factor was obtained was found to be 18.7 MPa√mm. The crack propagation rate was calculated analytically over a range of 2–4 mm with an increment of 0.5 mm. The number of cycles required for the crack to propagate over the successive 0.5 mm intervals was 97, 82, 71 and 63 cycles respectively.

Research on Analysis Method for Performance of Fuel Element Based on Thermal-Fluid-Solid Coupling

The existed fuel performance analysis tools are not applicable to the hollow prism fuel with special structure and operation conditions, so a new method is needed to assist the fuel design and evaluation. In this paper, a 3D fluid-thermal-solid coupling analysis method was established based on the COMSOL software by conjugate heat transfer technology and the equivalent material property models for particle reinforced composites, and had been verified with the General Electric data. Temperature and thermal stress of fuel elements in different sizes and axial power distributions were calculated with this method. The results show that maximum temperature exists at the side edge of prism, and maximum thermal stress exists at the thinnest inner wall. The thinner and longer fuel has the smaller maximum thermal stress and temperature. Flatting the axial power distribution in the entrance region can decrease the maximum thermal stress and temperature slightly. This analysis method can be used to optimize the design of the hollow prism fuel element.

U-type unileg thermoelectric module: A novel structure for high-temperature application with long lifespan

Strong thermal stress caused by high temperature and difference of thermal expansion coefficient (CTE) will negatively influence the lifespan of the thermoelectric module. In this work, a new high-temperature CaMnO3-based U-type unileg thermoelectric module, combining a unileg structure with pn-junction, is proposed and investigated. The novel design avoids the device failure due to different CTEs and high temperature gradients. As a result, the maximal thermal stress (σmax,TEM) of 3.31 GPa and fatigue life of 41686 cycles are 46 % and 132 % of those of traditional modules at 6 W and 300 K, respectively. To further relieve stress concentration, the effect of rounded corners (ru, rl), Ag layer thickness (HAg) and length of right legs (LR), have been studied. It has been found that larger ru, and rl are suitable to relieve the local stress concentration, and the lowest σmax,TEM and highest power (Pmax) are achieved at (ru,rl)=(0.1,0) and (0,0.5). Moreover, larger LR and HA are beneficial for mechanical properties by decreasing the peak stress and dispersing the high thermal stress regions, while module performance is improved at lower LR and HAg. Results obtained from this U-type unileg thermoelectric module should influence and guide the design and optimization of high-temperature thermoelectric generators.

Simulation and Analysis of Thermal Stress and Sintering Warpage of Planar Solid Oxide Fuel Cells

Solid oxide fuel cell (SOFC) is one of the new energy conversion technologies producing electricity and heat from fuel and oxidant through an electrochemical reaction. The high operating temperature has many advantages including high efficiency, flexible fuel adaptability and low emissions. However, it has also some drawbacks, e.g., thermal expansion mismatches among the involved materials, particularly when the temperature reaches around 1400 oC during the sintering process, which may cause non-uniform distribution of thermal stress and even further deformation and warpage observed in the cell manufacturing steps.A three-dimensional CFD (computational fluid dynamics) simulation model is developed to study the thermal stress distributed in the sintered function layers of the anode-supported planar SOFC unit cells (10×10 cm2) using a finite element method. Five layers are included, i.e., cathode and its separation layer (GDC/LSCF, 70 µm), anode support and active layers (Ni/YSZ, 550µm), and electrolyte layer (YSZ, 30 µm) between them. In terms of the thermal stress and deformation, the predicted results are presented and discussed for the sintered unit cells with different angels located around the four cornels.It is found that the maximum thermal stress occurs at the interface between the electrode and electrolyte; the magnitude and distribution of thermal stress at the interfaces are closely related to the material thermal properties; the maximum deformation about 13 mm in the thickness direction is predicted for the 90-angel shaped cornels at the sintering temperature 1400 oC, which is bigger than that for the case with the circular shaped cornels; the deformation magnitude depends not only on the maximum thermal stress, but also the difference between the maximum and minimum thermal stress. The findings and predicted results may be applied for optimization of design and sintering conditions for SOFC unit cells.AcknowledgementsThis work is supported by the National Key Research and Development Project of China (2018YFB1502204, 2018YFB1502203, 2018YFB1502205), the Ningbo major special projects of the Plan “Science and Technology Innovation 2025” (2018B10048). Figure 1

Effects of Flow Channel Arrangement and Electrolyte Thickness on Thermal Stress for Planar Solid Oxide Fuel Cell Stacks

Typical operating temperature for solid oxide fuel cells (SOFC) is between 700~800°C. A large temperature gradient and thermal stress caused by internal losses and electrochemical reactions may cause SOFC stack performance degradation and even structural damage, which has become a hindrance to its applications.In this study, a three-dimensional multiphysics CFD (computational fluid dynamics) model is developed and applied for a planar SOFC stack to study the temperature and thermal stress distribution, as well as effects of structure and design parameters, including the flow channel arrangement (e.g., co- and count-flow) and thickness of the electrolyte layer. The stack is composed of three-unit cells, metallic interconnect layers, sealing and anode/cathode current collectors.The simulation results reveal that the temperature difference in the counter-flow mode is smaller and the thermal stress is lower than those in the co-flow mode. The overall performance of the stack is better when the electrolyte layer thickness becomes smaller, but the stack temperature and the temperature gradient become higher. In addition, a large temperature gradient due to the thin electrolyte layer leads to a significant increase of the thermal stress in the electrolyte. The findings and research method from this study can be applied to optimize the design of the stack structures, by consideration of the maximum thermal stress and its distribution.AcknowledgementsThis work is supported by the National Key Research and Development Project of China (2018YFB1502204), the Ningbo major special projects of the Plan “Science and Technology Innovation 2025” (2018B10048).