Search Results (607)

To clarify the thermo-hydraulic performance and thermodynamic characteristics of rotational–perforated static mixer (RPSM) for laminar heat transfer enhancement in circular tubes, a three-dimensional steady laminar flow model was developed for inlet Reynolds numbers from 200 to 1000. The heat transfer enhancement, resistance increase, and irreversible losses of RPSM with two installation modes and Kenics were comparatively analyzed. The results show that RPSM (forward) exhibits the strongest practical heat transfer performance. Its convective heat transfer coefficient is on average 39.8% higher than that of Kenics, while its thermal effectiveness and number of transfer units are increased by 21.3% and 32.8%, respectively. However, the heat transfer enhancement of RPSM is accompanied by a significant increase in flow resistance. The Z-factors of RPSM (forward) and RPSM (backward) are approximately 3.4 and 6.2 times that of Kenics, respectively. Second law analysis shows that the Bejan numbers of all configurations are close to unity, indicating that total entropy generation is mainly dominated by heat transfer entropy generation. Although RPSM (forward) has a higher exergy destruction rate, its second law efficiency is on average 20.1% higher than that of Kenics. Flow–heat transfer coupling visualization shows that RPSM (forward) can maintain relatively continuous swirling and secondary flow structures, thereby promoting radial energy transport and temperature field uniformity. In contrast, RPSM (backward) induces stronger local recirculation and pressure loss, resulting in higher pumping power demand. Overall, for the specific RPSM geometry and Reynolds number range investigated in this study, RPSM (forward) shows advantages in heat transfer capacity and thermal exergy utilization, but these advantages are accompanied by a substantial flow resistance penalty. Therefore, further structural optimization should focus on retaining radial transport while reducing local pressure loss. Full article

To address the continuously increasing thermal load of aero-engines, fuel/lubricating oil heat exchangers are evolving toward higher heat transfer efficiency, lower flow resistance, and lighter weight. This paper numerically compares the thermo-hydraulic performance of a conventional shell-and-tube heat exchanger (STHE) and three typical types of printed-circuit heat exchangers (PCHEs) for aero-engine applications. The three PCHE configurations fall into two categories based on their flow channel geometries: continuous-rib structures (straight and Z channels) and a discontinuous-rib structure (airfoil channel). All models are established under identical core volume and equivalent diameter to ensure a fair comparison. The results show that the airfoil-channel PCHE achieves the best overall performance. Compared with the STHE, it increases the heat transfer rate by 63%, reduces flow resistance by 76%, expands heat transfer area by 125%, and reduces operating weight by 60%. Flow field analysis reveals that the airfoil channel enables efficient heat transfer without excessive flow resistance through three key mechanisms: leading-edge impingement, periodic boundary layer reconstruction, and uniform flow mixing. This study provides an important reference for the selection and optimization of high-efficiency compact heat exchangers in aero-engines. Full article

Sonoprocessing can significantly enhance the yield, rate, and efficiency of mechanical and chemical processes. A timely sonoprocessing application is the recovery of Critical Raw Materials (e.g., lithium, gold, copper) from e-waste. However, commercial sonoprocessing typically involves batch processing via ultrasonic baths or sonicators, which can be prohibitively expensive and cumbersome for industrial upscaling. In response, we present a novel configuration, an Ultrasonic Tube Transducer (UTT), that is suited for flow-through processing. Here, we demonstrate it in the processing of an aged lithium-ion battery anode following timed immersion in a citric acid solution. Optimal concentrations and durations are identified. Full article

The transition toward carbon-neutral energy systems has accelerated interest in hydrogen-fueled combustion technologies, where efficient fuel–air mixing is essential for stable and clean combustion. In the present study, the mixing characteristics of under-expanded supersonic jets injected into a pressurized environment are numerically investigated using validated computational fluid dynamics simulations. Two nozzle configurations are examined: a straight nozzle and sudden-expansion nozzles with different expansion ratios and expansion locations. The governing compressible flow equations are solved using the rhoCentralFoam solver with the SST k–ω turbulence model. The numerical framework is validated against Sod’s shock tube solution and experimental data for under-expanded supersonic free jets. The results show that sudden-expansion nozzles significantly modify the shock-wave structure, jet penetration, and lateral spreading compared with the straight nozzle. Among the investigated configurations, nozzles with intermediate expansion-section lengths exhibited pronounced Mach-disk oscillations with a dominant frequency of approximately 10 kHz. The normalized supersonic core length decreased from 17.79 for the straight nozzle to 5.50 for the best-performing sudden-expansion configuration, while the normalized jet half-width increased from 0.82 to 1.70, indicating substantially enhanced mixing performance. The findings demonstrate that nozzle geometry strongly governs the trade-off between flow stability and mixing enhancement in high-pressure supersonic jets. Full article

Aiming at the technical bottleneck that traditional porous structures can hardly achieve mechanical load-bearing and acoustic regulation simultaneously, this study designs and fabricates three implicit surface porous structures (Gyroid, Diamond, Lidinoid) based on the bionic principle of trabecular bone. Experimental characterization and numerical analysis of their mechano-acoustic coupling performance are systematically carried out. Selective Laser Melting (SLM) technology is employed to realize the integrated forming of 316L bionic structures. Quasi-static compression experiments and finite element simulations are conducted to reveal the progressive deformation mechanism and energy absorption characteristics of different topological configurations. The results indicate that the Diamond structure exhibits the optimal comprehensive performance in terms of load-bearing capacity, specific energy absorption and isotropy. On this basis, the sound absorption and sound insulation performances of the structures are evaluated via an acoustic impedance tube test. The results show that the Diamond structure possesses a remarkably higher sound absorption coefficient and sound insulation value in the high-frequency range than other configurations, demonstrating excellent acoustic energy dissipation and sound wave isolation capability. The research indicates that the synergistic optimization of mechanical and acoustic performances can be achieved by regulating the Triply Periodic Minimal Surface (TPMS) topological configuration. Benefiting from its efficient stress transfer paths and intricate sound wave propagation channels, the Diamond structure realizes the coupling of high load-bearing capacity, superior energy absorption and favorable acoustic performance. This work provides a theoretical basis and technical support for the design of bionic porous structures in multifunctional scenarios such as bone implants and protective noise reduction. Full article

With the ongoing trend of miniaturization and intelligent power transmission equipment, the compact design of environmentally friendly gas-insulated switchgear (GIS) has emerged as a critical technical challenge. This study presents a detailed case study of a 40.5 kV dry air-insulated switchgear under specific dimensional constraints. Specifically, the cabinet width was reduced from 1000 mm to 800 mm, significantly narrowing the phase-to-phase and phase-to-ground clearances. A high-fidelity three-dimensional electric field model was established using the finite element method to evaluate the dielectric stress distribution within the enclosure. Numerical results indicate pronounced electric field concentrations at critical regions—including copper busbar joints, disconnector contacts, and the inlet bushing shielding rings—where local intensities exceeded the insulation safety threshold. To mitigate these issues, integrated design refinement strategies were evaluated, encompassing the structural modification of shielding rings, the application of silicone rubber coatings, and insulation reinforcement via heat-shrinkable tubing. Comparative analysis and experimental results demonstrate that the refined configuration effectively suppressed the peak electric field intensity. Finally, the design was validated through comprehensive dielectric tests, including a 215 kV lightning impulse withstand voltage test. This work may offer useful engineering references and quantitative data for the ultra-compact design of eco-friendly switchgear under similar constraints. Full article

A computational fluid dynamics (CFD) analysis is conducted to systematically investigate heat transfer enhancement in tubes fitted with grooved twisted tapes and to identify the groove geometry that provides the best thermo-hydraulic performance. Three grooved twisted tape configurations—circular-grooved twisted tapes (CGTT), rectangular-grooved twisted tapes (RGTT), and triangular-grooved twisted tapes (TGTT)—are evaluated and compared with a smooth tube and a conventional twisted tape over a Reynolds number range of 5000–20,000 under isothermal wall conditions. The grooved twisted tapes enhance heat transfer through the combined effects of swirl-induced secondary flows and groove-generated flow disturbances, which intensify turbulent mixing and reduce the thickness of the thermal boundary layer. Compared with the plain tube, the grooved configurations increase the Nusselt number by 1.472–1.98 times while increasing the friction factor by 3.21–3.58 times. Relative to the conventional twisted tape, the grooved designs provide an additional 8.0–12.1% enhancement in heat transfer with only a marginal increase of 0.2–1.5% in friction factor. The thermodynamic analysis indicates that the CGTT configuration exhibits the lowest entropy generation rate and exergy loss throughout the investigated Reynolds number range. In particular, the CGTT achieves a Bejan number of 0.999841 at Re = 5000, demonstrating an excellent balance between heat transfer enhancement and frictional losses. Furthermore, the CGTT attains the highest thermal performance factor (TPF) of 1.294 at Re = 5000 and maintains TPF > 1.0 over the entire Reynolds number range. The overall performance ranking is consistently established as CGTT > TGTT > RGTT based on comprehensive analyses of velocity fields, streamline patterns, turbulent kinetic energy distributions, temperature contours, and thermodynamic characteristics. Although the present study identifies the circular-groove configuration as the optimal design for a twist ratio (y/W) of 3.0, further parametric investigations involving variations in twist ratio, groove dimensions, and groove pitch are required to develop generalized design guidelines. Full article

Two semiflexible piezoelectric composite plate structures were developed, incorporating 1 × 9 and 2 × 9 arrays of PZT elements mounted on brass discs and mechanically secured by pop rivets within a thin plastic foil spacer positioned between two copper-clad PCB layers. This configuration provides reliable electrical contact, adequate mechanical compliance, and efficient conversion of mechanical vibration energy into electrical energy. In addition, a multifunctional thermoelectric device was realized, consisting of four cubic modules arranged around a rectangular tube and enabling both handheld operation and coupling to hot or cold surfaces. Each cube is equipped with optimized finned heat sinks and integrates four thermoelectric elements on each face. Experimental results show that each cube generates approximately 6 mW, when handheld and with icy water injected into the central tube, demonstrating its suitability as a compact and versatile thermal energy harvester. Under low-light conditions, a solar panel is supplemented by this hybrid piezoelectric–thermoelectric energy harvesting system that combines the output of a piezoelectric composite plate with the dual outputs of a thermoelectric device using an electronically isolated summing block to ensure source decoupling. Energy storage and management are implemented using a capacitor buffer for the piezoelectric device, two voltage boosters for the thermoelectric outputs, and an automatic ultra-low-power pulse width modulation buck regulator for charging supercapacitors at 5 V. Full article

This study investigates the energy absorption capacity of large three-honeycomb cell cores of different geometrical configurations, focusing on the influence of the constructive parameters on their impact response. The analyzed sandwich structures were additively manufactured using Onyx (a nylon-based composite) for the core cells and integrated into an assembly consisting of 6060-aluminum face sheets and encapsulated within a 6060-aluminum tube. These configurations represent a realistic engineering solution for lightweight structures designed for energy absorption. The analyses were conducted for two impact energy levels, 20 J and 50 J, enabling the evaluation of the structural sensitivity to different dynamic loading conditions. The results indicate a significant reduction in peak force with an increasing number of cells along the height. Compared to the single-cell configuration, the peak force decreases by approximately 15% for the two-cell configuration and 22.5% for the three-cell configuration, corresponding to a reduction of roughly 9% between the two- and three-cell cases. These findings highlight the critical role of geometry in optimizing the impact performance of honeycomb structures and provide relevant insights for the design of additively manufactured energy-absorbing crush-type components in engineering applications. Full article

This study investigates the effects of filament winding parameters (tension and mosaic pattern) on the mechanical performance of thin-walled fiber-reinforced polymer composite tubes under internal pressure. The pressure was generated through axial compression of an elastomeric insert, providing a controlled alternative to conventional hydrostatic burst testing. Tubes were manufactured with different combinations of winding tension (10–50 N) in the ±55° and hoop layers. Within the ±55° layer, several mosaic pattern configurations were tested. Structural responses were evaluated using pressure testing, Digital Image Correlation (DIC), and Scanning Electron Microscopy (SEM). 20 N was identified as the most efficient tension level, improving interlaminar integrity and increasing hoop tensile strength by approximately 8–13%. Specimens with a hoop layer failed abruptly by hoop-dominated brittle fracture, characterized by longitudinal splitting and fiber rupture in the circumferential direction. Among the investigated mosaic configurations, the 3/3 pattern demonstrated the most efficient structural response—the mean hoop tensile strength (1088 ± 43 MPa) was approximately 31–40% higher than that of the remaining configurations (722–798 MPa). Overall, the results indicate that both winding tension and mosaic pattern influence the failure pressure, with optimized configurations contributing to improved pressure resistance and structural consistency. Full article

The tube-notching process is widely used to manufacture structural joints and ducting systems for fluid transport. In these applications, accurate intersection angles and proper fit-up geometry are essential to ensure reliable assembly and system performance. Consequently, CNC-based automation is increasingly adopted to improve productivity in operations where precision and cycle time are critical. The main problem, however, lies in the complexity of generating accurate cutting trajectories for tube–tube intersections and converting them into machine-executable commands. This study addresses this gap by proposing a simple, novel mathematical model for toolpath generation capable of producing intersection profiles at arbitrary joint angles, including lateral offset (non-coaxial) configurations. A systematic procedure was developed to convert the resulting trajectories into G-code, which was processed in a low-cost CNC plasma cutter designed to experimentally validate the toolpaths. The machine incorporates a fourth axis to enable bevel cutting during tube processing. Experimental results demonstrate stable operation, high dimensional accuracy (error ±0.1°), and consistent cut quality for trajectories generated by the proposed model, confirming the feasibility of the low-cost CNC plasma system and its scalability to diverse fabrication requirements. Full article

Z- and U-type parallel pipe network configurations are widely used in engineering applications such as solar collectors, fuel cells, microchannels, spargers, and irrigation systems. Although the Z configuration is more commonly employed, the U configuration may provide advantages under specific operating conditions. This study presents a comparative analysis of the two configurations in terms of flowdistribution uniformity and pressure drop. A three-dimensional computational fluid dynamics (CFD) model was developed to simulate realistic solar collector conditions, including both fluid and solid domains together with detailed inlet and outlet junctions. The system consists of manifolds and headers with a diameter of 20 mm and a length of 1150 mm, connected to ten parallel tubes of 7 mm diameter and 1780 mm length. The analysis was conducted over a wide range of inlet Reynolds numbers (Re_D = 100–5000) to represent diverse practical operating conditions. The CFD model was validated against experimental data from the literature and showed good agreement. Flowdistribution uniformity was evaluated using two quantitative indicators. The results show that flow maldistribution increases with Reynolds number in both configurations; however, the U configuration exhibits significantly improved flow uniformity at higher Reynolds numbers. In addition, both configurations exhibited comparable pressure drop characteristics over the investigated operating range. The findings suggest that the U configuration is better suited to high-flow-rate applications that require improved hydraulic and thermal uniformity, while the Z configuration remains effective at lower Reynolds numbers. Full article

Efficient capture of respirable dust remains difficult in fully mechanized excavation roadways because fine particles readily migrate with airflow beyond the effective spray region. Here, a wind-assisted negative-pressure dust suppression device was developed by integrating annular Venturi entrainment with a mechanical air duct, enabling coupled airflow induction and droplet transport. The device was optimized using nozzle atomization tests, CFD-based orthogonal simulations, and laboratory-scale validation. The results show that an SK508 solid-cone nozzle provides suitable atomization for Venturi-induced suction. Using induced air inlet velocity and diffuser-inlet static pressure as evaluation indicators, the optimal Venturi unit was obtained at 0.1 MPa water pressure, 0.4 MPa air pressure, a 15° diffuser angle, and a throat-center nozzle position. For the integrated device, the best configuration was ten Venturi tubes, an impeller rotational speed of 2400 r/min, and an impeller position of 300 mm from the air duct inlet. In laboratory-scale tests, the complete wind-assisted negative-pressure mode outperformed fan-only, spray-only, wind-assisted spray, and negative-pressure secondary dust suppression modes, achieving maximum total and respirable dust suppression efficiencies of 87.39% and 86.68%. The results demonstrate the feasibility of coupling mechanical airflow with Venturi entrainment and support subsequent field-scale validation. Full article

Lunar lava tubes are subsurface cavities generated by volcanic activity and are regarded as promising targets for exploration because they can offer natural shielding and potentially support future lunar infrastructures as protected shelters and scientific laboratories. Autonomous navigation in these environments remains challenging due to the absence of illumination, sparse or repetitive geometric features, uneven terrain, and intermittent communications that limit teleoperation. In this framework, the Italian Space Agency (ASI) is pursuing a dedicated mission, and OHB Italia has been appointed the prime contractor to perform a candidate system-architecture study for lava tube exploration. This paper presents the activities and results related to the definition of the subsurface Guidance, Navigation, and Control (GNC) algorithm for a rover/hopper system. To address the above constraints, this study investigates the requirements for autonomous onboard navigation, focusing on sensor selection for Simultaneous Localization and Mapping (SLAM) as a fundamental prerequisite for mission success. A weighted-criteria evaluation framework is developed to assess various sensing modalities, considering mission-specific constraints. Based on this analysis, a sensor configuration optimized for GPS-denied and unilluminated environments is proposed. The effectiveness of the selected sensing architecture is validated through a simulation campaign conducted in simulation environments (CoppeliaSim v4.10.0/MATLAB 2025a), using two representative SLAM pipelines (ICP and LOAM) in LiDAR-only and LiDAR + IMU configurations. Finally, a modular Guidance, Navigation, and Control (GNC) architecture incorporating frontier-based exploration is proposed. Full article

Metal hydride (MH) systems offer a compelling route to solid-state hydrogen storage, yet their practical charging rate is fundamentally limited by the low effective thermal conductivity of the hydride bed and the substantial exothermic heat generated during absorption. Addressing this thermal bottleneck without sacrificing hydride volume remains a central challenge in MH reactor design. This study proposes an integrated thermal enhancement strategy in which transverse fins are coupled with a sinusoidal corrugated heat transfer tube, combining the boundary-layer disruption effect of corrugated geometry with the extended heat transfer surface provided by fins. A three-dimensional transient numerical model is developed within a porous-medium framework to compare straight-tube and corrugated-tube reactors equipped with different fin arrangements. The influences of corrugated-tube inlet radius, fin length, and fin inclination angle on hydrogen absorption performance are then systematically evaluated. The results show that positioning transverse fins on the upper side of the wave crests establishes the most direct conductive pathway between the hydride bed and the coolant, while appropriate fin geometry effectively suppresses low-conversion dead zones and improves the spatial uniformity of the reaction field. Compared with the finless sinusoidal corrugated-tube reactor and the conventional transverse-finned straight-tube reactor, the optimized configuration shortens hydrogen storage time by 62.74% and 42.05%, respectively, confirming that the synergistic combination of transverse fins and corrugated-tube geometry constitutes an effective and compact thermal management solution for MH hydrogen storage reactors. Full article