Search Results (3,811)

Abrasive flow machining (AFM) is an effective finishing process for complex internal surfaces, particularly cavities, intersecting holes, and micro-channels that are difficult to access using conventional tools. However, when low-viscosity abrasive media is used (here defined, relative to conventional putty-like viscoelastic AFM carriers (with apparent viscosities of 10³–10⁵ mPa·s), as a water-based slurry with an apparent viscosity below 300 mPa·s over the operating shear-rate range), unfavorable flow conditions during the initial polishing stage can induce local over-polishing, erosion depressions, stepped patterns, and cavitation pits, resulting in non-uniform surface quality. The relationship between these flow behaviors and polishing defects remains insufficiently understood. To address this issue, this study investigates the AFM process applied to turbine blade film cooling holes through combined experimental and numerical approaches. The observed defects include erosion depressions, stepped surface patterns, and cavitation pits. The effects of abrasive injection pressure, flow velocity, hole geometry, abrasive viscosity, and particle size on defect formation are systematically examined. The results show that the initial abrasive filling level strongly affects defect distribution by altering the evolution of shear fields and void regions within the hole. Experimentally, at high Reynolds numbers (Re > 2 × 10⁴), intensified local shear and cavitation promote defect formation, while a moderate inclination angle (45–60°) and a higher aspect ratio (>8) are favorable for polishing uniformity. Complementary numerical simulations further indicate that smaller abrasive particles (<5 μm) and a moderate abrasive viscosity (~60 mPa·s) are predicted to improve polishing uniformity. This study clarifies the fluid-dynamic origin of polishing defects in film cooling holes and provides process guidance for suppressing local over-polishing, cavitation, and uneven material removal. Full article

Pump start-up and shutdown, flow-rate adjustment, and tripping operations during drilling can induce bottomhole pressure fluctuations. These fluctuations may alter fracture aperture and change the development of lost-circulation pathways. To investigate the dynamic evolution of fracture aperture under fluctuating pressure, a thermo-hydro-mechanical (THM) coupled numerical model was established using ABAQUS. Bottomhole pressure fluctuations were induced by applying periodic perturbations to the inlet flow rate. The effects of fluctuation amplitude, fluctuation duration, and drilling-fluid temperature were then analyzed. The results indicate that fracture aperture exhibits a transient response before reaching a stable state. The fluctuation amplitude has a significant effect on the maximum transient fracture aperture. When the fluctuation amplitude increases to 30%, the maximum fracture aperture increases by 44%. In contrast, the fracture that has already formed may undergo reclosure during the low-pressure stage. The fluctuation duration mainly affects the persistence of the fracture opening and reclosure process, but has a relatively weak effect on the maximum fracture aperture. A decrease in drilling-fluid temperature promotes fracture opening and tip propagation. When the formation temperature is 100 °C, low-temperature drilling fluid increases the maximum fracture aperture by 3.06% and the fracture length by 13.89% compared with the isothermal reference case. These findings indicate that fracture aperture under fluctuating pressure cannot be characterized only by its stabilized value. The maximum transient fracture aperture, minimum fracture aperture, and temperature-induced changes in fracture morphology should also be considered. This study provides a numerical insight into the transient response of fracture aperture to bottomhole pressure fluctuations and drilling-fluid temperature during drilling in stress-sensitive fractured formations. Full article

Tunnel construction in tectonically active mountainous regions is frequently hampered by elevated geothermal conditions, threatening construction safety and long-term infrastructure performance. In the Yunnan–Guizhou Plateau, characterized by complex fault systems and intense hydrothermal activity, rigorous assessment of geothermal hazard susceptibility along tunnel corridors is of critical engineering importance. However, the sparsity of geothermal observational data renders conventional assessment approaches insufficient, as they fail to quantify predictive uncertainty, which is essential for reliable risk decision-making. To address this gap, this study proposes a three-stage framework that integrates multi-source data fusion with Monte Carlo-based uncertainty quantification, using the Nige Tunnel as a case study. Ten conditioning factors were incorporated, with temperature-weighted positive samples constructed from field-surveyed hot springs. Gaussian noise injection and fractal buffer randomization were applied across 500 Monte Carlo iterations of an L2-regularized logistic regression model, evaluated by leave-one-out cross-validation. The three-stage assessment framework achieved robust predictive performance (mean leave-one-out cross-validation area under the curve (LOO-AUC) = 0.824) under sparse-sample conditions. High and Very High susceptibility zones account for 14.2% of the study area, concentrated along fault traces and collocated with hydrothermal discharge locations, with the Nige Tunnel traversing predominantly High to Very High susceptibility zones. Fault distance emerges as the dominant predictive factor, surpassing heat flow and Moho depth, indicating that structural permeability is the rate-limiting control on geothermal fluid enrichment in fault-dominated systems. The findings offer scientific support and methodological insights for risk zoning and hazard mitigation design in tunnel engineering projects in comparable geological settings. Full article

Hydraulic radial force from rotor–stator interaction causes pump vibration and bearing wear. To regulate this, this study proposes a low-vibration impeller design framework combining delayed detached-eddy simulation (DDES), Spearman correlation, sensitivity analysis, and multi-objective NSGA-II optimization, while explicitly treating hydraulic radial force as a primary design objective under an unchanged volute configuration, and is supported by multi-condition experiments. Four key parameters are defined: blade wrap angle (φ), governing passage diffusion; outlet blade angle (β), determining exit fluid trajectories; tangential cutting diameter (D_t), controlling shroud radius; and oblique cutting angle (ζ), adjusting near-hub boundaries. Sensitivity analysis indicates that D_t dominantly controls head and force regulation (42.3% head contribution), while β governs efficiency. Multi-objective optimization identifies an optimal low-vibration configuration (φ = 126°, β = 36°, D_t = 136 mm). Under rated conditions, this design curtails mean radial force by 26.6% (from 9.10 to 6.68 N) and blade-passing-frequency amplitude by 11.9%, while efficiency at 0.4Q_d increases by 6.75 percentage points. Flow-field analysis demonstrates that force reduction stems from improved circumferential pressure uniformity, jet-wake suppression, and weakened trailing-edge vortical transport near the volute tongue. These results highlight the framework’s design innovation and practical value for low-vibration optimization of centrifugal pumps and related turbomachinery. Full article

Rankine cycle CO₂ pumped thermal energy storage (R-CPTES) offers high-density, emission-free grid storage, but existing designs are limited by modest turbine inlet temperatures and produce electricity only, leaving their thermal potential unused. This paper introduces a Rankine CO₂ storage cycle driven by a high-concentration parabolic dish collector (PDC) and configured solely for combined heat and power, representing a combination of point focus solar energy with CO₂ pumped thermal storage that has received limited attention in the literature. During discharge, the dish superheats the working fluid and raises the high temperature turbine inlet from 456 °C to 500 °C, boosting net power. A heating recovery exchanger placed ahead of the second regenerator then extracts useful heat from the turbine exhaust for district or process supply, without the absorption refrigeration subsystem used in comparable cooling inclusive designs. The aim is to characterise this system through energy, exergy, and parametric analysis. A closed, pinch-consistent model is developed under steady-state assumptions using the Span–Wagner equation of state, with the discharge low pressure, discharge mass flow rate, and PDC outlet temperature varied independently and jointly at a fixed 10 MPa high-pressure boundary. The analysis reveals a power-versus-heat trade-off governed by the discharge pressure and bounded by physical limits rather than interior optima, shows that the solar superheat is a prerequisite for cogeneration, and identifies the system as heat-transfer destruction dominated, with the latent cold storage the largest single source of irreversibility. At the design point the system delivers 16.1 MW of power and 2.5 MW of heat, attaining a storage round-trip efficiency of 73.2% (electricity-only), a solar-inclusive electrical efficiency of 58%, an energy utilization factor of 67%, and an overall exergy efficiency of 61.3%. A preliminary economic assessment gives a levelised cost of storage of 0.10–0.18 $/kWh, competitive with comparable CO₂ storage systems. The proposed system thus provides a simple, fossil-free cogeneration solution for high-DNI regions based on a modular, point focus solar configuration. Full article

Under the “dual carbon” strategy, the organic Rankine cycle (ORC) represents a key technology for efficiently recovering low-grade industrial waste heat in inland factories. This study addresses ORC operational instability caused by seasonal temperature fluctuations and high cooling-water costs in inland regions. An ORC system powered by industrial waste heat is investigated. A steady-state simulation model is developed in Aspen Plus to analyze the effects of expansion pressure, condensation pressure, cooling-water flow rate, and working-fluid flow rate on system performance, and to filtrate parameters to maximize economic returns. The results demonstrate that optimal expansion pressure yields maximum net shaft power. Condensation pressure and the cooling-water flow rate are closely linked, necessitating a balance between power generation revenue and cooling costs. An optimal range for working-fluid flow rate is also identified. Seasonal temperature variations significantly influence system performance. Higher summer temperatures increase condensation pressure and reduce revenue, while lower winter temperatures enhance revenue when filtrated parameters are used. This research provides theoretical and technical references for achieving efficient, cost-effective, year-round ORC operation in inland factories. In the case study, the analysis for seasonal temperature variations increases the total annual revenue by CNY 2.217 million, with an annual average system efficiency of 10.59%. Full article

In horizontal wells, sand readily settles at the bottom of the annulus under gravity, forming sand beds that may lead to string sticking in sand-washing operations. To clarify the dynamic evolution of annular sand beds, a horizontal wellbore sand-washing experimental system was developed. Clean water and a 0.3 wt% guar gum solution were used as washing fluids to investigate sand-bed front morphology, self-excited oscillation, stratified transport, and deposition height under different inlet Reynolds numbers. The results show that, during clean water sand-washing, the sand-bed front exhibited inflection-point instability, stagnation-point formation, and secondary bed branching with increasing inlet Reynolds number, accompanied by periodic self-excited oscillations. In contrast, no oscillation occurred in the guar gum solution, and the sand-bed front became more streamlined. For both fluids, stratified transport consisting of a convective layer and a shear-slip layer was observed above the sand bed, while the slip-layer thickness in the guar gum solution was approximately 45.0% lower than that in water. Based on dimensional analysis and experimental data, correlations for the dimensionless migration velocity of the sand front and the local Reynolds number were established. An implicit method for predicting the maximum sand-bed height was proposed, with an error below 1.15%. The results indicate that the sand-bed deposition height decreases nearly linearly with increasing inlet Reynolds number, whereas the absolute migration velocity of the sand front remains low, resulting in poor sand-washing efficiency. The findings provide guidance for optimizing sand-washing flow rates and assessing sand-sticking risks in horizontal wells. Full article

In this study, porous polyvinylidene fluoride (PVDF) hollow fiber (HF) membranes for membrane distillation applications were successfully prepared using TamiSolve^® NxG, an innovative lower-hazard solvent, through the non-solvent induced phase inversion technique. The influence of the bore fluid composition and bore fluid flow rate on membrane morphology and performance was systematically investigated while maintaining a fixed polymer dope formulation. The prepared hollow fibers were thoroughly characterized in terms of morphology, membrane thickness, porosity, contact angle, mechanical resistance, pore size, and pure water permeability. In addition, their performance was investigated through Direct Contact Membrane Distillation (DCMD) tests in order to evaluate their applicability in desalination processes. The developed PVDF HF membranes exhibited pore sizes comparable to those of commercial polypropylene (PP) membranes and achieved high permeate flux together with excellent salt rejection, demonstrating their promising potential for sustainable membrane distillation and desalination applications. Full article

In this study, the cooling performances of various nanofluids were compared under the operating conditions of a real automobile radiator, based on an internal combustion engine vehicle cooling system whose experiments had been previously completed. In the analyses, the radiator inlet fluid temperature was fixed at 70 °C, air inlet velocities were set to 6, 8, and 10 m/s, and fluid flow rates were taken as 17, 19, and 21 L/min. Under these conditions, the cooling capacities were evaluated for three different working fluids whose thermophysical properties were experimentally determined: 100% pure water, water-based 0.3% ZnO nanofluid, and water-based 0.3% ZnO + CuO hybrid nanofluid. Within the scope of this study, a Computational Fluid Dynamics (CFD) model was developed based on the aforementioned experimental parameters and validated with a maximum deviation of 6%. Using the validated model, additional CFD analyses were performed for water-based 0.3% Al₂O₃ and TiO₂ nanofluids, whose thermophysical properties were also experimentally determined, and their cooling performances were assessed. Based on the experimental and numerical results obtained, the highest cooling capacity was determined to be 20.8 kW in the 0.3% TiO₂ nanofluid, representing a 69.1% increase in cooling capacity compared to pure water. These findings clearly demonstrate that the use of nanofluids significantly enhances heat transfer performance in automotive cooling systems. Full article

Pin arrangement significantly affects rubber-melt mixing and extrusion in pin-barrel cold-feed extruders. However, internal flow details are difficult to observe experimentally, and efficient prediction of flow-field parameters remains unavailable. This study used a finite-element model preliminarily validated against measured temperatures, together with particle tracing, to compare configurations with 0, 2, 4, and 6 pins per group. A dataset of 140 pin arrangements was generated by Latin hypercube sampling and numerical simulation. A mind evolutionary algorithm-optimized back-propagation neural network (MEA-BP) was then developed to predict melt volume-averaged temperature and average shear rate. Pins increased melt velocity and shear heating and improved cross-sectional temperature uniformity. Among the four uniform configurations, the 4-pin-per-group configuration showed the fastest reduction in segregation scale with a moderate residence time, achieving a favorable balance between mixing adequacy and processing efficiency. Particle tracing indicated repeated fluid splitting and recombination, whereas further increases in the number of pins yielded limited benefits. Under identical data partitions, network settings, and evaluation conditions, MEA-BP achieved R² values of 0.957 and 0.872 for temperature and shear-rate prediction, respectively, outperforming GA-BP, PSO-BP, and conventional BP. Full article

In the process of offshore natural gas extraction, natural gas hydrates tend to form within the wellbore. This secondary hydrate formation can potentially cause severe blockages. Current prediction methods primarily rely on temperature–pressure curves, which often overlook the critical effects of high-velocity fluid flow, particularly the impact and drag forces acting on the hydrates. To address this limitation, this study proposes a novel risk prediction model that innovatively decomposes the hydrate-induced wellbore blockage into three distinct stages: implantation, scour, and fracture. Each stage is mathematically evaluated using a dedicated analytical model: the impulse equation for implantation, the negative pressure suction equation for scour, and the hydrate fracture toughness equation for fracture. A region is deemed at risk of hydrate blockage only when all three stage conditions are simultaneously satisfied. Sensitivity analysis focusing on four key parameters—hydrate particle size, temperature, gas flow rate, and impact angle—revealed that increasing either the hydrate particle size during nucleation or the extraction temperature significantly reduces the risk of secondary hydrate blockage. Moreover, a typical case study demonstrated that the application of this three-stage model considerably narrows and refines the predicted risk area compared to traditional thermodynamic models. These results provide a solid theoretical foundation for accurately predicting secondary hydrate blockage risks and offer targeted strategies for flow assurance and mitigation in critical wellbore sections. Full article

Plate heat exchangers (PHEs) play a critical role in the energy efficiency of heat pump systems. However, non-uniform two-phase flow distribution across parallel channels remains a key limitation, as it may cause local dryout and degrade heat transfer performance. To address the limitations of existing prediction approaches, a hybrid modeling framework coupling computational fluid dynamics (CFD) simulations with a distributed parameter model is developed. The model is validated against experimental data under 12 representative operating conditions. The results show that the average prediction errors for the total mass flow rate, pressure drop, and heat transfer rate are within 3%, ±10%, and ±5%, respectively. The influences of refrigerant outlet conditions and inlet distributor geometry on flow distribution uniformity are systematically investigated, identifying the dominant factors governing pressure drop and the mechanism by which distributor orientation improves uniformity. Quantitative optimization shows that an orifice orientation of 225° reduces flow non-uniformity by 67.8% and enhances the heat transfer rate by 4.33% compared with the distributor-free design. The proposed method is robust across various operating scenarios and provides a reliable, quantitative tool for optimizing PHE inlet distributor designs. Full article

Natural circulation is a key passive heat removal mechanism in advanced reactor systems, including Molten Salt Reactors (MSRs). Owing to the high operating temperatures and material challenges associated with molten salts, surrogate fluids with Prandtl numbers comparable to those of molten salts have emerged as promising candidates for studying heat transfer phenomena in MSRs. The present study marks the first experimental and numerical investigation using Therminol-66 (Th-66) simulant oil as a surrogate fluid for molten salts in a natural circulation (NC) test loop setup at the University of Idaho Thermal-Hydraulics Laboratory. Experimental temperature measurements and energy-balance-based mass flow rate estimations were used to validate a three-dimensional computational fluid dynamics (CFD) model developed in ANSYS FLUENT. Two numerical configurations were considered: an adiabatic-wall model and a model incorporating distributed heat losses. The inclusion of heat losses significantly improved predictive accuracy, reducing the maximum relative error in heater outlet temperature to 16.7%. The largest deviation of 35.5% was observed at the heater inlet, primarily due to differences in power distribution and hydraulic resistance between the experimental system and the simplified numerical model. The CFD model systematically overpredicted the mass flow rate, mainly as a result of geometric simplifications (e.g., omission of flanges and minor loss elements) and the assumption that the total heater power was applied directly to the immersed heater rods. On the experimental side, distributed heat losses and indirect mass flow rate estimation introduced additional uncertainty. Nevertheless, the CFD model successfully captured the overall thermal and hydraulic trends across all operating conditions. The validated simulations further provided detailed insight into local and global temperature and velocity distributions within the heater and cooler sections. The results highlight the importance of accurately representing thermal losses and hydraulic resistance to achieve reliable prediction of natural circulation behavior in surrogate MSR systems. Full article

The magnetic susceptibilities of various electrically insulating ordinary fluids depend on their local states, such as their density and temperature. When such fluids, which can be characterized as either paramagnetic or diamagnetic and occur commonly in nature, are subjected to magnetic field gradients, it induces an effective body force—the Kelvin force. This force, which depends on the susceptibility and the gradient of the square of the magnetic field strength, can become one of the effective mechanisms for modulating the flow and transport, particularly where terrestrial gravity becomes negligible, such as in free space or under microgravity conditions. For the first time, we developed a theoretical model demonstrating that a viscous current can be generated due to the contrasts between the magnetic susceptibilities of the intruding and ambient fluids in the presence of gradients in magnetic fields, analogous to the viscous gravity current in terrestrial situations. We derived similarity solutions for the two-dimensional and axisymmetric currents arising from a balance between the Kelvin buoyancy and viscous forces with a prescribed power law for the magnetic field strength. These determine the shape and various spreading relationships of the viscous current. For a prescribed time variation in the source flux, it is shown that a family of scaling laws exists for the spreading rate and the thickness of the current, which depend on the steepness of the magnetic field gradient. Unlike gravity, since the driving horizontal buoyancy arising from the Kelvin force is externally specified, it potentially offers a mechanism to control the characteristic shape and the rate of motion of the viscous current. Full article

Single-phase oil immersion is a promising alternative to air cooling for high-power servers, but the high viscosity of dielectric fluids amplifies the bypass flow around the CPU heat sink via the adjacent random-access memory (RAM) channels, degrading thermal performance. A simplified hydraulic-thermal analysis shows that this bypass penalty cannot be eliminated by reducing the fin pitch of a rectangular-fin heat sink alone. A staggered pin-fin heat sink is therefore proposed, with pin diameter D, longitudinal pitch S_d, and transverse pitch S_t optimized by three-dimensional CFD using PAO-6. The optimum geometry is D = 2.8 mm, S_t = 6 mm, S_d = 8.45 mm. The heat sink is fabricated and tested in a commercial server at oil inlet temperatures of 30–45 °C and flow rates of 3–6 LPM. At 3 LPM, the pin-fin immersion server reduces the CPU thermal resistance by 22.29% relative to a rectangular-fin immersion server using the same oil, and by 38.37% relative to an air-cooled server. The partial Power Usage Effectiveness (pPUE) reaches 1.015, an 88.09% improvement over the air-cooled baseline (pPUE = 1.126), confirming that pin-fin geometries effectively mitigate the bypass penalty in single-phase oil immersion cooling. Full article