Search Results (1,122)

The thermal performance of multilayer building wall systems under variable outdoor temperature conditions is an important factor in evaluating building energy efficiency and indoor thermal comfort. This study presents a simplified analytical formulation based on the classical transient heat conduction theory together with a numerical model based on the finite difference method (FDM) implemented in the MATLAB R2026a (Update 5) environment. The analysis includes five types of multilayer wall systems with different structural compositions and thermal masses, combined with three thermal insulation materials (expanded polystyrene (EPS), mineral wool, and aerogel) and various insulation thicknesses, resulting in a total of 55 wall assembly configurations. The investigated wall systems are evaluated using the thermal transmittance coefficient (U-value), decrement factor, time lag, maximum heat flux, and the temporal variation in the interior wall surface temperature. The results demonstrated that the dynamic thermal behavior of multilayer wall systems depends on the combined effects of the thermal mass of the load-bearing layer, the type and thickness of the thermal insulation, and the thermophysical properties of the constituent materials. The comparison between the analytical formulation and the MATLAB simulations demonstrates consistent trends in the predicted thermal behavior of the investigated wall systems, supporting the applicability of the proposed analytical–numerical approach for the preliminary assessment of the thermal performance of multilayer building wall systems. Full article

We present FDS and AERMOD simulations of the Alaska Clean Seas (ACS) oil burn experiments to improve dispersion modeling of large, open-air fires relevant to industrial settings. We propose a method in which FDS smoke fields with available ground measurements are used to empirically calibrate AERMOD configured using volume sources to represent the fire source. FDS is first run for the three ACS experiments at high resolutions (~10 m) and verified against ground monitoring to provide detailed three-dimensional smoke fields. The fractional allocation of total fire emissions (weights, w_i) is then empirically specified for each volume source i so AERMOD smoke predictions fit both the ground level measurements and FDS simulations to acceptable accuracy. Runs for volumes at the surface (i = 1), 100 m AGL (i = 2) and 300 AGL (i = 3) and w_i = [0.01, 0.09, 0.9]–[0.04, 0.36, 0.6] accurately represent these data, suggesting this range as suitable for fire heat fluxes (~800–3000 kW/m²), wind speeds (5–10 m/s) and PBL depths (300–500 m with and without capping temperature inversions) of the three ACS experimental burns. Further work exploring the applicability of this AERMOD setup to a broader range of conditions is ongoing. Full article

This paper presents a numerical method for solving transient one-dimensional heat conduction problems in multilayer slabs with temperature-dependent thermal conductivities. The governing nonlinear partial differential equations are formulated separately in each layer, allowing for distinct material properties. Perfect thermal contact at internal interfaces is enforced through continuity of temperature and heat flux, while general boundary conditions are imposed at the external boundaries, including prescribed temperature, specified heat flux, and convective exchange. A key feature of the proposed approach is to discretize the partial differential equations first in time using the implicit Euler method, thereby reducing the original problem to a sequence of nonlinear two-point boundary value problems with interface (transmission) conditions. A second-order finite difference scheme is employed for spatial discretization, and the resulting system is expressed in global form using a unified indexing strategy. The system is solved at each time step by Newton linearization, yielding a sparse Jacobian matrix that is tridiagonal in the interior and locally extended at the interfaces. Efficient banded solvers lead to O(N) cost per time step, where N is the number of spatial nodes. Numerical experiments confirm the expected accuracy, unconditional stability, and computational complexity of the method. Full article

The results of a numerical modeling of the laminar water flow and mixed conductive–convective heat transfer in highly elongated heatsink with continuous rectangular microchannels, and a width-to-length ratio of 625 (i.e., 0.2 mm to 125 mm), are presented, along with two methods of fluid entry (along and perpendicular to the base of the heatsink) for a wide range of surface heat flux density q from 30 to 2000 kW/m² and water volume flow rate from 10 to 50 L/h (${Re}_D=26-128$). It has been demonstrated that: (1) The elongated microchannel maintains its effectiveness in heat removal by water, even under conditions of high q-value; however, in the terminal sections the temperature can approach the maximum permissible operating level for high-loaded silicon electronic components (~95–100 °C). (2) For microchannel heatsinks, the direction of the incoming flow is not of significant influence, since the microchannel structure, even with a height of 2.5 mm, exhibits substantial diffusivity and the flow in the inlet area rapidly turns along the heat distribution base; this flow further possesses the same characteristics as in the case of the input flow parallel to the axis of the microchannels. The developed model allows for the optimization of geometric, kinematic and thermal parameters of highly efficient microchannel devices, depending on the expected operating conditions. Full article

Given the modernization of power systems in recent years, the quality of electrical energy is changing. With the increasing prevalence of harmonic components and rising current densities, conductor efficiency has become critically important. This study investigates the skin effect as a function of conductor geometry within the framework of electromagnetic field theory. Classical circular cross-section cable geometries and rectangular busbar systems were compared under an AC current of 1350 A (peak) across a frequency range of 50–500 Hz. The findings are comparatively presented, and their electromagnetic and thermal implications are discussed. Numerical modeling and simulation studies were performed using the Finite Element Method. COMSOL Multiphysics^® software AC/DC Module 6.2 version was used for the analyses. In the simulation studies, the magnetic flux density distribution within the conductor and the current concentration induced by eddy currents were analyzed. Frequency-dependent behavioral characteristics were examined in the analyses. The results revealed that the conductor with circular geometry exhibited a more severe skin effect. The rectangular conductor used in busbar systems was found to effectively distribute the current density across its surface area. Thus, rectangular geometry optimizes AC resistance. The analysis results revealed that conductor design and material selection depend not only on the cross-sectional area but also on the geometric shape factor. In this context, it was determined that conductor design has a decisive effect on electromagnetic power losses, which directly govern the heat generation potential within high-current systems. This study serves as a technical guide to evaluate frequency-dependent electromagnetic performance across a 50–500 Hz range—reflecting frequencies relevant to harmonic components—to assist in the design and optimization of high-current energy distribution systems. Full article

Regarding heat conduction in sliding contact pairs, this paper investigates the interfacial heat partition problem with conduction heat flux taken into account to address the issue of the heat partition coefficient falling outside its physically reasonable range. The main contributions of this study are as follows. First, conduction heat flux is explicitly introduced, and the governing equation for the heat partition coefficient incorporating conduction heat flux is derived via Green’s function method. Subsequently, to tackle the nonlinearity caused by the time-varying velocity and heat source of the contact pair, least-squares estimation is adopted to solve for the heat partition coefficient and conduction heat flux. The results indicate that under extreme operating conditions with drastic variations in heat source and velocity, traditional heat partition models yield unphysical results where the heat partition coefficient is less than 0 or greater than 1, whereas the modified model effectively resolves this issue. Furthermore, this paper analyzes the effects of material parameters, motion characteristics, and thermal loads on heat partition. The findings of this work provide a reference for interfacial thermal design and thermal management of various sliding contact pairs. Full article

Rapid urban-industrial development has intensified surface warming in global cities, including India, posing critical challenges for sustainable urban environments. While advanced AI and remote sensing methods have mapped urban heat patterns, a fundamental thermodynamic understanding of how cities generate, absorb, store, and dissipate heat with the urban land transformation remains underexplored. This study conceptualizes the urban geo-thermodynamics mechanism as a comprehensive framework to quantify urban surface energy exchanges, heat flux dynamics, and thermal responses in the Haldia urban-industrial region (103.84 km²) of eastern India. The analysis employs Landsat-derived impervious surface expansion, land surface temperature (LST), and normalized difference vegetation index (NDVI), NASA POWER radiation fluxes, world settlement footprint 3D structural (2023) and material stock (2024) data, and census-based population records (1991–2021). The integrated mathematical formulations were developed after the remote sensing-GIS-based statistical analysis for the urban energy balance through the Urban Thermodynamic Index (UTI), Urban Heat Retention Efficiency (UHRE), and Urban Cooling Potential (UCP) indices, which were developed from energy balance equations linking net radiation (Q*), anthropogenic flux (${\mathrm{Q}}_{\mathrm{F}}$), sensible and ground heat (${\mathrm{Q}}_{\mathrm{H}}$, ${\mathrm{Q}}_{\mathrm{G}}$), and latent heat flux (${\mathrm{Q}}_{\mathrm{E}}$). The results reveal a 36% increase in UTI and a 28% rise in UHRE between 1991 and 2021, indicating enhanced surface heat accumulation and anthropogenic energy input associated with built-up area and population growth (22.87–53.37 km²) and (1452–2375 person/km²). In contrast, UCP declined by 22%, reflecting reduced evaporative cooling due to vegetation loss, with the regression-based calibration (R² = 0.89; RMSE = 0.74 °C) validating strong correspondence with observed LST. These findings demonstrate a quantifiable link between thermodynamic processes and the transformation of the urban morphological landscape. The proposed mathematical-thermodynamic structure provides a scientific, GIS-based statistical method for urban heat risk assessment, energy-efficient planning, and geo-thermal environmental management, supporting global initiatives toward climate-resilient and sustainable urban development. Full article

Effective evaluation of building fabric is essential to understanding building performance. Traditional methods, such as ISO 9869-1, provide point U-values but do not always capture the complete picture, and new measurement-led approaches are needed to support building retrofit. Heat3D is a novel iOS application that performs rapid U-value measurements of building elements by mapping thermographic images from a mobile infrared camera onto an augmented reality (AR) model of a room, from which heat flux across the element is calculated. A field trial of 22 UK properties during the 2019–2020 winter heating season assessed Heat3D’s heat flux measurements against traditional heat flux plates, with 90% of 295 Heat3D surveys falling within the combined uncertainty of the reference method. A second field trial, conducted over the 2020–2021 winter heating period, evaluated a new timelapse iteration of the method capable of measuring wall U-value within approximately 60 min; 90% of 42 Heat3D surveys fell within the combined confidence interval of the ISO 9869-1-measured U-value. These results indicate that Heat3D offers a viable, rapid alternative to traditional methods for both heat flux and U-value measurement. Full article

An adaptive immersed boundary method (IBM) for simulating non-isothermal incompressible flows with convective heat transfer involving a rotating circular cylinder is developed. Both Dirichlet- (isothermal) and Neumann (zero heat flux)-type temperature boundary conditions are implemented. In addition to the discrete momentum forcing and energy forcing adopted to effectively satisfy the prescribed velocity and temperature boundary conditions, a mass source/sink term is introduced into the continuity equation to meet the mass conservation at the immersed boundary. The Navier–Stokes equations are solved using the fractional step method implemented on a staggered Cartesian grid system. Time stepping is performed using a second-order Adams–Bashforth/backward-differentiation method, while spatial derivatives are approximated with a second-order centered scheme. Testing of the flow induced by a rotating disk demonstrates that the spatial accuracy of the presented algorithm is second-order. Furthermore, the proposed method is validated by forced convective flow past a rotating isothermal circular cylinder. Finally, mixed Rayleigh–Bénard convection in a square cavity with an embedded adiabatic rotating circular cylinder is simulated, showing that heat transport can be greatly enhanced by increasing the rotating rate and radius of the cylinder at larger Prandtl numbers in the laminar regime. Full article

This research presents a physics-informed deep learning framework for investigating the magnetohydrodynamic flow of a dissipative non-Newtonian micropolar nanofluid induced by a stretching sheet, incorporating Stefan blowing, internal heat generation, and the zero nanoparticle mass flux condition. The physical model consists of the interplay between the microrotation dynamics, resistance of porosity on the microrotation, Brownian diffusion, and thermophoretic transport phenomenon. The numerical solutions for the nonlinear yielded equations that result from the above interaction are obtained by employing a PINN that considers the laws of physics and boundary conditions. With this technique, the flow behavior, temperature, concentration, and microrotation fields can be predicted accurately without requiring huge datasets. This shows the ability of PINNs to numerically treat highly-coupled nonlinear transport equations in a very efficient manner compared to other traditional methods. The important discoveries from this study include that the porous and magnetic factors increased the skin friction coefficient, but the magnetic effect and viscous dissipation decreased the rate of heat transfer, and the thermophoresis effect decreased the rate of mass transfer while the Brownian effect increased it. The precision of the PINN algorithm is confirmed by comparison of the results with the earlier findings, which proves very high accuracy and hence the robustness of the current computing framework. Results of this research are useful for the development of some thermal management systems, energy converters, cooling methods, chemical reaction processes, fuel cell technology, porous media reactors, and ocean engineering involving the transport of complicated non-Newtonian nanofluids. Full article

To achieve high interconnect density in 2.5D packages, various microscale structures such as through-silicon vias (TSVs), microbumps, and redistribution layers (RDLs) are employed. These features typically exist at the micron scale, whereas other package components span millimeter to centimeter scales, resulting in a wide range of physical dimensions within the package. Although finite element analysis (FEA) has proven effective for evaluating the mechanical and thermal characteristics of 2.5D packages, the inherent multi-scale nature poses significant computational challenges and numerical convergence issues, severely hindering the design and analysis of increasingly dense packages. To address this problem, this paper proposes an efficient numerical homogenization method for the mechanical and thermal analysis of 2.5D packages. The method employs periodic boundary conditions (PBCs) based on the concept of referential statistical volume elements (rSVEs). In this approach, typical microstructures—including TSVs, microbumps, and RDL traces together with the surrounding matrix material—are treated as a homogeneous medium, and the equivalent material properties of the multi-scale structures are evaluated. These properties include the stiffness matrices (from which the equivalent Young’s modulus, shear modulus, and Poisson’s ratio can be derived), coefficients of thermal expansion, and thermal conductivity. Validation results demonstrate that the proposed method ensures continuity of displacement, stress, strain, and heat flux across opposite surface pairs of the rSVEs. Compared with experimental measurements and other existing homogenization techniques, the method accurately determines the equivalent material properties of complex multi-scale structures without being restricted to specific geometries, while significantly improving computational efficiency. Finally, the proposed numerical homogenization method is successfully applied to wafer warpage analysis during the manufacturing process and to thermal analysis under operating conditions. The results indicate that the method achieves high computational efficiency while maintaining accuracy in both mechanical and thermal analyses of 2.5D packages, thereby laying a solid foundation for the development of next-generation 2.5D package structures. Full article

Anisotropic polymers fabricated via additive manufacturing exhibit complex thermal transport profiles that are challenging to characterize using steady-state techniques. We present a transient thermal method utilizing a short rectangular current pulse excitation to determine the directional thermal diffusivity and conductivity of anisotropic materials. The measurement is conducted on finite specimens, where the low diffusivity of the polymer media results in a highly attenuated and dispersed rear-side temperature profile over an extended transient window. Conduction losses to the adjacent coolers are accounted for by solving the one-dimensional heat conduction equation on an asymmetric multi-layer sandwich structure using the implicit Crank–Nicolson method. Because thermal diffusivity and conductivity are not independent quantities ($\lambda =a\rho c$), the inverse problem is deliberately formulated to estimate the diffusivity alone: the volumetric heat capacity is predetermined and held fixed, and the conductivity follows directly as $\lambda =a\rho c$. This removes the ill-conditioning that would otherwise arise from treating $\lambda$ and a as free, independent parameters in the fit. A two-parameter non-linear least-squares fit is applied to the rear-side temperature rise following Savitzky–Golay noise filtering to estimate the directional diffusivity and effective heat flux. The method is validated using an isotropic reference standard to rule out false system anisotropy, and is subsequently applied to additively manufactured polymer specimens to resolve print-induced directionality through sequential, axis-aligned (unidirectional) measurements along the axial and transverse printing directions. The validity of the one-dimensional reduction is confirmed quantitatively by two- and three-dimensional anisotropic simulations of the exact geometry, which bound the lateral-spreading bias below $0.01\%$ even for the highest-anisotropy specimen, and the robustness of the method to sensor thermal response, signal filtering, and effective-flux estimation is quantified. A rigorous evaluation of the expanded metrological uncertainty demonstrates the high accuracy and reliability of this low-energy excitation technique for highly dispersing media, making it a viable and highly accessible alternative for evaluating material anisotropy. Full article

The growing adoption of hybrid and plug-in electric vehicles increases heat generation in power electronic modules, driving demand for effective thermal management materials and reliable Al/Cu joining methods. However, large-area Al/Cu joints are challenging as conventional brazing requires high temperatures and flux, and fusion welding performs poorly with dissimilar metals. Contact-Reaction Brazing (CRB), which relies on eutectic-phase formation during heating, presents a promising alternative. Direct CRB of AA6063 and Cu might lead to severe aluminum dissolution above 570 °C. To mitigate this, large-area CRB of AA6063/Cu using a 4104 aluminum-foil interlayer is examined. Brazing temperature, holding time, and pressure are systematically varied to evaluate their influence on joint formation. Interfacial microstructures are characterized by SEM and XRD. Shear testing is used to assess fracture behavior and mechanical performance. A satisfactory shear strength of 48.8 MPa is achieved for the AA6063/AA4104/Cu joint under a brazing temperature of 540 °C, a holding time of 10 min, and an applied pressure of 600 Pa. Full article

The power density of modern high-power integrated processors keeps rising rapidly. Among them, chiplet-based high-power AI accelerators exhibit local peak heat flux exceeding 1 kW/cm², which leads to concentrated hotspots, severe internal temperature gradients, device performance degradation and reliability deterioration. Conventional heat dissipation approaches are limited by the bottleneck of series interfacial thermal resistance and fail to meet the cooling demands of complex integrated architectures. Chip-level thermal management serves as a core method to suppress hotspots near heat sources and reduce overall system thermal resistance, which guarantees long-term stable operation of high-power integrated processors and plays a vital role in improving the energy efficiency and service life of computing platforms. This paper systematically reviews mainstream chip-level thermal management technologies for high-power integrated processors, covering heterogeneous integration of high-thermal-conductivity substrates, embedded microchannel liquid cooling, solid-state active heat pumps, multi-physics co-design and advanced packaging manufacturing processes. The basic working principles and state-of-the-art research progress of each cooling technology are elaborated in detail. The common engineering bottlenecks, including ultra-high heat flux endurance, packaging process compatibility, fluid leakage risks and multi-layer interfacial thermal resistance, are summarized, and the future development trends of this field are clarified. This review can provide comprehensive theoretical guidance for structural design and large-scale engineering implementation of near-junction thermal management solutions for various high-power integrated processors, especially high-computing-power AI accelerators. Full article

Fire-induced temperature fields in double-steel-plate concrete structures are strongly governed by steel–concrete interfaces, where global temperature error alone is insufficient to characterize interface heat-transfer behavior. This study presents an interface-aware, surface-temperature-driven framework for rapid prediction of temperature fields and interpretation of interface behavior in fire-exposed composite structures. Full-field temperatures are reconstructed using surface-temperature histories, spatial coordinates, and material-region labels. To explicitly evaluate interface behavior, paired steel-side and concrete-side temperatures are extracted to compute temperature jumps and heat fluxes based on Fourier’s law. On this basis, an equivalent interface heat-transfer parameter $h_{\mathrm{eff}}$ is introduced as a physically interpretable descriptor that links interface temperature discontinuity and contact heat flux through $q_{\mathrm{contact}}=h_{\mathrm{eff}}(T_s-T_c)$. This formulation enables direct assessment of interface consistency from the predicted temperature field, rather than indirect inference from global error metrics. An FEM-generated dataset comprising 150 two-dimensional transient fire-heating cases is used, covering perfect-bond, constant-conductance, and temperature-dependent interface conditions. The proposed model achieves an overall validation RMSE of 7.73 °C. Local RMSEs are 11.91 °C, 14.86 °C, and 2.00 °C at the fire-exposed surface, front interface, and back interface, respectively. The predicted $h_{\mathrm{eff}}$ shows strong agreement with reference values, with a correlation coefficient of 0.956. In addition, the normalized contact heat-flux error decreases from 0.31 to 0.26. A locked checkpoint held-out test further confirms robustness, yielding an overall RMSE of 7.71 °C and an $h_{\mathrm{eff}}$ correlation of 0.946. The proposed framework is applicable to rapid thermal analysis of interface-dominated composite structures under fire exposure when surface-temperature histories, material-region labels, and paired interface samples are available. Overall, the results indicate that the method improves interface interpretability while maintaining accurate and computationally efficient temperature-field prediction. Full article