Thermal Failure Research Articles

Thermal property and failure behaviors of Gd doped LaZrCeO coatings with feathery microstructure

LaZrCeO coatings are promising candidates to substitute Y2O3-stabilized ZrO2 in advanced gas turbine engines. In this study, Gd doped LaZrCeO coatings were deposited by electron beam physical vapor deposition. This study focuses on the phase, microstructure, thermal property, and thermal durability of (La1-xGdx)2(Zr0.7Ce0.3)2O7 coatings. The as-deposited coatings show relatively good thermal shock life and thermal cycling life. The broken regions are observed on the interface of thermal barrier coatings. The failure behaviors are relevant with crack evolution and thermally grown oxide growth. This study might guide the investigation of advanced coatings under high temperature.

Performance of Two-Dimensional Functionally Graded Anode Supported Solid-Oxide Fuel Cells

Abstract Ceramic materials used in solid-oxide fuel cells (SOFCs) are subjected to high thermal stresses which is a result of the unequal thermal expansion coefficient of different layers. As a result, SOFCs are susceptible to failure at elevated temperatures, and therefore the maximum operating temperature is limited. Consequently, the power density is limited as well. Fuel cells with electrodes that have graded compositions in the thickness direction have been investigated to control the thermal expansion. In this study, two-dimensional grading is proposed for the electrodes and compared with the one-dimensional grading in terms of thermal stress and performance. A comprehensive model is developed for high-temperature SOFCs that include the momentum, species, energy, and charge transport equations. Furthermore, the bilinear elastoplastic model is used for the calculation of thermal stresses and failure of solids. Two-dimensional functionally graded electrodes are studied in which the grading is implemented in the thickness and length directions. Results indicate that continuous one-dimensional grading functions reduced thermal stresses by 40% for m = 0.8 compared with conventional electrodes. It also improved the electrochemical performance, as the maximum power density increased by 15%. For the 2D piecewise linear grading function, a further improvement of reducing thermal stresses by an extra 16.5% is obtained. Two-dimensional graded SOFCs can therefore operate at higher temperatures safely in terms of thermal stresses. This creates an opportunity to fabricate high-temperature, compact SOFCs for high-power applications.

Numerical simulation of the mixing behaviour of hot and cold fluids in the rectangular T-junction with/without an impeller

• The thermal mixing features in a T-junction with/without an impeller are compared at M R = 0.49. • The mixing behaviour with the impellers are analyzed at different blade numbers and diameters. • The temperature uniformity parameter is defined to investigate the mixing uniformity in the T-junction. • The criterion of mixing length is proposed according to the mass mean temperature. Thermal stratification is the main reason for thermal fatigue failure in the rectangular T-junction. An impeller is set in the mixing zone in the rectangular T-junction to improve the mixing behaviour of hot and cold fluids under the deflecting jet with the inflow momentum ratio of M R = 0.49. Blade numbers and blade diameters are investigated for the range of N p = 2 ∼ 4 and D p * = 0.33 ∼ 0.8, respectively. By the application of large-eddy simulation, the flow fields and temperature fields are obtained in this work. The flow fields show the mixing behaviour between hot and cold fluids can be promoted by setting the impeller with a constant rotation speed, and three flow patterns including the wall jet, deflecting jet and impinging jet will be observed in the T-junction, which is effective for breaking the thermal stratification. Temperature fluctuation and temperature gradient calculated by mean temperature are compared with that of no impeller. It is found that by adding the impeller the temperature gradient is reduced while the temperature fluctuations almost keep the same. The criterion of mixing length is proposed according to the mass mean temperature and the mixing lengths for different conditions are obtained, as well as the temperature uniformity parameter is proposed to evaluate the mixing degree in the T-junction. The results indicate that the relationship between the mixing length and blade diameter is not monotonic and the optimal operating point is around D p * = 0.5 for the impeller of 2 blades. By combining the temperature fields and pressure drops, the results indicate among N p = 2 ∼ 4, the impeller of 3 blades is the best choice. Temperature power spectrum density is also investigated and it is possible to control the critical frequency of temperature fluctuation in the duct by changing the blade numbers.

Research on the thermal failure mechanism of an opposed-contact gallium arsenide photoconductive semiconductor switch in avalanche mode

The switching mechanism and the thermal process of a gallium arsenide (GaAs) photoconductive semiconductor switch (PCSS) with an opposed-contact is investigated by numerical simulation of the two-dimensional (2D) structure using temperature-dependent physical parameters of the carriers in GaAs. Triggered by a low-energy laser pulse, the PCSS switches on due to the formation and evolution of multiple powerful avalanche domains. The 2D evolving characteristics of the avalanche domains on the two sides of photogenerated plasma during the switching transient are comparatively analysed. It is found that the ionizing centre of each domain moves with the drift of accumulated electrons inside the domain. Meanwhile, the evolution of avalanche domains causes an obvious thermal effect along the drift path of ionizing centres during the switch-on stage of PCSS. Then, the temperature keeps increasing at the edge of the anode and cathode although the switching current starts dropping after the conduction of PCSS, and finally peaks at ∼491 K and ∼541 K, respectively. The simulation results indicate that the 2D filamentary current flows along the drift path of ionizing centres inside the avalanche domains, which finally leads to filamentary erosion after continuous operation of the PCSS. On the basis of numerical simulation, an experiment with opposed-contact GaAs PCSS with 2.5 mm gap at the bias field of ∼90 kV cm−1 is performed. The thermal erosion is found to initially accumulate at the edge of the electrodes and then spreads along the current channel into the GaAs substrate, which is in accordance with the simulation results and analysis.

Acceleration of selective lithium ion transport of PAES-g-2PEG self-assembled flexible solid-state electrolytes for lithium secondary batteries

The solid-state lithium secondary battery (LiB) is a promising alternative to resolve the drawbacks of conventional LiB, but it still suffers from low ionic conductivity and mechanical instability. Accordingly, the flexible self-assembled solid electrolytes (SEMs) based on poly(arylene ether sulfone) (PAES) grafted with double poly(ethylene glycol) (PEG) (PAES-g-2PEG) is prepared to maximize the ion conductivity by creation of large PEG conducting domains without thermal and mechanical failure via reinforcement of PAES matrix. The addition of ionic liquid (IL) along with ethylene carbonate (EC) results in a significant improvement in a selective lithium ion conductivity because of the improved molecular mobility of PEG segments and formation of [Li+(EC)x, (x = 1–5)] complexes for feasible single-ion transport. Consequently, the PAES-g-2PEG membranes containing IL-EC mixture (7:3, v/v) achieve the ionic conductivity of 1.15 × 10−3 S cm−1 and Li-ion transference number of 0.51 at room temperature. The PAES-g-2PEG membranes exhibit excellent mechanical flexibility and thermal stability with the onset degradation temperature of 250 °C. Due to the significant suppression of polysulfide permeation as well as high conductivity, the Li/SEM/S cell assembled with PAES-g-2PEG membranes delivers the discharge capacity of 987 mAh g−1 with 98.6% of coulombic efficiency, retaining 94.7% after 200 cycles at 0.2 C-rate.

Investigation of thermal performance of Maxwell hybrid nanofluid boundary value problem in vertical porous surface via finite element approach

The study of thermo-physical characteristics is essential to observe the impact of several influential parameters on temperature and velocity fields. The transportation of heat in fluid flows and thermal instability/stability is a charming area of research due to their wider applications and physical significance because of their utilization in different engineering systems. This report is prepared to study thermal transportation in Maxwell hybrid nanofluid past over an infinite stretchable vertical porous sheet. An inclusion of hybrid nanofluid is performed to monitor the aspects of thermal transportation. Keeping in mind the advantages of thermal failure, non-Fourier theory for heat flux model is utilized. Aspects of external heat source are also considered. The mathematical formulation for the considered model with certain important physical aspects results in the form of coupled nonlinear PDEs system. The obtained system is reduced by engaging boundary layer approximation. Afterwards, transformations have been utilized to convert the modeled PDEs system into ODEs system. The converted nonlinear ODEs system is then handled via finite element method coded in symbolic computational package MAPLE 18.0. Grid independent survey is presented for the validation of used approach and the comparative analysis has been done to confirm the reliability of obtained solution. The obtained solution is discussed and physical aspects have been explored and recorded against numerous involved influential variables. Motion into hybrid nanoparticles and nanoparticles becomes slow down versus higher values of Forchheimer and Darcy’s porous numbers. Thermal growth is enhanced for the case of hybrid nano-structures rather than for case of nanofluid. Thickness regarding momentum layer is dominated for hybrid nanoparticles rather than case of nanoparticles.

Monitoring thermal defects in rail and rail joints using piezo impedance-based structural health monitoring (PISHM)

Rail track derailment has been proven to be the cause of most of the rail accidents in recent years. High-temperature strains in railways caused by rail traction and thermal variation are the main causes of derailment, which lead to buckling. The likelihood of passenger deaths and maintenance costs will be reduced if thermal strains and failure in rails are detected early. This research attempts to provide a preventative strategy for detecting thermal strains and deformation caused by temperature fluctuations at railways. Using the electromechanical impedance (EMI) technique, piezoelectric sensors were used to acquire piezo coupled structural signatures for lab-sized rail samples, i.e. plain rail and rail joints, for gradual temperature escalation and repeat heat cycle. The experimental conductance signatures were obtained for the incremental rise in temperature (30–80 °C) in ambient conditions, and repetitive thermal cycles. To better diagnose structural problems induced only by the effect of heat on the host structure, thermal compensation is proposed. The piezo–coupled signatures for thermal changes in rail and rail junctions (weld and bolt) were found to be particularly effective in detecting incipient structural alterations for both steady and cyclic temperature variations. Statistical damage index was used to quantify the damage for all types of rail-joint bar caused due to temperature variation. Overall, this study has paved an experimental technique that can be used to detect early damage in rail and rail joints due to thermal loading.

In-depth study on diffusion of oxygen vacancies in Li(NixCoyMnz)O2 cathode materials under thermal induction

It is generally believed that an increase in Ni content will severely reduce the lattice structure stability of the cathode material, causing it to release more oxygen during thermal induction. However, the thermal degradation mechanism at the microscopic level remains unclear, which hinders the safety design of cathodes. In this work, we focus on the secondary particles of different Li(NixCoyMnz)O2 cathodes, report the formation and condensation of oxygen vacancies on the surface in detail, and quantitatively analyze the oxygen vacancy concentration distribution inside the particles after thermal failure. The results reveal that the increase of Ni content promotes the oxygen vacancies to diffuse deeply from the surface of the secondary particles to the bulk under thermal induction, resulting in an increase of oxygen vacancy concentration in the bulk of the secondary particles and the release of more oxygen. When the Ni content x in Li(NixCoyMnz)O2 increases to 0.8, both the surface layer and bulk exhibit high oxygen vacancy concentrations, leading to an overall failure of the secondary particles. Furthermore, we suggest that the formation and evolution of intergranular cracks inside the secondary particles depend on the oxygen vacancy concentration gradient. Our work provides a new idea for future research on the thermal stability of cathode and the thermal safety design of Ni-rich cathode materials.

The Effects of Temperature and Solute Diffusion on Volume Change in Sn-Bi Solder Alloys

The different rates of thermal expansion of the many materials that make up an electronic assembly combined with temperature fluctuations are the driver of the thermal fatigue failure of solder joints. A characteristic of the Sn-Bi system, which provided the basis for many of the low process temperature solder alloys that the electronics industry is now adopting, is the very temperature-sensitive solubility of Bi and Sn in the other phase. In this study, in situ synchrotron powder x-ray diffraction was used to characterize the temperature dependence of the lattice parameters of the βSn and Bi phases in Sn-57wt%Bi and Sn-37wt%Bi. The effects of temperature and solute were separated by comparing with the data from pure βSn and pure Bi and verified using density functional theory calculations. Furthermore, the coefficients of thermal expansion of βSn and Bi during heating were also derived to reveal the thermal expansion behavior.

Temperature prediction of substation equipment based on back-propagation neural network -simulated annealing

The substation is an important part of the smart grid. The stable operation of electrical equipment in the substation is related to the stability of the grid. According to the statistical results, among the common substation equipment failures, thermal failures have a larger proportion. Thermal faults can be monitored through the surface temperature of the equipment, and predicting the changing trend of the equipment temperature in advance is of great significance for reducing equipment faults in substations. For this reason, this paper proposes a method for predicting the temperature of substation equipment based on BP neural network-simulated annealing algorithm, using equipment parameters, environmental information parameters, etc. to predict the temperature of electrical equipment in the substation, so as to realize early warning of thermal faults in substation equipment. Through comparative analysis, it is verified that the method proposed in this paper can accurately predict the temperature of substation equipment, which provides strong guarantee and support for the safety management of substation electrical equipment.

Generalized Burnout Model for Circuit Simulation

Accurate analysis of susceptibility of circuits from damage due to electrostatic discharges (ESDs), electromagnetic pulses, and lightning effects is required to ensure reliable operation of electronic devices and systems. A generalized theory of calculating semiconductor device thermal failure was developed for the use in circuit simulation. Thermal convolution integrals were developed from simple physical assumptions and used to predict device damage. This basic model was normalized to a generic failure function, and then, generalized to better match empirical test data of semiconductor device failure. This representation was transformed into the Laplace domain and further generalized to incorporate the steady-state thermal response of the device and provide numerical stability. The thermal convolution integral representation was used to derive a simple expression for Wunsch–Bell burnout parameters from ESD ratings of devices. A model was developed using the Laplace domain representation of the device failure theory. This circuit model allows for burnout predictions using commercial circuit simulation software and follows the theoretical equation with 2% error. The developed equations and circuit models allow for a simple susceptibility analysis of circuits using commercial software and readily available ESD ratings of semiconductor devices.

Dynamic thermophysical modeling of thermal runaway propagation and parametric sensitivity analysis for large format lithium-ion battery modules

Thermal runaway and its propagation are bottlenecks for the safe operation of lithium-ion battery systems. This study investigates the influence of characteristic thermophysical parameters during battery thermal runaway, such as the self-heating temperature (T1), triggering temperature (T2), mass loss, and critical heat transfer power (Pc), on the failure propagation behavior in a battery system. A parametric study is conducted based on a failure propagation model. This model not only captures the behavior of thermal failure, but also accounts for the changes in the thermophysical parameters before and after thermal runaway. The results of the modeling analysis demonstrate that increasing T1 and T2 can both delay the thermal runaway propagation. The delay achieved by increasing T2 is greater than that observed by increasing T1. The peak heat transfer power Pc plays a critical role in delaying the thermal runaway propagation. When the peak heat transfer power level is greater than Pc, thermal runaway propagation mainly results from heat transfer, whereas when the peak heat transfer power level is less than Pc, thermal runaway propagation mainly arises from self-heating. This study reveals the dynamic mechanism of thermal runaway propagation within a battery module, thus providing guidance for the safety design of battery systems.

Feasibility study for the integration of optical filtration and nano-enhanced phase change materials to the conventional PV-based solar systems

The overheating problem of the PV panels and its consequences (e.g. electrical performance degradation, thermal failure, and the short life spans) opened the gate to many studies that are aiming to solve this problem. The most recent studies have proposed replacing the conventional PV and PV/Thermal (PVT) systems with new systems that depend on optical filtration (OF) and nano-enhanced phase change materials (nanoPCM). This work provides a combined review, for the two approaches with a comprehensive numerical assessment for the feasibility of using OF and nanoPCM in different integration to the conventional single PV and hybrid PVT systems. The results declared that using OF, side by side, with the cooling fluid (CF) appeared as one of the best ways for PV cooling. It has allowed for a reduction of 42.1% and 6.3%, on the average PV temperature, compared to the conventional PV and PVT systems, respectively. To the moment, solar obstruction put the system with OF as more thermally, while less electrically, efficient compared to the PVT system. Apart from the OF, using nanoPCM, at low nanoparticle loadings, is not recommended as it can increase the average PV temperature by 81.2% at five suns solar concentrations. However, the enriched nanoPCM (high loadings) is considered an excellent way for thermal regulation to achieve a low-temperature gradient along with the PV panel. A more detailed explanation of the results is presented in the manuscript. This work is considered the first to cover such comparisons that result in an understanding of the pros and cons of the OF and nanoPCM and their expected value when integrated to different PV-based hybrid solar systems.

A Study on the Interface Diffusion of In<sub>2</sub>O<sub>3</sub>/ITO Multilayer Thin-Film Thermocouple

In2O3/ITO multilayer thin film thermocouple is a new type of semiconductor thin-film thermocouple, which has broad application prospects. The interface diffusion between the layers is the main cause of its thermal oxidation failure. In this paper, an interface diffusion model of multilayer films is established based on Fick's second law. A sample of In2O3/ITO thin-film thermocouple was prepared, then designed and conducted high temperature test. According to the test results, the diffusion of substances between the film layers was analyzed. Based on the established interface diffusion model, a simulation calculation is carried out. The influence of interface diffusion on the life of In2O3 and ITO sensitive layer was quantitatively analyzed.

LaYZrO/YSZ Double Ceramic Layer Thermal Barrier Coatings by EB-PVD: Thermal Performance, Morphology and Failure Behavior

LaYZrO/YSZ Double Ceramic Layer Thermal Barrier Coatings by EB-PVD: Thermal Performance, Morphology and Failure Behavior

Triboelectrification in moving particle flow

Triboelectrification in an insulative granular system is a common natural phenomenon, but until now it has not been well understood. The space on the moon or Mars is suffused by a large amount of fine dust. These tiny dust particles are so adhesive that they can easily stick to any exposed surfaces, which may provoke serious problems, such as reducing the efficiency of solar panels, and resulting in the thermal control failure and the false instrument readings. In recent years, dust removal by using an electrodynamic field is considered as an effective method to mitigate dust pollution. Research shows that the triboelectrification on the particle surface contributes most to the electrostatic source of lunar dust. Consequently, the study of the mechanism of triboelectrification is very important in removing dust particles. In this paper, an analytical model based on the high-energy electron hypothesis is developed to predict the triboelectric charge distribution among particles. The particle size dependence of the tribo-charge is obtained, and the influence of the size range on the tribo-charge probability is also demonstrated. An upper limit for the charge distribution is revealed, and its possible cause is discussed. The particle dynamics simulation is carried out to investigate the charge transfer during particle collisions, thereby verifying the prediction results obtained by theoretical analysis.

Thermal Cycling Behavior and Failure Mechanism of the Si-Hfo2 Environmental Barrier Coating Bond Coats Prepared by Atmospheric Plasma Spraying

Thermal Cycling Behavior and Failure Mechanism of the Si-Hfo2 Environmental Barrier Coating Bond Coats Prepared by Atmospheric Plasma Spraying

Імовірнісний аналіз теплової надійності вузлів цегляних стін житлових будівель

When the temperature of the inner surface of the enclosing structures falls below the dew point, moisture from the indoor air may condense on it. Thermal characteristics of building materials, outdoor and indoor air temperatures and dew points are random variables or processes. This necessitates a probabilistic assessment of the possibility of thermal failures by the criterion of condensate formation in areas of increased heat transfer of enclosing structures. This work is performed in order to analyze the probabilistic thermal reliability of the characteristic units of brick walls of residential buildings erected in the second half of the 20th century, in the design condition and after thermal modernization by installing additional facade insulation. To analyze the level of thermal reliability, six characteristic units of brick walls were selected. The nodes were analyzed in the initial state, taking into account the uniform facade insulation, as well as with additional local insulation of areas of increased heat transfer. The calculations were performed according to the previously developed author's method, which is based on estimating the probability of falling of the random temperature of the inner surface of the wall below the random temperature of the dew point. The initial data take into account the statistical characteristics of the following random variables: conditional heat transfer resistance of the wall in the zone of heat conduction, dew point temperature, indoor air temperature, outside air temperature for each month of the heating period. The result of the calculation is the probable annual duration of the state of thermal failure according to the criterion of condensate formation on the inner surface of the walls in the critical areas of the nodes. It is established that the units of brick walls with a thickness of 51 cm in the design condition have an insufficient level of thermal reliability. Uniform facade insulation allows to reduce the duration of thermal failures of three nodes from the six considered to values not exceeding 10 minutes during the year. In some areas of the other three nodes (adjacency of the side and top faces of the window, adjacency of reinforced concrete balcony slab) the duration of thermal failures remains unacceptably long even when performing additional local insulation of these areas.

Dissimilar metal weld failure of steam piping in a hydrogen unit of petroleum refinery

Steam generation from hot reformer effluent in a hydrogen unit of a petroleum refinery increases the refinery margin. Upstream and downstream piping in hydrogen plant were constructed by SA335 P22 (AS) and type SS304L (SS) materials, respectively. This paper reports failure of dissimilar pipe weld after six months of high pressure steam service. Visual inspection indicates several ratchet marks initiated from outer wall surface at heat affected zone (HAZ) of AS pipe accompanied with brittle fracture. Further, failed samples were examined for chemical analysis, micro-hardness, fractography & elemental analysis and microstructural analysis. Fractographic results indicated that the dissimilar weld was failed due to thermal fatigue. Moreover, microstructural analysis revealed the presence of martensite in AS HAZ region with higher micro-hardness. In-spite of fixed operating temperature at 600 °C, there was a difference in thermal expansion that induced large strain gradient at interface and result in low cycle thermal fatigue failure. Type 308L filler metal was directly employed for dissimilar welding without buttering at interface layer was the main cause of failure. The principal factors that were responsible for Dissimilar Metal Weld (DMW) failure are discussed with respect to Schaeffler diagram and correct welding procedure for failure prevention is proposed. It is further recommended to employ 309/309L filler metal at interface layer according to ASME codes & standards to avoid DMW failure.

Diagnosis and Classification Decision Analysis of Overheating Defects of Substation Equipment Based on Infrared Detection Technology

Substation equipment is not only the main part of the power grid but also the essential part to ensure the development of the national economy and People's Daily life of one of the important infrastructure. How to ensure its normal operation and find the sudden failure has become a hot issue to be solved urgently. For thermal fault diagnosis needs to classify and identify different power equipment first, this paper designed an SVM infrared image classifier, which can effectively identify three types of common power equipment. The classifier extracts HOG features from the infrared images of power equipment processed by the above segmentation and combines them with SVM multiclassification to achieve the purpose of improving the recognition accuracy. The experiment uses the classifier to identify three kinds of equipment, and the results show that the comprehensive recognition accuracy of the classifier is more than 95.3%, which is better than the traditional classification method and meets the demand for classification accuracy. In this paper, the traditional method of relative temperature difference is improved by using the temperature data of the infrared image, which can automatically judge the thermal failure level of electric power equipment. Experiments show that the diagnosis system designed in this paper can classify faults and give treatment suggestions while judging whether there are thermal faults for three types of power equipment, which verifies the feasibility and effectiveness of the substation infrared diagnosis technology designed in this paper.