Search Results (6,443)

This work investigates the intricate dynamics of the Carreau hybrid nanofluid’s inclined magnetohydrodynamic (MHD) flow, exploring both active and passive control modes. The study incorporates critical factors, including Arrhenius activation energy across a stretched sheet, chemical interactions, and nonlinear thermal radiation. The formulation of the boundary conditions and governing equations is inherently influenced by symmetric considerations in the physical geometry and flow assumptions. Such symmetry-inspired modeling facilitates dimensional reduction and numerical tractability. The analysis employs realistic boundary conditions, including convective heat transfer and control of nanoparticle concentration, which are solved numerically using MATLAB’s bvp5c solver. Findings indicate that an increase in activation energy results in a steeper concentration boundary layer under active control, while it flattens in passive scenarios. An increase in the Biot number ($Bi$) and relaxation parameter ($\mathsf{\Gamma }$) enhances heat transfer and thermal response, leading to a rise in temperature distribution in both cases. Additionally, the 3D surface plot illustrates elevation variations from the surface at low inclination angles, narrowing as the angle increases. The Nusselt number demonstrates a contrasting trend, with thermal boundary layer thickness increasing with higher radiation parameters. A graphical illustration of the average values of skin friction, Nusselt number, and Sherwood number for both active and passive scenarios highlights the impact of each case. Under active control, the Brownian motion’s effect diminishes, whereas it intensifies in passive control. Passive techniques, such as zero-flux conditions, offer effective and low-maintenance solutions for systems without external regulation, while active controls, like wall heating and setting a nanoparticle concentration, maximize heat and mass transfer in shear-thinning Carreau fluids. Full article

Heating, ventilation, air conditioning, and refrigeration (HVAC&R) systems account for a significant share of global energy demand, prompting intensive research into advanced thermal enhancement techniques. Among these, nanofluids—colloidal suspensions of nanoparticles in base fluids—have shown promise in boosting heat transfer performance. This review provides a structured and critical evaluation of nanofluid applications in HVAC&R systems, synthesizing research published from 2015 to 2025. A total of 200 peer-reviewed articles were selected from an initial pool of over 900 through a systematic filtering process. The selected literature was thematically categorized into experimental, numerical, hybrid, and AI/ML-based studies, with further classification by fluid type, performance metrics, and system-level relevance. Unlike prior reviews focused narrowly on thermophysical properties or individual components, this work integrates recent advances in artificial intelligence and hybrid modeling to assess both localized and systemic enhancements. Notably, nanofluids have demonstrated up to a 45% improvement in heat transfer coefficients and up to a 51% increase in the coefficient of performance (COP). However, the review reveals persistent gaps, including limited full-system validation, underexplored real-world integration, and minimal use of AI for holistic optimization. By identifying these knowledge gaps and research imbalances, this review proposes a forward-looking, data-driven roadmap to guide future research and facilitate the scalable adoption of nanofluid-enhanced HVAC&R technologies. Full article

The heat exchanger in a hydropower unit plays a critical role in ensuring the stability of the unit and improving operational efficiency. This paper conducted a global flow-field/heat-transfer numerical analysis of multi-tube heat exchangers in hydropower units (with 98 tubes) and applied it to optimization research under actual operating conditions. Using a three-dimensional two-phase flow model, this work systematically analyzes the effects of different sand content and particle size on heat-transfer performance, revealing the impact of particle-flow and fluid-flow nonuniformity on heat-exchange efficiency. This research fills the gap in existing studies regarding the analysis of the impact of complex operating conditions on hydropower unit radiators. To address the issues of nonuniform flow fields and poor flow mixing in existing heat exchangers, an improved inlet/outlet structural-optimization plan is proposed. The original cylindrical inlet/outlet is replaced with a square structure, and its area is increased. The optimized structure improves flow uniformity, reduces flow losses, enhances heat-transfer performance by 7.7%, and achieves a significant reduction of 0.53 K in oil temperature. The findings of this study provide theoretical and engineering guidance for the design and optimization of heat exchangers in hydropower units and are of high value for practical applications. Full article

This study presents a simulation-driven methodology for the design and optimization of a lightweight drone frame. Starting with a CAD model developed in SolidWorks, finite element analysis (FEA) and computational fluid dynamics (CFD) which are used to evaluate stress, deformation, fatigue behavior, and aerodynamic performance. Topology optimization is then applied to reduce non-critical material and enhance the stiffness-to-weight ratio. CFD-informed refinements further help to minimize drag and improve airflow uniformity. The final design is fabricated using fused deposition modeling (FDM) with PLA, enabling rapid prototyping and experimental validation. Future work will explore advanced materials to improve fatigue resistance and structural durability. Full article

In response to the growing demand for lightweight and high-efficiency industrial equipment, this study addresses the critical issue of lubrication failure in high-speed, heavy-duty gear reducers, which often leads to reduced transmission efficiency and premature mechanical damage. A three-dimensional transient multiphysics-coupled model of oil-jet lubrication is developed based on computational fluid dynamics (CFD). The model integrates the Volume of Fluid (VOF) multiphase flow method with the shear stress transport (SST) k−ω turbulence model. This framework enables the accurate capture of oil-jet interface fragmentation, reattachment, and turbulence-coupled behavior within the gear meshing region. A parametric study is conducted on oil injection velocities ranging from 20 to 50 m/s to elucidate the coupling mechanisms between geometric configuration and flow dynamics, as well as their impacts on oil film evolution, energy dissipation, and thermal management. The results reveal that the proposed method can reveal the dynamic evolution characteristics of the gear injection lubrication. Adopting an appropriately moderate injection velocity (30 m/s) improves oil film coverage and continuity, with the lubricant transitioning from discrete droplets to a dense wedge-shaped film within the meshing zone. Optimal lubrication performance is achieved at this velocity, where oil shear-carrying capacity and kinetic energy utilization efficiency are maximized, while excessive turbulent kinetic energy dissipation is effectively suppressed. Dynamic monitoring data at point P further corroborate that a well-tuned injection velocity stabilizes lubricant-velocity fluctuations and improves lubricant oil distribution, thereby promoting consistent oil film formation and more efficient heat transfer. The proposed closed-loop collaborative framework—comprising model initialization, numerical solution, and post-processing—together with the introduced quantitative evaluation metrics, provides a solid theoretical foundation and engineering reference for structural optimization, energy control, and thermal reliability design of gearbox lubrication systems. This work offers important insights into precision lubrication of high-speed transmissions and contributes to the sustainable, green development of industrial machinery. Full article

Mixer-settlers are pivotal in the solvent extraction industry, yet spatial control of agitation to intensity separation remains underexplored. This study proposes a novel strategy by localizing agitation strictly within the dispersion band. Through the developed computational fluid dynamics coupled population balance model (CFD-PBM) resolving droplet breakup/coalescence dynamics and laboratory experiments, it demonstrates that the agitator position critically governs dispersion band thickness and separation efficiency. It should be emphasized there was no significant difference between the experimental and the simulated. Optimal separation is achieved only when the agitation zone overlaps the dispersion band, balancing droplet fragmentation and coalescence while minimizing turbulence in settling regions. Conventional uniform agitation designs are suboptimal due to spatial sensitivity. The CFD-PBM framework establishes a physics-based tool for scalable mixer-settler design, enabling energy-efficient separation by decoupling mixing and settling energetics. This work provides an advanced solution for using the solvent extraction via targeted agitation optimization, emphasizing both scientific rigor and industrial applicability. Full article

Solid particle thermal energy storage technology demonstrates extraordinary thermal stability across wide temperature ranges and possesses significant cost-effectiveness that meets stringent economic requirements for long-duration energy storage. These distinctive characteristics enable this technology to continuously support increasing decarbonization demands and drive the strategic progression of sustainable energy transformations. This review work conducts a thorough analysis of three representative reactor types: packed beds, moving beds, and fluidized beds, focusing on how particle thermophysical properties affect heat transfer and storage performance. The paper analyzes pressure drop and heat transfer correlations to reveal the coupling effects between particles and working fluids that impact system efficiency. By comparing hydrodynamic behavior across different reactor types, the study identifies optimization strategies and technical challenges. The review paper concludes by outlining future research directions for enhancing system efficiency, supporting industrial deployment, and facilitating integration with next-generation renewable energy technologies. Full article

The increasing deployment of pumps-as-turbines in small-scale hydropower applications in off-design conditions strengthens the need for the monitoring of the operation and maintenance (O&M) needs. PATs (pumps-as-turbines, pumps operated in reverse to generate electric current) are increasingly used because of their low cost as micro-hydropower plants; however, limited research has focused on their maintenance needs during operation. This is an important consideration given their use under conditions for which they were not originally designed. One of the most challenging O&M issues in hydromachinery is cavitation, which can harm turbines and reduce their efficiency. In this study, Computational Fluid Dynamics (CFD) was used for 15 different simulations of PAT configurations and their cavitation behaviour was investigated under varying inlet pressure and mass flow conditions. A cavitation strength indicator was developed using linear regression, describing the strength of cavitation from 0 (no cavitation) to 100 (extreme cavitation). This parameter depends on mass flow rate and head, which are easily measured parameters using standard sensors. With this approach, it is possible to monitor cavitation status in a continuous manner in a working PAT without the need for complex sensors. With this application, it is also possible to avoid costly damage, shutting down turbines when cavitation strength is exceptionally high. Full article

Chip-level cooling has become a thermal bottleneck in next-generation data centers. Although previous studies have optimized evaporator wick structures, they are limited to a single condensation path and ignore the combined effects of the loop heat pipe (LHP) orientation on the capillary wick (CW) replenishment and reflux subcooling. To bridge this gap, this study successfully designed an innovative flat-plate evaporator water-cooled LHP with a parallel condensation pipeline. Experiments were conducted with a 20 °C coolant and at a 4 L/min flow rate across nine orientations. The heat transfer characteristics of LHPs with parallel and series condensation pipelines were compared. The analysis focused on the relationship between the working fluid (WF) replenishment of the CW and the WF reflux temperature in the compensating chamber (CC). The experimental results demonstrated that the parallel condensation LHP could sustainably dissipate 750 W without thermal runaway. At this power, the minimum junction temperature of 82.34 °C was measured at orientation 2 (+60°). For low power and at the nine orientations, the series LHP generally had lower temperatures. However, when the power exceeded 600 W, the parallel LHP showed lower temperatures at orientations 1 (+90°), 2 (+60°), and 3 (+30°). At orientation 9, the parallel LHP had lower temperatures when the power surpassed 200 W. Theoretical analysis indicated that the orientation changes affected the heat transfer via the WF reflux temperature, reflux resistance, and CW replenishment rate. Furthermore, the LHP system we developed in this study is capable of fully satisfying the cooling requirements of data center server chips. Full article

Coal seam floor water inrush is one of the most significant hazards affecting the safety of coal mine operations. To prevent water inrush incidents, it is critical to investigate the evolution of fault characteristics during the mining of working faces. This study takes the 4104 working face of the Heshan mine in China as the engineering case, and a fluid–solid–damage coupling numerical model of the mining process is established. COMSOL multiphysics software is employed to analyze the evolution of fault characteristics in the coal seam floor under mining-induced disturbances. The results show that under mining disturbances, the stress on the fault plane decreases initially and then increases, with higher stress at the sides and lower stress in the center. These stress variations induce alternating states of sliding and stability on the fault plane, indicating that fault reactivation manifests as a dynamic, non-equilibrium process. As the rock mass gradually deteriorates, the stress field at the fault zone undergoes redistribution, leading to fault reactivation. This process further exacerbates damage to the rock mass, resulting in a continuous increase in the permeability coefficient within the fault zone, thereby elevating the probability of water inrush hazards. Areas with more severe damage typically exhibit higher permeability, forming high-risk zones for water inrush. This study explores the characteristics of fault reactivation and its relationship with the seepage field, providing a theoretical basis for coal mining enterprises to prevent and control fault-induced water inrush. Full article

This study investigates natural convection of liquid metal in an annular enclosure with a square cross-section using three-dimensional numerical simulations. Liquid metals, with low Prandtl numbers, exhibit oscillatory transitions at lower Rayleigh numbers than conventional fluids. While previous studies focused on full-circle domains where steady or irregular flows were observed, this work examines the effect of angular partitions on flow dynamics. The results reveal that periodic three-dimensional oscillatory flows arise in domains with specific angular sizes, such as quarter circles, whereas full-circle domains produce irregular or steady flows. Angular wave numbers vary spatially and temporally during transitional growth. The emergence of half-symmetric oscillatory modes highlights the role of symmetry constraints imposed by the geometry and boundary conditions. These transitions are closely tied to symmetry breaking and mode selection. A linear stability perspective helps clarify the critical factors that determine the transition type. These findings underscore that angular segmentation and periodic boundary conditions are essential for sustaining regular oscillatory convection. This study contributes to the understanding of symmetry-governed convection transitions in low-Prandtl-number fluids and has potential implications for industrial processes, such as semiconductor crystal growth, where flow uniformity and thermal stability are crucial. Full article

The present work analyzes the combined viscoelectric and steric effects on electroosmotic flow in a soft channel with polyelectrolyte coating. The structured channel surface, which controls the electric potential, creates two different flow regions: the electrolyte flow within the permeable polyelectrolyte layer (PEL) and the bulk electrolyte. Thus, this study discusses the interaction of various electrostatic effects to predict the electroosmotic flow field. The nonlinear governing equations describing the fluid flow are the modified Poisson–Boltzmann equation for the electric potential distribution, the mass conservation equation, and the modified Navier–Stokes equations for the flow field, which are solved numerically using a one-dimensional (1D) scheme. The results indicate that the flow enhances when increasing the electric potential magnitude across the channel cross-section via the rise in different dimensionless parameters, such as the PEL thickness, the steric factor, and the ratio of the electrokinetic parameter of the PEL to that of the electrolyte layer. This research demonstrates that the PEL significantly enhances control over electroosmotic flow. However, it is crucial to consider that viscoelectric effects at high electric fields and the friction generated by the grafted polymer brushes of the PEL can reduce these benefits. Full article

The present study reports the outcome of an experimental study of organic vapor trailing edge flows. As a working fluid, the organic vapor Novec 649 was used under representative pressure and temperature conditions for organic Rankine cycle (ORC) turbine applications characterized by values of the fundamental derivative of gas dynamics below unity. An idealized vane configuration was placed in the test section of a closed-loop organic vapor wind tunnel. The effect of the Reynolds number was assessed independently from the Mach number by charging the closed wind tunnel. The airfoil surface roughness and the trailing edge shape were evaluated by experimenting with different test blades. The flow and the loss behavior were obtained using Pitot probes, static wall pressure taps, and background-oriented schlieren (BOS) optics. Isentropic exit Mach numbers up to 1.5 were investigated. Features predicted via a simple flow model proposed by Denton and Xu in 1989 were observed for organic vapor flows. Still, roughness affected the downstream loss behavior significantly due to shockwave boundary-layer interactions and flow separation. The new experimental results obtained for this organic vapor are compared with correlations from the literature and available loss data. Full article

Snow and ice accumulation on transportation infrastructure presents significant safety and maintenance challenges in cold regions, while conventional removal methods are both energy-intensive and environmentally detrimental. This study proposes a passive Heat Pipe–Coupled Geothermal Snow Melting System (HP-GSMS) that harnesses shallow geothermal energy to maintain snow-free surfaces without external energy input. Using Fluent-based CFD simulations, the system’s thermal performance was evaluated under various working fluids (ammonia, carbon dioxide, water) and pipe materials (stainless steel, aluminum). A one-dimensional thermal resistance model validated the CFD results under ammonia–stainless steel conditions, predicting a heat flux of 358.6 W/m² compared to 361.0 W/m² from the simulation, with a deviation of only 0.66%, confirming model accuracy. Ammonia demonstrated superior phase-change efficiency, with the aluminum–ammonia configuration yielding the highest heat flux (up to 677 W/m²), surpassing typical snow-melting thresholds. Aluminum pipes enhanced radial heat conduction without compromising phase stability, while water exhibited poor phase-change performance and CO₂ showed moderate but stable behavior. Additionally, a dynamic three-node RC thermal network was employed to assess transient performance under realistic diurnal temperature variations, revealing surface heat fluxes ranging from 230 to 460 W/m², with a daily average of approximately 340 W/m². These findings demonstrate the HP-GSMS’s practical viability in cold climates and underscore the importance of selecting low-boiling-point fluids and high-conductivity materials for scalable, energy-efficient, and low-carbon snow-melting applications in urban infrastructure. Full article

Efficient simulation of multiphase, multicomponent fluid flow in heterogeneous reservoirs is critical for optimizing hydrocarbon recovery. In this study, we investigate advanced linearization techniques for fully implicit compositional reservoir simulations, a problem characterized by highly nonlinear governing equations that challenge both accuracy and computational efficiency. We implement four methods—finite backward difference (FDB), finite central difference (FDC), operator-based linearization (OBL), and residual accelerated Jacobian (RAJ)—within an MPI-based parallel framework and benchmark their performance against a legacy simulator across three test cases: (i) a five-component hydrocarbon gas field with CO₂ injection, (ii) a ten-component gas field with CO₂ injection, and (iii) a ten-component gas field case without injection. Key quantitative findings include: in the five-component case, OBL achieved convergence with only 770 nonlinear iterations (compared to 841–843 for other methods) and reduced operator computation time to 9.6 of total simulation time, highlighting its speed for simpler systems; in contrast, for the more complex ten-component injection, FDB proved most robust with 706 nonlinear iterations versus 723 for RAJ, while OBL failed to converge; in noninjection scenarios, RAJ effectively captured nonlinear dynamics with comparable iteration counts but lower overall computational expense. These results demonstrate that the optimal linearization strategy is context-dependent—OBL is advantageous for simpler problems requiring rapid solutions, whereas FDB and RAJ are preferable for complex systems demanding higher accuracy. The novelty of this work lies in integrating these advanced linearization schemes into a scalable, parallel simulation framework and providing a comprehensive, quantitative comparison that extends beyond previous efforts in reservoir simulation literature. Full article