Search Results (2,661)

Coke deposition on the inner wall of helical coils in organic heat carrier (OHC) furnaces imposes additional thermal resistance, which impairs heat transfer and may trigger tube over-temperature failure. However, the quantitative coupling among the coking degree, flow conditions, and wall temperature response in helical coils remains insufficiently characterized. To address this gap, a three-dimensional steady-state conjugate heat-transfer model that resolves the additional thermal resistance of the coke layer is established using computational fluid dynamics (CFD). A dimensionless coking degree ω, defined as the ratio of coke layer thickness to inner tube radius, is introduced to parameterize the deposition state. Parametric simulations are performed at ω = 0–20%, with oil inlet velocities of 1–3 m/s. As ω increases from 0% to 20%, the maximum outer wall temperature rises by 66.1% (344 °C to 572 °C), whereas the maximum inner wall temperature decreases by 6.5%. The inner–outer wall temperature difference increases by over two orders of magnitude (1.61 °C to 251 °C), and the heat absorption of thermal oil declines by 53.4%. Raising the inlet velocity lowers the outer-wall temperature under clean-wall conditions, whereas this cooling effect is markedly diminished under severe coking. These findings provide a quantitative basis for the early-stage diagnosis of coking and safety evaluation of OHC furnaces. Full article

Sentry box buildings present excessive energy consumption and poor thermal comfort due to the lightweight envelope. Therefore, a framework integrating passive design with multi-objective optimization and cascading active airflow mode optimization for sentry box buildings was developed in the study. First, a parametric model for the prototype of sentry box buildings in the cold zone of China was developed. The global sensitivity analysis based on the treed Gaussian process was employed to select key design variables. Furthermore, backpropagation neural network prediction models for the UDI, PPD, and EUI of sentry box buildings were developed based on the dataset, which was generated via Latin hypercube sampling and building performance simulation in Grasshopper. Subsequently, the NSGA-II algorithm was selected for multi-objective optimization, combined with entropy-weighted TOPSIS analysis, to determine the optimal values of the design variables for sentry box buildings. Finally, the optimal airflow mode and velocity of sentry box buildings for summer and winter were selected through cascaded CFD simulations. The results indicate that the window-to-wall ratio is the most influential design variable across the optimization objectives of sentry box buildings. The prediction models achieve high accuracy, with the lowest coefficient of determination R of 0.994 and the highest mean squared error of 0.001. The optimized design improved performance across all objectives compared to the prototype of sentry box buildings, with UDI increasing by 77.433%, and PPD and EUI decreasing by 18.282% and 28.668%, respectively. Interestingly, the sentry box buildings should adopt a horizontal attached airflow mode at 1.5 m/s in summer and a vertical attached airflow mode at 1.8 m/s in winter. In summary, a decision-support tool was introduced in the study for the early design stage to assist in selecting optimal design solutions for the sentry box buildings. Full article

This study investigates the transient thermo-hydrodynamic behaviour of millimetric water droplets impacting heated solid substrates under subcooled conditions. The effects of wall temperature, wall material, and impact velocity on droplet spreading, heat transfer, and cooling performance are examined using high-resolution CFD simulations, validated against in-house experimental measurements of transient temperature evolution. The results show that droplet spreading is highly affected by impact inertia, with higher velocities producing faster radial expansion and larger maximum spreading. In contrast, the thermal response is strongly influenced by substrate properties. Steel exhibits steeper temperature gradients and stronger localized cooling within the substrate, while aluminium, owing to its higher thermal diffusivity and effusivity, sustains higher total heat-transfer rates at the wall–liquid interface. Increasing wall temperature significantly enhances the absolute heat-transfer rate due to the larger thermal driving potential, although normalized temperature profiles indicate reduced relative cooling. The analysis highlights the distinct roles of hydrodynamic and thermal mechanisms: impact velocity governs the lateral distribution of cooling, whereas substrate properties control the depth-wise thermal response. These findings provide a comprehensive understanding of droplet-induced cooling from a substrate perspective and offer insights for optimizing material selection and operating conditions in spray cooling, surface quenching, and high-heat-flux thermal management applications. Full article

Controlling pollutant dispersion in high-rise buildings is crucial for public health. Vertical pollutant diffusion in stairwells occurs under thermal and wind effects. However, most existing studies rely on idealized boundary conditions. To address this, this study uses field-measured wall temperatures and a window wind velocity as boundary conditions for transient CFD simulations. We investigate the vertical diffusion characteristics of buoyant (CH₄) and dense (CO₂) pollutants under thermal pressure, window velocity, and wind–thermal coupling in a high-rise residential building in Taiyuan. Results show an asymmetric “fast-up, slow-down” diffusion under thermal pressure, a relatively symmetric profile under window velocity, and a hybrid pattern under coupling where the upper region is wind-dominated and the lower region resembles thermal-driven diffusion. Wind–thermal coupling most significantly enhances upward diffusion. Using the arrival time of CH₄ at the 28th floor (about 15 m above the source floor) as the benchmark, the diffusion rate under coupling is about 200% faster than under thermal pressure alone, and about 50% faster than under the window-velocity condition alone. Differences in density lead to variations in dispersion, with CH₄ exhibiting higher rates, concentrations (2–4 orders greater), and a broader influence range than CO₂. This work interprets the synergistic regulatory mechanism between driving forces and pollutant density, providing a theoretical basis for ventilation optimization and pollution control in high-rise buildings. Full article

This study investigates the mechanical performance, high-temperature resistance, and microstructural characteristics of ground granulated blast furnace slag (GGBFS)-based geopolymer composites reinforced with boron nitride (BN)-modified hemp nanofibers. BN-modified hemp nanofibers (PVA-mBN/Hemp) were produced via electrospinning and incorporated into geopolymer mixtures at varying ratios ranging from 0 to 4 wt%. The effects of nanofiber content on composite properties were evaluated through mechanical testing, ultrasonic pulse velocity (UPV) measurements, and exposure to elevated temperatures (300–1200 °C), supported by SEM-EDS, FTIR, and XRD analyses. The results indicate that low nanofiber additions (0.5–1 wt%) improve flexural strength by up to 15%, although compressive strength is slightly reduced due to increased porosity. UPV measurements confirm the changes in internal structure. At elevated temperatures, nanofiber-reinforced samples exhibit enhanced residual strength compared to the control specimens, particularly at moderate temperatures, whereas significant degradation occurs above 900 °C. Microstructural analyses reveal improved fiber-matrix interaction, reduced crack propagation, and enhanced thermal stability attributed to BN modification. Overall, the incorporation of 0.5–1 wt% BN-modified hemp nanofibers provides an effective balance between mechanical performance and high-temperature resistance, highlighting their potential for use in sustainable and fire-resistant construction materials. This study contributes to the United Nations Sustainable Development Goals (SDGs), particularly SDG 9 (Industry, Innovation, and Infrastructure), SDG 11 (Sustainable Cities and Communities), and SDG 12 (Responsible Consumption and Production). Full article

In this work, a partitioned coupling algorithm is developed by integrating the improved discrete velocity method (IDVM) with the lattice Boltzmann flux solver (LBFS) to address conjugate heat transfer (CHT) in microscale systems across all flow regimes. Specifically, the flow field is solved by the IDVM, generating a heat flux that acts as a Neumann boundary condition at the interface for the solid domain. Subsequently, the LBFS calculates the thermal distribution inside the solid, and the updated temperature at the interface is then applied to the fluid computations as a Dirichlet condition. The proposed framework effectively combines the strengths of the IDVM in modeling rarefied gas flows with the advantages of the LBFS in handling heat conduction in complex geometries. Crucially, the current approach implicitly captures temperature jump discontinuities at the conjugate boundary, bypassing the requirement for supplementary jump conditions. To evaluate its performance, several CHT test cases involving rarefied gas in microchannels were conducted. Computational evidence suggests that the scheme is robust across diverse flow regimes. Full article

This paper proposes an experimental, intelligent optimization approach to improve the thermal cooling performance of an overclocked graphics processing unit (GPU). A closed-loop liquid-cooling system was built and tested utilizing deionized water and a silver (Ag) nanofluid coolant (0.015% vol.) across a variety of microchannel heat sink topologies with varying fin spacing. Key thermal performance indicators, including GPU temperature, coolant outlet temperature, and thermal resistance, were measured at different coolant flow rates. Experiments revealed that raising the flow velocity and decreasing the fin gap considerably enhanced cooling performance, while the Ag nanofluid consistently lowered GPU temperature by 1–3 °C compared to water. An Artificial Neural Network (ANN) surrogate model was constructed and trained using experimental data to support predictive analysis and system optimization, achieving excellent predictive accuracy with low RMSE. The trained ANN model was combined with the Non-dominated Sorting Genetic Algorithm II (NSGA-II) to perform multi-objective optimization, aiming to minimize GPU temperature and thermal resistance while improving heat removal. The Pareto-optimal solutions revealed that nanofluid-based cooling offered the best trade-off circumstances, with optimal designs occurring at moderate flow rates and small fin spacing. The ANN-NSGA-II multi-objective optimization results indicated that the best thermal performance of the GPU cooling system was achieved when using Ag nanofluid (0.015 vol.%) as the coolant, with an optimal coolant flow rate in the range of 1.30–1.84 LPM and an optimal fin/channel spacing of 0.57–0.71 mm, producing GPU temperatures of 29.18–29.66 °C, coolant outlet temperatures of 29.06–29.41 °C, and a minimized thermal resistance of 0.0106–0.0152 °C/W; thus, overall, the suggested ANN-NSGA-II framework works well as a practical design tool for improving GPU cooling systems and may be used to other high-heat-flux electronic thermal management applications. Full article

The growth of the global population has led to increased demand for agricultural products, resulting in greater agricultural waste production. One sustainable response to this challenge is using agricultural waste as raw material in building materials. This study examines the potential for partial replacement of natural aggregates in concrete with agricultural waste from typical Mediterranean fruits: sour cherry pits, grape seeds, ground olive pits, and carob seeds. To evaluate the effect of treatment on the behavior of agro-waste aggregates, ground olive pits were used untreated, treated with ash water, or treated with seawater. Carob seed concrete deteriorated during water curing due to seed swelling and tannin-related degradation, revealing its unsuitability without prior stabilization. Partial replacement of natural aggregates with agricultural waste resulted in decreased density, ultrasonic pulse velocity (UPV), dynamic elastic modulus, compressive strength, and thermal conductivity, while increasing saturated water absorption. Treatment with ash water on ground olive pits improved the interfacial transition zone (ITZ), resulting in 29% increase in compressive strength relative to untreated ground olive pits. Concrete with ash water treated ground olive pits demonstrated the highest practical potential among all tested agro-waste concretes. Full article

Waste heat recovery from automotive exhaust gases represents an important strategy for improving vehicle energy efficiency. This study experimentally investigates the performance of a thermoelectric generator (TEG) system based on TEC1-12706 modules running under different cold-side cooling conditions and incorporating a Hot Rolled Steel (HRS) protective layer on the hot side. The HRS plate was used to ensure uniform heat distribution and protect the thermoelectric module against thermal shocks generated by a 250 °C heat source. Four cooling regimes were experimentally analyzed: natural convection and forced airflows equivalent to 40, 60, and 90 km/h. The results proved that increasing airflow intensity significantly improved the temperature difference across the module, from approximately 16 ± 2 °C under natural convection to nearly 40 ± 2 °C at the highest airflow velocity. Correspondingly, the steady-state voltage generated increased from approximately 0.25 ± 0.01 V to over 0.60 ± 0.01 V under an 82 Ω resistive load. The measured hot-side temperature remained below 75 °C in all experimental conditions, confirming the thermal protection capability of the HRS layer. The experimental data also revealed a near-linear relationship between voltage and temperature difference, consistent with the Seebeck effect. The proposed configuration shows the feasibility of combining thermal protection and forced convection cooling to improve the stability and electrical performance of thermoelectric waste heat recovery systems intended for low-power automotive auxiliary applications. Full article

High-voltage self-blast circuit breakers feature complex gas flow field dynamics during the arc interruption process due to the multiple gas chambers and valves in the interrupter. The structure of key interrupter components and the characteristics of the operating mechanism significantly influence the gas flow field behavior, thereby affecting the breaking performance. The C₄F₇N gas mixture is currently the most promising alternative to SF₆. However, the influence mechanisms of various factors on its breaking performance remain unclear, which limits the design of C₄F₇N-based self-blast interrupter chambers. This paper investigates the impact of nozzle throat length and mechanism stroke on the breaking performance of a 126 kV double-motion self-blast circuit breaker prototype by establishing a magnetohydrodynamic (MHD) arc model for C₄F₇N gas mixtures. The results indicate that a longer throat length can enhance the pressure-buildup capability in the expansion chamber to some extent, but its effect on short arcing times is limited, whereas it has a more pronounced influence on medium and long arcing times. However, it also impedes arc energy dissipation, potentially reducing the breaking capability for short and medium arcing times while improving performance for long arcing times. A larger mechanism stroke not only ensures a greater contact gap at current zero for long arcing times but also accelerates the gas flow velocity between the contacts, facilitating arc energy dissipation and enhancing the thermal interruption performance. Full article

This study systematically investigated flow boiling characteristics within a novel three-layer microchannel heat sink with 3/4 open-ring pin fin arrays, designed for high-heat-flux thermal management of low-carbon metallurgical reactors. Two-phase flow regimes, pressure drop, and wall temperature responses were analyzed. To evaluate the impact of functional surface material properties on thermo-hydraulic behavior, a hydrophilic nano-coating modification was applied to the inner copper channel walls for comparison. Increasing the flow rate triggered a transition from a vapor-dominated confined slug flow to a liquid-dominated dispersed bubble flow, which effectively improved the thermo-hydraulic stability. Hydrophilic surface modification resulted in an average pressure drop reduction of 33% and significantly diminished the sensitivity of flow resistance to velocity variations. Through hydrophilic treatment, the localized vapor film effect at high velocities was suppressed, and temperature field homogenization was promoted, yielding a maximum convective heat transfer coefficient of 7760 W/(m²·°C), i.e., 72.9% enhancement over the baseline heat sink. The underlying mechanism is attributed to the formation of a stable near-wall thin liquid film and the promotion of high-frequency nucleate boiling. These results will be of high relevance for developing efficient cooling solutions for power electronics, thereby supporting the advancement of low-carbon metallurgical reactors. Full article

This paper probes into the propagation characteristics of Rayleigh waves in a partially saturated, porous, thermo-viscoelastic half-space, with full consideration of the fractional viscoelastic effect and thermal coupling effect. A fractional Zener model is introduced to depict the thermo-viscoelastic mechanical behavior of the solid skeleton by constructing a complete set of governing equations that include mass balance, generalized Darcy’s law, momentum balance, and generalized heat conduction. Field equations are derived by means of Helmholtz vector decomposition, and the dispersion equation, and the phase velocity expression of Rayleigh waves are obtained by combining the traction-free and adiabatic boundary conditions of the medium. The impacts of key material properties, such as medium saturation, intrinsic permeability, medium viscoelasticity, and thermal expansion coefficient, on the dispersion feature of Rayleigh waves are discussed in detail. Numerical analysis results show that an increase in the thermal expansion coefficient will lead to a rise in Rayleigh wave phase velocity, in which the increase in P1 compressional wave velocity plays a dominant role among the velocities of various types of waves. Meanwhile, the attenuation coefficient of Rayleigh waves presents a decreasing trend and gradually tends to be stable with the growth of the thermal expansion coefficient. Similarly, the phase velocity of Rayleigh waves also increases with the rise in fractional order index, which is jointly dominated by the velocity enhancement of P1 waves and S waves. In addition, the attenuation coefficient of Rayleigh waves increases first and then decreases with the increase in fractional order index and reaches the peak value when the fractional order index is about 0.4. The research results reveal the influence of laws of thermal expansion characteristics and viscoelasticity on Rayleigh wave propagation and provide theoretical support for the analysis of wave propagation characteristics in porous media in relevant engineering applications. Full article

Plastic injection molding in cleanrooms involves high thermal loads and strict particle limits. The hot surfaces of the injection molding machine and peripherals increase the cooling demand of the heating, ventilation, and air conditioning system to an undefined amount. Moreover, the generation of buoyancy-driven plumes has the potential to disturb the cleanroom airflow around the injection mold, thereby risking cross contamination of the manufactured components. The present study quantifies the global heat load of injection molding machines in an ISO Class 7 cleanroom with a laminar flow microenvironment around the mold. Therefore, a measurement-based method to determine the heat load of a complete injection molding production cell is applied to a hydraulic and an electric machine. This method revealed that the heat load of the isolated machines is process-independent, whereas the total heat load of the complete production cell scales linearly with mold temperature. Moreover, the emitted heat to the cleanroom is considerable lower than the injection molding machine’s installed power. Secondly, the airflow regime and particle transport in the mold area are analyzed. This is achieved by means of schlieren visualization and aerosol measurements. The introduction of a modified Archimedes number, incorporating mold size and convective heat flux, has led to the observation of a correlation between flow regimes and the resulting particle load. This enables the selection of case-dependent FFU velocities that deviate from the conventional recommendation of an air speed of 0.45 m/s ± 20%. Despite the presence of a filter-fan unit, the particle load near the injection mold cavity increases for flow conditions that exceed a critical Archimedes number. Full article

This study presents a data-driven framework to predict and optimize the quality of date juice (DJ) produced from two commercially important Saudi cultivars (Sukkary and Khlass) using physicochemical and processing variables as model inputs. A total of 1600 experimental runs were performed by systematically varying initial fruit moisture content, extraction temperature (20, 40, 60, and 80 °C), mixing velocity (10, 20, 30, 40, and 50% of maximum speed), and date-to-water ratios (1:1, 1.5, 2, 2.5, and 3 w/w). The produced juices were characterized at 25 °C for water activity, moisture content, density, pH, total soluble solids (°Brix), turbidity, viscosity, hydroxymethylfurfural (HMF), browning index, extraction time, electrical energy consumption, and an integrated Quality Index (Qi). A feed-forward artificial neural network (ANN; 7–15–1) with a hyperbolic tangent transfer function was developed and validated using normalized datasets, and its performance was benchmarked against multiple linear regression (MLR). The ANN consistently outperformed MLR for Qi prediction, achieving higher coefficients of determination and lower error indices across training, testing, and validation, indicating strong generalization and minimal overfitting. Sensitivity analysis highlighted total soluble solids, moisture content, and HMF as the most influential predictors of Qi. Optimal juice quality (Qi ≥ 0.91) was repeatedly achieved under moderate thermal conditions (≈60 °C), with 40% mixing velocity and a 1:2.5 date-to-water ratio, providing a practical operating window for producing juice at the target °Brix while limiting thermal quality deterioration. Overall, the proposed ANN-based model provides an actionable decision-support tool for process optimization and quality standardization, supporting the transition of date-juice manufacturing toward Industry 4.0 through data-driven monitoring and adaptive control strategies. Full article

Herringbone gear pairs are critical in high-speed aerospace transmissions, where windage power loss significantly impacts efficiency and thermal management. This study proposes a prediction method that decomposes the total windage loss into five components based on structural features: the tooth, end, circumferential, and relief groove surface losses for both gears, and the meshing extrusion loss. Theoretical models for each component are established to form a complete prediction method using fluid–structure interaction principles. CFD simulations analyze the velocity, pressure, and energy fields around the gear pair, with windage loss integrated via fluid torque on gear surfaces. Results indicate that windage loss escalates rapidly and becomes non-negligible when the driving gear speed exceeds 7000 rpm. The prediction model demonstrates strong agreement with CFD simulations, with a maximum relative error of 13.6%. Analysis reveals that the driving gear contributes the largest share of the total gear pair loss, with meshing extrusion accounting for 20.1–23.6%. For a single herringbone gear, the tooth surface is the primary source of loss (~83%), followed by the end surface (~8%), while relief groove and circumferential losses remain below 10%. This research provides a validated theoretical foundation for optimizing efficiency and thermal control in high-speed aerospace gear systems. Full article