Search Results (2,166)

Friction pairs in wet clutches operate under complex conditions, which can cause surface damage and reduce overall clutch reliability. Surface texturing is an established technique for improving the tribological performance of such mechanical interfaces. Inspired by the wet adhesion properties of tree frog foot pads, a bionic regular hexagonal micro-texture was designed on the mating steel plate. A three-dimensional transient computational fluid dynamics (CFD) numerical methodology was developed and rigorously verified via pin-on-disc friction experiments. Subsequently, this verified numerical framework was extrapolated to establish disc-on-disc CFD models. The results demonstrated that the bionic hexagonal micro-texture altered flow field characteristics, increasing the local maximum flow velocity by 7.9% compared to untextured surfaces. Furthermore, the micro-textured grooves expanded the effective area for convective heat transfer and facilitated local fluid exchange, reducing the maximum average bulk temperature by 20.5% and the maximum radial temperature by 20.7%. Adjusting the structural parameters of these micro-textures further regulated the interfacial flow and temperature fields; notably, deeper grooves induced vortices at land region edges, accelerating flow velocity and decreasing the overall radial temperature gradient. This study provides a theoretical reference for enhancing the thermo-hydrodynamic performance of wet clutch friction pairs. Full article

Hybrid nanofluids possess exceptional thermal conductivity, but one of the major concerns with nanoparticles is agglomeration. While the usage of surfactants or dispersants can be used to mitigate this issue, numerical investigation and sensitivity analyses can be more affordable when attempting to optimize and design a thermal device. The consideration of thermal radiation with conductive and convective heat transfer and appropriate nanoparticles may provide a greater solution without compromising the efficacy of hybrid nanofluids. In the present work, the concept of magnetohydrodynamics (MHD) is used to examine the impact of thermal radiation on a stable, two-dimensional, incompressible hybrid fluid consisting of nanoparticles (MWNCT)${\mathrm{-Fe}}_3{\mathrm{O}}_4$ and water flowing over a vertical surface. The flow is governed by established equations of fluid dynamics, which use the Rosseland diffusion model to incorporate radiation effects. The implicit finite difference (IFD) was used to solve the mathematical equations. Sensitivity analyses were conducted as functions of volume fraction, radiation and magnetic variables. This study also examines the streamlines and isotherm lines with respect to the volume fraction, radiation parameter and magnetic parameter of the heat source. The results indicate that for a fixed radiation parameter, increasing the nanoparticle volume fraction by up to $20\%$ leads to a reduction of approximately $37\%$ in the skin friction coefficient, while the corresponding Nusselt number increases by nearly $50\%$. Furthermore, the introduction of a magnetic field parameter significantly suppresses wall shear stress and modifies the thermal boundary layer thickness, demonstrating the competing interaction between Lorentz-force-induced momentum damping and radiation-enhanced thermal diffusion. These quantified trends highlight the sensitivity of coupled momentum and heat transport to combined magnetic and radiative effects in hybrid nanofluid systems. Full article

Detonation phenomena in reactive flow systems continue to pose significant challenges for accurate simulation, particularly in 3D validation against experiments and achieving community standardization for schemes. Among the primary difficulties is the selection of suitable convective schemes, which are essential for capturing the complex dynamics of wave propagation and reaction fronts. This study provides a comprehensive historical review of the development and implementation of convective schemes in OpenFOAM, covering the period from 2013 to the present. In addition to documenting the evolution of these methods, we present a detailed technical description of various convective approximation techniques used in detonation simulations within OpenFOAM. This includes an exploration of their underlying principles, advantages, and limitations. Our analysis synthesizes key findings from recent studies and offers practical guidance to researchers when choosing schemes for specific detonation scenarios. It is found that currently, within OpenFOAM, the dominant schemes for convection are the HLLC and KN. Full article

Folic acid, an essential vitamin for human health, plays a crucial role in maintaining intestinal homeostasis and functional stability, and its absorption is frequently impaired in Crohn’s disease, where it is closely associated with clinical complications and nutritional management. Nevertheless, the quantitative relationship between the complex multiscale architecture of intestinal villi, their morphological dynamics, and the efficiency of folic acid absorption remains insufficiently understood, primarily because existing studies rely on oversimplified representations of villous geometry and neglect the internal vascular structure, thereby limiting their ability to capture the coupled transport processes within individual villi. While existing studies have considered the influence of villous morphology on intestinal absorption, they generally rely on oversimplified representations and do not account for the internal structural organization of villi. This study aims to elucidate the quantitative relationship between villous multiscale architecture and folic acid absorption efficiency under pathological conditions of Crohn’s disease. Herein, a two-dimensional multiphysics numerical model is developed that integrates the external environment of intestinal villi with their internal microstructure, simulating folic acid transport via diffusion and Michaelis–Menten kinetics, coupled with convection–diffusion in the microvascular network under Stokes flow conditions. We find a reduction in villus height to 400 μm or local blood flow velocity to 0.01 mm/s leads to a marked decrease in folic acid absorption capacity, by approximately 57% and 50%, respectively. These changes are primarily attributed to inflammation-induced villus atrophy, which reduces the effective absorptive surface area. Furthermore, reduced blood flow velocity lowers the Peclet number, facilitating the accumulation of folic acid within the villi, which in turn further reduces the efficiency of folic acid absorption. This work contributes to a deeper understanding of how diseases affect the absorptive function of intestinal villi and provides a theoretical basis for the pathological mechanisms of the gut. Full article

Based on the Advanced Geostationary Radiation Imager (AGRI) and Geostationary High-speed Imager (GHI) information in the Fengyun-4B (FY-4B) satellite, we propose a convective initiation (CI) nowcasting algorithm for Sichuan Province, China. The algorithm optimizes satellite reflectance by considering multi-channel brightness differences, visible reflectance, and cloud-top cooling by exploiting the Farneback optical flow, where the cloud is followed by false cooling due to cloud motion. Moreover, the high temporal resolution of GHI enables the detection of early cumulus cloud growth. The algorithm was developed using daytime CI events in the coverage area of Mianyang radar station from 22 July to 9 August 2023, and the remaining areas in the Chengdu scan area were used for validation. The results showed that the proposed method achieves a probability of detection (POD) of 83.1%, a false alarm ratio (FAR) of 33.0%, and a critical success index (CSI) of 58.9%. Compared with the AGRI-only method and the SATCAST algorithm, the POD increases by 5.4% and 8.4%, respectively, while the CSI improves by 1.3% and 2.3%. The average lead time reaches 34.2 min, which is 4.6 min longer than AGRI-only and 7.9 min longer than SATCAST. This suggests that AGRI and GHI data improve the spatiotemporal resolution of CI nowcasting. This approach improves the early detection of convective initiation under the climatic background of warm cloud convection in Sichuan, offering new insights for short-term warnings of regional convective weather. Full article

Located in the north of Yunnan Province, China, the Wuding geothermal area is a typical medium- and low-temperature geothermal system with strong hydrothermal activity and development potential as a clean and renewable energy resource. This study systematically investigates the main controlling factors of the Wuding geothermal field through field investigation, hydrochemical analysis, and stable isotope analysis, and puts forward a genetic model of the geothermal field. The results show that the Wuding geothermal field is a medium- to low-temperature, conduction-dominated geothermal system, and its geothermal water is predominantly of the Ca–HCO₃ (calcium bicarbonate) type. The recharge area lies at an altitude above 2250 m, which is speculated to be within the mountainous area in the southwest of the study area. The underground hot water in the area is immature water. The source water circulates to the deep heat storage zone along faults, rises to the surface through heat convection, and is exposed as hot springs. Upon discharge, the geothermal water mixes with shallow cold water, with cold-water dilution accounting for up to 85% of the total volume. Using the silica thermometer, cation thermometer, and silicon enthalpy model, the maximum temperature of heat storage is estimated to be 91 °C, with the depth of geothermal water circulation reaching 2200 m. The thermal reservoir is composed of dolomites of the Upper Cambrian Erdaoshui Formation (∈3e) and Sinian Dengying Formation (Zbd). Its heat source is heat flow from the upper mantle and the decay of radioactive elements. Continuous heat flow to the thermal reservoir is maintained through the fold fracture zone and faults in the core of the Hongshanwan anticline. The proposed genetic model of the Wuding geothermal field provides a scientific basis for the sustainable redevelopment and utilization of this geothermal resource and is of significance for regional low-carbon energy use and socio-economic sustainable development. Full article

This paper investigates the formation mechanism and key influencing factors of freckle defects that arise during the directional solidification of a novel third-generation nickel-based single crystal superalloy turbine blade. A combined experimental and multi-physics numerical simulation approach was adopted. The results indicate that freckle formation primarily originates from solutal convection, which subsequently triggers a cascade of processes, including the development of convection-induced segregation channels, flow-driven dendrite fragmentation, and the migration and aggregation of dendrite fragments. The severity of freckling is closely dependent on both the casting’s position within the furnace and its local geometric characteristics. Castings located in regions with poorer heating conditions exhibit lower temperature gradients and slower solidification rates, significantly increasing their susceptibility to freckle formation. Similarly, on a given casting, the side subjected to less favorable heating is more prone to freckle initiation. The freckle number varies non-monotonically along the blade height, increasing from 3 to a maximum of 16, with a temporary decrease near the platform and a final reduction near the top. This trend is mainly attributed to thickness-dependent channel segregation, as well as freckle propagation into the interior and coalescence at higher positions. This study provides a crucial theoretical basis for understanding the formation mechanism of freckle defects in nickel-based single crystal superalloys and offers valuable guidance for optimizing blade manufacturing processes, reducing solidification defects, and enhancing blade quality and service performance. Full article

Carbon dioxide (CO₂) hydrate slurries have emerged as promising candidates for cold thermal energy storage (CTES) and refrigeration systems due to their high latent heat, controllable flow behavior, and environmentally friendly nature. These slurries are formed by dispersing solid CO₂ hydrate particles in a liquid phase, forming a multiphase system with tunable thermophysical and rheological properties. The performance of these slurries is dependent on nucleation kinetics, particle sizes and their distribution, solid content, and thermal transport characteristics under flow conditions. This review paper gives an assessment of CO₂ hydrate slurries from a thermofluid’ perspective by focusing on key aspects such as hydrate nucleation mechanisms, viscosity behavior, shear response, thermal conductivity, convective heat transfer, and slurry stability. Particular attention is given to the role of surfactants and nanoparticle additives that enhance hydrate formation and improve slurry performance. The addition of nanofluids is discussed both in terms of their effect on thermal properties as well as in flow stability. Full article

Immersion cooling has been widely investigated in battery thermal management due to its high cooling efficiency; however, the influence of coolant properties on the thermal behavior and temperature uniformity of large-capacity energy storage battery modules remains unclear. In this study, a three-dimensional numerical model is developed to investigate the thermal performance of an immersion-cooled battery module consisting of 52 prismatic cells. The cooling performance of silicone oil (SO), synthetic hydrocarbon (SH), and two synthetic esters (SE) with different viscosities is systematically compared under various discharge rates and volumetric flow rates. The battery thermal model was validated through single-cell experiments under natural air convection conditions. The research results indicate that at a 0.5C discharge rate, the 30 cSt SE achieves a reduction in maximum battery pack temperature of 6.3% and 7.0% compared to SO and SH, respectively. Furthermore, the maximum temperature difference is significantly reduced by 22.9% and 25.4% under the same conditions. Due to differences in the inherent properties and flow heat transfer characteristics of the coolant, at a volumetric flow rate of 12 L/min, the 30 cSt SE resulted in a 15.8% reduction in module temperature difference compared to the 20 cSt SE. To further evaluate the internal thermal balance of the battery module, two thermal uniformity indicators were introduced to quantify the consistency of the highest temperature of individual cells and the internal temperature difference. Considering both the temperature performance and thermal uniformity at the module level, from a heat dissipation performance perspective, the 30 cSt SE demonstrates significant potential for thermal management of large-scale prismatic battery packs. Full article

This study experimentally investigates a compact side-exhaust piezoelectric synthetic jet actuator equipped with outlet flaps and compares its performance with a flap-free baseline design. The flap concept is intended to mitigate hot-air recirculation during the suction phase and thereby improve near-field cooling in confined layouts. Experiments were conducted under a 350 Hz, 60 Vpp driving signal with an exit dimension of 20 mm × 1 mm. An initial screening campaign evaluated 24 flap configurations by varying flap length, thickness, and installation distance; the results showed that overly long flaps impose substantial blockage and momentum loss, and therefore the flow analysis was narrowed to a practical flap length of 29.5 mm. The final velocity characterization focuses on two representative flap thicknesses (0.1 mm and 0.5 mm) and three installation distances (5, 10, and 15 mm from the exit). For heat transfer evaluation, the nozzle-to-target spacing was varied from 5 to 50 mm in 5 mm increments. The modified actuator demonstrates improved near-field cooling performance, with the best case achieved using 0.1 mm flaps installed at 5 mm, yielding a maximum Nusselt number enhancement of 6.24% relative to the baseline at very small spacings. Furthermore, the thermal benefit becomes more pronounced at elevated heat source temperatures, with the strongest improvement observed around 60–80 °C (up to ~13% at 60 °C). These results provide practical design guidance for enhancing localized convective heat transfer in compact electronics cooling applications. Full article

Enhancing convective heat transfer in solar air heaters (SAHs) without disproportionate hydraulic penalty remains critical for decentralized low-carbon heating. This study experimentally investigates a serpentine-channel SAH equipped with distributed three-dimensional vortex generators under outdoor winter conditions. The configuration combines curvature-induced secondary motion with distributed vortex generation to intensify absorber–air heat transfer. Experiments were conducted over a mass flow range of 0.012–0.061 kg s⁻¹, corresponding to a Reynolds number range of 2.1 × 10³–1.07 × 10⁴, using a smooth duct as the reference configuration. The enhanced configuration achieved peak thermal efficiencies of 81.6–85.4%, compared with 65.8–67.7% for the smooth collector, while daily averaged efficiency increased from 56–59% to 71–75%. Although pressure drop increased, thermo-hydraulic performance remained superior across the investigated Reynolds number range. Exergy efficiency was consistently higher for the enhanced system and remained within optical limit constraints. Environmental assessment based on grid emission factor displacement indicates approximately 33% greater annual CO₂ mitigation potential, corresponding to about 6.6 tonnes over a 20-year service life. The levelized cost of heating was estimated at 3.1–4.4 ₹ kWh⁻¹. These results indicate that compound curvature–vortex transport intensification can improve thermal efficiency and increase carbon mitigation potential under realistic operating conditions. Full article

Rayleigh–Bénard convection (RBC) provides a benchmark for studying buoyancy-driven instabilities and heat transport in confined fluids. Heat transfer scaling in cylindrical geometries is well established, whereas the role of the anisotropy induced by the domain geometry, such as elliptical shapes, has not fully explored. This study presents direct numerical simulations of RBC in two domains of equal height, $H=0.0124$ m, and different cross-sections: a circular cylinder with radius ${\displaystyle R=3.11\times {10}^{-3}}$ m and an elliptical cylinder with semi-axes equal to ${\displaystyle R_{\max }=3.11\times {10}^{-3}}$ m, ${\displaystyle R_{\min }=1.55\times {10}^{-3}}$ m, respectively. The simulations, performed at Rayleigh number $\mathit{Ra}=2\times {10}^6$ and Prandtl number $\mathit{Pr}=1.68$ (for water) under the Boussinesq approximation, reveal that (i) the average Nusselt number is comparable in both cases ($⟨\mathit{Nu}⟩\approx 38.23$ for the circular case and $⟨\mathit{Nu}⟩\approx 39.22$ for the elliptical one) and (ii) the different domain geometries influence the thermal transport mechanism and flow organization. Specifically, in the cylindrical cell, heat transfer is regulated by a large-scale circulation roll, whereas in the case of the elliptical shape, the domain is populated by thermal plumes driving the convective dynamics. The latter phenomenon is evidenced by larger Nusselt number fluctuations at the lower and upper plates, with a standard deviation increasing from $\sigma \approx 2.21$ in the circular cylinder to $\sigma \approx 4.57$ in the elliptical domain. These results highlight that the geometric anisotropy modifies the coupling between boundary layers and the core flow dynamics, leading to enhanced intermittency without affecting the magnitude of the heat flux. Therefore, the elliptical domain is suitable for applications characterized by enhanced mixing. Full article

A single-tank molten-salt heat-exchanger storage system is promising for small-scale industrial heat supply, yet transient natural convection and heat transfer in closed tanks remain insufficiently understood. This study develops a physical model and performs numerical simulations of a top-heated single-tank sensible thermal storage unit using a realistic post-discharge, non-uniform initial temperature field. During charging, an upward plume forms near the heating rod, with heat concentrated around the rod and weak flow in remote regions. Two large-scale circulation cells separated by an inclined thermocline are observed, and the interface shifts downward over time. To address short storage duration, a segmented-heating strategy is proposed by varying the heating-section height. Results show that heater height strongly governs flow and storage performance: compared with full-length heating, 2/3-, 1/2-, and 1/3-length configurations extend storage duration by 93%, 100%, and 103.9%, respectively. Lowering the heating zone toward the tank bottom effectively prolongs storage and improves thermal efficiency. Full article

Gas-cooled reactors are highly sophisticated energy systems in which numerous physical phenomena take place at the same time. Among these, the effective removal of heat from the reactor core is of great importance. In gas-cooled reactors, convective heat transfer and the conditions under which it occurs are critical to both the performance and safety of these reactors. Convective heat transfer in gas-cooled reactors is particularly complex due to the thermo-physical properties of gaseous coolants, high operating temperatures, and diverse flow regimes. It is commonly characterized using empirical and semi-empirical correlations. Each correlation is valid only within specific ranges of operating and geometric conditions, making the appropriate selection of correlations essential for accurate reactor design and reliable safety assessment. The aim of this review is to provide a comprehensive evaluation of the models and correlations applicable to the description and modeling of convective heat transfer in selected types of gas-cooled reactors. For each reactor type, the relevant correlations are categorized and summarized in tables, along with their ranges of applicability and inherent limitations. In total 154 correlations were reviewed. The findings highlight that convective heat transfer in different types of gas-cooled reactors is described differently. This article offer a consolidated reference of correlations useful for engineers and researchers working in the field of heat transfer and nuclear reactor engineering. In addition, remaining challenges are discussed and future research directions are proposed to support improved heat transfer modeling for current and next-generation gas-cooled reactor technologies. Full article

The twin-blade planetary mixer is critical for processing highly viscous materials in the chemical and polymer industries, yet optimizing its mixing characteristics alongside energy efficiency remains challenging. This study investigates the twin-blade planetary mixer, using computational fluid dynamics simulation methods to analyze the operating parameters and multi-objective optimization of performance in viscous systems. First, the multi-axis stirring process was simulated numerically based on the Planetary Motion Method, revealing the working process at the cross-section and of the blades, thereby unveiling a mixing mechanism driven by cyclic transitions between local shear-intensive kneading and global convective circulation. Then, through orthogonal experiments and ANOVA, the dominant role of the hollow blade’s self-rotation speed on performance was clarified. Furthermore, based on Kriging and NSGA-II, with LINMAP employed for decision making, an optimal parameter combination, specifically a hollow blade self-rotation speed of 94.86 rpm, a speed ratio of 0.063, and a blade-to-bottom height of 2.79 mm, successfully achieved an 8.15% reduction in power consumption, a 20.03% increase in global axial flow, and a 5.01% enhancement in maximum kneading pressure. Full article