Thermal Failure Research Articles

Thermal dynamic and failure research on an air-fuel heat exchanger for aero-engine cooling

This paper presents a novel air-fuel heat exchanger used for the cooled cooling air technology in aero-engines. The helical tube heat exchanger weighing 1.1 kg with an area density of 214 m2/m3 can cool the hot air down 260 K at the air flow of 0.3 kg/s with relative airside pressure drop less than 0.6%. Empirical correlations by multiplying a constant of 1.06 and 0.837 can well predict the pressure drop and convective heat transfer coefficient respectively for hot gas cross-flowing helical tube bundles. Furthermore, in the tube failure tests to simulate the fuel control system fault and flight mode conversion, the straight tube can work continuously for more than 360 s under the extremely high tube wall temperature of over 1200 °C in the heat flux sudden increase test, while the bent tube could continue to glow brightly for 30 min. Coke morphology and chemical composition analysis revealed that increased thermal stress caused by gradually thicker coke layer takes a major cause in the heat flux sudden increase test. The secondary flow in bent tubes can effectively improve the convective heat transfer performance and reduce the formation of coke deposition, thereby improving the tube working life.

Mine-used Flameproof Inverter Heat Dissipation Design and Its Performance Analysis

Flameproof inverter for mine-used have a significant warming effect during operation, resulting in reduced reliability and susceptibility to thermal degradation and thermal failure. However, there is a lack of thermal analysis research on the operation mechanism and process evaluation of mining inverters. This paper analyzes the electrical characteristics of internal power devices and calculates the power loss. Secondly, on the basis of comparing the influence of flow rate, structural parameters and installation location on the thermal performance, the forced water cooling + air cooling + natural cooling method is used to optimize the design of the thermal system. Finally, ANSYS Icepak is used to conduct a comprehensive numerical simulation analysis of the internal temperature field characteristics and convective heat transfer characteristics. The simulation verifies the effectiveness of the heat dissipation-based design, and the results show that: the internal components of the mining explosion-proof inverter are not more than 80°C, which is much lower than the value specified in the relevant standards, and it has a good heat dissipation performance, which effectively guarantees the safe, stable and reliable operation of the mining explosion-proof inverter.

INVESTIGATION OF TRANSIENT RESISTANCE AND ELECTRICAL EROSION OF SERIAL CONTACT PARTS RELAY PKL - 2204

In this study, the processes of the occurrence of an electric arc and its duration on the contact details of the PKL-2204 series relay are considered in detail. The patterns of changes in electrical erosion, which is a function of current strength and the number of switchings, were also studied. A detailed analysis of the process of opening the contact details was carried out based on the voltage oscillogram. Studies have shown that this process can be considered in three main stages. The first stage is marked by the separation of the contact parts, and at the very moment of the break of the working surfaces, there is a sharp jump in voltage from 45 mV to 13.5 V, accompanied by the formation of an electric arc. The second stage, lasting about 3.5 ms, is characterized by the weakening of the current to zero, and the arc is completely extinguished on the oscillogram. The third stage is marked by the appearance of a voltage peak on the oscillogram, which occurs when the arc is extinguished and is caused by the inductance L=240 mH. This analysis helps to better understand the process of contact opening and may have practical applications in the field of electrical engineering and electronics. Analysis of the results of our research indicates the presence of metals that have high resistance to erosion, regardless of their role as an anode or cathode. Among these metals, we can note nickel, copper, niobium, molybdenum, silver, and others, which show resistance to erosion even when the polarity changes, that is, they are erosion-resistant both at the anode and at the cathode. In particular, among such metals it is worth noting silver, molybdenum and niobium, which demonstrate extraordinary resistance to erosion in various conditions. These results may have important implications for the development of erosion-resistant materials for electronic devices and other applications. On the basis of the conducted research, it was found that the electroerosion resistance of contact parts made of СрН-10 material depends on several factors, including the current strength, the duration of arc burning, the number of commutations, and the physical and mechanical properties of the contact material. Research into the microstructure of the material during the current switching process revealed thermal, mechanical, and fatigue failure. During this process, the low-melting component of the cathode material melts and intensively evaporates, which leads to the formation of a dispersed and bumpy surface. The working surface of the anode is covered with finely dispersed silver particles, which are transferred from the cathode through the gaseous or liquid phase. The analysis of the spectra of the surface layers indicates a significant occurrence of nickel on the working surface of the cathode, which confirms the priority of evaporation of silver from the surface of the contact part during current switching. The study of the effect of chemically active reagents on transient resistance showed that in humid air with a high content of ammonia, hydrogen sulfide, sulfur dioxide, and carbon dioxide, the transient resistance of contact parts increases by 5-7 times.

Experimental determination of metals generated during the thermal failure of lithium ion batteries

This work describes the deliberate failure of lithium-ion cells, and subsequent analysis of both the smoke and near field residue for the metals commonly found in battery cathodes.

Research Progress of Sandwich-structured Flexible Energy Storage Dielectric Materials

Polymer dielectric materials show wide applications in smart power grids, new energy vehicles, aerospace, and national defense technologies due to the ultra-high power density, large breakdown strength, flexibility, easy processing, and self-healing characteristics. With the rapid development of integration, miniaturization and lightweight production of electronic devices, it is required to develop such storage and transportation dielectric system with larger energy storage density, higher charge and discharge efficiency, good thermostability and environmental friendly. However, the contradiction between dielectric constant and breakdown strength of dielectric materials are the key factors and bottleneck to obtain high performance dielectric materials. It is accepted that controlling charge distribution and inhibiting charge carrier injection are important to improve the energy storage characteristics of polymer dielectrics. In recent years, designing sandwich or stacking structured materials exhibits outstanding advantages in inhibiting charge injection and promoting polarization, thereby the permittivity and breakdown strength of polymer dielectrics can be simultaneously enhanced. Accordingly, this paper reviews the research progress of sandwich-structured polymer dielectric films in improving the energy storage performances from the perspectives of materials composition, structural design, and preparation methods. The influence of dielectric polarization, charge distribution, charge injection, interfacial barrier and electrical dendrite growth on the energy storage performance and the synergistic enhancement mechanisms in such sandwich-structured dielectric materials are systematically summarized, implying good development and vast application prospects. In brief, introducing easy polarization, wide-gap and deep-trap nanofillers has greater designability and regulation in the dielectric and breakdown properties. In addition, using the hard layer as the outer layer can reduce charge injection more effectively, achieving high breakdown resistance performance easily. Sandwich structure design also possesses advantages over other methods in maintaining good flexibility and dielectric stability of dielectric materials, thus becoming a hot-topic research area in recent years. In the future, it is necessary to combine low conductivity and high thermal conductivity of dielectric polymers to achieve high temperature energy storage and efficiency. Research on recyclable, self-repairing sandwich insulating films is good for the service life and safety of electronic components and will further expand the application of dielectric polymers. Finally, effective evaluation of sandwich-structured dielectric and energy storage performances through simulation and theoretical modeling is very helpful to reveal the breakdown and thermal failure mechanisms, and theoretically guide the design of polymer dielectric materials.

Research Progress of Thermal Failure Mechanism and Ternary Blending to Improve Thermal Stability of Organic Solar Cells

Research Progress of Thermal Failure Mechanism and Ternary Blending to Improve Thermal Stability of Organic Solar Cells

Fatigue life evaluation of gold wire bonding solder joints in MEMS pressure sensors

The failure of the gold wire bonding solder joint of a MEMS pressure sensor caused by the thermal cycling test was investigated with thermal cycling experiments and fatigue simulations. The results show that the maximum stress and strain occurred at the root of the solder joint on the substrate. With the accumulation of strain caused by thermal cycles, the bonding area of solder joint became smaller and the shear force of solder joints reduced to 22.3% after 1600 thermal cycles. The solder joints on the substrate failed after 1940 thermal cycles in plastic fatigue simulations and 3.16 × 108 thermal cycles in creep fatigue simulations. Plastic fatigue is the major factor for thermal failure of gold wire bonding.

Experimental research on flammability characteristics and ignition conditions of hybrid mixture emissions venting from a large format thermal failure lithium-ion battery

When the concentration of gas is below its lower flammable limit and the content of the particles is below its minimum explosible concentration, it can be explosible. Thermal abuse tests for 50 Ah lithium-ion batteries were conducted under an inert atmosphere. The battery failure venting emissions were collected and their composition was identified previously. It still needs further research for the flammability characteristics and ignition conditions for hybrid mixture emissions venting from a large format lithium-ion battery thermal failure. In this study, the likelihood, severity, and kinetics of the batteries' hybrid mixture emissions flammability have been researched. To analyze battery emission flammability characteristics, five indexes have been investigated; they are ignition temperature (Tig), ignition time (τig), maximum explosion pressure (Pmax), pressure rise maximum rate ((dP/dτ)max), and size-normalized maximum rate pressure rise (KSt). Based on quantitative analysis for the hybrid mixture flammability characteristics, it indicates that particle size and gas content can impact hybrid mixture emission flammability characteristics. As for the mixture with finer particles, the optimum combustion condition of the particle and gas concentration pairs were 0.3 and 0.7. The ignition temperature for the optimum combustion conditions was 495 °C. The pressure rising velocity was 23 Mpa/s during ignition. High solvent content and low particle concentration are the conditions for optimum combustion. This indicates that the gas admixture solvent plays a major role in the combustion kinetics of the mixture emission. This research offers a fundamental perspective and provides preventive and protective thermal safety designs that are more suitable for large format commercial battery thermal systems.

A fast-modeling algorithm to predict the thermo-field emission and thermal stability of field emitter arrays

In the last decades, numerical simulation has become a precious tool to assist the design and study of electron sources based on regular arrays of field emitters. Simulations of field emitter arrays (FEAs) require 3D treatment to account for the interactions between neighbor emitters. Therefore, modeling the thermal evolution of FEAs involves high computational resources due to the multi-physics approach and time dependency. The present paper proposes an algorithm which gives a fast prediction of the self-heating of a large array of N axisymmetric field emitters. It consists in finding for each emitter the equivalent 2D axisymmetric situation yielding the same electron current at 300 K as in the 3D array. The 3D modeling is thus efficiently split into N simulations in 2D, with a significant computation time reduction by at least one order of magnitude. The proof of concept uses 3×3 arrays of ideal emitters. Our results show a correct prediction, within a few percent, of the array thermo-field current and maximum temperature—two quantities of high interest for thermal failure and breakdown voltage considerations. The algorithm paves the way for including thermal effects in future optimization studies of realistic FEAs.

Measurement of ceramics cracking during water quenching by digital image correlation

Measuring the thermal shock crack growth process is crucial for revealing ceramic materials and structures’ thermal shock failure mechanisms and evaluating their reliability. We used a self-made water quenching system to conduct thermal shock tests on alumina and zirconia ceramics. The thermal shock process was recorded by high-speed digital image correlation (DIC) during the test. The process of thermal shock crack initiation and propagation in two kinds of ceramics was determined by analyzing the speckle image change on the sample’s surface. It is found that the crack growth rate of alumina is faster than that of zirconia, which is caused by different material parameters. This paper presents an in-situ measurement method for the initiation and propagation of thermal shock cracking in ceramic materials. It can provide a measurement method to identify and predict the thermal shock damage of ceramic components.

Nauclea latifolia herb root waste reinforced epoxy polymer composite: The study of effects, modelling, certainty and sensitivity analysis

The requirement for cleaner and healthy environment is a drive for waste recycling programs. In this study, suitable reinforcement for composite production was extracted from Nauclea latifolia herb root waste (NLHRW) through alkalization. Proximate composition and crystallinity of NLHRW and alkalized NLHRW (ANLHRW) were determined using gravimetric method and X-ray diffractometer (XRD). The individual and interaction effect of production factors (size, weight fraction, and mould compression force) on composite characteristics (flexural strength (FS), modulus (FM), and water absorption (WA)) of ANLHRW reinforced epoxy polymer composite was investigated, modeled and optimized using response surface methodology (RSM). The thermal stability and failure mechanism of the optimally developed ANLHRW reinforced composite were investigated using thermogravic analyzer (TGA) and Scanning Electron Microscope (SEM). The sensitivities of the composite properties to production factors were investigated using Monte Carlo simulation (MCS). Results showed that alkali treatment improved the cellulose content and crystallinity of the fiber. Fiber size and weight fraction increased the FS and FM while mould compression force reduced the WA of the composite. The determined optimum composite production condition was 322.62 μm fiber size, 24.06 wt% fiber weight fraction and 98.10 N mould compression force to give a composite’s FS of 16.9905 MPa, FM of 1046.36 MPa and WA of 3.71057 %. The percentage validation error was 0.70, 0.56 and 0.80 % for FS, FM and WA respectively. The composite produced with the validated optimum condition showed a decrease in thermal resistance than cured unreinforced epoxy plastic and had varied failure mechanisms such as fiber pull out and fiber breakage. The composite properties were dominantly sensitive to fiber weight fraction. The composite produced can be applied in dry low-load bearing applications such as automobile interiors or wet no-load bearing application such as desert cooler pad.

LaYZrO/YSZ double ceramic layer thermal barrier coatings by EB-PVD: Thermal performance, morphology and failure behavior

Thermal barrier coatings have been widely investigated over the last decade. Lanthanum zirconate is known for its high melting point and good thermal stability in aircraft engine environment. Owing to the distinctive thermophysical properties, Y doping in pyrochlore La2Zr2O7 might be a promising TBCs material as the top ceramic layer. It remains a challenge to completely understand the LaYZrO/YSZ double ceramic layer TBCs properties and microstructure evolution during thermal cyclic. In this paper, LaYZrO/YSZ double ceramic layer TBCs have been prepared by EB-PVD. The phase structure, thermal performance, microstructure and thermal cyclic lifetime have been researched. Thermal conductivity has been decreased compared with YSZ and La2Zr2O7, simultaneously, coefficient of thermal expansion has been increased compared with La2Zr2O7. The failure behavior of LaYZrO/YSZ double ceramic layer TBCs have been elucidated as typical TGO growth mode and specific sintering crack evolution mode. This study of properties and failure behaviors might provide the valuable investigation and thought for other advanced TBCs.

Building a Digital Twin Simulator Checking the Effectiveness of TEG-ICE Integration in Reducing Fuel Consumption Using Spatiotemporal Thermal Filming Handled by Neural Network Technique

Scholars seek to recycle wasted energy to produce electricity by integrating thermoelectric generators (TEGs) with internal combustion engines (ICE), which rely on the electrical conductivity, β, of the thermal conductor strips. The TEG legs are alloyed from iron, aluminum and copper in a strip shape with specific characteristics that guarantee maximum thermo-electric transformation, which has fluctuated between a uniform, Gaussian, and exponential distribution according to the structure of the alloy. The ICE exhaust and intake gates were chosen as the TEG sides. The digital simulator twin model checks the integration efficiency through two sequential stages, beginning with recording the causes of thermal conductivity failure via filming and extracting their data by neural network procedures in the feed of the second stage, which reveal that the cracks are a major obstacle in reducing the TEG-generated power. Therefore, the interest of the second stage is predicting the cracks’ positions, Pi,j, and their intensity, QP, based on the ant colony algorithm which recruits imaging data (STTF-NN-ACO) to install the thermal conductors far away from the cracks’ positions. The proposed metaheuristic (STTF-NN-ACO) verification shows superiority in the prediction over [Mat-ACO] by 8.2% and boosts the TEGs’ efficiency by 32.21%. Moreover, increasing the total generated power by 12.15% and working hours of TEG by 20.39%, reflects reduced fuel consumption by up to 19.63%.

Simulation research on thermal protection performance of firefighting robots and design of protection system

In response to manufacturing strategy demand, fire accidents in petroleum, chemical, forestry, and high-rise buildings are on the rise. Although the firefighting robot can replace fire rescue workers who come into the dangerous rescue site, electronic devices’ thermal failure problem caused by high temperatures in the whole electronic equipment problem is bigger. The proportion of electronic device thermal failure has a significant impact on the normal operation of electronic equipment. How to dissipate heat quickly and avoid local high temperatures becomes a key problem. Most domestic and foreign scholars only study the influence of thermal protection materials themselves on robot protection systems, and few study the influence of heat insulation materials and heat dissipation materials on robot protection systems through appropriate structure combinations. Therefore, the establishment of comprehensive high-temperature fire situations on the fire protection robot automatic detection of smoke concentration and temperature of heat insulation material and heat dissipation material composition of folded tensile structure and liquid nitrogen cooling system thermal protection model of robot thermal protection performance research is of great significance, at the same time through COMSOL Multiphysics software to simulate the proposed model, Select the best heat dissipation materials and heat insulation materials, protect the internal electronic components in the fire accident sustained high temperature, can adjust the temperature as soon as possible, make it adapt to the change of temperature field, for the rescue process to gain 2~15 minutes time duration.

Reductive gas manipulation at early self-heating stage enables controllable battery thermal failure

<h2>Summary</h2> Li-ion batteries are regarded as unsafe due to the volatility and flammability of the organic liquid electrolytes. However, research on substitutes (solid, inorganic, etc.) still encounters tough obstacles toward commercialization. Here, we manage to control the thermal failure process of liquid batteries by manipulating the deleterious reactions at an earlier stage, where heat accumulates mildly before accelerating to catastrophes. We reveal that the reductive gases, specifically those with low bond dissociation energies (unsaturated hydrocarbons as alkenes and alkynes), can induce cathode crystal change with oxygen release and initiate and accelerate battery thermal failure from lower than 80°C. Four safety countermeasures to break this "reductive attack" pathway are designed and successfully prevent commercial Li-ion batteries from thermal runaway (capacity of 60 Ah and energy density of 280 Wh kg⁻¹). We anticipate that our new safety insights and methodologies will overcome the limitations of liquid electrolytes for safe energy applications.

Thermal mixing characteristics of T-junction incident along central axis based on Large-Eddy simulations

A large eddy simulation model was used to explore the temperature mixing characteristics of a T-junction in which a branch pipe extends into the main and the branch fluid is injected along the central axis of the main pipe. The influence of the incident velocity of the branch tube on the temperature fluctuation of the fluid mixing is considered. In the main mixing region, the dimensionless time-averaged temperature（T∗¯）is positively related to the dimensionless root mean square（Trms∗）, while the connecting pipe region shows the opposite trend. With the increase of the velocity ratio, the influence of the branch pipe structure on the main flow field gradually decreases. The rebound vortex accelerates the rupture of the vortex ring, and the higher injection speed of the branch pipe leads to an increase in the vortex strength and the range of mixing area, which enhances the mixing of the fluid and makes the temperature distribution of the flow field more uniform. Finally, through the power spectral density analysis of temperature fluctuations, it is not only found that the high-energy vortex ring falls off to the near-wall region, dominating the temperature fluctuation in this region, but also this type of T-junction greatly reduces the risk of thermal fatigue failure.

Evaluation of insulated gate bipolar transistor valve converter based unified power flow controller reliability and efficiency

The effectiveness and reliability of the unified power flow controller (UPFC) are determined by the insulated gate bipolar transistor (IGBT) valve. Thermal losses, conduction losses, and switching losses in the IGBT valve all affect the efficiency of UPFC. The failure rate of the converter valves is influenced by junction temperature, which has an impact on the converter's reliability. Piecewise linear electrical circuit simulation (PLECS) was used to simulate two IGBT valve-based converter legs working at 12000 Hz, part number GT30F123. By reference to the switching characteristics produced by PLECS, switching losses, conduction losses, and thermal losses are analyzed. Simulation results are corroborated with analytical measurements. The chance of achieving 100%, 50%, and 0% functioning modes are among the reliability indices that are analyzed. The chance of achieving a hundred percent, fifty percent, or zero percent functioning mode is assessed. The frequency of achieving the state probability and mean time to failures (MTTF) are obtained from probabilities using the Markov model. The thermal losses, failure rate, and lifetime of the UPFC are all quantified to give a complete picture of the UPFC's performance.

Numerical investigation of thermal failure of a fuel subassembly foot wall during molten material relocation under various flow blockage scenarios in sodium-cooled fast reactor

The innovative Fuel Assembly Inner DUct Structure (FAIDUS) design inherently offers a quick relocation path for the molten core material to descend downwards via the inner duct and arrive at the foot of the Subassembly (SA) following the local core meltdown during Total coolant Flow Blockage (TFB) accident. With its high thermal energy and continual heat generation, the amassed molten mass targets the surrounding foot structure, causing the foot wall to fail. The thermal damage progression and discrete failure of the foot wall govern the later phase of the melt relocation that signals the accident state. To understand the thermal damage progression of SA foot, transient numerical simulations are performed using a commercial computational fluid dynamics solver, ANSYS Fluent. An enthalpy-porosity approach based solidification/melting model is employed to predict the wall failure mechanism and associated event sequences. The computational model is validated against the wall failure test results available in the literature. Subsequently, the foot wall failure analysis is undertaken using a 2-D axisymmetric physical model for various plausible blockage occasions that initiate the TFB accident near the SA foot. The numerical solution endeavors to explicate the transient behavior of molten pool, convection-diffusion controlled phase interface development, thermal transport mechanism, liquid front propagation across the foot cross-section, and associated thermal hydraulics. The present findings indicate that the standard SA foot design perpetuates the accident scenario by releasing the molten mass through the ruptured wall segment after failure. To address this, an improved slotted discriminator-based foot design is proposed in the present study, and the effectiveness of the modified foot design in realizing a positive melt relocation to the core catcher is examined. The simulation results suggest that the modified foot design permits the intended melt release to the core catcher, confirming the Controlled Material Relocation (CMR) strategy and restraining the accident propagation to neighboring SA.

Research on the oxidation resistance and ultra-high frequency thermal fatigue shock failure mechanisms of the bilayer and multilayer nano-coatings on cemented carbide tools

The multilayer nano-coating shows excellent thermal stability and oxidation resistance which could be attributed to the multielement composition and multilayer structure. It is widely used in the machining of hard-to-cut materials, such as titanium alloy. The formation of serrated chip during cutting process of Ti-6Al-4V would result in the ultra-high frequency thermal fatigue shock on the coating surface, and this could induce the thermal fatigue failure of coating. In this study, the ultra-high frequency (20 kHz) thermal fatigue shock testing was developed to investigate the thermal fatigue failure mechanisms of the bilayer TiSiN/TiAlN coating and multilayer TiSiN/TiAlN nano-coating. It was achieved by using the pulsed laser system to irradiate the coating surface under different shock cycles, which could produce alternating thermal stress on coating surface. This creates a close simulation of the actual working conditions in high-speed machining of Ti-6Al-4V with serrated chip produced. Moreover, the high temperature oxidation experiments were performed to study the oxidation resistance of coating. The failure mechanisms of coating/substrate system under the constant thermal loads and dynamic thermal loads were compared and analyzed. The cutting performance of related coated tools was evaluated after turning Ti-6Al-4V. The correlation between the thermal fatigue shock resistance of coatings at ultra-high frequency and the wear behavior of coated tools was built. It can be concluded that the multilayer TiSiN/TiAlN nano-coating showed better properties of the resistance to thermal fatigue shock in machining Ti-6Al-4V.

Fabrication of ceramic sealing coatings for shell bionic structures and their failure mechanism during thermal cycling

The porous ceramic coating as a "brick" layer sprayed by air plasma spraying(APS) and MK resin as a "mud" layer prepared by a high viscosity spray gun were characterized and tested. Three specifications of the "brick-mud" layered ceramic sealing coating were fabricated through the cyclic and orderly deposition of the "brick" layer and "mud" layer, and the thermal cycling performance and failure mechanism of the three new coatings were studied. The results showed that the agglomerated Y2O3 partially stabilized ZrO2 (YSZ) particles had porous spherical structures and good sprayability, and the content of the YSZ phase in the prepared "brick" layer was 54.2%. The "mud" layer had good phase stability and was amorphous SiO2 at and below 1100 °C. The fracture toughness of the pure YSZ coating was 2.295 ± 0.135 MPa‧m0.5, and which of the “mud” layer was reduced by 72.3%. The thermal cycling life of the conventional coating was only 67.3 times, which of A1, A2 and A3 coatings with 2, 3 and 6 "mud" layers were increased by 32.4%, 124.8% and 88.3%, respectively. In the thermal cycling process, the "weak" layer in the "brick-mud" layered coating led to the redistribution of internal stress and reduced the stress concentration in the top coating (TC)/TGO interface. Moreover, the initiation of microcracks in the "weak" layer, along with the "crack branching" effect and the "crack deflection" effect during the crack propagation process, could consume partial internal stress. Thus, the crack growth rates in the TC coating/TGO interface of the A1, A2 and A3coatings were lower than that of the conventional coating due to the above stress release mechanisms. In addition, the thermal cycling lives of the three new coatings with 2, 3 and 6 "mud" layers were improved to different degrees because of different stress effects.