Transient Thermal Conditions Research Articles

Nanoporous Aramid Nanofiber Separators with High Modulus and Thermal Stability for Safe Lithium-Ion Batteries.

Developing high-safety separators is a promising strategy to prevent thermal runaway in lithium-ion batteries (LIBs), which stems from the low melting temperatures and inadequate modulus of commercial polyolefin separators. However, achieving high modulus and thermal stability, along with uniform nanopores in these separators, poses significant challenges. Herein, the study presents ultrathin nanoporous aramid nanofiber (ANF) separators with high modulus and excellent thermal stability, enhancing the safety of LIBs. These separators are produced using a microfluidic-based continuous printing strategy, where the flow thickness can be meticulously controlled at the micrometer scale. This method allows for the continuous fabrication of nanoporous ANF separators with thicknesses ranging from 1.6 ± 0.1µm to 2.7 ± 0.1µm. Thanks to the double-side solvent diffusion, the separators exhibit controllably uniform pore sizes with a narrow distribution, spanning from 40 ± 5nm to 105 ± 9nm, and a high modulus of 3.3 ± 0.5GPa. These nanoporous ANF separators effectively inhibit lithium dendrite formation, resulting in a high-capacity retention rate for the LIBs (80% after 240 cycles). Most notably, their robust structural and mechanical stability at elevated temperatures significantly enhances LIB safety under transient thermal abuse conditions, thus addressing critical safety concerns associated with LIBs.

A review of thermal shock behavior of ceramics: Fundamental theory, experimental methods, and outlooks

AbstractThe thermal shock resistance of ceramics is a key factor for determining the durability of ceramic components under transient thermal conditions and is also one of the key factors for evaluating the stability of ceramics under extreme thermal conditions. After rapid heating or cooling, the surface and internal thermal stress mismatches of ceramics can cause severe thermal damage. Two main types of ceramic thermal shock exist: rapid cooling and rapid heating thermal shock. This article presents a broad understanding and insight into fundamental theory and experimental methods for ceramic thermal shock testing. The experimental equipment and procedures, test result evaluation, and material characterization of ceramic thermal shock are summarized. Moreover, outlooks and perspectives are discussed for testing and characterizing ceramic thermal shock resistance. This review will be helpful to researchers performing studies in the relevant fields of ceramics.

Investigating the transient conditions of “Sabat” space and its influence on pedestrian sensations during thermal walks. Algiers’ Casbah case study

Cities are already witnessing the impacts of climate change. Prolonged heat exposure have a direct effect on pedestrians’ thermoregulatory system, causing serious heat-related issues in the form of fatigue and thermal exhaustion. While the human body is capable of maintaining heat balance, excessive heat exposure combined with increasing heat loads can deteriorate the thermoregulatory process which leads to discomfort. Walkability is one of the significant challenges for climate change mitigation. Balancing the dichotomy of walking to mitigate climate change, and mitigating climate change to walk emphasizes the importance of promoting resilient walkability. In this context, the term “resilience” is used to highlight the need to design urban spaces able to adapt to increased urban heat, enabling pedestrians to tolerate and recover from discomfort conditions. This study investigates the potential of the “Sabat”, a traditional semi-outdoor space with lift-up design, and its distribution in generating transient thermal aeraulic conditions, and reducing fatigue sensation, hence, supporting a positive walking experience. Thermal walks have been conducted in Casbah of Algiers during temperate and hot weather conditions, in the context of uphill walking. Results revealed the alliesthesial effect of cool-shaded and ventilated Sabats to reduce fatigue sensation, which was confirmed by the significant correlation at lag-(-1) (r = 0.504, p < 0.001). Findings shed light on the importance of maintaining dynamic alliesthesia to create modulated restorative opportunities and offer starting point for hypothesizing broader trends for future implementation of Sabat design in modern cities.

Effect of Transient Thermal Conditions in the Slag Region on Ladle Refining

Effect of Transient Thermal Conditions in the Slag Region on Ladle Refining

Investigating The Transient Thermal Aeraulic Conditions of The ‘Sabat’ Space in Traditional Mediterranean Cities

Cities are already experiencing the effect of climate change on their seasonal conditions, especially in the Mediterranean region where significant temperature increases are being observed. Walkability is an essential factor influenced by the global warming impacts and could significantly reshape the course of its magnitude. The current study is a part of a large research investigating the influence of transient thermal aeraulic conditions of ‘Sabat’ space, a traditional urban in-between space, on pedestrians’ walking experience in Mediterranean cities. The aim is to investigate the potential of Sabat in supporting a positive walking experience. The novel ‘thermal walk’ method was carried out to capture the dynamic pedestrian sensations, simultaneously, with mobile micrometeorological within two preselected walking routes in Algiers’ Casbah. This paper reports the mobile meteorological measurement of the ‘Casbah walk’ with the aim of exploring the potential of Sabat in generating transient thermal aeraulic conditions. The measurement campaigns were carried out for five days in late December (2022). The campaigns involved a total of 16 assessment points of covered (Sabat) and non-covered stops using a set of portable weather station TESTO 480. Results revealed the potential of Sabat in generating transient thermal aeraulic conditions within the street, and the significance of air temperature and shade in channeling wind inside Sabats. Air temperature, mean radiant temperature and relative humidity significantly differ between Sabats and non-covered spaces. The wind speed recorded the largest variation. Important spatial transitions may result in abrupt thermal aeraulic transients. Although current results are limited to warm winter conditions, findings contribute to a better understanding of the use of shade and wind patterns in mitigating prolonged heat exposure and highlight the potential of Sabat space, a traditional sustainable device, in creating restorative conditions for walking activity.

Influence of drought intensity on soil carbon priming and its temperature sensitivity after rewetting

Global climate change can affect the soil thermal and moisture condition, potentially disrupting microbial-mediated soil respiration and altering the soil C cycle. However, the complex relationship between the soil C turnover and transient thermal and moisture conditions is not fully understood. Specifically, quantitative understanding is lacking regarding the impact of drought-rewetting events and temperature on the response of soil organic carbon (SOC) decomposition rate to exogenous C input, known as the priming effects (PEs). Herein, we quantified glucose-induced PEs during the rewetting of soils incubated under two drought intensities [with 20 % and 33 % water holding capacity (WHC)], at different incubation temperatures (15, 25, and 35 °C). Moreover, the effect size of drought intensities on PEs and the temperature sensitivity of PEs were quantified using lnRR (Response Ratio) and Q10 of PEs. Glucose input triggered positive PEs after 21 d incubation and increased SOC decomposition by 29.7–72.7 %. Drought intensity showed positive effect (lnRR > 0) on PEs at lower temperatures (15 and 25 °C) but showed negative effect (lnRR < 0) on PEs at higher temperature (35 °C). At moderate drought intensity (33 % WHC) before rewetting, PEs increased significantly with incubation temperature (Q10 = 1.65). Contrastingly, at high drought intensity (20 % WHC), temperature did not significantly influence PEs during the 21-d incubation after rewetting (Q10 = 0.96). The combination of drought, temperature change and glucose addition significantly changed the abundances in the dominant bacterial phyla (Proteobacteria, Actinobacteria, and Chloroflexi) and fungal phylum (Ascomycota), which likely affect PEs. Furthermore, the decrease in the demand for microbial-driven N mining, which is a crucial factor in promoting positive PEs, was associated with drought intensity at high temperature (35 °C). Our study provided a quantitative and mechanistic understanding of the impact of drought intensity on PEs before rewetting and its temperature sensitivity.

Topology optimization of compliant mechanisms under transient thermal conditions

This work considers multi-material topology optimization of compliant mechanisms under transient thermal and quasi-static mechanical conditions wherein thermally actuated devices are optimized for different operating conditions. The materials are modeled using finite strain thermo-hyperelasticity and a two way coupling between the energy balance and equilibrium equations is investigated. The design updates are generated from the gradient-based method of moving asymptotes optimizer and the sensitivities are computed using the time dependent adjoint sensitivity analysis. Results show the impact of designing for short versus long actuation times.

Thermal diffusion in discontinuous media: A hybrid peridynamics-based machine learning model

This paper introduces a novel hybrid formulation of a peridynamics-based machine learning model for thermal diffusion analysis in one-dimensional and two-dimensional problems with evolving discontinuities. The hybrid model employs a multivariate linear regression approach to establish the relationship between the temperature values of material points, their neighboring points, and the applied external heat flux. The thermal modal analysis method uses the finite element method to generate training and testing data. An efficient numerical procedure is also developed to couple the peridynamics model and the peridynamics-based machine learning model. The model is analyzed under multiple configurations of micro-thermal conductivity functions for one-dimensional thermal bar problems, under both steady-state and transient loading conditions, to identify the configuration that exhibits superior convergence behavior towards the local solution. Furthermore, benchmark problems demonstrate the high accuracy of the formulated hybrid model, including the analysis of thermal plates with discontinuities, such as a plate with a hole, a plate with a pre-existing insulated crack, and plate with a bi-material interface with stationary and evolving discontinuances. The hybrid model effectively captures intricate discontinuities and boundaries while being computationally efficient, indicating its potential for thermal diffusion analysis in one- and two-dimensional problems with stationary and evolving discontinuities.

Development of testing procedures for assessing the thermal and optical performance of thermochromic coatings for buildings

In climates where cooling and heating demands are balanced, thermochromic (TC) building coatings represent a promising solution to reduce the overall energy consumption for space conditioning. The main TC type proposed for building application, based on leuco dye, is however affected by photodegradation and there is an increasing research interest towards more durable TC solutions. This study suggests outdoor and laboratory measurement procedures to characterize the performance of TC building coatings. In an outdoor experimental campaign, roof and façade components with leuco dye-based TC coating were tested for 13 consecutive days. Moreover, spectrophotometric measurements were carried out to: i) characterize the solar, light and near-infrared reflectance and color properties of TC panels in pristine conditions and at different aging stages in the colored/colorless phases; and ii) assess the switching process under transient thermal conditions with the newly developed procedure. In the outdoor monitoring campaign, a maximum surface temperature difference between TC panels (colorless phase) and reference ones of ∼35 °C was found. Moreover, a 0.1 reduction in solar reflectance of TC panel in the colorless phase was reported after 3 days of outdoor exposition due to photodegradation, and the hysteresis of the TC panels undergoing the switching process was measured.

Identification of key thermal couplings affecting the bentonite behaviour in a deep geological nuclear waste repository

Deep geological nuclear waste repositories use the multi-layer Engineered Barrier System (EBS) to isolate nuclear waste from the environment. The key component of the barrier is densely compacted bentonite, closely resembling claystone. Therefore, to ensure safety, we need a numerical model for the bentonite and the barrier that predicts EBS behaviour during transient thermal, hydraulic, mechanical and chemical conditions. The paper identifies key mechanisms and processes affecting the bentonite in the barrier due to temperature changes (thermal couplings) based on advanced fully-coupled Finite Element Method simulations. The paper investigates 1) non-isothermal infiltration experiment on FEBEX bentonite (Villar and Gomez-Espina, 2009) and, 2) Centro de Investigaciones Energeticas Medioambientales y Tecnologicas (Ciemat) test (Martin et al., 2006), presenting 10 simulation configurations that are set up by inactivating one thermal coupling/variable at a time. The difference between these simulations and the baseline model results, examined in terms of the net mean stress (swelling pressure), suction and fluid flow, give insights into the significance of investigated coupling. Results suggest that thermal couplings related to vapour density, viscosity, water retention curve, and molecular diffusivity are among the most influential. The study additionally highlights the importance of water transport as liquid and gas, and water evaporation and condensation.

Study on the relationship between the design parameters of bridge wire electric initiating devices and the electrothermal response curve

The parameter settings of the transient thermal response test conditions of bridge wire electric initiating devices are studied. The effects of bridge wire resistance parameters and charge pressure on the electrothermal response curve were explored. The results show that when the state of the bridge wire and the surrounding agents are basically the same, the electrothermal response curve can clearly reflect the difference in the resistance of the bridge wire. The larger the bridge wire resistance, the more sensitive the bridge wire to the electrical pulse, and the charging pressure parameters also have a significant impact on the electrothermal response curve. The smaller the charging pressure, the more sensitive the product electrothermal response. When the density of the agent is basically the same, the approximate response curve and parameter calculation results can be obtained.

Elastic core concept for modified Bree problems considering in-phase and out-of-phase loading conditions

The elastic core concept developed from the Bree problem can be used for structural integrity evaluation of high temperature components, such as creep ratcheting and creep fatigue. The simplified inelastic analysis method of the ASME 2013 III-1 NH Code adopts the idea of core stress, which protects against creep rupture and collapse of the structure by limiting the accumulated inelastic strain. Currently, the formulas of core stress and evaluation diagram of effective creep stress parameter for Tests B-1 and B-3 adopted by the APPENDIX NH-T are developed from the classical loading Bree problem, however, the related concepts and evaluation diagrams of modified Bree problems considering generalized loading conditions have not been reported. This paper first reviews the development history of the elastic core concept and its corresponding analysis methods. Based on the modified Bree problems considering in-phase and out-of-phase loading developed by Bradford, the corresponding formulas of the core stress in the non-plastic ratcheting zone are completely proposed, and the corresponding evaluation diagrams of effective creep stress parameters are constructed for the first time. By comparing the core stress formulas and effective creep stress parameter diagrams under three loading cases, the conservatism and applicability of the classical core stress method are discussed. In addition, the differences and relations between two creep ratcheting assessment methods applicable to transient and sustained thermal load conditions respectively are clarified. The new results and conclusions presented in this paper can deepen the understanding of structural response under complex loading conditions, and provide guidance for shakedown analysis and creep ratcheting assessment of high-temperature components.

Thermal Effect of Cylindrical Heat Sink on Heat Management in LED Applications

Light Emitting Diode (LED) applications are increasingly used in various microelectronic devices due to their efficient light generation. The miniaturisation of the LED and its integration into compact devices within the weight limit have resulted in excessive heat generation, and inefficient management of this heat could lead to the failure of the entire system. Passive and/or active heat sinks are used for dissipating heat from the system to the environment to improve performance. An ANSYS design modeller and transient thermal conditions were utilised in this study to design and simulate the LED system. The modeller performs its function by utilising the Finite Element Method (FEM) technique. The LED system considered in this work consists of a chip, thermal interface material, and a cylindrical heat sink. The thickness of the Cylindrical Heat Sink (CHS) fins used in the investigation is between 2 mm and 6 mm, whilst ensuring the mass of heat sinks is not more than 100 g. The input power of the LED chip is between 4.55 W and 25.75 W, as required by some original equipment manufacturers (OEMs). A mesh dependency study was carried out to ensure the results were synonymous with what can be obtained practically. The simulation results suggest that the power ratings did not affect the thermal resistance of the CHS. In addition, the thermal resistance increased with the increased thickness of the CHS fin. The efficiencies of the heat sink were found to increase with an increased thickness of the cylindrical fin and the accuracy between the calculated and simulated thermal efficiency ranges from 84.33% to 98.80%. Evidently, the CHS fin of 6 mm thickness is more efficient than the other CHS fins, as depicted in this study.

Experimental investigation of phase change material energy storage system integrated with thermoelectric generator under transient heat loads

ABSTRACT Thermoelectric generator (TEG) systems are often exposed to unstable heat loads with transient temperature boundary conditions. TEG behavior recognition in thermal fluctuations is necessary to increase its efficiency and protection. This research deals with the experimental study of thermoelectric module’s performance under transient thermal boundary conditions. Therefore, three types of novel prototypes of transient heat loads including rectangular, triangular, and sinusoidal were suggested. Also, a phase change material (PCM) was applied inside an aluminum box on the hot side of the module. In the mentioned system, the effect of PCM on the module performance in the unstable heat loads was investigated. Applying PCM led to the protecting the module against temperature fluctuations, storing the energy, and generating effective voltage for a long time after turning the heat source off. Voltage generation lasted for 59.5 min with 90 W input power in 3-min periods in the rectangular heat load. Meanwhile, after switching the heaters off, 42.8- and 50-min voltages were received from triangular and sinusoidal loads, respectively, each with the power ranging from 0 to 90 W in four periods, lasted for 3 min.

Dynamic melting behavior of volcanic ash subjected to thermal shock relevant to aviation hazards

The ingestion of volcanic ash by aircrafts is widely recognized as a potential hazard for aviation. By melting, adhering, and spreading, ash can permanently damage the thermal barrier coatings in jet engines; consequently, it is important to investigate the melting behavior of volcanic ash. Previous work has concentrated on the relatively isothermal process of melting at a slow heating rate using “characteristic temperatures” identified according to different geometrical characteristics. Characteristic temperatures serve well as the parameters to quantify the successive and continuous melting processes of volcanic ash under the approximately homogeneous isothermal condition. However, when the ash is ingested by a jet engine, there are large and transient thermal gradients, which differs from the near absence of temperature gradients induced in a sample throughout slow and constant heating. Therefore, experiments using slow heating rates and characteristic temperatures are limited in their utility, and new techniques are required. Here, we designed a thermal shock experiment to better reproduce the conditions of volcanic ash encountering a jet engine and proposed three characteristic times to discretize and quantify the continuous melting process of volcanic ash under thermal shock conditions. Three characteristic times are characterized by shape transitions of the specimens to spherical (St1), to hemispherical (Ht2), and to flow state (Ft3). Ash sampled from Eyjafjallajökull volcano, Iceland, was compacted into cylinders with diameters of 1–3 mm, and then thermally shocked to a target temperature of 1251, 1296, 1341, 1384 or 1427 °C. The three characteristic times follow exponential functions of the target temperature. Additionally, in the sintering regime, a retardation of densification was exhibited in the smaller cylinder employed here, whereas the subsequent spreading process was enhanced, resulting in a positive correlation between the size of the volcanic ash cylinder and the characteristic times in the spreading phase. We present a universal empirical function for the hemispherical state involving dimensionless target temperature and the ash's thermal properties. The function provides a fundamental basis for a dynamic melting timescale predicting model for yet smaller volcanic ash particles under even more intense transient thermal loading conditions than those studied here.

Inverse Heat Conduction Problem in Estimating Nuclear Power Plant Piping Performance

Abstract Most of today's operating nuclear plants that were originally designed for 30 or 40-year life are facing the long-term operation issues. Therefore, it is of meaningful importance to assess the time-dependent degradation and the aging of the relevant nuclear systems, structures, and components because of resulting loss of structural capacity. In this framework, the inverse method is implemented starting from temperatures at an accessible boundary, which are measured through a monitoring system. The reconstruction technique uses the elaborated signal provided by the monitoring system to determine temperature at inaccessible surface: this is the so-called inverse heat transfer problem. The inverse space marching method is applied. Analytical and numerical studies are performed taking into account thermal transient conditions in order to determine thermal loads. In particular, the developed code demonstrates to be able to reconstruct temperature and stress profiles in any section of the pipe with a good accuracy. In addition, the thermal loads obtained suggest that the investigated transient condition is not able to jeopardize the integrity of nuclear power plant, confirming the possibility of the plant extension of life.

Effect of Transient Thermal Conditions on Columnar-to-Equiaxed Transition during Laser Welding: A Phase-Field Study

The columnar-to-equiaxed transition (CET) is commonly observed in laser welds. It is able to prevent the growth of large columnar grains and consequently improve the mechanical properties of welded joints. In this paper, the CET behaviors at different locations in the laser weld of an Al–Mg alloy are observed experimentally and studied systematically. In order to describe the dynamic CET behaviors, an integrated phase-field (PF) model coupled with transient thermal conditions and a Gaussian heterogeneous nucleation model is developed. Investigations on columnar growth under steady conditions are performed first. In particular, the effects of thermal conditions, i.e., solidification rate and temperature gradient, on the constitutionally undercooled degree and region ahead of the solidification front are quantitatively studied. In a laser weld, it is found that the CET behaviors vary significantly along the thickness direction. Our PF simulation results indicate that the CET depends strongly on the locally transient thermal conditions in the fusion zone. The transient thermal conditions affect CET behaviors by dynamically adjusting the constitutionally undercooled degree and region during the solidification process. The predicted CET behaviors under transient conditions exhibit reasonably good agreements with corresponding experimental results.

Effect of surface loading pattern on the monosymmetric beams at elevated temperature

Nowadays constructional steel has become the desired choice of structural designers because of its structural properties over other materials. However, structural steel susceptible to fire hazard as material properties of steel decreases rapidly at high temperatures that led to the instability failure of the unrestrained flexural members. In this study, numerical analysis is carried out to investigate the effect of surface loading patterns and temperatures on the buckling behavior of monosymmetric I-section beams. The ISMB600 monosymmetric beam of lengths varying from 2.5 m to 20 m simulated and analyzed using FEM based software ABAQUS. The response of beams is studied under uniform thermal conditions as well as transient thermal condition with 50% load ratio. Considerable variation in buckling capacity is noticed at elevated temperature. Based on the present results, the loading pattern is found to exhibit a significant influence on the moment capacities. The comparison between the numerical results and codal provisions of Eurocode 3 revealed that the codal provisions of Eurocode 3 pertaining to the buckling behavior of monosymmetric I-beams lead to the over-conservative prediction for medium to high slender beams and unsafe for beams having low slenderness ratio.

Dynamic modelling of air temperature in breathing zone with stratum ventilation using a pulsating air supply

Transient thermal conditions in the breathing zone created by pulsating air supply, can improve thermal comfort compared with steady air supply under stratum ventilation. This study proposes a dynamic physical-empirical hybrid model for the transient air temperature in a stratum-ventilated classroom, concerning specific locations and dynamics in the breathing zone, accuracy to the second. The model is validated through experiments of four cases and twelve measurement points at the height of 1.1 m each case. The raw air temperature signal is divided into an approximation component maintaining the major fluctuations and a detail component representing the stochastic volatility, by a validated denoising structure using wavelet decomposition. Firstly, the dynamic model can accurately predict the raw air temperature, with the root mean square errors (RMSE) of 0.04–0.07 °C. Secondly, the rate of air temperature variation positively correlates to the air velocity variation between the idle/duty period and the steady state, as well as the supply air velocity deviation, with the Pearson correlation coefficient value of about 0.7 (p < 0.01). Thirdly, the dynamic models for the approximation component are consistent with that for the raw air temperature signal, with an improved coefficient of determination of 0.91–0.97, and the RMSE of 0.02–0.05 °C. The decomposition level is the key hyperparameter to denoise the air temperature signal for approaching the modelled value. Lastly, the first 20% of the approximation component is used to model the entire period, reducing measurement costs. The model performs well on accuracy, simplicity and robustness.

Quantification of extreme thermal gradients during in situ transmission electron microscope heating experiments.

Studies on materials affected by large thermal gradients and rapid thermal cycling are an area of increasing interest, driving the need for real time observations of microstructural evoultion under transient thermal conditions. However, current in situ transmission electron microscope (TEM) heating stages introduce uniform temperature distributions across the material during heating experiments. Here, a methodology is described to generate thermal gradients across a TEM specimen by modifying a commercially available MEMS-based heating stage. It was found that a specimen placed next to the metallic heater, over a window, cut by FIB milling, does not disrupt the overall thermal stability of the device. Infrared thermal imaging (IRTI) experiments were performed on unmodified and modified heating devices, to measure thermal gradients across the device. The mean temperature measured within the central viewing area of the unmodified device was 3-5% lower than the setpoint temperature. Using IRTI data, at setpoint temperatures ranging from 900 to 1,300°C, thermal gradients at the edge of the modified window were calculated to be in the range of 0.6 × 106 to 7.0 × 106 °C/m. Additionally, the Ag nanocube sublimation approach was used, to measure the local temperature across a FIB-cut Si lamella at high spatial resolution inside the TEM, and demonstrate "proof of concept" of the modified MEMS device. The thermal gradient across the Si lamella, measured using the latter approach was found to be 6.3 × 106 °C/m, at a setpoint temperature of 1,000°C. Finally, the applicability of this approach and choice of experimental parameters are critically discussed.