To address the issues of low classification efficiency in traditional vortex air classifiers and the difficulty of completely separating fine powder entrained in coarse powder, an improved structure equipped with a settling chamber and tangential tertiary air is proposed. The settling chamber utilizes gravitational settling to buffer and collect agglomerated coarse particles, effectively reducing the powder load in the classification zone and helping to stabilize the overall gas-solid two-phase flow field. The tangentially introduced tertiary air performs secondary pneumatic cleaning of fine powder on the surface of coarse particles during the settling process, using shear dispersion to bring the attached fine powder back into the classification zone, thereby significantly suppressing the carryover of coarse particles into the fine fraction. This combined structure enhances classification accuracy, improves flow field stability, and achieves efficient separation of fine and coarse powders. The modified classifier exhibits good practical engineering value in applications requiring high powder purity. After numerical simulation analysis, the following results are obtained: with a main air inlet velocity of 12 m/s, a tertiary air velocity of 2 m/s, a rotor speed of 600 rpm, the classification accuracy K = 0.74, and the cut size \mathrm{D_{50}} = 39.95μm. This study provides a theoretical basis for the optimization of vortex air classifiers.
Heat transfer and hydrodynamic characteristics are compared numerically for the straight, stepped, zigzag spiral and Archimedean helical tubes of various cross-sectional shapes under laminar flow conditions ranging between 1300 - 2500 of water and CuO-water nanofluid. The channel geometries considered are circular, square, rectangular, elliptic (oval), T-section, and I-section, with a total length of 1830 mm. The simulations are conducted with Ansys Fluent R2021. Heat transfer characteristics are examined for the inlet fluid temperature and the external tube surface heat flux system. Best cross-sections are chosen, and a fluid path is designed that leads to the maximum heat transfer efficiency and ease of frictional losses, using water as the working fluid. After optimizing the structure, CuO-water nanofluids with volume fractions of 1% and 2% are employed to assess enhancements in heat transfer and pressure drop relative to pure water. With the presence of spirally directed flow using a helical twisted channel, the I-shaped model exhibits much-enhanced thermal characteristics compared to those in linear channels, with further enhancement in maximum temperature at the outlet to (312.7 K) from the conventional round tube value of (305.7 K). On the other hand, as imposed with Archimedean helical flow pattern in conjunction with the I-shaped scenario, there is an increase in heat transfer improvement leading to outlet temperatures with values of (315.0 K) as opposed to straight channel results (312.7 K). Furthermore, promisingly higher levels of heat transfer are found for CuO for output temperatures ranging from (316.1 K) to (317.0 K), corresponding to nanoparticle concentrations of 1% and 2% respectively. It is also ascertained that an I-section together with an Archimedean helical trajectory showed higher thermal efficiency, although this leads to increased energy consumption arising from the dynamic resistance of the fluid flow. The results provide insights into a favorable approach to I-shaped channels for enhanced designs in advanced thermal systems.
The thermal performance of brazed plate heat exchangers (BPHEs) can be affected by flow maldistribution. In this study, a numerical model with porous media is established to predict the flow distribution of plate heat exchangers (PHEs), and the ε-NTU method was employed to evaluate the heat transfer efficiency of the PHE. It’s found that the flow maldistribution in PHE is serious, and there is an obvious difference between the velocity distribution and the mass flow distribution in the two-phase flow due to phase separation. To improve flow uniformity, orifice tube distributor (OTD) with baffles and groove type distributor (GTD) have been proposed and studied at different qualities. It turns out that quality has a great influence on nonuniformity. With the increase of quality, the nonuniformity of baseline design and OTD increased first and then decreased, while GTD showed different performances. Both distributors can reduce flow nonuniformity compared with the baseline design. Due to the baffles hindering the backflow, the OTD shows excellent performance at different qualities, with a 62% reduction in flow nonuniformity and a 20.3% increase in heat transfer effectiveness. The performance of GTD is slightly inferior to OTD, with 42% reduction in flow nonuniformity and 17% improvement in heat transfer effectiveness.
The hybrid nanomaterials have emerged as next-generation medium of heat transfer due to impressive thermo-physical features arising from synergistic interaction of multiple nanoparticles. Subject to emerging need of high-performance energy-efficient systems, the hybrid nanofluids offer potential applications to advanced thermal management in energy, engineering and industrial systems. This investigation predicts the unsteady magnetized flow of hybrid nanofluid due to elastic surface moving periodically with applications of bioconvection and nonlinear thermal radiation. The suspension of uranium dioxide (UO2), iron oxide (Fe3O4) nanoparticles has been assumed along with blood base fluid. The analysis further comprises the significance of mass transfer, Brownian diffusion, thermophoretic features and chemical reactive species. The hybrid nanofluid also considered the suspension of microorganisms. The normal impact of magnetic force has been neglected. An imposed transverse magnetic field is applied; the induced magnetic field is neglected under the low magnetic Reynolds number approximation, while the Lorentz force term is retained. The computations are based on implementation of homotopy analysis technique. The results are performed comparatively for mono nanofluid (Fe3O4/Blood) and hybrid nanofluid (UO2-Fe3O4/Blood). Physical interpretation of results has been examined with thermal applications. It has been observed that inclusion of hybrid nanofluid confirms more pronounced thermal sensitivity due to superior thermal features. The proposed model justifies applications in the thermal regulation in biomedical systems, thermal enhancement of electronics systems and peak-precision heat-management operations.
Optimization of wind farm layout is crucial for maximizing energy output and economically smooth operation. This study presents a novel approach that integrates a wind theory wake model with a genetic algorithm to optimize the locations and hub heights of wind turbines under varying wind directions by focusing on power generation as objective function. The findings indicate that, regardless of the optimization objective, the wind power output of the farm increases, and power costs decrease when compared to baseline conditions. Furthermore, the study reveals that optimizing turbine locations alone or in conjunction with hub height yields comparable improvements, surpassing the benefits of optimizing hub height alone. This research provides valuable insights for the design and operation of efficient wind energy systems, emphasizing the importance of considering wind conditions in layout optimization strategies.
The current work uses numerical simulation methods to evaluate the leakage and flow heat transfer of labyrinth seals while accounting for rub-groove wear. Firstly, an experimental system for investigating the leakage characteristics of labyrinth seals was established to verify that the computational accuracy of the numerical method used is suitable for this study. Secondly, in order to assess the influence of the clearance on the leakage and heat transfer coefficient distribution for the labyrinth seal with rub-groove wear, airflow velocity near the seal tooth tips is computed under different clearances. The estimated averaged heat transfer coefficient over the rotor surface reduces as the clearance decreases, owing to the lower speed vortices filled in the rub-groove. Finally, the geometric parameters of rub-groove wear (groove width and depth) are thoroughly examined in relation to flow leakage and local heat transfer coefficient distributions of the rotor for the labyrinth seal with rub-groove wear.
this paper systematically investigate the vibration characteristics and heat dissipation performance of piezoelectric fans through experimental and numerical approaches. A home-built apparatus is used to measure blade amplitude, wind velocity, and heat dissipation. An empirical linear relationship was established between the resonant frequency and blade amplitude under large-amplitude oscillations, facilitating accurate determination of the natural frequency. In heat dissipation tests, forced convection at a wind velocity of 60 cm/s shortened the cooling time by 36% and enhanced the heat dissipation efficiency by about 56% compared with natural convection. Furthermore, numerical simulations reveal a periodic horseshoe-shaped vortex around the vibrating fan, which enhances convective heat transfer along the heat source surface. This work provides a comprehensive understanding of the vibration-flow-thermal behavior of piezoelectric fans.
The Urban Heat Island (UHI) effect represents a key component of urban climate systems, and understanding its diurnal variability in riverine cities is essential for identifying factors governing urban thermal conditions. This study investigates the spatiotemporal variation of UHI intensity along the Serbian Danube corridor and its relationship with selected socio-spatial factors. Mean monthly air temperatures at 07:00, 14:00 and 21:00 h for May- September 2015 were analysed at 15 sites, with UHI calculated relative to the rural reference site at Vinca. Principal component analysis, multiple linear regression, hierarchical clustering and monthly correlations were applied. Mean UHI intensity shifted from slightly negative in the morning (UHI7h = - 0.22°C, SD = 1.47°C) to moderate at midday (UHI14h = 0.81°C, SD = 1.59°C), peaking in the evening (UHI21h = 3.32°C, SD = 1.53°C). Three principal components explained 75% of the variance, separating a density- proximity gradient, a settlement-size gradient, and an afternoon-evening dimension. Distance to the Danube was the only significant predictor of morning UHI (negative relationship). Monthly correlations confirmed that this inverse link persists throughout the warm season, strengthening in August and September. Cluster analysis identified three groups of sites with distinct socio-spatial profiles. Overall, UHI along the Danube is time-specific, highlighting the importance of incorporating diurnal variability and water body proximity into climate adaptation strategies.
To suppress methane explosions and reduce accident occurrence, this study employed a self-made vertical explosion pipeline platform to investigate the suppression characteristics of brucite powder on premixed methane-air explosions. The effects of equivalence ratio, suppressant concentration, and powder particle size on methane explosion pressure and flame propagation were systematically analyzed. The main findings are as follows. Under fuel-lean conditions (Φ = 0.8), the suppression effect was most pronounced: the flame color changed from pale blue to dull orange-yellow, the average flame propagation velocity decreased by 41%, and the explosion pressure dropped by about 28.6 %. Under fuel-rich conditions (Φ = 1.2), the flame velocity reached its maximum (30 m/s), yet the corresponding pressure rise was the most gradual, indicating a pressure-velocity decoupling phenomenon. When the powder concentration reached 200 g/ m^{3} , the explosion pressure decreased by 61.1 % compared to the blank group condition; the maximum and average pressure rise rates were reduced by 78.2 % and 81.1 %, respectively; the time for the flame to reach the top pipe outlet extended from 28 ms to 63 ms; the flame velocity dropped from 21.4 m/s to 9.5 m/s. This study also characterized the physical properties of brucite powders with three different mesh sizes. Among the three mesh sizes, the 1250-mesh ultrafine brucite powder exhibited the strongest inhibition performance: the explosion pressure dropped from 0.036 MPa (blank group) to 0.025 MPa, and the flame propagation velocity decreased from 21.4 m/s to 12.5 m/s. This study can provide a scientific basis for developing effective explosion prevention and suppression measures.
This study investigates the optimal boundary temperature control of a heat conduction process in a thermoelastic wire with rigidly fixed ends, governed by the Cattaneo-Hristov equation. To capture high-speed thermal responses, swift relaxation, and fading memory effects, the framework incorporates the Caputo-Fabrizio fractional derivative with a non-singular kernel. Control is achieved via symmetric Dirichlet boundary conditions to regulate internal temperature distributions. Using Laplace and finite Fourier-sine transforms, the model is reduced to fractional Volterra integral equations. The resulting semi-analytical solutions for the optimal control u(t) demonstrate the critical influence of the fractional order α on thermal profiles and maximal stress during rapid transitions.
The artificial neural network (ANN) plays a novel and innovative role in the of heat transfer by serving as a powerful predictive and data-driven modelling tool that captures complex thermal behaviors with excellent accuracy. This investigation aims to provide an optimized ANN model for oscillating flow of viscoelastic micropolar hybrid nanofluid with evaluation of heat and mass transfer. Hybrid nanofluid features characterize the suspension of aluminum alloy (AA7072-AA7075) with human blood as the base liquid. Both energy and concentration equations are modified by employing the relations of the advanced Cattaneo-Christov model. The radiated features have contributed to modifying the energy equation. Modeling of the problem leads to a nonlinear system of partial differential equations (PDEs), which are handled analytically. Based on the simulated numerical model, the ANN algorithm is implemented to predict the accuracy of the model. Understanding of machine learning algorithms has been examined through regression plots, fit functions, mean residual error, and histogram curves. Physical observations of models are revealed by evaluating the role of modeled parameters. By combining analytical simulations with ANN-driven predictive results, the analysis revealed a powerful framework for improving thermal performance, enhancing the flow stability, and enabling complex hybrid nanofluid systems. It has been observed that the developed ANN model exhibited excellent predictive capability with suitable convergence, while regression, mean square error and histogram confirmed its reliability and stable accuracy. The enhanced nanoparticles volume fraction and Brownian movement enhances the thermal impact of blood-based nanofluid. The larger micropolar fluid parameter and concentration relaxation presents a decay in the concentration diffusion.
Data-driven models for predicting the energy performance of residential complexes often rely on expert knowledge, making the modeling process time-consuming. This study presents a predictive framework that integrates automated machine learning (AutoML) with interpretability analysis. A typical parallel-arranged residential complex in Tianjin was used as a case study to forecast both energy use intensity (EUI) and photovoltaic generation potential (PVG). A dataset encompassing building morphology, layout, and envelope parameters was constructed, and six representative AutoML platforms (TPOT, FLAML, MLjar, AutoGluon, LightAutoML, and H2O AutoML) were employed to develop predictive models. The results indicate that all frameworks achieved high predictive accuracy, although performance varied: LightAutoML performed best for EUI prediction, MLjar for PVG prediction, and FLAML exhibited consistent performance across both tasks. Interpretability analyses-utilizing variable importance metrics, SHAP values, partial dependence (PD), and individual conditional expectation (ICE) curves-revealed that EUI is primarily influenced by floor height, building length, solar heat gain coefficient, and north-south window-to-wall ratio, whereas PVG is mainly affected by the number of floors, building spacing, building length, and building height. This framework enables rapid prediction using readily available design parameters and reveals both qualitative and quantitative relationships between key variables and energy performance, providing support for early-stage low-carbon planning and design optimization in residential complexes.
The battery thermal management system plays an important role in controlling temperature to ensure safe and stable battery operation. In this study, a traditional Z-flow airflow pattern was applied to a 4 × 6 lithium-ion battery module consisting of cylindrical 18650 cells. The effect of varying the cooling air inlet angle was investigated using computational fluid dynamics simulations to evaluate thermal performance. The results show that changing the inlet angle to 120° provides the most uniform cooling, with the maximum temperature and maximum temperature difference reduced by 5.03 K and 5.09 K, respectively, compared to the original Z-flow model. However, airflow distribution remained insufficient in regions farther from the inlet. To overcome this limitation, an improved design incorporating flow-control baffles and a redesigned outlet configuration was proposed. The optimized model further reduced the maximum module temperature to 308.50 K and the maximum temperature difference to 2.97 K. Although the pressure drop increased from 20.71 Pa to 31.65 Pa, the enhanced airflow circulation significantly improved temperature uniformity and cooling effectiveness. These results are based on CFD simulations under the specified operating conditions and are therefore limited to the investigated battery module configuration and airflow conditions. Future experimental validation is recommended to verify the practical applicability of the proposed design.
Louvered fin heat exchangers are widely used in automotive air conditioning systems owing to their compact structure and excellent heat transfer performance. To further improve their thermal-hydraulic performance, this study proposes a novel hyperbolic dimpled louvered fin. Numerical simulations were performed to compare the flow and heat transfer characteristics of the hyperbolic dimpled louvered fin with those of the conventional louvered fin over a Reynolds number range of 100-500. In addition, the structural parameters were optimized using response surface methodology. The results show that the dimpled structure enhances local flow disturbance, induces vortex formation, and improves convective heat transfer. The optimal parameter combination was determined as an aspect ratio of k = 4.3, a louver angle of θ = 29.4°, and a fin pitch of Lp = 2.08 mm. Among these parameters, the louver angle had the greatest influence on the comprehensive performance factor, and a significant interaction was observed between the louver angle and the aspect ratio. Under the optimized conditions, the hyperbolic dimpled louvered fin exhibited better overall performance than the conventional louvered fin. Compared with the conventional louvered fin, the heat transfer factor j increased by 2.3%-4.4%, the friction factor f increased by 2.5%-3.1%, and the comprehensive performance factor JF increased by 2.1%-3.5%. These results indicate that the proposed fin structure can enhance heat transfer while causing only a limited increase in flow resistance, providing useful guidance for the design of high-performance louvered fin heat exchangers.
Membrane structures have unique aesthetics and offer a potential to experiment with building forms and create new and captivating solutions for conventional designs. However, providing comfortable indoor conditions is mandatory to ensure maximal functionality, which can be specific in regard of the building function. This paper evaluates thermal and optical characteristics of membrane covered building. Measurements of weather parameters and indoor temperature and natural illumination levels in a PVC membrane-covered gym hall located near Nis were conducted. During the month of March, in two measuring points values of natural illumination exceeded 300lx for 47% and 58% of the time respectively. In measuring point 2, which was placed 2.6 meters higher than the measuring point 1, illumination was in average 27.7% higher. Average air temperature and operative temperature were below 18°C 74.68% and 76.39% of the time, respectively. The obtained results indicate that although membrane covered buildings have favorable optical characteristics, improvement of indoor thermal environment in them should be further investigated.
This study investigates the performance of a solar dish concentrator system equipped with vacuum conical and spiral cavity receivers, utilizing thermal oil as the working fluid. It specifically evaluates and compares the efficiency of vacuum and non-vacuum conical cavity receivers. The analysis is grounded in energy, exergy and environmental (3E) evaluation frameworks. These theoretical approaches assess the system’s thermodynamic efficiency (energy/exergy) and its environmental impact mitigation potential. The methodology involves a comparative analysis of vacuum and non-vacuum conical cavity receivers, as well as vacuum spiral receivers, to determine their effects on the solar dish collector’s efficiency. Thermal oil serves as the working fluid, and performance metrics (energy/exergy efficiency, overall system efficiency) are evaluated under real world conditions (e.g., seasonal variations, such as June and November 2021). The vacuum conical cavity receiver demonstrated superior performance, achieving energy and exergy efficiencies of approximately 73.45% and 17%, respectively, in June 2021. The highest improvements in energy (2.05%), exergy (2.17%), and overall efficiency (2.09%) were observed in November 2021 with the application of vacuum conical cavity receiver were compared to the non-vacuum one. The study underscores the role of vacuum receivers in enhancing solar system performance and provides policy recommendations to advance energy governance and sustainable energy practices through innovative solar technologies. These findings contribute to optimizing solar-efficient systems for sustainable development.
This study investigates the influence of a linear hydrogen concentration gradient on flame acceleration and deflagration-to-detonation transition (DDT) within obstructed environments. This study employs numerical simulation methods to model the hydrogen flame propagation by coupling turbulence modeling with detailed chemical kinetics. The numerical framework accurately captures the coupled heat transfer behavior using the Euler time integration scheme with the HLLC flux scheme. A baseline hydrogen concentration of 30 vol% is established, featuring linear vertical concentration gradients characterized by slopes of 130.91, 205.72, and 480.00. The simulation results demonstrate that combustion reactions proceed more rapidly in high-concentration regions. This accelerated reaction rate, coupled with boundary layer instability effects, generates localized pressure and temperature gradients that subsequently enhance flame propagation velocity. The characteristic behavior manifests as an increased frequency of flame oscillation and acceleration with higher concentration gradient slopes. This relationship suggests a direct coupling between mixture stratification intensity and combustion instability. Furthermore, while the overdrive detonation velocity exhibits a positive correlation with the gradient slope, the stable detonation velocity remains relatively consistent, being primarily governed by the overall hydrogen concentration.
An ultra-thin flat heat pipe with a sintered wick thickness of 0.5 mm and an overall thickness of 1.3 mm was designed. Visualization experiments were conducted to investigate the thermal performance and flow behavior of ethanol-water binary mixtures. The work aims to elucidate the condensation fractionation phenomenon and its impact on thermal resistance. The results show that binary mixtures known to exhibit excellent performance in conventional heat pipes undergo condensation fractionation in ultra-thin flat heat pipes. The different condensation points of the vapor components cause extensive condensation of water-rich vapor near the evaporation section. This fractionation intensifies with increasing heat load, leading to incomplete fluid circulation and significant heat transfer deterioration. As a result, thermal resistance remains persistently high. Furthermore, the mixture with a high ethanol mole fraction (90 mol%) is proposed as the optimal working fluid. It effectively mitigates condensation fractionation and achieves enhanced thermal performance.
This study primarily investigates the NH₃/H₂/air combustion characteristics within a two-layer porous burner employing a two-dimensional model with a detailed kinetics. The effects of inlet velocity (ug,in) and blending ratio on the combustion characteristics are systematically examined. It is shown that the gas temperature continuously increases from the inlet before entering the reaction zone due to the heat recirculation via porous medium, thereby expanding the stable combustion limit and lean flammability limit of the mixture. Under a hydrogen blending ratio of 20%, the NH₃/H₂ achieves stable combustion in the burner for \mathrm{u_{g,in}} =0.2 m/s-0.8 m/s and the equivalence ratio range of 0.5-0.65. The stable flames are stabilized just behind the interface when \mathrm{u_{g,in}} <0.9 m/s, then the flames are stabilized towards the burner outlet. The emission of NO increases monotonically with \mathrm{u_{g,in}} , ranging from approximately 5320 ppm at \mathrm{u_{g,in}} =0.2 m/s to over 18700 ppm at \mathrm{u_{g,in}} =0.8 m/s. In contrast, the \mathrm{NO_2} emissions remain relatively stable across the range of inlet velocities studied, fluctuating around 100 ppm. The flame tends to be stabilized towards the upstream as the equivalence ratio is increasing from 0.55 to 0.65 under \mathrm{u_{g,in}} =0.8 m/s and blending ratio of 0.2, while the NO is increasing linearly from 14310 ppm to 19690 ppm with the equivalence ratio. A preliminary experimental validation is conducted and the same variation trend with the experiment is obtained, but the deviation between the two methods is obvious. This study contributes to enhancing combustion stability, extending flammability limits, and reducing nitrogen oxide emissions, providing key theoretical support for the development of efficient, low-carbon combustion technologies.
The Free Piston Expander-Linear Generator is a high-performance Organic Rankine Cycle waste heat recovery technology. Based on a Free Piston Expander-Linear Generator experimental platform, this paper experimentally investigates the effects of intake temperature on the system’s piston motion, electrical output and energy conversion efficiency. Higher intake temperature elevates piston displacement, velocity and motion symmetry, and positively correlates with the generator’s output voltage and power, which hits a maximum of 31.06 W at 3.5 bar intake pressure and 20 Ω load resistance. A 3.5 bar pressure boosts the average power by 15 %-20 % compared with 3.0 bar, and a temperature-pressure synergy is observed: the output improvement induced by temperature is more prominent at low pressure, while its marginal effect weakens at high pressure. The energy conversion efficiency of the Free Piston Expander-Linear Generator rises with temperature but declines with increasing pressure and external load, with a maximum value of 41.03 % achieved in this study.
