Simple Thermal Model Research Articles

Inconsistencies in Simple Thermal Model Results for Near-Earth Asteroids between Infrared Telescope Facility SpeX and NEOWISE Data

Understanding the properties of near-Earth asteroids (NEAs) is key for many aspects of planetary science, particularly planetary defense. Our current knowledge of NEA sizes and regolith properties is heavily dependent on simple thermal models. These models are often used to analyze data from missions such as NEOWISE because they are well suited to deal with large volumes of data. However, simple model results based on NEOWISE data may be inconsistent with results based on other types of observation in some cases. In this work, we seek to better understand these potential inconsistencies, as well as the situations for which they are most prevalent. We do this by comparing simple model results based on Infrared Telescope Facility SpeX data to similar results based on NEOWISE data. This is carried out for six NEAs that represent a range of spectral types, shapes, and rotation states. We find that models based on SpeX and NEOWISE data for these six objects are inconsistent in some cases, even though the SpeX results are consistent with other methods and observations. We find that objects observed at fainter magnitudes and objects with more primitive compositions are more likely to produce inconsistent fits. These results highlight the importance of better understanding the limitations of simple models as applied to large survey data sets like NEOWISE. This is particularly true as we move into an era where our understanding of the NEA population will be dominated by future large surveys such as NEO Surveyor.

A thermal flexible rotor dynamic modelling for rapid prediction of thermo-elastic coupling vibration characteristics in non-uniform temperature fields

The flexible rotors within aero-engines operate in complex thermal environments, where temperature influences both the vibration frequency and amplitude. This study establishes a simple thermal flexible rotor dynamics model to rapidly and precisely predict thermo-elastic coupling vibration characteristics within a non-uniform temperature field. The thermal potential energy of the thermal rotor element is derived for any temperature field, and the motion equation is obtained using the Euler-Lagrange equation. Specifically, the generalized vector of an arbitrary point and cross-sectional non-uniform thermal stress of the thermal rotor element are considered in the thermal potential energy. The model's frequency error is less than 1% under identical boundary conditions. Numerical findings indicate that thermal stress, temperature-dependent material properties, and the coupling effect collectively reduce the natural frequency (NF), with thermal stress having a more pronounced impact under axial constraint. Additionally, thermal stress and material decrease the amplitude across a broad range of rotation speeds, contrasting with thermal bending. This model will play a key role in the iterative calculation of thermo-elastic coupling vibration control due to its accuracy and simplicity.

Development of ITER first wall heat load feedback control

Real-time monitoring and control of thermal loads on tungsten plasma-facing components is mandatory for ITER to avoid their overheating during plasma discharges. For the Start of Research Operations (SRO) phase, dedicated First Wall Heat Load Control (FWHLC) functions are included in the ITER Plasma Control System (PCS) to prevent the development of excessive plasma heat loads on the inertially cooled first wall (FW). In this work, we propose a FWHLC design with a model-based approach, which features a simplified thermal model for the FW armour. This control-oriented model simulates the thermal response of ITER FW to slow changes in plasma equilibrium and energy, which during ITER operation will be monitored by the real-time wide angle infrared camera system. This allows computationally efficient runs for rapid controller performance assessment but can also assist operation scenario design by pre-empting potential heat load issues. FWHLC is designed to react to measured and predicted FW temperatures overcoming predesigned limits with real-time variations of the plasma shape or auxiliary power references, aiming to reduce thermal loads before a premature plasma termination is required to protect the FW. The new scheme is tested in closed loop simulations, where perturbations to nominal ITER low current scenarios are introduced in the wall thermal model to trigger the response of FWHLC, supporting the effectiveness of the proposed policy.

Research on Temperature-Rise Characteristics of Motor Based on Simplified Lumped-Parameter Thermal Network Model

The thermal management of a driving motor is related to the performance and economy of the vehicle. The lumped-parameter thermal network (LPTN) method can provide a model basis for motor temperature-rise control and effectively shorten the development cycle of motor thermal performance design. In this study, an 80 kw water-cooled permanent magnet synchronous motor was used and the accurate thermal model of a motor was built using the LPTN. On the basis of the accurate thermal model, the simplified thermal model of a motor was obtained by reducing the complexity of the model. The temperature-rise test of the end winding and magnetic steel of the motor was carried out under some working conditions. The test conditions were selected according to continuous external characteristics and operating characteristics of the motor. Compared with the experimental results, the temperature-rise error of the two thermal models was less than 5%. The temperature-rise error of the simplified thermal model was less than 3% compared with the accurate thermal model. Therefore, the simplified thermal model can be used to quickly predict the temperature rise of the motor.

Heat transfer mechanism of superabsorbent polymers phase change energy storage cold-formed steel wall under fire

The superabsorbent polymer phase change materials (SAP materials) exhibit exceptional water absorption and retention properties, offering substantial potential for fire protection in steel structures, thereby reducing the need for sheathing boards and fire-retardant coatings, while minimizing energy consumption. Understanding the heat-mass exchange theory of SAP materials is crucial for enhancing their application in the building industry. This study develops a comprehensive theoretical model for heat-mass exchange in cold-formed steel (CFS) walls incorporating SAP materials. An equilibrium phase change model and a simplified thermal radiation model were developed to capture the water loss and dynamic heat exchange processes in SAP materials. These models were integrated into a transient fluid-solid-thermal coupling model using Ansys Fluent and User Defined Functions. In the case study, the newly developed numerical models can accurately predict temperature field changes in CFS walls with SAP materials, demonstrating the heat transfer mechanisms of hot and cold flanges at different temperature rise stages. The developed numerical model was used to investigate the effects of factors such as the moisture content of the SAP material, web depth, and flange width on the fire resistance of the CFS wall. Results indicated that increasing the wall stud height improves fire resistance, while increasing flange width has little effect on hot flange temperature. These findings provide a theoretical foundation and practical guidelines for the application of SAP phase change insulation materials in the building industry, promoting energy reduction and supporting sustainable construction practices.

Experimental study on fragmentation characteristics of molten stainless steel discharged into liquid Lead-Bismuth Eutectic pool

The LFR is a candidate for the Generation-IV nuclear systems, where the process of MFCI differs from that occurred in LWRs and SFRs. In the absence of experimental study and widely applied theoretical models for LFRs, experiments on the interaction between molten SS and liquid LBE are conducted in this study under eight conditions. The morphological characteristics and fragment sizes of the products are analyzed based on the hydrodynamic effect parameter (We) and thermal effect parameter (Tic). Simplified thermal fragmentation models are established, where the innermost layer of the solidified shell is subjected to the maximum tangential compressive stress, while the outermost layer is subjected to the maximum tangential tensile stress. As the shell thickness increases, the total tangential stress of the outermost layer decreases. The fragmentation will occur when the maximum tangential stress on the shell exceeds the shell tensile strength.

Coupled Electrical – Thermal – Electrochemical Model of a Battery Module

A battery module comprises of several lithium-ion cells connected in series and parallel configuration to obtain the desired voltage, current and power specifications. The overall response of a module can be affected by (i) the electrical topology, (ii) the thermal topology and (iii) the cell-to-cell variations. The distribution of current depends on the series/parallel assembly and variation in interconnect resistance in the module. Operation of a cell is accompanied by an increase in temperature. In a module, the thermal environment seen by a cell is different depending on whether it is an interior cell or a cell at the boundary of module exposed to environment. There is additional thermal cross talk between cells through heat conduction in metallic interconnects. Finally, there can be several reasons for cell-to-cell variation in a module. The cells used for building a module can have variable state of charge and internal resistance at the manufacturing level. As the module is cycled, the ageing of cells in a module can differ due to variation in current, evolution of range of lithiation of electrodes and the temperature of the cell.In this research work, we develop a coupled electrical, thermal, and electrochemical model to simulate the charge and discharge of a battery module with the overall aim of identifying the cell with largest performance degradation and most likelihood of failure. This physics-based modeling approach comprises of a simplified electrochemical and lumped thermal model of an individual cell. At the module level, the modeling framework is extended to include the electrical and thermal connectivity along with the electrochemical response.

Detrimental Increase of Spin-Phonon Coupling in Molecular Qubits on Substrates.

Molecular qubits are a promising platform for quantum information systems. Although single molecule and ensemble studies have assessed the performance of S = 1/2 molecules, it is understood that to function in devices, regular arrays of addressable qubits supported by a substrate are needed. The substrate imposes mechanical and electronic boundary conditions on the molecule; however, the impact of these effects on spin-lattice relaxation times is not well understood. Here we perform electronic structure calculations to assess the effects of a graphene (Cgr) substrate on the molecular qubit copper phthalocyanine (CuPc). We use a progressive Hessian approach to efficiently calculate and separate the substrate contributions. We also use a simple thermal model to predict the impact of these changes on the spin-phonon coupling from 0 to 200 K. Further analysis of the individual vibrational modes with and without Cgr shows that an overall increase in SPC between the vibrations modes of CuPc with the surface reduces the spin-lattice relaxation time T1. We explain these changes by examining how the substrate lifts symmetries of CuPc in the absorbed configuration. Our work shows that a surface can have a large unintentional impact on SPC and that ways to reduce this coupling need to be found to fully exploit arrays of molecular qubits in device architectures.

Validation of 3D and 2D thermal and electromagnetic models for high-frequency induction heating in crystal growth processes

Induction heating is crucial to various crystal growth techniques, including the Floating Zone (FZ) method, which is used for producing high-quality single silicon crystals. In this work, 3D and 2D axisymmetric numerical models for the high-frequency induction heating in the FZ process are implemented in open-source software tools Elmer and OpenFOAM. The models are compared and validated with in-situ measurements conducted on a model experiment of the FZ process, consisting of a flat inductor that heats a tin rod. The magnetic flux density distribution around the inductor is measured using a 3D induction coil probe, and the rod’s surface temperature is measured using an infrared camera. Both numerical models were found to be in good agreement with the experimental data, with deviations mainly due to geometric approximations and simplified thermal modeling. The present measurement setup can be used as a benchmark for other numerical models of high-frequency induction processes.

A Simple Thermal Model for Junction and Hot Spot Temperature Estimation of 650 V GaN HEMT during Short Circuit

Temperature is a critical parameter for the GaN HEMT as it sharply impacts the electrical characteristics of the device more than for SiC or Si MOSFETs. Either when designing a power converter or testing a device for reliability and robustness characterizations, it is essential to estimate the junction temperature of the device. For this aim, manufacturers provide compact models to simulate the device in SPICE-based simulators. These models provide the junction temperature, which is considered uniform along the channel. We demonstrate through two-dimensional numerical simulations that this approach is not suitable when the device undergoes high electrothermal stress, such as during short circuit (SC), when the temperature distribution along the channel is strongly not uniform. Based on numerical simulations and experimental measurements on a 650 V/4 A GaN HEMT, we derived a thermal network suitable for SPICE simulations to correctly compute the junction temperature and the SC current, even if not providing information about the possible failure of the device due to the formation of a local hot spot. For this reason, we used a second thermal network to estimate the maximum temperature reached inside the device, whose results are in good agreement with the experimental observed failures.

Sensitivity of a Lumped-Capacitance Building Thermal Modelling Approach for Energy-Market-Scale Flexibility Studies

Despite all the literature on building energy management, building-stock-scale models depicting its impact for energy-market-scale optimisation models are lacking. To address this shortcoming, an open-source tool called ArchetypeBuildingModel.jl has been developed for aggregating building-stock-level data into simplified lumped-capacitance thermal models compatible with existing open-source energy-system modelling frameworks. This paper aims to demonstrate the feasibility of these simplified thermal models by comparing their performance against dedicated building simulation software, as well as examining their sensitivity to key modelling and parameter assumptions. Modelling and parameter assumptions comparable to the existing literature achieved an acceptable performance according to ASHRAE Guideline 14 across all tested buildings and nodal configurations. The most robust performance was achieved with a period of variations above 13 days and interior node depth between 0.1 and 0.2 for structural thermal mass calibrations, and with external shading coefficients between 0.6 and 1.0 and solar heat gain convective fractions between 0.4 and 0.6 for solar heat gain calibrations. Furthermore, three-plus-node lumped-capacitance thermal models are recommended when modelling buildings with structures varying in terms of thermal mass. Nevertheless, the ArchetypeBuildingModel.jl performance was found to be robust against uncertain key parameter assumptions, making it plausible for energy-market-scale applications.

Heat sources for Variscan high‐temperature–low‐pressure metamorphism: Petrochronological constraints from the Trois Seigneurs massif, French Pyrenees

AbstractHigh‐temperature–low‐pressure metamorphism is commonly associated with intermediate to felsic magmatism in continental orogenic belts. The heat budgets and transfer mechanisms responsible for such elevated temperatures and partial melting of the upper crust are uncertain. The Trois Seigneurs massif, French Pyrenees, preserves a structurally continuous record of Variscan high‐temperature–low‐pressure metamorphism through a sequence of upper‐to‐mid‐crustal Paleozoic metasedimentary rocks. Conventional thermobarometry and phase equilibria calculations show that metamorphic conditions span ~2.5 kbar, 575°C to suprasolidus conditions of ~6 kbar, 700°C. Peak temperatures depend strongly on depth: temperature gradients of 50–60°C/km are present through the uppermost 12 km of the section; deeper portions (12–20 km) define restricted temperature conditions of ~650–700°C. The lowest‐grade metamorphic rocks preserve the largest spread in monazite 206Pb*/238U dates, from c. 325–285 Ma, while the spread in dates is restricted to c. 305–290 Ma in the highest‐grade rocks. Within this spread, each sample yields a well‐defined population of monazite 206Pb*/238U dates with peaks at c. 305 Ma in the andalusite schists, 295 Ma in the sillimanite schists, and 300 Ma in the migmatite sample. Monazite trace‐element compositions capture a systematic change with decreasing date and increasing metamorphic grade, including a more negative Eu‐anomaly and decreasing Sr concentrations, consistent with co‐crystallizing feldspar; increasing HREE and Y contents, consistent with xenotime breakdown; and decreasing Th/U, reflecting increasing U content during breakdown of inherited zircon. Zircon rims from a granite unit that formed via partial melting of the Paleozoic sedimentary package yields a 206Pb/238U‐207Pb/235U concordia age of 304.1 ± 3.73 Ma. These rims have trace‐element compositions reflecting cogenetic apatite and zircon growth during granite formation. Zircon from a calc‐alkaline granodiorite intrusion preserves a 40 Ma record of melt‐related activity in the lower crust that preceded the regional thermal climax. We interpret these petrochronological data to show that the Trois Seigneurs field gradient including andalusite schist and biotite granite samples represents a genuine geotherm through Variscan orogenic crust during the regional thermal climax at 305 Ma. When combined with constraints from other Pyrenean massifs, the form of the geotherm is consistent with a thermal scenario in which heat is advected to the upper crust by intermediate‐composition magmas generated in the lower crust. A simple thermal model for this process indicates that anatexis in the upper crust may plausibly occur within 10 Ma of the initiation of the lower‐crustal melting. Such a thermal scenario, however, requires focusing of melt through a fertile lower crust and an elevated Moho heat flux. We suggest that this process may have controlled the attainment of high‐temperature–low‐pressure metamorphic conditions along the Variscan belt and may currently be operating in zones of post‐orogenic continental extension.

A simplified mathematical modeling approach for thermal runaway of Li(Ni0.8Co0.1Mn0.1)O2 pouch cells based on thermal runaway experimental data

Currently, the numerical modeling methods used to characterize the thermal runaway and propagation mechanisms in NCM811 pouch batteries still face numerous challenges. This is primarily due to the uncertainties in thermal runaway reactions and the immense computational demands encountered when modeling begins at the granular level of the cell. To address this issue, this study designed a series of experiments for an NCM811 pouch battery. By employing experimental data, reasonable assumptions were made regarding the combined effects of solid-state thermal conduction, electrochemical heating, and fluid-solid heat transfer through gas jet streams. A simplified thermal runaway mathematical modeling method based on experimental data was proposed, effectively tackling the problem. This framework was then applied to thermal runaway experiments on a single NCM811 battery used in this study, providing essential input parameters for three-dimensional numerical modeling of modules composed of multiple batteries in multiphysics simulation software. The simulation results derived from the proposed method were in good agreement with experimental data. This study can characterize the thermal runaway and thermal propagation characteristics of battery modules using single-cell thermal runaway experiments. Moreover, the proposed modeling approach not only predicted the experimental outcomes of the NCM811 pouch battery with reasonable accuracy but also provided smoother data, elucidating the highly fluctuating trends observed in experimental data. This method also offers guidance for designing fire prevention and smoke exhaust systems for battery packs. This study presents a novel approach for the mathematical modeling of thermal runaway and thermal propagation in battery modules using NCM811 pouch batteries, contributing to the ongoing development of lithium-ion battery module design.

Dual harvesting from exhaust gas of diesel generators using thermoelectric generators and cold water tank

The present work concerns a dual harvesting concept applied to exhaust gas of Diesel generators using thermoelectric generators and cold water tank. To proceed, a simplified thermal modelling is developed and appropriate parametric analysis of power generation with the TEGs and heat recovered is conducted in function of the Diesel generator power and the TEG thermal conductivity and thickness. It was shown that powers up to 534 W can be generated with the TEGs and heat recovery rates up to 4463 W can be obtained for a Diesel generator power of 125 kW. Also, it was shown that the temperature difference across the TEGs and the power generated increase exponentially when the Diesel generator power and ratio of thickness to thermal conductivity of TEGs increase.

Flexibility Potential in the Austrian Building Sector

What would happen if 15% of the Austrian building stock in 2030 – both refurbished and newly-built – would use flexible heating/cooling systems to offer their flexibility on a market? How much annual residual loads from volatile renewable energy sources (RES) could be absorbed? Our simple agent-market model says: ~5% of RES surpluses and around 2% of RES residual loads. The cost of this operation is additional energy demand of about 30%, indicating an efficiency of approx. 70% in using these volatile supply peaks in flexible building operation. In this model, buildings are agents offering additional electricity consumption from pre-emptive HVAC operation, effectively using the building mass as storage, their energy demand is modelled in a simple thermal RC model. The grid flexibility demand is derived from future residual load scenarios and the offered flexibility depends both on signal parameters, mainly signal frequency and duration, and on key building parameters indoor temperature comfort bounds, building mass and thermal envelope quality.

GENETIC ALGORITHM-BASED OPTIMIZATION OF THE LASER-BEAM PATH IN ADDITIVE MANUFACTURING

This study presents a methodology of genetic-algorithm-based optimization of the laser-beam path for improving laser-based additive manufacturing (AM). A simple thermal model was developed to simulate the effects of laser-induced heat input on the temperature distribution within the substrate during the fabrication of one layer. The optimization approach aims to find solutions with more homogeneous temperature properties that minimize the thermal gradient on the substrate caused by laser-based AM. The laser beam, i.e., the tool-path planning, is formulated as the search for the optimal sequence of cell depositions that minimize the fitness function, which is composed of two components, i.e., the thermal fitness and process fitness. The thermal fitness is expressed as the average thermal gradient, and the process fitness regulates the suitability of the proposed tool path for the implementation of the AM process. Various tool-path generators are proposed to initialize the initial population of tool-path solutions. Genetic-algorithm-based tool-path optimization is proposed, where custom initialization, crossover and mutation operators are developed for application in laser-based AM. Simulation studies demonstrate the effectiveness of the genetic-algorithm-based optimization in finding solutions that minimize the fitness function and therefore provide both thermally and, for the AM process implementation, more suitable laser-beam-path solutions.

Continental Hotspots Tracks From an Analysis of GOCE Gravity Gradients Data

AbstractThis study aims to detect residual thermal anomalies along the path of a hotspot beneath the continental lithosphere using gradiometry data. We calculate perturbations in gravity vectors and gradients by employing a simple thermal anomaly model. The results highlight that the horizontal components of Bouguer gravity gradients, sensitive to source structure and elongation, exhibit substantial magnitudes, exceeding current detection levels. To improve signals from sources of different sizes and orientations, we apply a filtering approach involving wavelet transforms and rotated local frames. We also assess the impact of lateral crustal variations on the gravity field by introducing random density anomalies and a seismic crustal model, testing the method's ability to distinguish between these anomalies and thermal sources. Using Gravity field and steady‐state Ocean Circulation Explorer satellite data, we generated scale‐orientation diagrams aiming to identify signals aligned with the direction of plate movement and with a spatial scale of a few hundred kilometers (scale of the plumes). Maps of filtered Bouguer gravity gradients aligned with hotspot trajectories are generated for all continental hot plumes, with the position and the age of the intraplate volcanism to support the interpretation. While we do not show a clear signal in regions that are too tectonically complex or with lateral variations in the crust or at the lithospheric boundary correlated with the hotspot trace, we found observed signals with expected sign and amplitude over Hoggar, Tibesti, Darfour and Cameroon tracks in Africa and over Iceland and Jan Mayen in Greenland. However, determining corresponding mass source depths remains a complex task.

Genetic Algorithm-Based Framework for Optimization of Laser Beam Path in Additive Manufacturing

In this study, a genetic algorithm-based laser beam (LB) path optimization method is presented to improve laser-based additive manufacturing (LBAM). To emulate the LBAM process, LB irradiation of a thin metal substrate is applied. The LB path generation is formulated as the search for the optimal sequence of LB irradiation into the cells on the substrate that minimizes the fitness function, which is composed of two components, i.e., thermal fitness and process fitness. The thermal fitness is expressed by the average thermal gradient, and a simple thermal model is developed to simulate the effects of laser-induced heat input on the temperature distribution in the substrate. The process fitness regulates the suitability of the proposed LB path for the implementation of the LBAM process. In addition to standardized tool paths (i.e., raster, spiral, etc.), novel LB path generators are proposed to define the initial population of LB path solutions. To implement a genetic algorithm-based LB path optimization, a framework is proposed, and custom initialization, crossover, and mutation operators are developed for application in LBAM. The effectiveness of the proposed approach is demonstrated through a simulation case study aiming to identify LB paths that minimize the fitness function and thus provide more suitable LB path solutions with respect to the defined fitness function. Compared with the traditional trial-and-error LB path formulations, the proposed approach provides an improved and automated method for an efficient laser beam path selection in LBAM.

Delayed X-Ray Brightening Accompanied by Variable Ionized Absorption Following a Tidal Disruption Event

Supermassive black holes can experience super-Eddington peak mass fallback rates following the tidal disruption of a star. The theoretical expectation is that part of the infalling material is expelled by means of an accretion disk wind, whose observational signature includes blueshifted absorption lines of highly ionized species in X-ray spectra. To date, however, only one such ultrafast outflow (UFO) has been reported in the tidal disruption event (TDE) ASASSN–14li. Here we report on the discovery of a transient absorption-like signature in X-ray spectra of the TDE AT2020ksf/Gaia20cjk (at a redshift of z = 0.092), following an X-ray brightening ∼230 days after UV/optical peak. We find that while no statistically significant absorption features are present initially, they appear on a timescale of several days and remain detected up to 770 days after peak. Simple thermal continuum models, combined with a power-law or neutral absorber, do not describe these features well. Adding a partial-covering, low-velocity ionized absorber improves the fit at early times but fails at late times. A high-velocity (v w ∼ 42,000 km s−1), ionized absorber (UFO) provides a good fit to all data. The few-day timescale of variability is consistent with expectations for a clumpy wind. We discuss several scenarios that could explain the X-ray delay, as well as the potential for larger-scale wind feedback. The serendipitous nature of the discovery could suggest a high incidence of UFOs in TDEs, alleviating some of the tension with theoretical expectations.

Phase-controlled heat modulation with Aharonov-Bohm interferometers

A heat modulator is proposed based on a voltage-biased Aharonov-Bohm interferometer. Once an electrical bias is applied, Peltier effects give rise to a flow of heat that can be modulated by a magnetic flux. We determine the corresponding temperature changes using a simple thermal model. Our calculations demonstrate that the modulated temperature difference can be as large as 80 mK at base temperature about 600 mK with relative temperature variations reaching 10%. Our model also predicts, quite generally, the emergence of spin-polarized heat flows without any ferromagnetic contacts, if Rashba spin-orbit interaction is combined with the applied magnetic flux, which potentially paves the way towards caloritronic information processing. Published by the American Physical Society 2024