Search Results (288)

The present work examines how variations in working fluid temperature govern the hydrodynamic behavior of a space-rated micropump. Using perfluorotriethylamine as the operating medium, three-dimensional CFD simulations employing the SST k-$\omega$ turbulence closure were carried out across a broad thermal spectrum, and the resulting flow physics were interpreted through entropy generation analysis. Based on the entropy production theory, the influence laws of different inlet temperatures on the external characteristics, internal characteristics, and flow loss characteristics of the micropump were quantitatively analyzed. The results show that temperature mainly affects the micropump performance by changing the viscosity and density of the working fluid. At low temperatures, the fluid viscosity increases significantly, leading to increased flow resistance, intensified internal friction, reduced head and efficiency, and increased shaft power. As the temperature increases to 0 °C and above, the viscosity change tends to moderate, and the external characteristic parameters tend to stabilize. The internal characteristic analysis shows that under low-temperature conditions, the high-pressure region in the impeller area expands and the turbulent kinetic energy decreases, but the flow separation is to a certain extent suppressed. The region near the volute tongue and the impeller outer edge are the main areas of entropy production loss, and their entropy production rates increase significantly with decreasing temperature. Moreover, at low temperatures, the high entropy production regions expand from locally isolated distributions to continuous large-scale distributions. The impeller outer edge dominates total entropy production, driven by peak fluid linear velocity and intense shear interaction with the volute wall. The findings elucidate how working fluid temperature governs both the hydrodynamic performance and the irreversible loss characteristics of the micropump. These insights can directly inform the engineering design of thermal management loops intended for orbital applications under severe temperature swings. Full article

A unified transient deterministic lubrication model is developed for the analysis of rough, starved, and coated contacts within a single, fully-coupled numerical framework capable of resolving boundary, mixed, and full-film lubrication regimes. The model is formulated with the finite volume method on a curvilinear grid and extends conventional full-film formulations through the introduction of a semi-system methodology, enabling robust treatment of complex multi-regime conditions. A key distinguishing feature of the framework is the direct resolution of thermal effects within both the lubricant and solid domains through solution of the energy equation. Unlike many existing mixed lubrication models that rely on analytical temperature approximations, the present approach captures transient, asperity-scale temperature evolution explicitly, allowing accurate representation of local thermo-mechanical interactions. Two case studies are presented to demonstrate the capabilities of the model. The first examines transient starvation in rough contacts with isotropic sinusoidal topographies of varying wavelength, as well as random machined surfaces, revealing a strong dependence of lubricant entrainment, asperity interaction, and localised heating on surface morphology. The second study investigates the role of coating thermal properties under transient starved conditions, demonstrating strong coupling between heat transport, viscosity variations, and frictional response. Overall, the proposed framework provides a robust and physically consistent platform for the simulation of transient lubrication phenomena under realistic operating conditions, enabling detailed insight into roughness, starvation, and thermal effects across regimes using a fully-coupled approach. Full article

Oxidative degradation stands as the principal cause of gear oil failure and transmission system malfunctions in wind turbines. Electrochemical impedance spectroscopy (EIS) offers a novel technical avenue for the condition monitoring of gear oil. This research centers on the evolution mechanism of electrochemical properties during the oxidative degradation process, utilizing high-viscosity gear oil commonly employed in wind turbines as the research subject. Through a combination of accelerated oxidation tests, broadband EIS measurements, and equivalent circuit fitting, the study examines the variations in the electrochemical response of gear oil with respect to oxidation temperature and duration. The findings reveal that oxidative degradation does not modify the single-relaxation dielectric characteristics of the gear oil; however, various electrochemical parameters undergo systematic evolution. Following oxidation at temperatures ranging from 90 to 120 °C, the charge transfer resistance escalates by approximately 5.9-fold; the base resistance diminishes by 10% to 20%; both the admittance constant and dispersion index of the constant phase element (CPE) exhibit changes of less than 5%, indicating that the system retains its capacitive properties. During constant-temperature oxidation at 90 °C for durations spanning 50 to 175 h, the charge transfer resistance increases in an approximately linear fashion with oxidation time, while the base resistance continues to decline, and the CPE parameters remain largely stable. Various electrochemical parameters evolve monotonically with the extent of oxidation, with charge transfer resistance demonstrating the highest sensitivity to thermal oxidation and thus serving as a pivotal indicator for evaluating the degree of thermal oxidative degradation in gear oil. This study lays an experimental foundation for the application of EIS technology in the realm of online gear oil monitoring. Full article

Thermally conductive epoxy potting compounds require high filler loadings for effective heat dissipation. However, high filler loadings can increase viscosity and brittleness, thereby impairing processability and service reliability. In this study, a mesogen-containing reactive liquid–crystalline epoxy monomer (LCE) was designed, synthesized, and incorporated into a commercial thermally conductive epoxy potting compound to investigate its effects on thermal behavior, rheological and mechanical properties, thermal conductivity, and fracture-surface morphology. The chemical structure and thermotropic liquid–crystalline behavior of LCE were characterized via Fourier-transform infrared spectroscopy, proton nuclear magnetic resonance spectroscopy, differential scanning calorimetry, and polarized optical microscopy. Increasing LCE loading elevated the DSC-derived glass transition temperature (T_g) from 59 °C to 96 °C and markedly increased the room-temperature complex viscosity. Single-point measurements at 25 °C showed a monotonic decrease in thermal conductivity from 0.95 to 0.52 W/(m·K) with increasing LCE content. Mechanical testing revealed that the nominal 10% LCE formulation provided the best balance between load-bearing capacity and ductility among the tested formulations, whereas higher LCE loadings were associated with greater local microstructural variation and reduced mechanical properties. This study clarifies the modulation effect of LCE on the performance balance of highly filled epoxy potting compounds, providing valuable insights for future formulation optimization. Full article

Heated crude oil pipelines transporting high-pour-point, high-viscosity, and high-wax-content crude oil are increasingly operated under small-batch and multi-condition scenarios. Under such conditions, fixed-parameter models and experience-based operating strategies may fail to accurately describe the evolving thermo-hydraulic state, resulting in inaccurate temperature-safety assessment and conservative energy use. To address this problem, this study develops a hybrid modelling and simulation framework for the energy-efficient operation of heated crude oil pipelines. The framework integrates operating-state perception, online parameter inversion, transient thermo-hydraulic simulation, data assimilation, and rolling optimization. First, an online parameter inversion method based on inverse problem solving is established to dynamically identify the overall heat-transfer coefficient and friction correction factor from Supervisory Control and Data Acquisition (SCADA) measurements. Second, a transient thermo-hydraulic simulation and data-assimilation model is constructed to predict pressure, temperature, and safety margins under changing boundary conditions. Third, a constraint-aware rolling optimization strategy is introduced to coordinate heating and pumping operations while satisfying temperature and pressure constraints. The proposed framework is validated using a practical crude oil pipeline. Under a representative low-flow-rate condition, online parameter inversion corrects the overestimation of the thermo-hydraulic state by the fixed-parameter model: the total temperature drop along the pipeline is revised from 33.12 °C to 35.65 °C, and the minimum station-inlet oil temperature is revised from 24.77 °C to 21.61 °C. After optimization is introduced, the total operating energy consumption decreases from 11,715.65 kW to 11,287.43 kW, corresponding to a reduction of 3.66%, while all temperature and pressure constraints remain satisfied. Under time-varying boundary conditions, the rolling optimization strategy further adjusts heating-furnace operation according to variations in inlet flow rate, inlet oil temperature, and ambient temperature, thereby reducing cumulative heating energy consumption while maintaining safe operation. The results demonstrate that the proposed framework provides an implementable modelling and simulation approach for online state assessment, transient prediction, and energy-efficient operation of heated crude oil pipelines under variable operating conditions. Full article

The objective of this study was to evaluate the effect of prolonged mild thermal treatment (65 °C, 7 days) in the presence of flaxseed oil (0.16%, w/w), on the structural, pasting, texture, and emulsifying properties of cassava starch (CS). The resulting sample was designated as CS-oil-h. Confocal laser scanning micrographs showed oil on the interface of starch granules promoted granule agglomeration. DSC and FTIR analyses showed no detectable evidence of amylose–lipid complexes or new covalent bonds. Compared to CS, CS-oil-h exhibited slight variations in pasting temperature and peak time, and significantly lower peak, trough, breakdown, final, and setback viscosities. CS-oil-h gel showed higher hardness, adhesiveness, gumminess, and chewiness when compared to the CS gel. Crucially, CS-oil-h exhibited the best emulsifying ability (60.8%, volume of emulsion layer relative to total tube volume after 30 min standing) and emulsion stability (94.1%, after 7 days of storage). The result suggested that the prolonged mild thermal treatment may have promoted putative surface association between flaxseed oil and the surface of starch granules, which resulted in inhibition of pasting viscosity and improved gel properties and emulsifying ability. Full article

During continuous casting, the flow behavior of liquid steel in the tundish directly affects the temperature distribution of liquid steel, inclusion removal, and billet quality. In tundish-related research, water model experiments remain an intuitive method for investigating the flow process in the tundish. However, water model experiments are often conducted in different seasons, and variations in experimental temperature can change fluid properties such as density and viscosity, thereby affecting flow characteristics and the comparability of experimental results. In this study, a 1:3.57 transparent bare single-strand tundish model made of acrylic was used, and the differences in tracer transport processes at 7 °C and 20 °C, as well as the influence of different tracer dosages on the experimental results, were systematically investigated through flow visualization and stimulus-response experiments. The results showed that, under the 7 °C condition, the upward transport tendency of the pure ink tracer was weakened, the overall flow remained closer to the tundish bottom, the transport speed decreased, and the time required to reach the outlet was significantly prolonged. For the saturated KCl solution tracer, a lower temperature enhanced its transport along the bottom toward the outlet and suppressed its diffusion toward the liquid surface. The RTD results showed that, after the temperature was increased, the curves shifted to the left as a whole, and both the peak time and the mean residence time were shortened. The outflow percentage of tracer results showed that the difference for the 10 mL saturated KCl solution between the 7 °C and 20 °C conditions was the most significant. At 7 °C, the total outflow percentage of the 10 mL salt solution tracer at 1500 s was 76.86%, which was 22.97% lower than that at 20 °C. As the tracer dosage increased, the differences in the transport process, RTD curves, and outflow percentage curves under different temperature conditions gradually decreased, indicating that the effect of dosage on the experimental results gradually became stronger than that of temperature. These results indicate that the combined effects of experimental temperature and tracer dosage cannot be neglected in tundish water model experiments. Full article

Pultrusion is an efficient continuous manufacturing process for fiber-reinforced polymer (FRP) composites, but conventional open-bath impregnation has limitations such as resin exposure, quality variation, and resin loss. To overcome these limitations, closed-injection pultrusion (CIP) and short-pot-life resin systems have recently been introduced. However, the effects of processing variables on the quality and properties of composites manufactured using such resin systems have not been fully clarified. In this study, the effects of resin viscosity and pulling speed on the quality and mechanical properties of carbon FRP (CFRP) and glass FRP (GFRP) composites manufactured by CIP were investigated. CFRP and GFRP composites were fabricated at resin temperatures of 30 and 40 °C and pulling speeds of 300, 400, and 500 mm/min. The manufactured composites were evaluated in terms of void content, microstructure, hardness, and tensile properties. The results showed that increasing pulling speed increased void content and promoted macrovoids and locally poor impregnation, whereas the influence of resin temperature was relatively limited. Hardness, tensile strength, and elastic modulus decreased as pulling speed increased. These results demonstrate that CFRP and GFRP composites can be successfully manufactured by CIP using short-pot-life resin systems, and that precise control of resin viscosity and pulling speed is essential for achieving high quality and mechanical performance. Full article

The brake–release stability of electro-hydraulic thrusters (EHTs) significantly affects the safety of hydraulic braking systems, especially under low-temperature conditions with varying fluid viscosity. Most existing studies have focused on macroscopic braking characteristics, while the internal flow field variation and vortex evolution mechanism during the brake–release process remain insufficiently explored. In this work, transient CFD simulations are conducted to investigate vortex formation rules and flow field characteristics inside an EHT. Three typical vortex structures denoted as α, β, and γ are identified, and the independent and coupling influences of fluid dynamic viscosity and motor speed on vortex intensity and piston-bottom pressure are quantitatively analyzed. The results show that vortices α and β trigger flow disorder and additional hydraulic energy loss, while vortex γ optimizes flow uniformity and assists piston extension. Higher fluid viscosity exacerbates vortex development and pressure fluctuation, while increasing motor speed accelerates transient flow field evolution. This study clarifies the internal flow mechanism of EHT brake–release behavior and provides reliable parametric guidance for optimizing the low-temperature performance of electro-hydraulic braking systems. Full article

Hydrogen-fueled internal combustion engines (H₂-ICEs) impose unique challenges on engine lubrication because water is an inevitable combustion product. This review summarizes the current understanding of water-induced degradation mechanisms in engine oils for H₂-ICEs, with emphasis on physicochemical property variation, additive depletion, tribofilm evolution, and tribological performance. Water present in dissolved, emulsified, or free states can significantly alter lubricant viscosity, destabilize additive systems, and accelerate oxidative aging. In particular, water promotes the depletion of zinc dialkyldithiophosphate (ZDDP) through tribofilm removal and competitive adsorption at rubbing interfaces, while also inducing additive hydrolysis that transforms long-chain phosphates into shorter-chain species with inferior film-forming capability. These processes inhibit tribofilm growth and reduce the mechanical integrity of protective films, thereby deteriorating anti-wear performance. Although substantial progress has been made in understanding the role of liquid water in lubrication, the tribochemical effects of high-temperature water vapor under realistic H₂-ICE operating conditions remain largely unexplored. Future research should therefore focus on water vapor-dominated lubrication environments representative of hydrogen combustion, aiming to elucidate the underlying tribochemical mechanisms and support the development of dedicated lubricants for durable and reliable H₂-ICE operation. Full article

For continuous casting of strong reducing steels, the low-reactive aluminate-based mold flux consisting of CaO-SiO₂-Al₂O₃-CaF₂-Li₂O-B₂O₃-Na₂O with low SiO₂ content was designed. The correlation between the melt structure under high temperature and the crystallization phases during the cooling process and the change of viscosity was analyzed. The following conclusions were obtained. The polymerization degree of the mold flux consistently decreased as the w(CaO)/w(Al₂O₃) ratio increased from 0.93 to 1.65. Due to melt structure depolymerization, the viscosity at 1300 °C dropped from 0.132 Pa·s to 0.054 Pa·s. As the w(CaO)/w(Al₂O₃) ratio increases near the breaking temperature, the crystalline phases in the mold flux transition from LiAlO₂ to Ca₂Al₂SiO₇, and finally to a combination of Ca₁₂Al₁₄O₃₂F₂ and LiAlO₂. The rapid viscosity increase at the breaking temperature was primarily due to the precipitation of these phases. Furthermore, influenced by the changes in crystallization tendency and crystalline phase precipitation, the breaking temperature first decreased and then increased. Increasing the Li₂O mass fraction from 5% to 9% led to a decrease in the polymerization degree of the mold flux. Due to the depolymerizing impact of Li₂O on the slag network, the mold flux viscosity at 1300 °C decreased from 0.102 Pa·s to 0.047 Pa·s. The breaking temperature of the mold flux rose notably with a higher Li₂O mass fraction. At the breaking temperature, the crystalline phases in the mold flux transition from Ca₂Al₂SiO₇ to a combination of LiAlO₂ and Ca₁₂Al₁₄O₃₂F₂. The precipitation of these phases at the breaking temperature directly caused a rapid increase in viscosity. The results systematically reveal the coupling mechanism between melt structure, crystalline phase evolution, and viscosity variation of low-SiO₂ aluminate-based mold flux, which provides an important theoretical basis for composition design and performance regulation of mold fluxes for high-aluminum steel continuous casting. Full article

Online monitoring of polyacrylamide (PAM) concentration is needed for quality control in continuous fracturing-fluid blending and for closed-loop smart fracturing operations. This study evaluates the feasibility and current limits of an MR-based PAM assay route. Static CPMG-T2 tests on an existing 4.6 MHz magnetic resonance multiphase flowmeter (MRMF) platform showed that T2-based viscosity discrimination is useful when the PAM concentration is above approximately 3‰, but it becomes insufficient in the 1–3‰ low-concentration interval. A 20 MHz laboratory T2-D validation test indicated that the apparent diffusion coefficient responds more clearly to PAM-induced molecular-mobility variation than T2 alone. On this basis, a 23.5 MHz diffusion-capable online detector concept was developed, featuring a permanent-magnet module, a gradient-capable RF probe, compact spectrometer electronics, and a quasi-static bypass sampling process for oilfield installation. The revised interpretation framework combines T1, T2, diffusion coefficient, temperature, signal-quality indicators, repeatability checks, and calibration-domain gating. The present work defines a proof-of-concept route, and the validation requirements for online PAM concentration monitoring; final accuracy, repeatability, RMSE, confidence intervals, and field-calibrated acceptance thresholds must still be determined through controlled loop and field tests. Full article

Cable wires provide a viable technical pathway for the laser additive manufacturing of high-entropy alloys (HEAs). However, the complex interplay of structural and material parameters of cable wires leads to significant variations in molten pool dynamics, which poses challenges to the fabrication of high-quality HEA coatings. To clarify the effects of these key factors on molten pool behavior, a multi-physics numerical model for the laser cladding of Al₅₀Si₆Ti₈Cr₁₂Cu₁₂Ni₁₂ cable wires was established in this study. A dedicated physical model for cable wires was developed, and the Level Set Method was employed to track fluid interfaces throughout the cladding process. Based on the proposed model, the temperature distribution, stress fields, and elemental homogeneity within the molten pool were systematically investigated. The results reveal that chromium (Cr) addition induces a viscosity reduction, and a torsional pitch of ≤4 mm is critical for achieving defect-free, compositionally uniform HEA coatings, which provides novel insights for process optimization and alloy design of cable-wire laser cladding. Full article

The demand for eco-friendly viscosity modifiers in food, cosmetics, and lubricants has increased, promoting the development of high-performance, sustainable materials. Low-molecular-weight gelators (LMWGs) are promising candidates, though their behavior in complex systems remains underexplored. In this study, a novel alkylamido isophthalic acid-based LMWG (AIPA–gallic acid) was synthesized. Its performance was evaluated in vegetable oil, mineral oil, and cocoa butter using rheological measurements across varying concentrations and temperatures, with all dynamic rheological measurements conducted in the viscoelastic region. Cacao butter is solid at 15 °C, so the flow curve that can be obtained at this temperature should show high values not comparable with the other liquid oils. No slippage phenomenon was observed. Using a step-rate protocol before acquiring the flow curves, no time-dependent behavior (thixotropy) was observed. Frequency and flow sweep tests were used to assess viscoelastic properties, interaction strength, and coordination number. Results revealed that incorporating AIPA–gallic acid at 4 wt% increased the viscosity by 74 times (at 25 °C) in mineral oil, compared to an increase of about four orders of magnitude in vegetable oil. This suggests the formation of intermolecular interactions that lead to an increased momentum transport process, which is significantly higher in vegetable oil. In contrast, cocoa butter exhibited minimal rheological changes, suggesting that no gelation occurred. Analysis using the weak gel model confirmed that viscosity enhancement arises from a structured network in mineral and vegetable oils, but not in cocoa butter. Temperature-dependent variations in structural parameters further highlight the role of molecular interactions between the gelator and the oil matrix. Full article

This paper presents a performance analysis of a hybrid tilting pad journal bearing (TPJB) for reusable liquid methane (LCH₄) turbopumps. The numerical model incorporates temperature- and pressure-dependent density and viscosity of LCH₄ using fourth-order polynomial correlations based on the National Institute of Standards and Technology (NIST) data. A bulk-flow thermohydrodynamic analysis solves the Reynolds and energy equations considering turbulence, compressibility, recess inertia effects, and thermal mixing. The model calculates the pressure and temperature fields using the finite element and finite difference methods, respectively. The results of the static load and length-to-diameter ratio identify the available load range for the present bearing geometry. The cryogenic LCH₄ supplied through the recess locally suppresses temperature rise and produces spatial variations in its density and viscosity. The preload and radial clearance design can compensate for the limited load-carrying capacity of low-viscosity LCH₄, while they also can increase friction coefficient and temperature rise. The supply pressure ratio is the dominant parameter because it strengthens hydrostatic support and compensates for the weak hydrodynamic effect of LCH₄. In contrast, larger recess area weakens hydrostatic support and reduces dynamic coefficients. These results provide bearing-level design guidance for reusable LCH₄ turbopumps. Full article