Thermal Inhomogeneities Research Articles

Simulation investigation on heating characteristics of catalysts under microwave irradiation for decomposition of waste plastic

Microwave heating is a promising technique for heterogeneous catalytic reactions in plastic decomposition. The microwave-insensitive plastic material requires microwave-absorbing catalysts to facilitate catalytic-assisted decomposition and synergistic heating. However, the heating characteristics of catalyst particles within the microwave system is still unclear. In this study, the effects of particle size, particle arrangement direction, and particle shape on the microwave heating behavior of particles was investigated, and the model was experimentally validated and analyzed using infrared temperature data. The simulation results indicated that the heating rate increased as the particle size enlarged, with an average heating rate of 5.56 °C/s for the particle with a radius of 5 mm in comparison to 4.29 °C/s for that of 1 mm. Additionally, when particles were aligned parallel to the applied electric field, the electric field was intensely focused at the interparticle area, with a maximum electric field strength difference of 2.2 × 104 V/m in the samples. In contrast, the horizontal placement resulted in reduced electric field intensity (4.7 × 103 V/m) and lower temperatures (62 °C) near the areas adjacent to the particles compared to the maximum values in the particles. With respect to particle shape, cylindrical particles possessing larger aspect ratios exhibited superior heating performance due to the extended span of intraparticle microwave transmission aligned with the electric field direction but also resulted in increased thermal field distribution inhomogeneity. The research offers theoretical guidance to prevent catalyst sintering and promote microwave-assisted catalytic plastic decomposition.

Thermal fracturing of anthracite under low-energy microwave irradiation: An experimental study

Microwave-assisted coalbed methane (CBM) development is a very promising technology for engineering applications. The mechanism of the macro and micro thermal fracture of coal must be further discussed because of the thermal inhomogeneity of microwave caused by the heterogeneity and structural complexity of coal. In this study, the temperature, weight and P-wave velocity of anthracite were tested under low-energy microwave irradiation. The characteristics of fracture initiation, extension, and connectivity in coal after microwave irradiation were extracted from macroscopic and microscopic observations. Then the mechanisms of microwave thermal fracturing in anthracite were analyzed. The results showed that the temperature of anthracite under low-energy microwave irradiation varies asynchronously. The temperature distributions with high and low temperature partitions exhibit obvious bedding effects. The coal mass loss varies in stages with microwave irradiation time, first increasing slowly and then increasing dramatically above 500 °C. The P-wave velocity presents a decreasing trend with the increase of input microwave energy. Coal generates a complex fracture network at the micro and macro scales, with fractures expanding outwards in a divergent pattern. The nonuniformity of the temperature distribution promotes fracture development. It is related to the asynchronous heating caused by the mineral composition, water content, pore fracture structure, and electromagnetic field in coal. It is of great significance to improve the thermal fracturing efficiency by using the nonuniformity of microwave heat in the application of microwave-assisted CBM development.

Vibrationally driven particle formations in fluid systems with bimodal thermal inhomogeneities

This study builds on and extends an earlier investigation [Santhosh and Lappa, “On the relationship between solid particle attractors and thermal inhomogeneities in vibrationally-driven fluid-particle systems,” Phys. Fluids 35(10), 103316 (2023)]. As the predecessor work, it can be placed in a wider theoretical context, that is, a line of inquiry started a decade ago [Lappa, “The patterning behavior and accumulation of spherical particles in a vibrated non-isothermal liquid,” Phys. Fluids 26(9), 093301 (2014)] about the surprising ability of high-frequency vibrations imposed on a non-isothermal fluid containing dispersed solid particles to support the self-emergence of ordered particle structures. Here, the non-trivial relationship between the number and shape of the particle formations and the nature of the thermal conditions along the boundary of the fluid container is further explored by probing in detail the role of thermal spot multiplicity. The problem is approached in the framework of a hybrid Eulerian–Lagrangian numerical approach. The results indicate that completely new morphologies become accessible, which are not possible when only two walls are thermally active. Moreover, on increasing the angle ϕ formed by vibrations with the direction perpendicular to the adiabatic walls of the cavity, the compact surfaces formed by particles for ϕ = 0° are taken over by more complex formations, which give the observer the illusion of a flexible fabric formed by the intersection of many independent filamentary structures.

The Relevance of Surface Resistances on the Conductive Thermal Resistance of Lightweight Steel-Framed Walls: A Numerical Simulation Study

The accurate evaluation of the thermal performance of building envelope components (e.g., facade walls) is crucial for the reliable evaluation of their energy efficiency. There are several methods available to quantify their thermal resistance, such as analytical formulations (e.g., ISO 6946 simplified calculation method), numerical simulations (e.g., using finite element method), experimental measurements under lab-controlled conditions or in situ. Regarding measurements, when using the heat flow meter (HFM) method, very often, the measured value is based on surface conditions (e.g., temperature and heat flux), achieving in this way the so-called surface-to-surface or conductive thermal resistance (Rcond). When the building components are made of homogeneous layers, their Rcond values are constant, regardless of their internal and external surface boundary conditions. However, whenever this element is composed of inhomogeneous layers, such as in lightweight steel-framed (LSF) walls, their Rcond values are no longer constant, depending on their thermal surface resistance. In the literature, such systematic research into how these Rcond values vary is not available. In this study, the values of four LSF walls were computed, with different levels of thermal conductivity inhomogeneity, making use of four finite elements’ numerical simulation tools. Six external thermal surface resistances (Rse) were modelled, ranging from 0.00 up to 0.20 m2·K/W. The average temperature of the partition LSF walls is 15 °C, while for the facade LSF walls it is 10 °C. It was found that the accuracy values of all evaluated numerical software are very high and similar, the Rcond values being nearly constant for walls with homogeneous layers, as expected. However, the variation in the Rcond value depends on the level of inhomogeneity in the LSF wall layers, increasing up to 8%, i.e., +0.123 m2·K/W, for the evaluated Rse values.

An experimental investigation of liquid immersion cooling of a four cell lithium-ion battery module

The thermal management of a lithium-ion battery module subjected to direct contact liquid immersion cooling conditions is experimentally investigated in this study. Four 2.5 Ah 26650 LiFePO4 cylindrical cells in a square arrangement and connected electrically in parallel are completely immersed in the dielectric fluid Novec 7000. The thermal and electrical behaviour of the module is assessed at charging and discharging rates of 1C to 4C. Experiments are conducted with initially ambient temperature liquid, resulting in single phase natural convection cooling, as well as preheated liquid temperatures of 33 °C ± 0.5 °C to study the influence of the phase change process under pool boiling conditions. Superior performance is observed when two-phase immersion cooling conditions are established for discharge rates of 2C and above, limiting the average cell temperature rise to 1.9 °C at the end of 4C discharge, corresponding to a maximum temperature of 34.7 °C. For the most onerous charging rate of 4C, considered fast charging, this maximum temperature rise is limited to 1.3 °C, corresponding to a maximum temperature of 35 °C. Vigorous boiling is observed from the cells' electrodes, leading to more effective heat transfer from the locations of high heat flux. Excellent module thermal homogeneity is exhibited, maintaining a maximum temperature difference of 1.2 °C for all cases investigated. The axial temperature gradients of the module's individual cells are also greatly reduced under two-phase conditions. The influence of cell spacing within the module is also investigated for inter-cell spacings of 0.25D and 1D, where D is the cell diameter. Marginally improved heat transfer performance is observed for the more closely spaced cell arrangements, reducing the maximum cell temperatures and thermal inhomogeneity within the module.

Long-lived Northern Hemisphere convergence systems driven by upper-mantle thermal inhomogeneity

Abstract Plate reconstructions reveal that two secular centers of convergence formed beneath eastern Eurasia and North America no later than 200 Ma. The cause of these convergence centers, which featured flat subduction, slab stagnation, and/or continental margin subduction, remains uncertain. Here, we propose that upper-mantle thermal inhomogeneity, particularly an anomalously cool Northern Hemispheric upper mantle, was a fundamental driver of this long-lived convergence. By considering the pattern of observed thermal inhomogeneity, our numerical models show that flow-induced asymmetrical subduction will tend to develop toward cold mantle domains, even when the subducting plate is buoyant. The models can reproduce the diverse subduction styles observed in the Northern Hemisphere by including proposed pre-subduction plate distributions and/or properties.

A Combined Ground-based and JWST Atmospheric Retrieval Analysis: Both IGRINS and NIRSpec Agree that the Atmosphere of WASP-77A b Is Metal-poor

Ground-based high-resolution and space-based low-resolution spectroscopy are the two main avenues through which transiting exoplanet atmospheres are studied. Both methods provide unique strengths and shortcomings, and combining the two can be a powerful probe into an exoplanet’s atmosphere. Within a joint atmospheric retrieval framework, we combined JWST NIRSpec/G395H secondary eclipse spectra and Gemini South/IGRINS pre- and post-eclipse thermal emission observations of the hot Jupiter WASP-77A b. Our inferences from the IGRINS and NIRSpec data sets are consistent with each other, and combining the two allows us to measure the gas abundances of H2O and CO, as well as the vertical thermal structure, with higher precision than either data set provided individually. We confirm WASP-77A b’s subsolar metallicity ([(C+O)/H] = −0.61 −0.09+0.10) and solar C/O ratio (C/O = 0.57 −0.06+0.06) . The two types of data are complementary, and our abundance inferences are mostly driven by the IGRINS data, while inference of the thermal structure is driven by the NIRSpec data. Our ability to draw inferences from the post-eclipse IGRINS data is highly sensitive to the number of singular values removed in the detrending process, potentially due to high and variable humidity. We also search for signatures for atmospheric dynamics in the IGRINS data and find that propagated ephemeris error can manifest as either an orbital eccentricity or a strong equatorial jet. Neither are detected when using more up-to-date ephemerides. However, we find moderate evidence of thermal inhomogeneity and measure a cooler nightside that presents itself in the later phases after secondary eclipse.

The influence of the dowel mounting scheme in facade systems on the thermal protection properties of the enclosing structure

The use of hinged facade systems is a common solution that allows, with the right approach, to effectively solve a wide range of tasks: from issues of thermal protection of buildings and structures to the possibility of giving the building a unique architectural and artistic expression. Such facade systems are multilayer structures, which contain thermal engineering heterogeneities that affect the thermal protection properties of the enclosing structure as a whole. The purpose of the study presented in the proposed article is to study the effect of the dowel fastening scheme in facade systems on the thermal protection properties of the enclosing structure. The facade dowels in the considered enclosing structure will be point thermal inhomogeneities. The object of the study is a hinged facade system with a thin plaster layer. As part of the study, various schemes of fastening thermal insulation boards with facade dowels are considered. The efficiency of using facade dowels, the material of the spacer element of which are innovative materials with a low coefficient of thermal conductivity, is shown.

Prediction of Thermal Conductance of Complex Networks with Deep Learning

Predicting thermal conductance of complex networks poses a formidable challenge in the field of materials science and engineering. This challenge arises due to the intricate interplay between the parameters of network structure and thermal conductance, encompassing connectivity, network topology, network geometry, node inhomogeneity, and others. Our understanding of how these parameters specifically influence heat transfer performance remains limited. Deep learning offers a promising approach for addressing such complex problems. We find that the well-established convolutional neural network models AlexNet can predict the thermal conductance of complex network efficiently. Our approach further optimizes the calculation efficiency by reducing the image recognition in consideration that the thermal transfer is inherently encoded within the Laplacian matrix. Intriguingly, our findings reveal that adopting a simpler convolutional neural network architecture can achieve a comparable prediction accuracy while requiring less computational time. This result facilitates a more efficient solution for predicting the thermal conductance of complex networks and serves as a reference for machine learning algorithm in related domains.

Complex surface cracks detection and identification by laser array spots thermography with PCA-Frangi processing

In this paper, a method for rapid detection and automatic identification of complex surface cracks based on laser array spots thermography with PCA-Frangi processing is developed. With the Laser Array Spots Thermography (LAST), a complex surface crack in a relatively large surface area can be detected rapidly. In addition, a novel approach utilizing the PCA-Frangi algorithm for feature extraction is proposed to enhance the imaging performance of surface cracks with complex morphology. The results show that the proposed method can extract the cracks and eliminate the interference of array spots to crack identification. Furthermore, this method effectively mitigates the impact of thermal inhomogeneity and thermal noise during the heating process. Finally, the crack features are automatically identified. The simulation and experimental results illustrated that the method enables the accurate recognition of complex surface crack characteristics, further enhancing the overall performance of the crack detection with LAST.

On the relationship between solid particle attractors and thermal inhomogeneities in vibrationally driven fluid-particle systems

The present analysis extends earlier authors' work [Crewdson et al., “Two-dimensional vibrationally-driven solid particle structures in non-uniformly heated fluid containers,” Chaos 32, 103119 (2022); M. Lappa, “Characterization of two-way coupled thermovibrationally driven particle attractee,” Phys. Fluids 34(5), 053109 (2022); M. Lappa and T. Burel, “Symmetry breaking phenomena in thermovibrationally driven particle accumulation structures,” ibid.32(5), 053314 (2020); and M. Lappa, “The patterning behavior and accumulation of spherical particles in a vibrated non-isothermal liquid,” ibid.26(9), 093301 (2014)] on the existence of solid particle attractee in thermovibrational flow in order to identify new physical principles and enable increased control over the ability of particles to target desired locations into the host fluid. The causality between the thermal boundary conditions and the multiplicity and morphology of emerging particle structures is discussed, and new fundamental topological concepts are harnessed through the combination of two-dimensional and three-dimensional simulations. It is shown that the threefold relationship among the inclination of vibrations, the multi-directional nature of the imposed temperature gradient, and the dimensionality of the system itself can open up new pathways for additional classes of attractors. These can manifest themselves as compact particle structures or completely disjoint sets, apparently behaving as they were driven by different clustering mechanisms (coexisting in the physical space, but differing in terms of characteristic size, shape, and position). A variety of new solutions are presented for a geometry as simple as a cubic enclosure in the presence of localized spots of temperature on otherwise uniformly heated or cooled walls. In order to filter out possible asymmetries due to fluid-dynamic instabilities induced by the back influence of the solid mass on the fluid flow, the analysis is conducted under the constraint of one-way coupled phases.

Thermal and stoichiometry inhomogeneity investigation of large-format lithium-ion batteries via a three-dimensional electrochemical-thermal coupling model

Large-format lithium-ion batteries (LIBs) have attracted extensive concern due to the advantages of increasing energy density and reducing manufacturing costs. However, inhomogeneity is widely present in large-format LIBs, which may lead to local degradation or edge lithium plating, thereby reducing the battery durability and safety. In this study, an electrochemical-thermal (ECT) coupling model for large-format LIBs is developed to quantitatively investigate the battery inhomogeneity during charging and discharging. First, two different sizes of batteries with the same electrode material are disassembled and tested to obtain the battery model parameters. Second, a novel method for determining the parameters of the ECT coupling model for large-format LIBs is proposed to solve the technical challenge of difficult model parameter calibration. Specifically, the ECT coupling model parameters of large-format batteries are determined using those of small-format batteries. The experimental results show that the three-dimensional ECT coupling model exhibits high accuracy, with the root mean square error of voltage and temperature within 17.8 mV and 1.27 ˚C, respectively, at 1C discharge rate and SOC greater than 2.5 %. Finally, the temperature and stoichiometry coefficient inhomogeneity of large-format LIBs during charging and discharging under different conditions are analyzed quantitatively. The results show that the inhomogeneity of large-format LIBs increases significantly with increasing discharge rate and battery length. A large-format battery with a length of 900 mm achieves a balance between inhomogeneity and length. This study contributes to a quantitative understanding of the inhomogeneity of large-format LIBs and provides a model-based perspective for designing and optimizing large-format LIBs.

Dynamics of magnetic skyrmionium driven by voltage-controlled strain gradients

A magnetic skyrmionium with zero topological number has no skyrmion Hall effect during motion; hence, it has excellent application prospects in racetrack memory. Here, we investigate dynamics of magnetic skyrmionium driven by voltage-controlled in-plane strain gradients via both electromechanical and micromagnetic simulations. It is found that the skyrmionium can be efficiently driven along the direction of the in-plane strain gradients without deflection, that is, the skyrmion Hall angle is zero, and the velocity of skyrmionium can be effectively increased by reducing the magnetic damping constant and increasing the intensity of the strain gradient. Moreover, the driving force and velocity of the skyrmionium increase correspondingly with the increase in size. Most importantly, we demonstrate that the skyrmionium can be efficiently driven by strain gradients under realistic conditions with thermal noise and material inhomogeneity in the ferromagnetic film. The results presented in this study are promising for applications in skyrmionium-based information memory devices.

Flow and thermal mixing characteristics of a multi-jet bypass flue with main flue baffles

The decrease of inlet flue temperature of denitrification reaction unit is a major challenge that restricts the low load operation of thermal power units. In this study, a new bypass flue heating technology based on multi-pipe and multipoint was proposed. The effect of different baffle openings (RA), directions and position distance (Db) on the mixing characteristics of multiple jets was quantitatively investigated by the experimental system. Combined with the simulation, the changes of the baffle on the multi-jet flow and mixing are revealed. The results show that the mixing temperature increases with increasing RA, but high RA leads to a significant increase in the thermal mixing temperature inhomogeneity (ζT). As RA increases from 0.4 to 0.7, ζT rises from the minimum 0.368 to the maximum 0.559. The mixing temperature and ζT of the baffle in the +x direction are higher than those in the −x direction. When Db increases from 70 mm to 130 mm, the maximum heating effect decreases from 25.97 °C to 18.89 °C, and ζT decreases gradually at y/Dh = 1.25. The findings provide guidance for bypass flue modification and low load denitrification in engineering.

Thermal conductivity changing mechanism of frozen soil-rock mixture and a prediction model

The thermal conductivity of frozen soil-rock mixture (S-RM) is an important parameter affecting its temperature field distribution, and it is also the basic physical parameter for studying the thermal-melting disaster mechanism of S-RM slope in cold regions. However, the effect of ice-water phase change on the thermal conductivity of the frozen S-RM has not been reported. In this paper, the influence of temperatures and rock contents on the thermal conductivity of frozen S-RM were systematically studied by Hot Disk thermal conductivity and NMR tests. Considering the influence of ice-water phase change and high thermal conductivity and inhomogeneity of rock on the thermal conductivity of frozen S-RM, a new effective thermal conductivity (ETC) prediction model of frozen S-RM is established by introducing freezing rate coefficient and weighting ratio. The results showed that the thermal conductivity decreased with the increase of temperature and increased with the increase of rock contents. The correlations of the predicted results are all above 0.97, by calculating the correlation between the predicted value of thermal conductivity and the measured value. The thermal conductivity model has good prediction performance, and can be used to accurately predict the thermal conductivity of S-RM.

Robust atom optics for Bragg atom interferometry

Multi-photon Bragg diffraction is a powerful method for fast, coherent momentum transfer of atom waves. However, laser noise, Doppler detunings, and cloud expansion limit its efficiency in large momentum transfer (LMT) pulse sequences. We present simulation studies of robust Bragg pulses developed through numerical quantum optimal control. Optimized pulse performance under noise and cloud inhomogeneities is analyzed and compared to analogous Gaussian and adiabatic rapid passage pulses in simulated LMT Mach–Zehnder interferometry sequences. The optimized pulses maintain robust population transfer and phase response over a broader range of noise, resulting in superior contrast in LMT sequences with thermal atom clouds and intensity inhomogeneities. Large optimized LMT sequences use lower pulse area than Gaussian pulses, making them less susceptible to spontaneous emission loss. The optimized sequences maintain over five times better contrast with tens of momentum separation and offer more improvement with greater LMT. Such pulses could allow operation of Bragg atom interferometers with unprecedented sensitivity, improved contrast, and hotter atom sources.

A method for the reproducible and accurate determination of electrical resistances based on multi-layer joints in lithium-ion batteries

The transition from fossil fuels to renewable energy sources is significantly influenced by the development of energy storage systems such as batteries. One of the crucial steps in the production of lithium-ion batteries is the electrical connection of the individual electrodes by weld seams. Various joining processes, such as laser beam welding or ultrasonic metal welding, are used for this purpose. An important quality feature of the connections is a low electrical joint resistance, which is essential for reducing cell-internal energy losses and avoiding thermal inhomogeneities in the cells.The aim of this work was to determine the electrical resistance of the joint between a stack of foils and an arrester tab. For this purpose, a measuring method was developed and applied to different sample configurations. The influence of different probe tips on the measurement results was compared using single current collector foils and arrester tabs. The measurement of the electrical resistance was possible in the considered range with a maximum relative uncertainty of 2.38%. Using the presented approach made it possible to evaluate the influence of the seam trajectory on the electrical resistance for cell-internal contacting. In addition, the measuring method is suitable for comparing different welding strategies and, thus, for designing the cell-internal joining processes regarding the resulting electrical joint resistances.

The effect of water on coking and heat transfer inhomogeneity of supercritical aviation kerosene in a curved mini-channel

Water addition to aviation kerosene draws increasing attention in increasing heat sink and suppressing coke formation for regenerative cooling of scramjet engines. However, the effect of water on flow, reaction and heat transfer, particularly the thermal inhomogeneity in curved cooling channel is rarely reported. In the present study, the effect of water on coking and heat transfer inhomogeneity characteristics of China aviation kerosene, RP-3 studied in a uniformly heated curved mini-channel. A transient three-dimensional numerical simulation model with hybrid pyrolysis and steam reforming reactions of RP-3 is established and validated. The results show that there exists serious mass and thermal stratification in the curved mini-channel due to secondary flow and species diffusion. Specifically, RP-3 and water are diffused to concentrate at the bottom heating wall surface while coke deposition and light gaseous species, e.g., H2, CH4, CO are concentrated at the top heating wall surface. The thermal difference between the top and bottom heating walls is significant. Temperature and coke content of the top heating wall are much higher than those of the bottom heating wall. The gas film and coke deposition formed at the top heating wall surface lead to serious heat transfer deterioration. Therefore, the heat transfer coefficient at the bottom wall of the curved channel is much higher than that of the top wall. Water addition enhances secondary flow and thus exacerbates the coking and heat transfer inhomogeneity in the curved cooling channel. With water content increasing from 0 to 15 wt%, the secondary flow velocity increases by 288.2%, the conversion of RP-3 increases by 114.8% and the average coke content on the heating walls decreases by 40%. Meanwhile, the average heat transfer coefficient increases by 33.9% at the bottom heating wall but decreases by 18.0% at the top heating wall with the increase of water content.

Thermomagnetoelectroelasticity of finite bimaterial bodies in the presence of a bonding interlayer of high thermal conductivity and internal thin inhomogeneities

Thermomagnetoelectroelasticity of finite bimaterial bodies in the presence of a bonding interlayer of high thermal conductivity and internal thin inhomogeneities

Non-planar dielectrics derived thermal and electrostatic field inhomogeneity for boosted weather-adaptive energy harvesting.

Weather-adaptive energy harvesting of omnipresent waste heat and rain droplets, though promising in the field of environmental energy sustainability, is still far from practice due to its low electrical output owing to dielectric structure irrationality and unscalability. Here we present atypical upcycling of ambient heat and raindrop energy via an all-in-one non-planar energy harvester, simultaneously increasing solar pyroelectricity and droplet-based triboelectricity by two-fold, in contrast to conventional counterparts. The delivered non-planar dielectric with high transmittance confines the solar irradiance onto a focal hotspot, offering transverse thermal field propagation towards boosted inhomogeneous polarization with a generated power density of 6.1mW m-2 at 0.2 sun. Moreover, the enlarged lateral surface area of curved architecture promotes droplet spreading/separation, thus travelling the electrostatic field towards increased triboelectricity. These enhanced pyroelectric and triboelectric outputs, upgraded with advanced manufacturing, demonstrate applicability in adaptive sustainable energy harvesting on sunny, cloudy, night, and rainy days. Our findings highlight a facile yet efficient strategy, not only for weather-adaptive environmental energy recovery but also in providing key insights for spatial thermal/electrostatic field manipulation in thermoelectrics and ferroelectrics.