Search Results (232)

This study proposes a method for estimating the kinetic coefficient of friction (COF) for asphalt pavements by improving and applying Persson’s friction theory. The method utilizes the power spectral density (PSD) of the top surface topography instead of the full PSD to better reflect the actual contact conditions. This approach avoids including deeper roughness components that do not contribute to real rubber–pavement contact due to surface skewness. The key aspect of the method is determining an appropriate cutting plane to isolate the top surface. Four cutting strategies were evaluated. Results show that the cutting plane defined at 0.5 times the root mean square (RMS) height exhibits the highest robustness across all pavement types, with the estimated COF closely matching the measured values for all four tested surfaces. This study presents an improved method for estimating the kinetic coefficient of friction (COF) of asphalt pavements by employing the power spectral density (PSD) of the top surface roughness, rather than the total surface profile. This refinement is based on Persson’s friction theory and aims to exclude the influence of deep surface irregularities that do not make actual contact with the rubber interface. The core of the method lies in defining an appropriate cutting plane to isolate the topographical features that contribute most to frictional interactions. Four cutting strategies were investigated. Among them, the cutting plane positioned at 0.5 times the root mean square (RMS) height demonstrated the best overall applicability. COF estimates derived from this method showed strong consistency with experimentally measured values across all four tested asphalt pavement surfaces, indicating its robustness and practical potential. Full article

Although particulate matter (PM) pollution from vehicles’ exhaust has decreased significantly over the years, the contribution from non-exhaust sources (brakes, tyres) has remained at the same levels. In the European Union (EU), Euro 7 regulation introduced PM limits for vehicles’ brake systems. Regenerative braking, i.e., recuperation of the deceleration kinetic and potential energy to the vehicle battery, is one of the strategies to reduce the brake emission levels and improve vehicle efficiency. According to the regulation, the shares of friction and regenerative braking can be determined with actual testing of the vehicle on a chassis dynamometer. In this study we tested the regenerative capabilities of a plug-in hybrid vehicle, both in the laboratory and on the road, under different protocols (including both smooth and aggressive braking) and covering a wide range of driving conditions (urban, rural, motorway) over 10,000 km of driving. Good agreement was obtained between laboratory and on-road tests, with the use of the friction brakes being on average 7% and 5.3%, respectively. However, at the same time it was demonstrated that the friction braking share can vary over a wide range (up to around 30%), depending on the driver’s behaviour. Full article

During atmospheric reentry, a significant number of chemical reactions are produced inside the high-temperature shock wave formed upstream of the spacecraft. Chemical reactions can significantly alter the flowfield structure surrounding the vehicle and affect surface properties, including heat transfer, pressure, and skin friction coefficients. In this scenario, the primary goal of this investigation is to evaluate the Quantum-Kinetic chemistry model for computing rarefied reactive gas flow over simple and complex geometries. The results are compared with well-established reaction models available for the transitional flow regime. The study focuses on two configurations, a sphere and the Orion capsule, analyzed at different altitudes to assess the impact of chemical nonequilibrium across varying flow rarefaction levels. Including chemical reactions led to lower post-shock temperatures, broader shock structures, and significant species dissociation in both geometries. These effects strongly influenced the surface heat flux, pressure, and temperature distributions. Comparison with results from the literature confirmed the validity of the implemented QK model and highlighted the importance of including chemical kinetics when simulating hypersonic flows in the upper atmosphere. Full article

Surfactants can be utilized to improve oil recovery by changing the performance of reservoirs in rock pores. Kerogen is the primary organic matter in shale; however, high temperatures will affect the overall performance of this surfactant, resulting in a decrease in its activity or even failure. The effect of surfactants on kerogen pyrolysis has rarely been researched. Therefore, this study synthesized a polymeric surfactant (PS) with high temperature resistance and investigated its effect on kerogen pyrolysis under the friction of drill bits or pipes via molecular dynamics. The infrared spectra and thermogravimetric and molecular weight curves of the PS were researched, along with its surface tension, contact angle, and oil saturation measurements. The results showed that PS had a low molecular weight, with an MW value of 124,634, and good thermal stability, with a main degradation temperature of more than 300 °C. It could drop the surface tension of water to less than 25 mN·m⁻¹ at 25–150 °C, and the use of slats enhanced its surface activity. The PS also changed the contact angles from 127.96° to 57.59° on the surface of shale cores and reversed to a water-wet state. Additionally, PS reduced the saturated oil content of the shale core by half and promoted oil desorption, indicating a good cleaning effect on the shale oil reservoir. The kerogen molecules gradually broke down into smaller molecules and produced the final products, including methane and shale oil. The main reaction area in the system was the interface between kerogen and the surfactant, and the small molecules produced on the interface diffused to both ends. The kinetics of the reaction were controlled by two processes, namely, the step-by-step cleavage process of macromolecules and the side chain cleavage to produce smaller molecules in advance. PS could not only desorb oil in the core but also promote the pyrolysis of kerogen, suggesting that it has good potential for application in shale oil exploration and development. Full article

In recent years, there has been growing consumer interest in foods and cosmetics containing ingredients of natural origin. During the production process, a by-product of pomace is generated, which is regarded as a dispensable product by the food industry. However, studies have clearly indicated that fruit and vegetable pomace is a valuable source of many nutrients, whose beneficial effects on human health and appearance may represent an added value in its secondary use. Incorporating pomace into cosmetic products enhances their aesthetic value and can enrich them with naturally occurring polyphenols, which is in line with the circular economy model. In the present study, we determined selected mechanical properties of lip balms containing different amounts of grape pomace, for example, the kinetic friction against artificial leather, hardness, penetration performance, maximum shear force, and sample penetration resistance. Moreover, the antiradical activity against DPPH and the total phenolic content were determined, and the colour parameters were analyzed. All tests were conducted on lip balm samples containing 1, 3, and 5% fruit pomace and a control sample. Analysis of the penetration performance showed no statistically significant differences between the individual samples. However, differences in the values of other physical properties were noted. Moreover, the antiradical activity against the synthetic radical DPPH and the total phenolic content increases the value of lip balms with increasing amounts of pomace added. The colour of the lip balms also darkens with increasing amounts of pomace added. The innovative use of grape pomace is in line with sustainable development, and its properties enhance the effects of lip balms. Full article

The present work aimed to develop a simple simulation tool to support studies of slip and other non-traditional boundary conditions in solid–fluid interactions. A mesoscale particle model (movable automata) was chosen to enable performant simulation of all relevant aspects of the system, including phase changes, plastic deformation and flow, interface phenomena, turbulence, etc. The physical system under study comprised two atomically flat surfaces composed of particles of different sizes and separated by a model fluid formed by moving particles with repulsing cores of different sizes and long-range attraction. The resulting simulation method was tested under a variety of particle densities and conditions. It was shown that the particles can enter different (solid, liquid, and gaseous) states, depending on the effective temperature (kinetic energy caused by surface motion and random noise generated by spatially distributed Langevin sources). The local order parameter and formation of solid domains was studied for systems with varying density. Heating of the region close to one of the plates could change the density of the liquid in its proximity and resulted in chaotization (turbulence); it also dramatically changed the system configuration, the direction of the average flow, and reduced the effective friction force. Full article

The concept of thermodynamic efficiency is central to the theoretical understanding of tropical cyclone intensity and intensification, but the issue has remained controversial owing to the existence of distinct and incompatible definitions. Physically, thermodynamic efficiency relates to the fraction of the surface enthalpy fluxes and diabatic processes that contributes to the generation of the potential energy available (APE) for conversions into kinetic energy, so that the main difficulty is how best to define APE. In this study, we revisit the available energetics of axisymmetric vortex motions by redefining APE relative to a non-resting reference state in gradient wind balance instead of a resting state. Our approach, which accounts for both diabatic and frictional effects, reveals that the choice of reference state significantly impacts the prediction of APE generation and its conversion to kinetic energy. By using idealised numerical experiments of axisymmetric tropical cyclone intensification, we demonstrate that the APE production estimated from a non-resting reference state is a much more accurate predictor of APE to KE conversion than those based on other choices of reference states such as initial, mean, and sorted profiles. These findings suggest that incorporating the balanced dynamical structure of tropical cyclones into APE-based theories could lead to improved potential intensity models, with implications for forecasting and understanding cyclone behaviour. Full article

This article reports the effect of twisted tapes with continuous V-ribs on the thermal performance index characteristics of a heat exchanger tube. Numerical and experimental studies were conducted to investigate the influence of V-rib attack angles (β = 15°, 30°, and 45°) in forward and backward arrangements. This investigation employed 0.9 mm thick, continuous V-rib twisted tapes (CVRTs) made from aluminum sheets formed with a twist ratio of y/w = 4.0. The experimental results indicated that a continuous V-rib twisted tape (CVRT) was more effective in heat transfer improvement than a typical twisted tape (TT). This was due to swirl and longitudinal vortex flows that helped increase flow mixing and reduce boundary layer thickness. Decreased V-rib attack angles (β) led to greater heat transfer enhancement, pressure drop, and thermal performance index values due to the greater turbulent mixing of fluid. The numerical result revealed that a continuous V-rib twisted tape created strong longitudinal vortex flow, especially with higher attack angles. The Turbulent Kinetic Energy (TKE) and core fluid temperature increased with the insertion of CVRTs. Local Nusselt numbers also remained relatively high for heat exchanger tubes with CVRTs. The experimental study illustrated that a tube with a CVRT installed augmented heat transfer. In the experimentally studied cases, a backward arrangement had more heat transfer, a greater friction factor, and a better thermal performance index. Compared to a plain tube, a tube with CVRT installed, having β = 15°, 30°, and 45°, showed 76.8, 71.6, and 66.2% improved heat transfer, respectively. CVRTs with these three β-values, respectively, exhibited higher thermal performance than a TT. Among the investigated CVRTs, the backward-arranged tape with β = 15° offered the maximum thermal performance index, 1.13 at Re = 6000. The results are congruent with the simulation outcomes, hence supporting the CFD analysis. Full article

To enhance the efficient development of geothermal energy, this study investigates the heat transfer enhancement mechanisms in medium-depth coaxial underground heat exchangers (CUHEs) integrated with corrugated fins, using computational fluid dynamics (CFD) simulations. Nine distinct corrugated fin geometries were modeled, and the streamlines, velocity fields, temperature fields, and turbulent kinetic energy were analyzed across Reynolds numbers (Re) ranging from 12,000 to 42,000. The results demonstrate that corrugated fins significantly promote fluid turbulence and mixing, thereby augmenting convective heat transfer. Compared to smooth inner tubes, the Nusselt number (Nu) is enhanced by a factor of 1.43–2.19, while the friction factor (f) increases by a factor of 2.94–6.79. The performance evaluation criterion (PEC) improves with increasing fin width and decreasing fin spacing. The optimal configuration, featuring a fin width of 15 mm, a spacing of 60 mm, and a thickness of 15 mm, achieves a maximum PEC value of 1.34 at Re = 12,000, indicating a substantial improvement in heat transfer performance within acceptable pressure drop limits. This research innovatively explores the performance enhancement of CUHEs at high Re, systematically elucidates the influence of geometric parameters on heat transfer and flow resistance, and employs the PEC index to optimize the structural design. This provides significant theoretical support for the efficient engineering application of CUHEs in geothermal utilization. Full article

With the global shift in energy structure and the advancement of the “double carbon” strategy, methanol has gained attention as a clean low-carbon fuel in the engine sector. However, the corrosion–wear coupling failure caused by acidic byproducts, such as methanoic acid and formaldehyde, generated during combustion severely limits the durability of methanol engines. In this study, we employed a systematic approach combining the construction of a corrosion liquid concentration gradient experiment with a full-load and full-speed bench test to elucidate the synergistic corrosion–wear mechanism of core friction pairs (cylinder liner, piston, and piston ring) in methanol-fueled engines. The experiment employed corrosion-resistant gray cast iron (CRGCI), high chromium cast iron (HCCI), and nodular cast iron (NCI) cylinder liners, along with F38MnVS steel and ZL109 aluminum alloy pistons. Piston rings with DLC, PVD, and CKS coatings were also tested. Corrosion kinetic analysis was conducted in a formaldehyde/methanoic acid gradient corrosion solution, with a concentration range of 0.5–2.5% for formaldehyde and 0.01–0.10% for methanoic acid, simulating the combustion products of methanol. The results showed that the corrosion depth of CRGCI was the lowest in low-concentration corrosion solutions, measuring 0.042 and 0.055 μm. The presence of microalloyed Cr/Sn/Cu within its pearlite matrix, along with the directional distribution of flake graphite, effectively inhibited the micro-cell effect. In high-concentration corrosion solutions (#3), HCCI reduced the corrosion depth by 60.7%, resulting in a measurement of 0.232 μm, attributed to the dynamic reconstruction of the Cr₂O₃-Fe₂O₃ composite passive film. Conversely, galvanic action between spherical graphite and the surrounding matrix caused significant corrosion in NCI, with a depth reaching 1.241 μm. The DLC piston coating obstructed the permeation pathway of formate ions due to its amorphous carbon structure. In corrosion solution #3, the recorded weight loss was 0.982 mg, which accounted for only 11.7% of the weight loss observed with the CKS piston coating. Following a 1500 h bench test, the combination of the HCCI cylinder liner and DLC-coated piston ring significantly reduced the wear depth. The average wear amounts at the top and bottom dead centers were 5.537 and 1.337 μm, respectively, representing a reduction of 67.7% compared with CRGCI, where the wear amounts were 17.152 and 4.244 μm. This research confirmed that the HCCI ferrite–Cr carbide matrix eliminated electrochemical heterogeneity, while the DLC piston coating inhibited abrasive wear. Together, these components reduced the wear amount at the top dead center on the push side by 80.1%. Furthermore, mismatches between the thermal expansion coefficients of the F38MnVS steel piston (12–14 × 10⁻⁶/°C) and gray cast iron (11 × 10⁻⁶/°C) resulted in a tolerance exceeding 0.105 mm in the cylinder fitting gap after 3500 h of testing. Notably, the combination of a HCCI matrix and DLC coating successfully maintained the gap within the required range of 50–95 μm. Full article

The Second Law of Thermodynamics states that entropy S increases in a spontaneous process in an ideal isothermal and isolated system. Real systems are influenced by external forces and fields, including the temperature field. In this case, only entropy is not enough, and we suggest using a new function, $L_s$, which is analogous to the Lagrangian in classical mechanics. It includes total potential energy but instead of mechanical kinetic energy, $L_s$ includes the product ST, and the system always evolves towards increasing this modified Lagrangian. It reaches an equilibrium when total potential force is balanced by both entropic and thermal forces. All forces have the same units, Newton/mol, and may be added or subtracted. For condensed systems with friction forces, it is a molecular transport velocity, and not acceleration, which is proportional to the acting force. Our approach has several advantages compared to Onsager’s non-equilibrium thermodynamics with its thermodynamic forces, which may have different units, including 1/T for energy transport. For isolated systems, the description is reduced to Second Law and Clausius inequality. It easily explains diffusion, Dufour effect, and Soret thermodiffusion. The combination of electric, thermal, and entropic forces explains thermoelectric phenomena, including Peltier–Seebeck and Thomson (Lord Kelvin) effects. Gravitational and entropic forces together inside a black hole may lead to a steady state or the black hole evaporation. They are also involved in and influenced by solar atmospheric processes. Full article

Interfacial modification strategies for lithium metal anodes have emerged as a promising method to improve cycling stability, suppress lithium dendrite growth, and increase Coulombic efficiency. However, the reported chemical synthesis methods lead to side reactions and side products, which hinder their electrochemical performance. In this study, we propose a novel and facile red phosphorus-assisted solid-state friction method to in situ fabricate a uniform Li₃P interphase directly on the surface of lithium metal. Interestingly, the as-formed artificial Li₃P interphase with high ionic conductivity and lithium affinity features significantly enhanced interfacial stability and electrochemical kinetics. The symmetric cells based on Li@P with the Li₃P interphase achieved a prolonged lifespan, over 1000 h, at 1 mA/cm² with low polarization. When paired with a high-loading LiFePO₄ cathode (10.5 mg/cm²), the Li@P||LiFePO₄ full cell retained 88.9% of its capacity after stable cycling for 550 cycles at 2 C and further demonstrated the excellent performance and stability of the Li@P‖LiCoO₂ full pouch cell. This study provides an efficient and scalable strategy for stabilizing lithium metal anodes, expanding new ideas for the development of next-generation high-energy-density batteries. Full article

In complex geological environments, the discontinuous dynamic response behavior of jointed rock masses under the coupled effects of in situ stress and transient dynamic disturbances significantly exacerbates the risk of surrounding rock instability. This study establishes three-dimensional numerical models of various jointed rocks under uniaxial–biaxial–triaxial split Hopkinson pressure bar (SHPB) experimental systems through the coupling of the finite difference method (FDM) and discrete element method (DEM). The models adhere to the one-dimensional stress wave propagation assumption and satisfy the dynamic stress equilibrium requirements, demonstrating dynamic mechanical responses consistent with physical experiments. The results reveal that the synergistic–competitive effects between joint configuration and initial pre-compression jointly dominate the dynamic mechanical response of rocks. Multiaxial pre-compression promotes the development of secondary force chain networks, enhances rock impact resistance through multi-path stress transfer mechanisms, significantly improves strain energy storage density during peak stages, and drives failure modes to evolve from macroscopic through-going fractures to localized crushing zones. The spatial heterogeneity of joint configurations induces anisotropic characteristics in principal stress fabric. Single joint systems maintain structural integrity due to restricted weak plane propagation, while cross/parallel joints exhibit geometrically induced synergistic propagation effects, forming differentiated crack propagation paths that intensify frictional and kinetic energy dissipation. Through cross-scale numerical model comparisons, the evolution of force chain fabric, particle displacement distribution, microcrack propagation, and energy dissipation mechanisms were analyzed, unveiling the synergistic regulatory effects of the stress state and joint configuration on the rock dynamic response. This provides a theoretical basis for impact-resistant structure optimization and dynamic instability early warning in deep engineering projects involving jointed surrounding rock. Full article

In an attempt to reconciliate air-sea momentum flux estimates derived from open sea observations, from large eddy simulation output fields, and from wind-wave tank measurements, a series of dedicated experiments were conducted in the wind-wave tank of the Large Air-Sea Facility of Marseille, France. The turbulent friction velocity, upon which the momentum flux depends, was estimated from wind measurements by applying four classical methods including the eddy-covariance method and the inertial-dissipation method. The collected data were used to investigate some characteristics of the wave-influenced boundary layer that were predicted by previous simulations, and to quantify a wave-dependent term of the turbulent kinetic energy equation, the so-called imbalance term ${\varphi }_{\mathrm{imb}}$. Our results show that the turbulent stress decreases toward lower heights where the effect of waves is large, as in the simulations, and that ${\varphi }_{\mathrm{imb}}$ is in the range 0.3 to 0.7, which is comparable to the value found with open sea data (0.4). These preliminary results have to be confirmed with wave-following probes, because the estimated eddy-covariance flux slightly varied with height, thus it could not be strictly considered to be equal to a constant total flux. Full article

The West African atmospheric energy budget is assessed for the first time across three contrasting monsoon seasons (dry, wet, and moderate) using the latest version of the Canadian Regional Climate Model (CRCM6/GEM5). The model is driven by ERA5 reanalysis from the European Centre for Medium-Range Weather Forecasts (ECMWF). A formalism appropriate for regional climate energetics is employed to quantify the primary physical processes occurring during the West African Monsoon, with the aim of highlighting those that exhibit significant inter-seasonal variability. The atmospheric energy path shows that the time-mean available enthalpy (A_M) reservoir, reflecting high surface temperatures and a lapse rate characteristic of a dry atmosphere, dominates other energy reservoirs. A_M is converted into the time-mean kinetic energy (K_M) and the time-variability available enthalpy (A_E) reservoirs, which are converted into a time-variability kinetic energy reservoir (K_E) through barotropic and baroclinic processes. A_E is the lowest energy reservoir, confirming smaller temperature variations in the tropics compared to higher latitudes. Kinetic energy reservoirs K_M and K_E have the same order of magnitude, suggesting that mean flow is as important as eddy activities during the season. The atmospheric energy cycle computed for three contrasting rainy seasons shows that time-variability energy reservoirs (A_E and K_E) and main terms acting upon them, are proportional to the rainfall activity, being higher (lower) during rainy (dry) years. It also reveals that, while C_A (conversion from A_M to A_E) and the generation term G_E feed wave’s development, the frictional term D_E counteracts the generation of K_E to dampen the creation of transient eddies. These findings suggest that the atmospheric energetic formalism could be applied on West African seasonal forecasts and future climate simulations to implement adaptation strategies. Full article