Search Results (10,613)

The exploration and development of oil and gas resources in deep formations is a key strategic priority for national energy production. However, manual methods for handling gas kicks suffer from low operating accuracy and inefficiency during high-temperature and high-pressure deep well drilling. To address the need for real-time bottomhole pressure prediction and control, an efficient gas–liquid–solid computing model was developed based on the gas slip model and cuttings settling velocity model. By integrating this model with an automatic choke adjustment system, an automatic gas kick attenuation model for deep well drilling was established. Results show that, compared to the driller’s and wait-and-weight methods, the automatic gas kick attenuation method significantly reduces peak choke pressure due to its larger frictional pressure drop and higher cuttings hydrostatic pressure. The automatic attenuation method not only leads to an average reduction of 28.42% in maximum choke/casing pressure but also accelerates gas removal, achieving gas kick attenuation ten times faster than the driller’s method and seven times faster than the wait-and-weight method. The study also investigates the influence of gas solubility, well depth, gas influx volume, formation permeability, and drilling fluid volumetric flow rate on gas kick attenuation characteristics. The findings provide a solid foundation for improving the efficiency of gas kick management in deep well drilling operations. Full article

Solar air heaters play a crucial role in distributing heated air at low to medium temperatures. The heart of these systems lies in the absorber plate, which directly absorbs solar heat energy and then efficiently transfers it to the flowing air. However, the challenge lies in achieving optimal thermal efficiency by modifying the absorber plate roughness. Traditional smooth absorber plates have a limited contact area for heat transfer, leading to suboptimal performance. Using passive techniques, such as corrugation on the absorber plate, may increase thermal efficiency by creating turbulence in the laminar sublayer. In this study, corrugated solar air heaters are considered, with the absorber plates roughened into square, semicircular, and triangular ribs. The flow characteristics of heat due to the roughness of the absorber plate is simulated using the computational fluid dynamic (CFD) technique. The ANSYS Fluent 2019R3 is used to investigate the turbulent air flow in the absorber plate. The simulation analyses are performed over a Reynolds number range of 4000–18,000 using three different pitches. As the main contribution, two different model equations, namely M1 and M2, for the correlation model of the solar heat transfer were proposed to predict the Nusselt number, where M2 is an original model and M1 is newly established with the fine-tuned coefficients. Also, for the first time in the literature, the recent swarm optimization algorithm, namely Honey Formation Optimization with Single Component (HFO-1), is used to optimize the solar air heater and a comparison study with a popular non-swarm optimization, namely the Generalized Reduced Gradient (GRG) optimization, is provided. The Nusselt number was obtained using HFO-1 with a percentage error (MAPE) of 2.15% and 0.86% for the models M1 and M2, respectively. Moreover, the average achievement of HFO-1 on the proposed correlation models is 50% better than that of the GRG optimization, with respect to the RMSE. Full article

The mechanism of iron enrichment in ferrogabbro remains a controversial subject. This study provides valuable insights derived from the Dashanshu intrusion, located in the Emeishan Large Igneous Province in southwestern China, which features ferrogabbro with a notably high iron content (total Fe₂O₃ reaching up to 21.6 wt.%). The ferrogabbro samples exhibit distinctive petrographic features, including the early crystallization of plagioclase prior to pyroxenes, amphibole replacing pyroxenes, and magnetite–ilmenite intergrowth filling the interstices between plagioclase and pyroxenes. A quantitative mineral analysis based on micro-X-ray fluorescence element mapping reveals a positive correlation between Fe-Ti oxides and bulk-rock iron contents, suggesting that the formation of ferrogabbro is primarily attributed to the accumulation of Fe-Ti oxides. Petrographic characteristics combined with oxygen fugacity determinations indicate that the primitive magma had a low content of water and was moderately oxidized (ΔFMQ − 0.13 to ΔFMQ + 1.35). These conditions suppress the early crystallization of Fe-Ti oxides, thereby allowing for an enrichment of iron in the residual magma. Following the crystallization of plagioclase and pyroxenes, increased water content—evidenced by amphibole replacing pyroxenes—triggers extensive crystallization of Fe-Ti oxides. Due to their late-stage crystallization, these oxides do not settle within the magma, which possesses a high crystallinity (>50%) and consequently exhibits non-Newtonian fluid behavior. This results in the localized accumulation of Fe-Ti oxides and the formation of a ferrogabbro layer. However, the late-stage crystallization of Fe-Ti oxides also impedes the sinking and flow-sorting processes that are essential for the development of economically valuable Fe-Ti oxide layers. This may account for the lack of an economically valuable Fe-Ti oxide layer within the Dashanshu intrusion. Full article

Hydraulic fracturing is a widely employed technique for stimulating unconventional shale gas reservoirs. Supercritical CO₂ (SC-CO₂) has emerged as a promising fracturing fluid due to its unique physicochemical properties. Existing theoretical models for calculating breakdown pressure often fail to accurately predict the outcomes of SC-CO₂ fracturing due to the complex, nonlinear interactions among multiple influencing factors. In this study, we conducted fracturing experiments considering parameters such as fluid type, flow rate, temperature, and confining pressure. A fully connected neural network was then employed to predict breakdown pressure, integrating both our experimental data and published datasets. This approach facilitated the identification of key influencing factors and allowed us to quantify their relative importance. The results demonstrate that SC-CO₂ significantly reduces breakdown pressure compared to traditional water-based fluids. Additionally, breakdown pressure increases with higher confining pressures and elevated flow rates, while it decreases with increasing temperatures. The multi-layer neural network achieved high predictive accuracy, with R, RMSE, and MAE values of 0.9482 (0.9123), 3.424 (4.421), and 2.283 (3.188) for training (testing) sets, respectively. Sensitivity analysis identified fracturing fluid type and tensile strength as the most influential factors, contributing 28.31% and 21.39%, respectively, followed by flow rate at 12.34%. Our findings provide valuable insights into the optimization of fracturing parameters, offering a promising approach to better predict breakdown pressure in SC-CO₂ fracturing operations. Full article

The present paper reports the theoretical results on the thermal performance of proposed Integrated Hybrid Nanofluid Hemi-Spherical Fin Model assuming a combination of Fe₃O₄-Ni/C₆H₁₈OSi₂ hybrid nanofluid. The model leverages the concept of symmetrical geometries and optimized nanoparticle shapes to enhance the heat flux, with a focus on symmetrical design applications in thermal engineering. The simulations are carried out by assuming a silicone oil as a base fluid, due to its exceptional stability in hot and humid conditions, enriched with superparamagnetic Fe₃O₄ and Ni nanoparticles to enhance the heat transfer capabilities, with the aim of contributing to the field of nanotechnology, electronics and thermal engineering, The focus of this work is to optimize the heat dissipation in systems that require high thermal efficiency and stability such as automotive cooling systems, aerospace components and power electronics. In addition, the study explores the influence of key parameters such as heat transfer coefficients and thermal conductivity that play an important role in improving the thermal performance of cooling systems. The overall thermal performance of the model is evaluated based on its heat flux and thermal efficiency. The study also examines the impact of the shape optimized nanoparticles in silicone oil by incorporating shape-factor in its modelling equations and proposes optimization of parameters to enhance the overall thermal performance of the system. Darcy’s flow model is used to analyse the key parameters in the system and study the thermal behaviour of the hybrid nanofluid within the fin by incorporating natural convection, temperature-dependent internal heat generation, and radiation effects. By using the similarity approach, the governing equations were reduced to non-linear ordinary differential equations and numerical solutions were obtained by using four-stage Lobatto-IIIA numerical technique due to its robust stability and convergence properties. This enables a systematic investigation of various influential parameters, including thermal conductivity, emissivity and heat transfer coefficients. Additionally, it stimulates interest among researchers in applying mathematical techniques to complex heat transfer systems, thereby contributing towards the development of highly efficient cooling system. Our findings indicate that there is a significant enhancement in the heat flux as well as improvement in the thermal efficiency due to the mixture of silicone oil and shape optimized nanoparticles, that was visualized through comprehensive graphical analysis. Quantitatively, the proposed model displays a maximum thermal efficiency of 57.5% for lamina shaped nanoparticles at $N_c$ = 0.5, $N_r$ = 0.2, $N_g$ = 0.2 and ${\Theta }_a$ = 0.4. The maximum enhancement in the heat flux occurs when $N_c$ doubles from 5 to 10 for $m_2$ = 0.2 and $N_r$ = 0.1. Optimal thermal performance is found for $N_c$, $N_r$ and $m_2$ values in the range 5 to 10, 0.2 to 0.4 and 0.4 to 0.8 respectively. Full article

In metal cutting, a large amount of mechanical energy converts into heat, leading to a rapid temperature rise. Excessive heat accelerates tool wear, shortens tool life, and hinders chip breakage. Most existing thermal studies have focused on dry machining, with limited research on the effects of cutting fluids. This study addresses that gap by investigating the thermal behavior of cutting tools during continuous and interrupted turning with cutting fluid. Tool temperatures were first measured experimentally by embedding a thermocouple in a defined position within the tool. These experimental results were then combined with simulations to evaluate temperature changes, heat partition, and cooling efficiency under various cutting conditions. This work presents novel analytical and numerical models. Both models accurately predicted the temperature distribution, with the analytical model offering a computationally more efficient solution for industrial use. Experimental results showed that tool temperature increased with cutting speed, feed, and cutting depth, but the heat partition into the tool decreased. In continuous cutting, cooling efficiency was mainly influenced by feed rate and cutting depth, while cutting speed had minimal impact. Interrupted cutting improved cooling efficiency, as the absence of chips and workpieces during non-cutting phases allowed the cutting fluid to flow over the tool surface at higher speeds. The convective cooling coefficient was determined through inverse calibration. A comparative analysis of the analytical and numerical simulations revealed that the analytical model can underestimate the temperature distribution for complex tool structures, particularly non-orthogonal hexahedral geometries. However, the relative error remained consistent across different cutting conditions, with less error observed in interrupted cutting compared to continuous cutting. These findings highlight the potential of analytical models for optimizing thermal management in metal turning processes. Full article

This study presents a comprehensive 3D numerical analysis of thermal stratification, fluid dynamics, and heat transfer efficiency across six hot water storage tank configurations, identified as Tank-1 through Tank-6. The objective is to determine the most effective design for achieving uniform temperature distribution, stable stratification, and efficient heat retention in sensible heat storage systems, with potential for integration with phase change materials (PCMs). Using COMSOL Multiphysics 5.6, simulations were conducted to evaluate key performance indicators, including the Richardson number, capacity ratio, and exergy efficiency. Among the tanks, Tank-1 demonstrated the highest efficiency, with a capacity ratio of 84.6% and an exergy efficiency of 72.5%, while Tank-3, which achieved a capacity ratio of 70.2% and exergy efficiency of 50.5%, was identified as the most practical for real-world applications due to its balanced heat distribution and feasibility for PCM integration. Calculated dimensionless numbers (Reynolds number: 635, Prandtl number: 4.5, and Peclet number: 2858) indicated laminar flow and dominant convective heat transfer across all the configurations. These findings provide valuable insights into the design of efficient thermal storage systems, with Tank-3’s configuration offering a practical balance of thermal performance and operational feasibility. Future work will explore the inclusion of PCM containers within Tank-3, as well as applications for heat pump and solar water heaters, and high-temperature heat storage with various working fluids. Full article

In extreme marine environments, the interaction between offshore wind turbine pile foundations (OWTPFs) is critical, and the associated hydrodynamic loads are complex. This study focused on fixed OWTPFs and used computational fluid dynamics (CFD) to numerically simulate the flow field around pile foundations under the combined action of focusing waves and current. The objective was to investigate the influence of different focusing wave and current parameters on the hydrodynamic properties of the pile foundations. The findings indicate the following: (1) When the wave and current directions are opposite, the maximum wave force on the pile foundations is greater than when they are aligned. (2) Large-amplitude focusing waves around pile foundations generate secondary loads, which are nonlinear and lead to a rapid increase in the wave force. These secondary loads are short-lived and particularly prominent near the front row of pile foundations. (3) The influence of the group pile effect diminishes under high-amplitude waves, where the wave component dominates the generation of the dimensionless wave force, and the impact of the current on this force decreases. Full article

The annular flow payload is among the first batch of space science experimental projects carried out on the Fluid Physics Rack of the China Space Station. This paper provides a detailed introduction to the development of the payload, ground validation, and in orbit experiments. The payload, sized 320 mm × 200 mm × 220 mm, includes an annular flow model and supports supply (24 V, 12 V, and 5 V), communication, and data transmission. A multi-functional heating column in the annular flow model was designed, allowing for the column to operate in fixed, rotating, and lifting scenarios. In the first round, 96 sets of space experiments covering volume ratio ranges from 0.45 to 1.06 were carried out. The annular flow liquid surface state, temperature oscillation, and infrared temperature field evolution were obtained. Mode decomposition shows the oscillatory convection of the m = 4 travelling wave, and contains m = 3, m = 6, and m = 8 waves. Full article

This article analyses the use of low-temperature PCMs in devices supplementing a room ventilation system to prevent the overcooling effect. In this study, the phase change is numerically simulated in an axisymmetric system consisting of two tubes. One is filled with RT11HC with an initial temperature of 0 °C, while air with an inlet temperature of 20 °C flows through the other, heating the PCM and causing it to melt. Calculations are performed using commercial software with the apparent heat method for a system of given dimensions. Spatial distributions of the system temperature and liquid volume fraction at different time moments (from 0 to 120 min) are determined. It is found that the results depended mainly on the method of determining the latent heat. For the beginning of the charging process (t < 40 min), the values of the liquid phase fraction determined by the H and S methods are similar, while the one determined by the G method is definitely higher (even three times at t = 10 min). In turn, the outlet air temperature determined by the S method is lower than that determined by the other methods. The size and shape of the mesh have no significant effect on the results. Full article

Solar electric and solar thermal energies are often considered as part of the solution to the current energy emergency. The pipes of flat plate solar devices are normally heated by their upper surfaces giving rise to an asymmetric temperature field in the bulk of the fluid, which influences the heat transfer process. In the present work, a study of the characteristic length of tubes, or most efficient distance at which heat transfer occurs, in flat photovoltaic-thermal (PVT) hybrid solar devices has been carried out using three heat transfer fluids: water, [Emim]Ac ionic liquid and ionanofluid of graphene nanoparticles suspended in the former ionic liquid. The mean objective of the study was to know whether the heat transfer occurs in optimal conditions. Experimental measurements have been made on a commercial PVT device, and numerical simulations have been performed using the HEATT^® platform to determine the characteristic length of the process. The tests conducted showed a clear improvement in the temperature jump of the fluid inside the collector when INF is used compared to water and ionic liquid and even a higher overall energy efficiency. Electricity generation is not greatly affected by the fluid used, although it is slightly higher when water is used. Slower fluid velocities are recommended if high fluid outlet temperatures are the goal of the application, but this penalizes the overall thermal energy production. The characteristic process length is not typically achieved in parallel tube PVT collectors with ordinary flow rates, which would require a speed, and consequently, a flow rate, about 10 times lower, which penalizes the performance (up to four times), although it increases the fluid outlet temperature by 234%, which can be very interesting in certain applications. Ionanofluids may in the medium term become an alternative to water in flat plates or vacuum solar collectors for applications with temperatures close to or above 100 °C, when their costs will hopefully fall. The results and methodology developed in this work are applicable to solar thermal collectors other than PVT collectors. Full article

Meteorological factors, specifically wind direction and magnitude, influence the dispersion of atmospheric pollutants due to road traffic by affecting their spatial and temporal distribution. In this study, we are interested in the effect of the evolution of horizontal wind components, i.e., in the plane perpendicular to the altitude axis. A two-dimensional numerical model for solving the coupled traffic flow/pollution problem, whose pollutants are generated by vehicles, is developed. The numerical solution of this model is computed via an algorithm combining the characteristics method for temporal discretization with the finite-element method for spatial discretization. The numerical model is validated through a sensitivity study on the diffusion coefficient of road traffic and its impact on traffic density. The distribution of pollutant concentration, computed based on a source generated by traffic density, is presented for a single direction and different magnitudes of the wind velocity (stationary, Gaussian, linearly increasing and decreasing, sudden change over time), taking into account the stretching and tilting of plumes and patterns. The temporal evolution of pollutant concentration at various relevant locations in the domain is studied for two wind velocities (stationary and sudden change). Three regimes were observed for transport pollution depending on time and velocity: nonlinear growth, saturation, and decrease. Full article

As a key pressure control component of a hydraulic system, the noise of the direct-acting pressure reducing valve affects the working state of the system directly. However, the existing pressure reducing valves generally have the problem of excessive pure noise. In order to solve this problem, this study explored various structural combinations with the aim of improving the noise level of a direct-acting pressure reducing valve. Firstly, the flow field model of the direct-acting pressure reducing valve was established by using FEA (Finite Element Analysis), and the relationship between the flow field state and noise state was demonstrated through CFD (Computational Fluid Dynamics) simulation. Secondly, the position, number, and diameter of the oil holes on the valve spool were comprehensively analyzed, and the sound field analysis using LMS Virtual Lab was carried out. Finally, a prototype of the pressure reducing valve was manufactured, and the noise level before and after improvement was compared. The results showed that the effective sound pressure after improvement was reduced by 6.1% compared with that before at 50% of the opening, which verified the precision of the simulation model. The research results could provide a guideline for the design and improvement of direct-acting pressure reducing valves. Full article

The Darrieus vertical axis wind turbine (VAWT) is categorized as a lift-based turbomachine. It faces challenges in the low tip speed ratio (TSR) range and requires initial torque for the starting operation. Ongoing efforts are being made to enhance the turbine’s self-starting capability. In this study, Computational Fluid Dynamics (CFD) simulations were utilized to tackle the identified challenge. The Unsteady Reynolds-Averaged Navier–Stokes (URANS) approach was employed, combined with the shear–stress transport (SST) $k-\omega$ turbulence model, to resolve fluid flow equations. The investigation focused on optimizing the placement of auxiliary blades by considering design parameters such as the pitch angle and horizontal and vertical distances. The goal was to increase the turbine efficiency and initial torque in the low-TSR range while minimizing efficiency loss at high-TSR ranges, which is the primary challenge of auxiliary blade installation. Implementing the auxiliary blade successfully extended the rotor’s operational range, shifting the rotor operation’s onset from TSR 1.4 to 0.7. The optimal configuration for installing the auxiliary blade involves a pitch angle of 0°, a horizontal ratio of 0.52, and a vertical ratio of 0.41. To address the ineffectiveness of auxiliary blades at high-TSRs, installing deflectors in various configurations was explored. Introducing a double deflector can significantly enhance the overall efficiency of the conventional Darrieus VAWT and the optimum rotor with the auxiliary blade by 47% and 73% at TSR = 2.5, respectively. Full article

The development of the Modular High-Temperature Gas-Cooled Reactor is a significant milestone in advanced nuclear reactor technology. One of the concerns for the reactor’s safe operation is the effects of a loss-of-flow accident (LOFA) where the coolant circulators are tripped, and forced coolant flow through the core is lost. Depending on the steam generator placement, loop or intracore natural circulation develops to help transfer heat from the core to the reactor cavity, cooling system. This paper investigates the fundamental physical phenomena associated with intracore coolant natural circulation flow in a one-sixth Computational Fluid Dynamics (CFD) model of the Oregon State University High Temperature Test Facility (OSU HTTF) following a loss-of-flow accident transient. This study employs conjugate heat transfer and steady-state flow along with an SST k-ω turbulence model to characterize the phenomenon of core channel-to-channel natural convection. Previous studies have revealed the importance of complex flow distribution in the inlet and outlet plenums with the potential to generate hot coolant jets. For this reason, complete upper and lower plenum volumes are included in the analyzed computational domain. CFD results also include parametric studies performed for a mesh sensitivity analysis, generated using the STAR-CCM+ software. The resulting channel axial velocities and flow directions support the test facility scaling analysis and similarity group distortions calculation. Full article