Search Results (320)

This study investigates steady-state heat transfer in a three-layer cylindrical system with angular non-uniformity of the temperature field. For the considered geometry, a mathematical model of heat conduction is formulated in cylindrical coordinates with piecewise constant thermophysical properties and continuity conditions at the interfaces between layers. The direct problem is solved analytically using a Fourier series expansion of the temperature field with respect to the angular coordinate. Based on experimental temperature measurements obtained for various configurations of soil layers, an inverse problem is formulated and solved to reconstruct the thermal conductivities of the individual layers and the heat transfer coefficient at the external boundary. To stabilize the solution, a regularized least-squares approach is employed. The convergence of the recovered parameters with respect to the harmonic number is analyzed, and the averaged reconstructed values are compared with the exact parameters used in the direct problem. The obtained results demonstrate the stability and accuracy of the proposed method, confirming its applicability to the identification of thermophysical parameters in multilayer soil systems based on experimental data. Full article

East Antarctica is composed of a composite Precambrian shield largely covered by a thick ice sheet. Information on the thermal structure of the East Antarctic lithosphere is critical to the understanding of the geological history and ice sheet dynamics of this region. To better describe the lithospheric thermal structure, Curie-point depths are first estimated through the inversion of aeromagnetic anomaly data using the wavenumber-domain centroid method, and the Curie point estimates is further employed to determine a lithospheric thermal thickness model by integrating the 1D steady-state heat conduction equation. Our results show that the variations in both the Curie-point depth and thermal thickness estimates have strong spatial consistency with known major geological provinces, such as ancient cratons and younger orogens. Moreover, our findings show a hot and thin lithosphere in the Gamburtsev Subglacial Mountains and Dronning Maud Land, whereas a cold and thick cratonic lithosphere is found in the Wilkes and Aurora Subglacial Basins and the hinterland of Enderby Land. A few local-scale thermal anomalies are also observed in cratonic areas, indicating that some of these areas have lost their cratonic signature. The new thermal thickness model provides direct constraints that can be used to trace early tectonic–thermal activities in East Antarctica. Full article

Biomass waste is a renewable energy source applied in various forms of energy, including electricity, heat, and fuel. Fuel generated through the pyrolysis of gas-fired industrial burners has played a crucial role in decreasing carbon emissions and addressing the greenhouse effect. This work investigated the efficiency of pyrolysis in gas-fired industrial burners using a numerical study using Computational Fluid Dynamics (CFD). The study observed the effects of varying combustion power levels (200 kW, 700 kW, and 1000 kW) and operational pressures (105.5 kPa and 211 kPa). The numerical analysis employs the k-ω standard viscous model for turbulence and assumes steady-state conditions. Grid testing and validation were conducted based on prior studies. The results show that the highest efficiency was achieved at 62.03% using a combustion power level of 1000 kW and an operating pressure of 211 kPa. The selected parameters are the recommended configuration for practical applications. Full article

In response to the problems of high energy consumption and difficulty in precise regulation of electric tracing anti-icing systems for polar marine engineering equipment in low-temperature, strong-wind, and high-humidity environments, this paper conducts experimental measurement and predictive modeling research on the convective heat transfer characteristics of electric heat-traced circular cylinders in cross-flow. First, a controllable environmental experimental system was set up to obtain 144 sets of steady-state convective heat transfer data under different combinations of wind speed, temperature, humidity, and heat flux density. Based on this, a Nusselt number (Nu) prediction model using a fully connected Deep Neural Network (DNN) was constructed, and its performance was evaluated through five-fold cross-validation. The results show that the DNN model can effectively capture nonlinear mapping relationships among multiple factors, and its prediction accuracy ($R^2$ = 0.9828) is superior to that of traditional machine learning models. Furthermore, the Shapley Additive Explanations (SHAP) method was introduced to analyze the multi-factor coupling mechanisms, quantify the contribution of each input variable to the Nu prediction, and provide a data-driven reference for the optimization of engineering parameters under extreme polar conditions. Full article

This research paper investigates the solution of diffusion equations characterized by Third-Kind (Robin) boundary conditions within n-dimensional complex domains. The analysis is conducted in the $L_2$ Hilbert space, which facilitates the substantiation of both the existence and uniqueness of solutions through variational methods. Analytical solutions are derived for multidimensional domains by employing the Fourier method and spectral analysis techniques. Complementing this theoretical framework, a high-accuracy numerical approach based on the Associated Legendre Polynomials Collocation Spectral Method (ALP-CSM) with Chebyshev–Gauss–Lobatto nodes is developed. Rigorous convergence analysis confirms spectral accuracy, with numerical examples in one, two, and three dimensions demonstrating error decay from $\mathcal{O}\left({10}^{-3}\right)$ to machine precision $\mathcal{O}\left({10}^{-15}\right)$. The mathematical impact of Third-Kind boundary conditions on the diffusion rate and the steady state of the system is demonstrated. The obtained results provide a robust tool for modeling physical processes, particularly in systems involving heat exchange on the surfaces of complex-structured domains, offering both theoretical insight and computational efficiency. Full article

Dimethyl ether (DME) is a promising alternative fuel for compression ignition (CI) engines due to its potential to simultaneously reduce nitrogen oxides (NO_x) and particulate matter (PM) emissions while maintaining diesel-equivalent power. However, its combustion behavior under varying injection timing and exhaust gas recirculation (EGR) conditions remains insufficiently characterized for practical calibration. This study investigates the combustion, emissions, and performance of DME relative to diesel using a fully instrumented John Deere 6068CI550 single-cylinder research engine modified for high-pressure common-rail DME operation. Baseline tests were conducted at three ISO 8178 C1 steady-state modes with matched combustion phasing, load, and EGR to isolate fuel property effects. Injection timing and EGR sweeps were then performed at 1600 rpm and 50% load. Results show that DME produces 10–35% lower NO_x and orders-of-magnitude lower PM than diesel while maintaining comparable thermal efficiency. DME exhibits a single-stage premixed heat release structure with reduced peak apparent heat release rates and 4–5° shorter combustion durations than diesel. Stable combustion was sustained up to 55% EGR, beyond which incomplete combustion increased carbon monoxide (CO), total hydrocarbons (THC), and fuel consumption. Optimal low-emission operation occurred near CA50 ≈ 16° ATDC and EGR levels of 30–40%. These findings demonstrate DME’s ability to mitigate the traditional diesel NO_x–PM tradeoff and support its viability as a low-emission CI fuel. Full article

This work investigates the design, simulation, and characterization of thin-film platinum resistive heaters fabricated by magnetron sputtering. Finite element simulations were performed in COMSOL Multiphysics to analyze heat generation and temperature distribution as a function of heater geometry under steady-state conditions. The influence of convective heat transfer on temperature uniformity and thermal efficiency was systematically examined. Platinum thin films deposited by magnetron sputtering were characterized in terms of their structural, morphological, and electrical properties. The crystallographic structure was analyzed using X-ray diffraction, while the surface morphology and microstructure were examined by atomic force microscopy and scanning electron microscopy. Electrical conductivity measurements were carried out to evaluate resistive behavior relevant to heater performance. All characterizations were conducted for as-deposited samples and after post-deposition annealing at 500 °C to assess the effect of thermal treatment on film stability and properties. The simulation results were experimentally validated by infrared thermography, allowing a direct comparison between calculated and measured temperature distributions. The combined numerical and experimental approach enables the correlation among the deposition conditions, microstructural evolution, geometry, and electrical heating performance, providing guidelines for the optimization of thin-film platinum resistive heaters. Full article

Road noise has become a dominant interior noise source in electrified vehicles, especially at low and medium speeds. In practical active road noise control (ARNC) systems, the error microphones capture not only the road noise component correlated with the reference sensors but also non-coherent disturbances such as wind noise, engine harmonics, and heating, ventilation and air conditioning (HVAC) noise. These disturbances degrade the convergence stability and steady-state attenuation of the conventional filtered-x least mean square (FxLMS) algorithm. This study analyzes FxLMS under non-coherent interference and develops two robustness optimization methods. Under the small-step-size assumption, a statistical convergence model is derived for stationary random inputs, together with the corresponding convergence region and steady-state error expressions. Based on this analysis, a multichannel cascaded controller (MCC) and a bounded variable-step-size (VSS) FxLMS algorithm are proposed. Offline simulations and dSPACE-based experiments are conducted on a single-channel HVAC duct ANC test platform and a vehicle test bench. The vehicle-bench tests use controlled tonal excitations and should be interpreted as an intermediate validation step before real-driving broadband tests. Average noise reduction (ANR) and the norm of the adaptive-filter coefficients are used to evaluate robustness. Both MCC and VSS improve attenuation and reduce coefficient fluctuations under non-coherent interference. Relative to fixed-step FxLMS, the maximum ANR improvement reaches 15.8 dB in simulation and 14.2 dB in the real-time duct experiment. Within the controlled tonal and tonal-plus-white-noise conditions tested here, VSS achieves robustness improvements close to those of MCC with much lower computational cost; therefore, it is a practical candidate for further onboard ARNC evaluation rather than a completed validation under real-driving broadband road noise. Full article

An analytical solution is presented for transient heat conduction in a two-layer composite cylinder subjected to outer-surface convection with a general time-dependent ambient temperature. Using Duhamel’s principle, closed-form series expressions are derived and then specialized to harmonic ambient fluctuations, recovering the classical constant-ambient solution in the zero-frequency limit. A parametric study shows that the ratio of the inner layer conductivity to the conductivity of the outer layer strongly shapes interfacial gradients and mean-temperature evolution, with sensitivity concentrated at small ratios and diminishing when the ratio is larger than 0.1. Increasing Biot number accelerates the heat transfer and approaches the isothermal-surface limit as it becomes extremely large. The geometric aspect ratio is most influential when the inner layer is resistive, and becomes weak for large conductivity ratio, supporting thin-coating approximations. Under harmonic ambient fluctuations, the response rapidly reaches a periodic steady state; higher frequency decreases amplitude and increases phase lag, while larger Biot numbers amplify oscillations and reduce delay. The coupled effects of the aspect ratio and the conductivity ratio govern penetration and phase behavior. Full article

Accurate thermal characterization of building insulation materials is essential for reliable energy performance assessment, regulatory compliance, and the development of high-performance envelopes. On one hand, the growing adoption of innovative insulating products, such as nanoporous materials, aerogel-based composites, bio-based panels, and thin insulating coatings, helps to enhance buildings’ energy efficiency by means of sustainable raw materials. On the other hand, conventional measurement techniques encounter significant challenges, due to their heterogeneity, reduced thickness, and unconventional geometries. In this study, an intra-laboratory comparison of three widely used methods for thermal conductivity determination is presented: the Transient Plane Source (TPS, Hot Disk) method, the Guarded Hot Plate (GHP) method, and the Heat Flow Meter (HFM) method. A total of twelve insulating materials, spanning super-insulating cores, insulating renders, bio-based panels, and nanocomposite coatings, were experimentally characterized under controlled laboratory conditions. A view on the analyzed insulating materials’ cradle-to-grave environmental impact is also given, to enhance the users’ awareness for the highly informed choice. The results highlight systematic differences between transient and steady-state approaches, with TPS measurements generally exhibiting larger deviations for materials characterized by surface roughness, limited thickness, or strong internal heterogeneity. In contrast, GHP and HFM methods show closer agreement when specimen geometry and stabilization requirements are satisfied. The influence of contact resistance, probing depth, specimen preparation, and uncertainty propagation is critically analyzed for each technique. The study provides practical insights into the applicability limits of commonly used thermal characterization methods and emphasizes the importance of selecting measurement techniques in relation to material morphology and testing constraints. These findings support more reliable thermal property assessment of emerging insulation materials and contribute to improved consistency between laboratory measurements and energy performance evaluations for buildings. Full article

On-orbit space cameras face high heat dissipation and non-ideal thermal contact interfaces. Thermal interface material (TIM) performance affects detector stability and imaging quality. However, traditional fillers are not clearly suitable for large-area, low-pressure, and non-ideal conditions. This paper assumes that embossed indium foil compensates for interface irregularities at micro and macro scales. It thus reduces interface thermal resistance (ITR). We propose embossed indium foil as a TIM. We build an evaluation framework from surface thermal resistance to component-level validation. Experiments are conducted on a steady-state heat flux platform. We measure ITR of four foil thicknesses (0.1–0.3 mm) under different pressures (0.17–1.38 MPa) and temperatures (10–30 °C). Results show strong pressure dependence. At low pressure (<0.6 MPa), thinner foils perform better due to lower bulk resistance. At high pressure (>0.6 MPa) and large area (0.06 m²), thicker foils show advantages. Their higher plasticity better compensates surface errors. Engineering tests confirm the method’s effectiveness. A 0.285 mm embossed indium foil reduces ITR from 3055 to 750 mm²·°C·W⁻¹, a 75.5% reduction. This study proves embossed indium foil fills micro-gaps and compensates macro-shape errors. It provides quantitative support for spacecraft thermal design. Full article

The Earth–Air Heat Exchanger (EAHE), also referred to as an air–soil heat exchanger, represents an effective passive cooling technology that exploits the thermal inertia of the ground. This study presents a combined experimental and analytical investigation of an EAHE system installed at the Faculty of Sciences of Agadir (Morocco). A steady-state analytical model based on convective heat transfer between the airflow within a buried duct and the surrounding soil is developed to describe the axial evolution of air temperature along the exchanger. The model is formulated under a sensible heat transfer framework, where the influence of humidity is accounted for through its effect on the thermophysical properties of moist air, while latent heat transfer and condensation phenomena are neglected. An instrumented experimental setup was implemented to perform continuous measurements of air temperature and relative humidity over a seven-month monitoring period. The experimental results indicate that the outlet air temperature remains stabilized within the range of 23.5–23.8 °C, despite significant variations in ambient temperature (13–38 °C). A parametric analysis is conducted to assess the influence of duct diameter, airflow velocity, and humidity through its effect on moist air properties on the thermal performance of the system. The close agreement between experimental observations and analytical predictions demonstrates the validity and predictive capability of the proposed model. These findings highlight the potential of EAHE systems as an effective passive cooling solution for greenhouse applications in semi-arid climatic conditions. Full article

Soil thermal conductivity is a key parameter in modeling heat transfer, temperature-driven moisture migration, artificial ground freezing, and geothermal systems. However, most existing thermal-conductivity models do not account for temperature effects. This study aims to determine the temperature-dependent thermal conductivity of silty and fine sandy soils at elevated temperatures using a steady-state heat cell method, addressing the limitations of transient probe techniques, which are affected by air voids and heat loss at the needle–soil interface. The experiment employs a heat cell under one-dimensional steady-state heat-transfer conditions, with sufficiently small temperature gradients to prevent temperature-induced moisture migration, and measures the soil’s thermal properties at steady state by indirect temperature and heat-flux measurements using various sensors. The test observations showed well-correlated thermal conductivity readings from steady state and transient probe methods at room temperature. Furthermore, the measured thermal conductivity of the sandy soil demonstrated a near-linear increase with temperature, with the highest dependence at 15.1% and 22.5% saturation for Benbrook (SM) and fine-grained Ottawa (SP) sands, respectively. Several commonly used existing thermal conductivity models were used to fit the measured thermal conductivity. A new thermal conductivity model was developed, incorporating a temperature-dependent correction based on the best-fit model. The proposed model could more accurately capture the increased thermal conductivity of soils with temperature. The findings will significantly improve the modeling of soil-temperature-dependent multi-physics behavior. Full article

The sustainable renovation of ageing industrial buildings presents both a challenge and an opportunity to enhance energy efficiency while preserving architectural and structural integrity. This study develops an integrated methodological framework for assessing and optimising multilayer wall systems in such conversions, combining thermal, environmental, and durability analyses. Six composite wall configurations were designed and numerically evaluated using steady-state 2D heat conduction and vapour-diffusion models. The results reveal substantial thermal improvement compared to the reference uninsulated brick wall (U = 1.41 W/m²·K). The proposed systems achieved U-values between 0.351 and 0.172 W/m²·K, meeting or surpassing European energy standards. The BP–EPS wall exhibited the lowest U-value (0.172 W/m²·K), while the FC–EPSR configuration achieved superior corner performance with a 2D surface temperature (Tsi) of 17.99 °C and the highest surface temperature factor (fRsi = 0.943), along with a reduced condensation risk, indicating more balanced overall performance. Weight and thickness reductions of up to 80.5% and 52%, respectively, were observed, enhancing retrofit feasibility and space efficiency. Life Cycle Assessment results indicated that optimised wall configurations reduced embodied carbon (A1–A3) by up to 78% and total life cycle emissions (A1–A3 + B6) by over 86% relative to the reference case. Vapour-diffusion analysis confirmed the FC–EPSR wall’s lowest condensation fraction, indicating excellent hygrothermal durability. Multi-criteria evaluation using the simple additive weighting method and Monte Carlo robustness analysis verified FC–EPSR as the most balanced and reliable system. Overall, the findings present a validated and replicable pathway for the sustainable renovation of industrial buildings, supporting the goals of European carbon neutrality and the circular economy. Full article

Inductors are critical components in power electronic systems, yet their thermal behavior is often approximated using simplified lumped models that neglect internal gradients and transient spatial effects. This paper presents a benchmarking study of analytical thermal modeling approaches for cylindrical inductors, including 0D lumped, 1D radial, and 2D radial–axial transient formulations. Starting from the general heat conduction equation in cylindrical coordinates, closed-form or semi-analytical solutions are discussed under uniform internal heat generation and convective boundary conditions. The proposed framework provides a benchmark-oriented analytical reference for selecting the appropriate thermal model complexity in reliability-oriented design of inductive components in power electronic systems. The models are applied to a representative two-layer cylindrical inductor composed of a ferrite core and a copper winding, under identical loss and cooling assumptions, considering two axial lengths in order to assess geometric influence. Steady-state temperature levels, transient responses, modal time constants, and axial gradient indicators are extracted to quantify the differences among modeling levels. The results show that the dominant thermal behavior is governed by a single slow mode with a time constant on the order of one hour. The spatially averaged temperature predicted by the 0D model deviates by less than 2.5% from the 2D solution in steady-state conditions, with the 1D model providing accurate predictions when axial gradients remain weak. Full article