Search Results (278)

Efficient separation of cocoa shell and kernel is a critical operation in semi-finished cocoa processing, where conventional mechanical methods such as grinding, cutting, and rubbing often generate excessive heat, leading to cocoa butter melting and degradation of kernel quality due to its high fat content. To overcome these limitations, this study pro-poses a dynamic impact-based framework for a small-scale centrifugal cracking system, in which fracture is induced by controlled kinetic impact rather than compressive loading. A combined theoretical and experimental investigation was conducted on roasted cocoa beans at a small industrial scale. Mechanical characterization showed that the mean and maximum shell fracture forces were 23.515 N and 54.382 N, respectively, while kernel fracture forces were significantly higher at 91.896 N and 195.327 N. A dynamic analysis of the centrifugal cracker identified a critical rotational speed range of 812–975 rpm, corresponding to impact velocities of 17.14–20.57 m/s and kinetic energies of 0.17–0.25 J per bean. Experimental validation indicated an optimal operating range of 860–900 rpm, achieving less than 1.1% uncracked beans and less than 2% fine nibs (<3 mm). Below 800 rpm, incomplete cracking was observed, whereas speeds above 950 rpm increased kernel fragmentation. These results demonstrate that precise control of impact energy is the key factor governing efficient centrifugal cracking performance in cocoa processing. Full article

Ocean current energy is abundant, yet its exploitation is severely constrained by the low-velocity conditions typical of most marine environments, where conventional lift-type turbines exhibit poor self-starting capability and low efficiency. This review provides the first comprehensive synthesis of research on free-stream Archimedes spiral hydrokinetic turbines (ASHTs), a class of drag-dominated rotors developed specifically for low-velocity kinetic energy harvesting. A unified classification is introduced, dividing ASHTs into single-blade long-axis (SL-ASHT) and three-blade short-axis (TS-ASHT) configurations. The energy conversion mechanisms, governed by pressure difference and hydrodynamic force synergy within helical passages, are elucidated, and the influence of critical geometric parameters is assessed. For SL-ASHTs, the analysis highlights exceptional self-starting capability (cut-in velocity: 0.1 m/s), a starting torque coefficient of 0.52, a maximum power coefficient of 0.51, and passive yaw adaptability that limits efficiency variation to below 2% over yaw angles of 0–40°. TS-ASHTs feature a compact architecture and higher rotational speed, facilitating direct generator coupling. With variable blade-angle distributions, thin airfoils, and non-uniform gap ratios, the power coefficient reaches 0.312. Performance-enhancement measures, including multi-parameter optimization, ducts, and winglets, deliver power gains of up to 35%, 122%, and 12%, respectively. This review further identifies critical barriers to engineering deployment: sediment erosion, cyclic fatigue, performance degradation under large yaw angles, and wake interactions. Future priorities include multi-objective optimization, advanced materials and flow control, full-scale sea trials, multiphysics coupling, array layout optimization, and hybrid energy system integration. By establishing a coherent classification and performance-evaluation framework, this work demonstrates that ASHTs offer strong potential as core devices for large-scale utilization of low-velocity ocean current and river hydrokinetic energy. Full article

This study investigates the aerodynamic and thermal impacts of tire sidewall cooling fins on a passenger vehicle using high-fidelity computational fluid dynamics (CFD) simulations. Continuous heat accumulation from tire rotation and road friction can degrade structural durability. To address this thermal challenge, a parametric study was conducted on the DrivAer notchback vehicle model across various fin angles from −67.5° to 67.5°. The results revealed a distinct design space that offers simultaneous aero-thermal improvements. Specifically, the 22.5° fin configuration demonstrates a dual-benefit performance, achieving a 3.79% net reduction in overall vehicle drag alongside a 17.36% increase in the average heat transfer coefficient (HTC). Conversely, the −22.5° configuration yields the maximum cooling enhancement with a 30.49% increase in average HTC but incurs a 2.52% drag penalty. Microdrag and Turbulent Kinetic Energy (TKE) analyses successfully explain the underlying fluid mechanisms governing these trade-offs. These findings provide practical design guidelines for flow control on rotating wheels, showing that tire sidewall geometries can enhance full-vehicle aerodynamic efficiency and tire thermal reliability. Full article

The theory of hole superconductivity has developed over more than three decades through a sequence of steps addressing distinct physical problems. This paper identifies and documents a recurring structural pattern in that development: ideas introduced to solve one problem were only later recognized as being required by independent physical constraints. By tracing a series of such delayed conceptual unifications, spanning pairing mechanism, charge expulsion, electrodynamics, spin structure, rotation, relativity, thermodynamics and momentum conservation, we highlight that the framework evolves by constraint tightening rather than by ad hoc embellishment. While this does not establish the correctness of the theory, it provides evidence that it is responding to real physical requirements uncovered progressively, in contrast to theories that accommodate discrepancies or new constraints primarily through auxiliary assumptions and ultimately fail. Full article

Pumped hydro storage (PHS) systems, increasingly deployed in power systems with large shares of wind and solar generation, can play a key role in managing power system frequency. Variable-speed pumped hydro storage (VS-PHS) systems, in particular, have potential for rapid primary frequency response by enabling the quick release of machine rotor kinetic energy. However, using conventional proportional–integral (PI) control for converters and governors can result in large speed deviations and torque imbalance during fast system transients. This issue is intensified in PHS plants with slow hydraulic response, such as those with long penstocks or slow guide-vane adjustments, potentially violating mechanical operating constraints. This paper develops a model predictive control (MPC) strategy for coordinated governor and converter control, accounting for operational constraints. The proposed approach improves coordination of hydraulic and electrical systems, utilising DC-link storage and proactive guide-vane action for rapid power adjustments. Dynamic simulations using a complex nonlinear plant demonstrate that MPC redistributes energy extraction between the DC-link storage and the rotating mass while respecting their imposed limits. Furthermore, robustness tests indicate that MPC performance is sustained under plant nonlinearities and measurement noise. These results highlight the advantages of predictive control for supporting frequency response in VS-PHS systems. Full article

Currently, most design solutions are disc brake systems, in which, during braking, the rotating disc, along with the wheel, rubs against stationary brake pads, converting kinetic energy into thermal energy released into the atmosphere. Brake pads are made of composite materials. One of the key components is copper. Its presence is crucial and plays a crucial role in friction materials. In this work, an attempt was made to replace copper, which is unfortunately harmful to both the environment and humans, with aluminum powder and polytetrafluoroethylene powder. Samples of the proposed prototype friction materials were manufactured, and their thermal and tribological properties were determined (research described in the previous work). Knowledge of the materials’ properties allowed for simulation studies. Calculations were prepared for three different scenarios. The results showed that the heating process using the proposed materials during braking is very similar to that of materials with a conventional composition. Of the materials tested, composition where copper was replaced by polytetrafluoroethylene and aluminum in a 4:1 ratio gave the most promising results. In tests, this material had the lowest maximum brake pad temperature values, which contributes to a reduced risk of fading. Also, by “pushing” thermal energy into the brake disc, it contributes to the fastest dissipation of this energy. This suggests that the materials can be used in real-world braking systems. Full article

The low thermal conductivity of phase-change materials (PCMs) remains a primary barrier to rapid charging in shell-and-tube latent heat thermal energy storage (LHTES). This work proposes a hierarchical multi-branch Y-shaped fin network with extended conductive pathways and evaluates its performance through a two-stage numerical framework, including two-dimensional (2D) geometric screening of fin topology and arrangement followed by three-dimensional (3D) simulations under practical operating conditions. The enthalpy-porosity method and the Boussinesq approximation are used to resolve transient melting and buoyancy-driven convection in RT35 paraffin. In the 2D comparison, the optimized multi-branch topology improves temperature uniformity and advances the melting front more effectively than finless and straight-fin structures, reducing complete melting time by 68.6% and 41.4%, respectively. Rotational arrangement further affects the coupling between conductive paths and natural-convection cells; the best arrangement shortens melting time by 29.8% relative to alternative layouts. In the 3D model, increasing inlet velocity from 0.06 to 0.16 m/s reduces melting time by 44.3% but produces limited gains in stored energy, indicating diminishing returns at high flow rate. Increasing inlet temperature from 333 to 363 K is more influential, reducing melting time by 47.9%, increasing stored energy by 10.6%, and raising average heat-flux density from 500.10 to 1062.16 W/m². The results demonstrate that the hierarchical branched fin network accelerates thermal charging by redistributing and extending conductive pathways, while inlet temperature governs both melting kinetics and final storage capacity. Full article

The morphological and structural state of rough solid electrodes usually has a complex effect on the kinetics of an electrochemical process. In order to correctly distinguish the influence of different factors on the rate of an electrode reaction, it is necessary to first separate a purely geometric current rise caused by the surface area increase. At the same time, it is necessary to take into account that surface roughness itself often not only leads to a geometric rise in the electrode area, but also contributes to a change in the kinetic parameters of the electrochemical process. As a consequence, the conclusion regarding an electrocatalytic effect will be reasonable only if the roughness effect is correctly taken into account. The most difficult problem is to establish the role of roughness when experimental electrochemical data are obtained under mixed diffusion–kinetic control of the electrode process. However, the use of appropriate theoretical approaches is required to correctly determine the kinetic characteristics of the electrochemical stage, i.e., of the charge transfer stage. This paper establishes the influence of the morphology and structure of electrodeposited copper coatings on the kinetics of the cathodic reduction of nitrate ion, which occurs in a mixed diffusion–kinetic mode, using the theoretical model of chronoamperometry of an electrochemical process on a rough electrode developed earlier by the authors. Several Cu-electrodes with roughness and structure, the parameters of which vary widely enough, were obtained by cathodic deposition from sulfate solutions of different compositions. The integral (roughness factor) and local (average roughness) characteristics of the surface morphology were determined by methods of underpotential deposition and atomic force microscopy, respectively. Structural investigation of the electrodeposited coatings was carried out by X-ray diffraction to determine their crystallographic structure and average crystallite size. The methods of voltammetry and a rotating disk electrode revealed the mixed kinetics of the electroreduction of ${\mathrm{NO}}_3^{-}$ ions. The kinetic parameters of the charge transfer stage on the copper coatings with a roughness factor of f_r ≤ 3.5 are determined for the first time in this paper by treatment of the experimental current decay curves with the non-linear theoretical equation obtained by the authors for the chronoamperogram of the process on rough electrodes. It was found that the rate constant of the charge transfer stage and the exchange current density of the nitrate ion electroreduction increase by about 50%, with an increase in the average surface roughness from 25 to 120 nm. Considering that this effect is not caused by a purely geometric increase in the true surface area of the electrode, and that the average crystallite size is approximately the same (25 ± 2 nm) for all investigated coatings, it can be concluded that the electrocatalytic activity of copper increases in the reaction of the cathodic reduction of nitrate ions during the transition to copper electrodes with the higher average surface roughness. Taking into account XRD data, the role of the structural and morphological state in the kinetics of the electroreduction of nitrate ions has been established. The smoothest polycrystalline coating was found to be the least electrocatalytically active in this reaction. On the contrary, the roughest coatings with the most prominent plane (220) show the highest activity, which increases with increasing average roughness, possibly due to the growth of defects and excess energy of such curved surfaces. Full article

Global shifts in energy policy have contributed to an increase in electricity generation from renewable sources, which introduces unique issues with volatility and grid reliability. Robust grid-scale energy storage methods must fill the gap between generation and consumption. Flywheel energy storage (FES) is a mechanical technology that utilizes the stored kinetic energy of a rotating body, but is typically only suited for shorter-term frequency regulation due to significant windage losses. In this work, a novel Python 3.13-based simulation and optimization tool is presented and used to optimize geometric design parameters for efficiency, energy density, and other metrics. The simulation utilizes a 1 degree-of-freedom, multi-regime fluid friction model with a time-marching algorithm. The optimization functionality utilizes pyswarms, a particle swarm optimization package, with adjustable search parameters and cost functions to evaluate simulation results. Optimization parameters include geometric parameters of rotor radius, shaft radius, airgap width, and airgap height; material properties of mass and moment of inertia; and initial angular velocity. An optimal initial angular velocity is found for a particular geometry, lasting 30 times longer until self-discharge versus the worst values. This work can inform the design of flywheel systems to minimize windage losses and promote the technology’s utility for longer-term energy storage. Full article

The effect of high-gravity fields, generated by rapid rotation, on CO₂ adsorption in activated carbon beds is examined. Adsorption-desorption kinetics is monitored before, during, and after short rotation periods at up to 5000 rpm. Rotation induced a reproducible transient bump in headspace pressure, quantitatively attributed to a centrifugal free energy shift (~12.2 J/mol) that overfilled weak adsorption sites beyond their static equilibrium. The bump mechanism is described by fold catastrophe theory, with a critical angular velocity (ω_c = 3500 rpm) triggering a sudden transition to a high-occupancy branch. Post-rotation, constant-rate zero-order desorption from shallow sites overlapped with a slower pseudo-first-order adsorption process as deep, previously inaccessible pores became available, increasing CO₂ capacity by 2.5%. Kinetic modeling produced an apparent diffusivity of 1.2 × 10⁻⁵ m²/s and a structural accessibility time constant of ~25 h. Thermodynamic analysis showed that rotation improved the overall free energy of adsorption and altered entropy in a manner consistent with the observed adsorption-desorption sequence. These results demonstrate that rotational fields can enhance CO₂ uptake, modify kinetic pathways, and trigger threshold phenomena in porous adsorbents. Full article

Erosive wear in pipe elbows subjected to liquid–solid two-phase flow is a major cause of material degradation and service failure in industrial piping systems. In this study, erosion characteristics of pipe elbows were investigated through erosion mapping experiments and numerical simulations. The effects of flow velocity and particle diameter on erosion location and intensity were analyzed. Erosion was found to be mainly concentrated on the outer wall of the elbow within the angular range of 10° to 90°, and both erosion intensity and affected area increased with increasing particle diameter and flow velocity. Dean vortices were shown to play an important role in particle transport and erosion distribution, especially for small particles. Inspired by the ribbed morphology of shells, a biomimetic elbow was further designed and evaluated through an orthogonal numerical study considering flow velocity, particle diameter, rib number, and rib diameter. The results indicate that the ribbed structure can effectively improve erosion resistance by altering particle trajectories, reducing particle impact probability, and dissipating kinetic energy through low-velocity rotating flow between adjacent ribs. This finding provides useful inspiration for addressing erosive wear problems in engineering applications. Full article

In the aerospace industry, thin-web gears are preferred for achieving high power-density transmission. However, thin-webbed structures always lead to out-of-plane resonance during the transmission process, which commonly happens in helical gears, manifesting as severe vibration at a specific rotational speed. To address this, a shaft–web–ring dynamic model is proposed. The shaft, gear web, and gear ring are modelled based on the Timoshenko straight beam, Mindlin plate, and Timoshenko bent beam theory. Simultaneously, the potential energy caused by the time-varying meshing stiffness is coupled to the gear ring. The kinetic and potential energies of each discretized finite element of the components are derived based on elastic deformation theory, and the governing equations of each element are obtained using Hamilton’s principle. The model is verified through a modal experiment. The comparison with traditional rotor-gear models has demonstrated the significance of gear body flexibility in helical gears with thin webs. The effects of the web thickness and helix angle on dynamic response are studied, revealing that gear web elasticity and an appropriately high helix angle can effectively reduce vibrations at the support bearing, prevent excessive vibrations, and contribute to vibration and noise reduction in the transmission system. Full article

Micro-scale counter-rotating wind turbines (CRWTs) offer enhanced potential for wake energy recovery. This study proposes an integrated cascade–coupling design framework for high-solidity CRWTs, in which rear rotor geometry and rotor coupling are co-designed based on stereoscopic particle image velocimetry measurements of the front rotor wake. Experiments are conducted at a tip-speed ratio of $\lambda =1.0$, solidity $\sigma =1.25$, spacing ratios of $d=0.6R_T$, $1.0R_T$, and $3.0R_T$, and a tip radius of $R_T=70$ mm. At the physical limit spacing of $d=0.6R_T$, the integrated design increases the system power coefficient by 24.1% while limiting front rotor power reduction to 17.2%, compared to a 10.3% system gain and 34.5% front rotor suppression for the baseline mirrored configuration. Wake measurements confirm near-complete absorption of rotational kinetic energy from the front rotor wake without exacerbating upstream interference. These results demonstrate that cascade-based energy extraction and coupling-based interference mitigation can operate synergistically, enabling compact, high-performance micro-scale CRWTs suitable for space-constrained and urban energy applications. Full article

Flip-flow screens are widely used for the efficient separations of wet fine materials. To explore the separation characteristics of the particle and screen plate in the flip-flow screening process, a flip-flow plate impact experimental system was built. The experimental system was based on a spherical inertial measurement device and a semi-industrial flip-flow screen system. In this study, we first derive the impact mechanics equation of the flip-flow screen plate on the particle and analyze the influence of the main parameters on the maximum impact force. Subsequently, we investigated the kinematic characteristics of the particle impacted by the screen plate at different moving positions, the variation of the centerline acceleration mechanism, and determined the angular velocity in the collision process. Additionally, we further clarified the alteration in the rules of translational and rotational kinetic energy of the particles in the collision process. This study addresses a research gap in the phenomenological modelling of particulate screening process. At the same time, it provides theoretical support for the accurate control of the flip-flow screening process. Full article

During microencapsulation, agitation is typically required to achieve the homogeneous dispersion of the reaction mixture, with the mixing and dispersion efficiency within the reactor being predominantly determined by the rotational speed. However, when the agitation speed exceeds a certain threshold, cavitation occurs during the stirring process. This cavitation phenomenon can significantly influence the properties of the resulting microcapsules. Therefore, this study combines the CFD simulation method with microcapsule preparation experiments, focusing on the occurrence of cavitation during the stirring process and its effect on the particle size of the prepared microcapsules. The CFD simulations analyzed flow field characteristics under different agitation speeds within the beaker, including phase distribution contours, streamline patterns, turbulent kinetic energy fields, and shear stress distributions. Different fluid flows were established by changing the rotating speed of the paddle, and the influence of each fluid flow on the particle size and distribution of the prepared microcapsules was determined. Particular emphasis was placed on examining the influence of rotational speeds ranging from 550 to 850 rpm on microcapsule particle size. Experimental validation confirmed that the impeller speed of 650 rpm provided superior flow field control, yielding microcapsules with the narrowest particle size distribution. This study elucidates the mechanism through which cavitation influences the microencapsulation process, thereby providing both theoretical insights and experimental support for the optimization of microcapsule preparation techniques. Full article