Search Results (222)

Fibre Bragg grating (FBG) grid sensors are an underexplored technology with potential to benefit nuclear thermal hydraulics experiments. This paper presents a new FBG grid sensor consisting of 38 FBGs across 8 flow-crossing chords. Using this sensor, experiments determined for the first time that an FBG grid can detect large air bubbles rising in standing liquids—demonstrated in both columns of water and 20W50 automotive oil. The instrument’s sensitivity was quantified by comparing its measurements to high-speed camera recordings. Analysis of Bragg wavelength shift timings on each chord enabled the surface of a bubble to be reconstructed using the air–oil data. Finally, the increase in Bragg wavelength when bubbles interact with the FBG grid suggests a variant sensing principle different from that reported in the literature for FBG grids in flowing liquids. Full article

Air flotation separation technology has emerged as one of the core techniques for oily wastewater treatment in oilfields, owing to its advantages of high throughput, high separation efficiency, and short retention time. Originally applied in mineral processing, this technology was first introduced to oilfield produced water treatment by Shell in 1960. With the optimization of microbubble generators, advances in microbubble generation technology—characterized by small size, high stability, and uniformity—have further expanded its applications across various wastewater treatment scenarios. To optimize the separation performance of a horizontal compact closed-loop cyclonic air flotation unit, this study employs CFD numerical simulation to investigate two key aspects: First, for the flotation zone, the effects of structural parameters (deflector height, inclination angle) and operational parameters (gas–oil ratio, bubble size, inlet velocity) on flow patterns and gas distribution were systematically examined. Device performance was evaluated using metrics such as gas–oil ratio distribution curves and flow field characteristics, enabling the identification of operating conditions for stratified flow formation and the determination of optimal deflector structural parameters. Second, based on the Eulerian multiphase flow model and RSM turbulence model, a numerical simulation model for the oil–gas–water three-phase flow field was established. The influences of key parameters (bubble size, throughput, gas–oil ratio) on oil–water separation efficiency were investigated, and the optimal operating conditions for the unit were determined by integrating oil-phase/gas-phase distribution characteristics with oil removal rate data. This research provides theoretical support for the structural optimization and engineering application of horizontal compact closed-loop cyclonic flotation units. Full article

This study focuses on the suitability of Core Annular Flow (CAF) technologies for transporting heavily viscous oil lubricated with water in a horizontal conduit. Using Computational Fluid Dynamics (CFD) and Large Eddy Simulation (LES) techniques with ANSYS Fluent software (Ansys 2022 R2), the research aims to analyze the flow behaviour of heavy oil-water mixtures in horizontal pipes. Specifically, the study examines turbulent CAF to gain insights into how gravity influences the three-phase flow of heavy oil, water, and air. The simulations consider standard horizontal pipes and explore the impact of temperature variations and the presence of air on the annular flow’s behaviour and pressure gradients. The study’s findings, supported by both simulated and experimental results from literature, demonstrate consistent outcomes and contribute to understanding the effectiveness of LES in modelling such complex flows. Overall, this work is novel because it uses an integrated approach to apply advanced numerical techniques, such as LES, to heavy oil, water, and air flows in a horizontal pipe. This approach advances both fundamental understanding and real-world applications in industrial contexts. Full article

Underwater acoustics is the optimal method for long-distance information transmission in aquatic environments. Hydrophones, as the core component of sonar systems, have found widespread application across multiple fields. However, existing types of hydrophones exhibit limited detection capabilities under low-signal conditions. To enhance low-frequency long-range detection performance, the development of new hydrophones featuring low power consumption, low frequency, high sensitivity, and miniaturization has become a research priority, with breakthroughs sought in the principle of electroacoustic conversion. Therefore, this study designed a frustum-cone triboelectric hydrophone (FCTH) based on friction layer materials, utilizing an indium-tin oxide (ITO) flexible conductive film on a polyethylene terephthalate (PET) substrate and a Polytetrafluoroethylene (PTFE) film. The sensor consists of a waterproof, sound-transparent polyurethane flow guide, silicone oil, and a frustum-cone triboelectric sensing unit based on a coupled membrane–cavity structure. The frustum-cone triboelectric sensing unit, based on a thin-film-perforated-tube resonance structure, enables omnidirectional detection of low-frequency hydroacoustic signals. The miniaturized design significantly reduces the volume of the FCTH. The acoustic–electric conversion relationship of the FCTH was derived using acoustic theory, thin-film vibration theory, and Maxwell’s displacement current theory. Furthermore, the low-frequency response characteristics of the frustum-cone triboelectric sensing unit were analyzed. The FCTH achieves a wide-frequency response ranging from 50 Hz to 12,000 Hz, with omnidirectional sensitivity and a maximum sensitivity of −174.6 dB. The FCTH achieves a wide-frequency response capability of 50 Hz to 12,000 Hz, with omnidirectional sensitivity and a maximum sensitivity of −174.6 dB. Additionally, through acoustic signal acquisition experiments in air, indoor, and outdoor water environments, the FCTH has been validated to possess excellent underwater acoustic detection performance and application potential across multiple scenarios. Full article

Existing faulty coal-fired units generally achieve oil-free stable combustion only at loads over 30%, failing to meet low load regulation demands. To address the insufficient flexibility of boilers, a novel flame-stabilization theory was developed for retrofitting a 350 MW faulty coal-fired unit boiler. Based on the actual burner dimensions of the 350 MW unit boiler, a geometric scaling ratio of 1:7 between model and actual burners was established. Phase Doppler Anemometry (PDA) was employed to conduct gas particle flow experiments on the model burner, revealing the impact of different primary air velocities on the gas particle flow characteristics of the novel stabilized flow burner. The analysis of experimental results suggests that, When the primary air velocity is 9 m/s, a central recirculation zone forms at the burner outlet. At a primary air velocity of 10 m/s, an annular recirculation zone develops with a relatively large coverage area. When the primary air velocity increases to 11 m/s, the extent of the annular recirculation zone diminishes. At a primary air velocity of 10 m/s, an extensive annular recirculation zone forms at the burner outlet, which appears to provide sufficient energy for the ignition of pulverized coal. Elevated pulverized coal concentration near the burner centerline facilitates the formation of a high-temperature oxygen-lean reducing atmosphere, suppressing fuel-based NO_x generation. Therefore, it is recommended to set the actual operating parameters of the novel stabilized flow burner based on the 10 m/s primary air velocity condition in the gas particle flow experiments. Full article

The aircraft air-cycle system (ACS) provides cabin cooling, dehumidification, and pressurization. As a key component, the water separator removes free moisture from the air, preventing turbine icing/blockage under high humidity and avoiding humidity-induced electronics failures, thus ensuring reliable ACS operation. Existing studies focus mainly on oil and chemical applications, with limited work for aircraft ACS. To address this research gap, this study investigates a straight-through cyclone water separator for aircraft ACS applications. We built a test platform to measure separation efficiency and conducted experiments at swirl angles of 20°, 30°, and 40°. A simulation model based on the Reynolds Stress turbulence model and a discrete phase model was established, and its simulation efficiency agreed with experiments within 4.1%. Simulation on water separator under high-pressure and low-pressure conditions were conducted, revealing internal flow fields and droplet dynamics. Results show each swirl angle has a distinct high-efficiency operating range, enabling selection according to system parameters across air mass flow rates; under varying humidification rate, the 40° swirl generator performed best. Simulations further indicate that higher operating pressure markedly improves performance: pressure loss decreased from 4.5 kPa to 0.7 kPa, while separation efficiency increased by 30.7%. Full article

Nowadays, immersion cooling-based battery thermal management systems have demonstrated their effectiveness in controlling the temperature of lithium-ion batteries. While previous scientific research has primarily concentrated on traditional dielectric fluids such as mineral oil, the current research investigates the effectiveness of the dielectric fluid FC-40. A three-dimensional Computational Fluid Dynamics model of an eight-cell 18650 battery system was constructed using ANSYS Fluent 19.2 to examine the effect of cooling fluids (air, mineral oil, and FC-40), velocity of flow (0.01 m/s to 0.15 m/s), discharge rate (1C to 5C), and inlet/outlet size (2.5 mm to 3.5 mm) on thermal efficiency as well as pressure drop. The findings indicate that employing FC-40 as the dielectric fluid significantly reduces the peak cell temperature, with an absolute decrease of 2.80 °C compared to mineral oil and 15.10 °C compared to air. Furthermore, FC-40 achieves the highest uniformity with minimal hotspot. On the other hand, as the fluid velocity increases, the maximum temperature of the battery drops, reaching a minimum of 26 °C at a velocity of 0.15 m/s. Otherwise, at lower flow velocities, the pressure drop remains minimal, thereby reducing the pumping power consumption. Additionally, increasing the inlet and outlet diameter of the fluid directly improves cooling uniformity. Consequently, the temperature dropped by up to 4.3%. Finally, the findings demonstrate that elevated discharge rates contribute to increased heat dissipation but adversely affect the efficiency of the thermal management system. This study provides critical knowledge for the enhancement of battery thermal management systems based on immersion cooling using FC-40 as a dielectric. Full article

The in situ conversion of oil shale with air injection has the advantage of self-generated heat. The fragmentation degree of oil shale affects the oxidative pyrolysis process. In this paper, the basic properties of oil shale were analyzed, and weight loss observation and high-pressure TGA-DSC (thermogravimetric analysis and differential scanning calorimetry) tests in an air atmosphere were conducted using the cores and particles. The oil shale’s oxidative pyrolysis characteristics and the effect of its particle sizes were evaluated. The results show that the porosity and permeability conditions, TOC (total organic carbon), and inorganic mineral composition of oil shale are highly heterogeneous, with higher permeability and greater TOC along the bedding direction. The derivative of the TGA curve shows a single peak, and the heat flow curve shows a double peak that can be used to determine the oil shale’s oxidation type. The oxidative pyrolysis stage of organic matter can be divided into three temperature ranges, of which the medium temperature range is where the most combustion weight loss and heat release occurs. The activation energy of oxidative pyrolysis, which is affected by factors such as particle size, organic matter content, and pyrolysis temperature, is 46.92–248.11 kJ/mol, indicating the varying degrees of difficulty in initiating the reaction under different conditions. The pre-exponential factor is 3.15 × 10²–6.27 × 10¹¹ 1/s, and the enthalpy value is 2.575–4.045 kJ/g. The combustion indexes and reaction enthalpy under different particle sizes are more correlated with their own organic matter content. As oil shale particle size decreases, the variation law of the activation energy and pre-exponential factor changes with temperature from an initial continuous increase to a decrease, then increases again with the smallest kinetic parameters in the medium temperature zone. A small particle size, high organic matter content, and high pressure are more conducive to initiating the oxidative pyrolysis reaction to achieve in situ conversion of organic matter. Full article

Under extreme operating conditions, the internal lubricating flow field of high-speed gear transmission systems exhibits a transient oil–gas multiphase flow, predominantly governed by cavitation-induced phase transitions and turbulent shear. This phenomenon involves complex mechanisms of nonlinear multi-physical coupling and energy dissipation. Traditional lubrication theories and single-phase flow simplified models show significant limitations in capturing microsecond-scale flow features, dynamic interface evolution, and turbulence modulation mechanisms. To address these challenges, this study developed a cross-scale coupled numerical framework based on the Lattice Boltzmann method and large eddy simulation (LBM-LES). By incorporating an adaptive time relaxation algorithm, the framework effectively enhances the computational accuracy and stability for high-speed rotational flow fields, enabling the precise characterization of lubricant splashing, distribution, and its interaction with air. The research systematically reveals the spatiotemporal evolution characteristics of the internal flow field within the gearbox and focuses on analyzing the nonlinear regulatory effect of baffle geometric parameters on the system’s energy transport and dissipation characteristics. Numerical results indicate that the baffle structure significantly influences the spatial distribution of the vorticity field and turbulence intensity by reconstructing the shear layer topology. Low-profile baffles optimize the energy transfer pathway, effectively reducing the flow enthalpy, whereas excessively tall baffles induce strong secondary recirculation flows, exacerbating vortex-induced energy losses. Simultaneously, appropriately increasing the spacing between double baffles helps enhance global lubricant transport efficiency and suppresses unsteady dissipation caused by localized momentum accumulation. Furthermore, the geometrically optimized double-baffle configuration can achieve synergistic improvements in lubrication performance, oil film stability, and system energy efficiency by guiding the main shear flow and mitigating localized high-momentum impacts. This study provides crucial theoretical foundations and design guidelines for developing the next generation of theory-driven, energy-efficient lubrication design strategies for gear transmissions. Full article

In this study, the oxidative upgrading of heavy oil residues using polymer-containing waste for the sustainable production of bitumen was investigated. Oxidation was performed at temperatures of 250–270 °C for 3–4 h with the addition of 2–3 wt.% polyethylene-based waste, under an air flow of 7 L/min. The physical and mechanical characterization of the resulting bitumen demonstrated compliance with oxidized modified bitumen grades OMB 100/130 and OMB 70/100. FTIR spectroscopy revealed the formation of carbonyl and sulfoxide functional groups, indicating the effective oxidative transformation of the bitumen matrix and partial incorporation of polyethylene fragments. NMR spectroscopy confirmed increased aromaticity and carbonyl content, while also detecting polyethylene-derived signals, suggesting compatibility and integration of the polymer waste into the oxidized structure. The thermal and rheological results showed that the optimal conditions for producing high-quality oxidized bitumen involved the use of 2% polymer waste at 270 °C for 4 h, yielding enhanced physical properties and chemical stability. These findings support the feasibility of using polymer-containing waste for bitumen upgrading, offering both environmental and technical advantages. The method not only improves the quality of bitumen but also contributes to waste valorization and circular economy practices in the road construction industry. Full article

Using Excel and its Solver feature, a novel method of analyzing the component reactions of an overall reaction is outlined. As an example, autothermal reforming (300–700 °C) of acetic acid (AA), a significant component of pyrolysis oil, was considered. The overall reaction can be viewed as comprising five individual reactions: reforming, oxidation, water–gas shift, reverse Boudouard, and methanation. A laboratory apparatus was set up in which acetic acid, air, and water were continuously fed to a BASF dual-layer catalytic reactor in plug flow at 1 atm. For this setup, it is easy to construct a material balance in Excel in which five factors, f_i, are defined which represent the fraction of reactant going to each of the individual five reactions. Using the Solver feature of Excel, it can readily be determined which of the five factors f_i produce the best match of the calculated exit gas composition with the measured gas concentrations for CO, CO₂, H₂, CH₄, and O₂. Furthermore, a program such as GasEq or Aspen can then be used to calculate the theoretical equilibrium gas composition at a given condition. Using this equilibrium gas composition and Solver, the individual (f_i)_equilb can be calculated. Thus, the ratio f_i/(f_i)_equilb is an indication of how close each component reaction is to equilibrium. In this way, an idea is gained of which of the individual component reactions need to be improved or inhibited or if operating parameters should be adjusted. For the specific case of autothermal reforming of acetic acid, the steam reforming reaction requires at least 600 °C to approach equilibrium. In contrast, the oxidation reaction goes to equilibrium throughout the temperature range, completely consuming oxygen. The water–gas shift reaction appears to approach equilibrium to the extent of 71–90% throughout the temperature range. The reverse Boudouard reaction is favored at lower temperatures; in fact, coking was predicted and found at the low temperature of 300 °C. Full article

As a core component of aero-engines, double-row ball bearings’ lubrication performance directly impacts the operational stability of the aircraft engine. However, existing under-race lubrication designs primarily rely on empirical knowledge, with insufficient understanding of the complex oil–air two-phase flow mechanisms, leading to bottlenecks in optimizing lubrication efficiency. Therefore, based on the computational fluid dynamics (CFD) method, a two-phase flow model for double-row ball bearings was established to systematically analyze the influence patterns of key parameters—including rotational speed, oil supply rate, number of under-race holes, diameter of under-race holes, and oil properties (viscosity, density)—on the distribution of the oil–air two-phase flow. The findings reveal that (1) the oil in the circumferential direction of the bearing cavity exhibits periodic distribution characteristics correlated with the number of under-race holes; (2) the self-rotation effect of balls hinders the migration of oil toward the outer raceway region, resulting in a significant reduction in the oil volume fraction within the bearing cavity; (3) compared with the single-sided oil supply configuration, the double-sided oil supply structure demonstrates superior lubrication performance. These research results provide theoretical support and reference data for the optimal design of under-race lubrication systems for double-row ball bearings. Full article

This review covers the current state, challenges, and future directions of catalytic combustion technologies for mitigating fugitive methane emissions from the fossil fuel industry. Methane, a potent greenhouse gas, is released from diverse sources, including natural gas production, oil operations, coal mining, and natural gas engines. The paper details the primary emission sources, and addresses the technical difficulties associated with dilute and variable methane streams such as ventilation air methane (VAM) from underground coal mines and low-concentration leaks from oil and gas infrastructure. Catalytic combustion is a useful abatement solution due to its ability to destruct methane in lean and challenging conditions at lower temperatures than conventional combustion, thereby minimizing secondary pollutant formation such as NO_X. The review surveys the key catalyst classes, including precious metals, transition metal oxides, hexa-aluminates, and perovskites, and underscores the crucial role of reactor internals, comparing packed beds, monoliths, and open-cell foams in terms of activity, mass transfer, and pressure drop. The paper discusses advanced reactor designs, including flow-reversal and other recuperative systems, modelling approaches, and the promise of advanced manufacturing for next-generation catalytic devices. The review highlights the research needs for catalyst durability, reactor integration, and real-world deployment to enable reliable methane abatement. Full article

The increasing demand for high-efficiency cooling technologies necessitates improved methods to prevent degradation and ensure reliable operation of lithium–ion batteries. Conventional PCM (phase change material)-based cooling systems are limited by low thermal conductivity and uneven phase change processes, which lead to non-uniform thermal distribution and diminished performance. In response to these challenges, this study introduces a hybrid thermal management system that combines an indirect liquid-cooling structure with multiple cooling channel configurations within a PCM-based battery pack. Numerical simulations were conducted to systematically assess the thermal performance of the proposed design. Experimental validation with various cooling media showed that PCM achieved the greatest reduction in temperature (47%) and the longest isothermal duration (56 min) under air-cooled conditions, surpassing thermally conductive adhesive (40%) and silicone oil (26%) for temperature decrease. Vertical temperature differentials were effectively reduced, staying below only 2 °C for silicone oil and reaching a maximum of 4 °C for PCM. Phase change evaluation indicated that after 30 min of operation, only 37% of the PCM volume had melted, highlighting localized constraints in heat transfer. Comparative analysis among four liquid-cooling channel arrangements (A–D) and a standalone PCM system demonstrated that configuration D exhibited the highest cooling capability, lowering the battery surface temperature by as much as 9 °C (17.8%). Flow rate analysis determined that increases above 0.2 L/min resulted in only modest thermal improvements (<1 °C), with 0.108 L/min identified as the most efficient rate. Relative to PCM-only designs, the advanced hybrid cooling system achieved significantly enhanced thermal regulation and temperature uniformity, underscoring its promise as a superior solution for lithium–ion battery thermal management. Full article

Modern advanced aero-engine bearing systems typically exhibit structural and loading characteristics with high DN values. The harsh thermal environment and multi-physics loads under operating conditions render the reliability of bearing structural systems particularly sensitive to lubrication efficiency and bearing chamber temperature. This study performs simulation analyses of oil return processes and their influencing factors in an aero-engine main bearing chamber with complex structural features. The results show two primary causes of reduced scavenging performance. On the one hand, the local low-speed region at the inlet of the scavenge pipe causes some oil to fail to enter the scavenge pipe normally. On the other hand, the air in the bearing chamber is disturbed by the rotation of the rotor, which makes oil enter the oil sump with a tendency to return to the oil collection annulus, thereby causing poor oil return. Furthermore, two structural improvements of the oil sump are proposed. These improvements avoid the disruptive effects of circumferential fluid motion in the oil collection annulus on the pressure and velocity distribution within the bearing chamber, thereby improving scavenging performance. Full article