Search Results (1,116)

Newton’s law of cooling requires a reference temperature ($T_{ref}$) to define the heat-transfer coefficient ($h$). For external flows with multiple temperatures in the freestream, obtaining $T_{ref}$ is a challenge. One widely used method, referred to as the adiabatic-wall (AW) method, obtains $T_{ref}$ by requiring the surface of the solid exposed to convective heat transfer to be adiabatic. Another widely used method, referred to as the linear-extrapolation (LE) method, obtains $T_{ref}$ by measuring/computing the heat flux ($q_s^{\prime \prime }$) on the solid surface at two different surface temperatures ($T_s$) and then linearly extrapolating to $q_s^{\prime \prime }=0$. A third recently developed method, referred to as the state-space (SS) method, obtains $T_{ref}$ by probing the temperature space between the highest and lowest in the flow to account for the effects of $T_s$ or $q_s^{\prime \prime }$ on $T_{ref}$. This study examines the foundation and accuracy of these methods via a test problem involving film cooling of a flat plate where $q_s^{\prime \prime }$ switches signs on the plate’s surface. Results obtained show that only the SS method could guarantee a unique and physically meaningful $T_{ref}$ where $T_s=T_{ref}$ on a nonadiabatic surface $q_s^{\prime \prime }=0$. The AW and LE methods both assume $T_{ref}$ to be independent of $T_s$, which the SS method shows to be incorrect. Though this study also showed the adiabatic-wall temperature, $T_{AW}$, to be a good approximation of $T_{ref}$ (<10% relative error), huge errors can occur in $h$ about the solid surface where $|T_s-T_{AW}|$ is near zero because where $T_s=T_{AW}$, $q_s^{\prime \prime }\ne 0$. Full article

As a novel carbon material, multi-walled carbon nanotubes (MWCNTs) have attracted significant research interest in energetic applications due to their high aspect ratio and exceptional physicochemical properties. However, their inherent structural characteristics and poor dispersion severely limit their practical utilization in solid propellant formulations. To address these challenges, this study developed an innovative reverse-engineering strategy that precisely confines MWCNTs within a three-dimensional Fe₂O₃ gel framework through a controllable sol-gel process followed by low-temperature calcination. This advanced material architecture not only overcomes the traditional limitations of MWCNTs but also creates abundant Fe-C interfacial sites that synergistically catalyze the thermal decomposition of glycidyl azide polymer-based energetic thermoplastic elastomer (GAP-ETPE). Systematic characterization reveals that the MWCNTs@Fe₂O₃ nanocomposite delivers exceptional catalytic performance for azido group decomposition, achieving a >200% enhancement in decomposition rate compared to physical mixtures while simultaneously improving the mechanical strength of GAP-ETPE-based propellants by 15–20%. More importantly, this work provides fundamental insights into the rational design of advanced carbon-based nanocomposites for next-generation energetic materials, opening new avenues for the application of nanocarbons in propulsion systems. Full article

Electrohydrodynamic atomization (EHDA) has significant advantages for microencapsulating compounds in various structures using biopolymers, where more research using pure starch is required. Concerning this, jicama starch and its hydrolysates have not yet been tested, despite their unique characteristics, which come from an alternative low-value-added crop source. Rapid acid hydrolysis of jicama starch with H₂SO₄ resulted in dextrins with a degree of hydrolysis (DE) from 0.4 to 19% within 1–12 h, and syrup solids at 24 h (DE = 42%). This process modifies the water retention capacity of jicama starch, gel viscosity, surface tension, and electrical conductivity. Hydrolyzed starch particles obtained by electrospraying (10 kV, L = 10 cm, Q = 2 mL/h) showed Feret diameters and roundness significantly influenced (p ≤ 0.05) by the degree of hydrolysis rather than the concentration of solids. It was found that hydrolyzed jicama starch with a DE < 6.3% can be used as the sole wall material to form particles by electrospraying, as they facilitate the formation of stable and rounded like-microspheres particles; this was not feasible above this threshold. The results suggest that the jicama starch’s ability to be used as a wall material in the electrospray synthesis of particles or microspheres appears to be determined by the degree of hydrolysis. Full article

To meet the rapid maneuverability and lightweight demands of micro-nano satellites, a space micro solid thruster using 3D-printed short glass fiber reinforced polyamide 6 (PA6GF) composites was developed. Thruster shells with wall thicknesses of 4, 3, and 2.5 mm were designed, and ground ignition tests were conducted to monitor chamber pressure and shell temperature. Compared with conventional metallic thrusters, PA6GF composites have exhibited excellent thermal insulation and sufficient mechanical strength. Under 8 MPa and 2773 K ignition conditions, the shell thickness was reduced to 2.5 mm and could withstand pressures up to 10.37 MPa. These results indicate that PA6GF composites are well-suited for space micro solid thrusters with inner diameters of 15–70 mm, offering new possibilities for lightweight space propulsion system design. Full article

To compensate for the instability of renewable energy sources during China’s energy transition, large thermal power plants must provide critical operational flexibility, primarily through deep peaking. To investigate the combustion performance and wear and tear of a 600 MW pulverized coal boiler under deep peaking, the gas–solid flow characteristics and distributions of flue gas temperature, wall heat flux, and wall wear rate in a 600 MW tangentially fired pulverized coal boiler under variable loads (353 MW, 431 MW, 519 MW, and 600 MW) are investigated in this study employing computational fluid dynamics numerical simulation method. Results demonstrate that increasing the boiler load significantly amplifies gas velocity, wall heat flux, and wall wear rate. The maximum gas velocity in the furnace rises from 20.9 m·s⁻¹ (353 MW) to 37.6 m·s⁻¹ (600 MW), with tangential airflow forming a low-velocity central zone and high-velocity peripheral regions. Meanwhile, the tangential circle diameter expands by ~15% as the load increases. The flue gas temperature distribution exhibits a “low-high-low” profile along the furnace height. As the load increases from 353 MW to 600 MW, the primary combustion zone’s peak temperature rises from 1750 K to 1980 K, accompanied by a ~30% expansion in the coverage area of the high-temperature zone. Wall heat flux correlates strongly with temperature distribution, peaking at 2.29 × 10⁵ W·m⁻² (353 MW) and 2.75 × 10⁵ W·m⁻² (600 MW) in the primary combustion zone. Wear analysis highlights severe erosion in the economizer due to elevated flue gas velocities, with wall wear rates escalating from 3.29 × 10⁻⁷ kg·m⁻²·s⁻¹ (353 MW) to 1.23 × 10⁻⁵ kg·m⁻²·s⁻¹ (600 MW), representing a 40-fold increase under full-load conditions. Mitigation strategies, including ash removal optimization, anti-wear covers, and thermal spray coatings, are proposed to enhance operational safety. This work provides critical insights into flow field optimization and wear management for large-scale coal-fired boilers under flexible load operation. Full article

Against the backdrop of the green circular economy, the exploration of reliable and sustainable applications of lignocellulosic biomass (LCBM) has emerged as a critical research frontier. The utilization of LCBM as a ruminant roughage source offers a promising strategy to address two pressing issues: the “human-animal competition for food” dilemma and the environmental degradation resulting from improper LCBM disposal. However, the high degree of lignification in LCBM significantly restricts its utilization efficiency in ruminant diets. In recent years, microbial pretreatment has gained considerable attention as a viable approach to reduce lignification prior to LCBM application as ruminant feed. White-rot fungi (WRF) have emerged as particularly noteworthy among various microbial agents due to their environmentally benign characteristics and unique lignin degradation selectivity. WRF demonstrates remarkable efficacy in enzymatically breaking down the rigid lignocellulosic matrix (comprising lignin, cellulose, and hemicellulose) within LCBM cell walls, thereby reducing lignin content—a largely indigestible component for ruminants—while simultaneously enhancing the nutritional profile through increased protein availability and improved digestibility. Solid-state fermentation mediated by WRF enhances LCBM utilization rates and optimizes its nutritional value for ruminant consumption, thereby contributing to the advancement of sustainable livestock production, agroforestry systems, and global environmental conservation efforts. This review systematically examines recent technological advancements in WRF-mediated solid-state fermentation of LCBM, evaluates its outcomes of nutritional enhancement and animal utilization efficiency, and critically assesses current limitations and future prospects of this innovative approach within the framework of circular bioeconomy principles. Full article

This study employs Particle Image Velocimetry (PIV) technology to investigate the statistical properties and flow structures of the turbulent boundary layer over smooth walls and riblet walls with yaw angles of 0, ±30° in both clear water and liquid–solid two-phase flow fields. The results indicate that, compared to the smooth wall, streamwise riblet walls and 30° divergent riblet walls can reduce the boundary layer thickness, wall friction force, comprehensive turbulence intensity, and Reynolds stress, with the divergent riblet wall being more effective. In contrast, convergent riblet walls have the opposite effect. The addition of particles leads to an increase in boundary layer thickness and a reduction in wall friction resistance, primarily by reducing turbulence fluctuations and Reynolds stress in the logarithmic region of the turbulent boundary layer. Moreover, the two types of drag-reduction riblet walls can decrease the energy content ratio of near-wall streak structures and suppress their motion in the spanwise direction. Their impact on burst events is mainly characterized by a reduction in the number of ejection events and their contribution to Reynolds shear stress. In comparison, convergent riblet walls have the complete opposite effect and also enhance the intensity of burst events. The addition of particles can fragment streak structures and suppress the intensity and number of burst events, acting similarly on drag-reduction riblet walls and further strengthening their drag reduction characteristics. Full article

Based on admirable porous media performance and the popularity of additive manufacturing technology, gradient porous media are progressively being applied in increasing fields. In this study, convection heat transfer within a square vented cavity, partially occupied by two copper metal foam layers of $10$ and $20$ PPI saturated with nanofluid, was assessed numerically. The left wall was heated uniformly and non-uniformly by applying multi-frequency spatial heating following a sinusoidal function. Governing equations, including continuity, the Darcy–Brinkmann–Forchheimer model, and local thermal non-equilibrium energy equations, were adopted and solved by employing the finite volume method. The influences of relevant parameters, including nanoparticle concentrations $\left(0\%\le \phi \le 10\%\right)$, Reynolds number ($1\le Re\le 100$), inlet and outlet port aspect ratios $\left(0.1\le D/H\le 0.4\right)$, three outlet vent opening locations ($\left(S_o=0\right)$ left, ($S_o=\left(H/2-D/2\right)$) middle, and ($S_o=\left(H-D\right)$) right), sinusoidal offset temperature (${\theta }_o=0.5$, $1$), frequency ($f=1, 3, 5$), and amplitude ($A=0-1$), were examined. The results demonstrate that flow and heat transfer fields are impacted mainly by these parameters. Streamlines are more intensified at the upper-left corner when the outlet opening vent is shifted towards the right-corner upper wall. Fluid- and solid-phase Nusselt number increases $Re$, $D/H$, ${\theta }_o$, $A$, and $f$ are raised, specifically when $A\ge 0.3$. The Nusselt number remains constant when the frequency is raised from $3$ to $5$, definitely when $D/H\ge 0.25$. In uniform and non-uniform heating cases, the Nusselt number of both phases remains constant as the outlet port is shifted right for $Re\le 10$ and slightly for higher $Re$ as the outlet vent location is translated from left to right. Full article

Combustion processes in compression ignition engines lead to the inevitable generation of nitrogen oxides, which cannot be limited to the currently desired levels just by optimising the in-cylinder processes. Therefore, simulation-based engine development needs to include all engine-related aspects which contribute to tailpipe emissions. Among them, the SCR (selective catalytic reduction) aftertreatment-related processes, such as urea–water solution injection, urea decomposition, mixing, NOx catalytic reduction, and deposits’ formation, are the most challenging, and require as much attention as the processes taking place inside the cylinder. Over the last decade, the urea-SCR aftertreatment systems have evolved from underfloor designs to close-coupled (to the engine) architecture, characterised by the short mixing length. Therefore, they need to be tailor-made for each application. This study presents the CFD-based development of a multi-platform SCR system with a short mixing length for mobile non-road applications, compliant with Stage V NRE-v/c-5 emission standard. It combines multiphase dispersed flow, including wall wetting and urea decomposition kinetic reaction modelling to account for the critical aspects of the SCR system operation. The baseline system’s design was characterised by the severe deposit formation near the mixer’s outlet, which was attributed to the intensive cooling in the mounting area. Moreover, as the simulations suggested, the spray was not appropriately mixed with the surrounding gas in its primary zone. The proposed measures to reduce the wall film formation needed to account for the multi-platform application (ranging from 56 to 130 kW) and large-scale production capability. The performed simulations led to the system design, providing excellent UWS–exhaust gas mixing without a solid deposit formation. The developed system was designed to be manufactured and implemented in large-scale series production. Full article

This study examines the labyrinth seal disc of an aero-engine, specifically analysing the radial deformation caused by centrifugal force and heat stress during operation. This distortion may lead to discrepancies in the performance attributes of the labyrinth seal and could potentially result in contact between the labyrinth seal tip and neighbouring components. A numerical analytical model incorporating the rotor and stator cavities, along with the labyrinth seal disc structure, has been established. The sealing integrity of a standard labyrinth seal disc’s flow channel is evaluated and studied at different clearances utilising the fluid–solid-thermal coupling method. The findings demonstrate that, after considering radial deformation, a cold gap of 0.5 mm in the conventional labyrinth structure leads to stabilisation of the final hot gap and flow rate, with no occurrence of tooth tip rubbing; however, both the gap value and flow rate show considerable variation relative to the cold state. When the cold gap is 0.3 mm, the labyrinth plate makes contact with the stator wall. To resolve the problem of tooth tip abrasion in the conventional design with a 0.3 mm cold gap, two improved configurations are proposed, and a stability study for each configuration is performed independently. The leakage and temperature rise attributes of the two upgraded configurations are markedly inferior to those of the classic configuration at a cold gap of 0.5 mm. At a cold gap of 0.3 mm, the two improved designs demonstrate no instances of tooth tip rubbing. Full article

The paper deals with the issue of obtaining iron-sulfur-containing binders through their mechanochemical treatment using mutual neutralization and detoxification structure formation, and the curing stage of arbolite concrete composites based on industrial waste under long-term loading were also studied. Due to abrasion and impact, the mutual neutralization and detoxification methods of industrial waste toxic components through their mechanochemical treatment on the structures of ball mill LShM-750, were used to obtain iron-sulfur-containing binders. Pyrite cinders acted as oxidizing agents, and elementary technical sulfur had reduced properties. To determine the rate of creep strain growth, the load on prism samples was applied in the form of specially made spring units at stress levels of 0.15 R_bn, 0.44 R_bn, and 0.74 R_bn, where R_bn is the prism strength of iron-sulfur-containing arbolite concrete in compression. The strength and fracture formations of lightweight iron-sulfur concrete were studied using strain gauge apparatus and depth strain gauges glued on shredded reed fibers using adhesive, installed before concreting. It was revealed that the introduction of a sulfur additive within the range from 10 to 13% increases the compressive strength of iron-sulfur-containing concrete composites prepared with that of mortars at a water/solid ratio equal to 0.385 in wet and dry states. It is found that the deformations occurring under applied load growth proportionally to it, and deviation from this regularity was observed for lightweight iron-sulfur-containing concrete only at high compressive stresses. It was also proved that the destruction of iron-sulfur-containing arbolite occurs sequentially. First, the destruction of the mortar component is observed, and then the organic aggregate in the form of crushed reed fiber is destroyed. It was confirmed that arbolite concrete composite can be used as an effective wall material for civil engineering structure, especially in seismic regions of Kazakhstan. Full article

The forming methodology influences the physicochemical, mechanical, and microstructural properties. In this study, which aims to develop a geopolymeric material for potential insulation applications in buildings such as vertical walls, geopolymers were developed using industrial wastes from different industries: slate stone cutting sludge (SSCS) and chamotte (CH) were used as precursors, and olive stone bottom ash (OSBA) and sodium silicate (Na₂SiO₃) were used as alkaline activators. Two forming methods were evaluated: uniaxial pressing and casting of the material, varying the forming method and the liquid/solid ratio. The results showed that the pressed geopolymers achieved higher bulk densities (up to 2.13 g/cm³) and significantly higher compressive strength (28.04 MPa at 28 days), attributable to a higher compactness and degree of geopolymer reaction. In contrast, the casting geopolymers exhibited surface efflorescence, related to slower curing and higher porosity, which reduced their compressive strength (17.88 MPa). In addition, the pressed geopolymers showed better thermal stability and fire performance. These results demonstrate that the variation of the forming method has a direct influence on the material properties of geopolymers, and that the pressing process allows for a reduction of the alkaline activator content, thus reducing its environmental footprint. Full article

This study employed high-pressure ultrasonic-microwave-assisted extraction (HP-UMAE) to extract gingerols from ginger. The extraction yield and total polyphenol content of the extracts were determined. Their antioxidant activity was assessed by DPPH and ABTS radical scavenging assays, and compared with extracts obtained by leaching extraction, reflux extraction, ultrasonic-assisted extraction (UAE), microwave-assisted extraction (MAE), and ultrasonic-microwave-assisted extraction (UMAE). The results demonstrated that HP-UMAE achieved the highest extraction yield and the strongest ABTS radical scavenging activity among the evaluated methods. Furthermore, HP-UMAE extracts exhibited the highest concentrations of key gingerol constituents: 6-gingerol (14.29 mg/L), 8-gingerol (0.38 mg/L), 10-gingerol (1.95 mg/L), and 6-shogaol (4.32 mg/L). This enhanced efficacy is attributed to the synergistic combination of ultrasonic cavitation and microwave-induced thermal effects under elevated pressure. This synergy creates conditions promoting cellular wall disruption, facilitating the release of intracellular components, while concurrently enhancing solvent penetration and gingerol solubility. Scanning electron microscopy (SEM) analysis confirmed the significant structural damage inflicted on ginger cell walls following HP-UMAE treatment. The process parameters for HP-UMAE were optimized using single-factor experiments. The optimal extraction conditions were determined as follows: microwave power 800 W, ultrasonic power 1000 W, liquid-to-solid ratio 55:1, and temperature 100 °C (corresponding pressure 2 MPa). Under these optimized parameters, the extraction yield and ABTS radical scavenging rate reached their peak performance, yielding values of 4.52% and 43.23%, respectively. Full article

This study consisted of the injection molding simulation of polycaprolactone (PCL)-based nanocomposites reinforced with multi-walled carbon nanotubes (MWCNTs) for biomedical implant manufacturing. The simulation was additionally supported by experimental validation. The influence of varying MWCNT concentrations (0.5%, 5%, and 10% by weight) on key injection molding parameters, i.e., melt flow behavior, pressure distribution, temperature profiles, and fiber orientation, was analyzed with SolidWorks Plastics software. The results proved the low CNT content (0.5 wt.%) to be endowed with stable filling times, complete mold cavity filling, and minimal frozen regions. Thus, this formulation produced defect-free modular filament sticks suitable for subsequent 3D printing. In contrast, higher CNT loadings (particularly 10 wt.%) led to longer fill times, incomplete cavity filling, and early solidification due to increased melt viscosity and thermal conductivity. Experimental molding trials with the 0.5 wt.% CNT composites confirmed the simulation findings. Following minor adjustments to processing parameters, high-quality, defect-free sticks were produced. Overall, the PCL/MWCNT composites with 0.5 wt.% nanotube content exhibited optimal injection molding performance and functional properties, supporting their application in modular, patient-specific biomedical 3D printing. Full article

The electroosmotic flow (EOF) of non-Newtonian fluids plays a significant role in microfluidic systems. The EOF of Powell–Eyring fluid within a parallel-plate microchannel, under the influence of both electric field and pressure gradient, is investigated. Navier’s boundary condition is adopted. The velocity distribution’s approximate solution is derived via the homotopy perturbation technique (HPM). Optimized initial guesses enable accurate second-order approximations, dramatically lowering computational complexity. The numerical solution is acquired via the modified spectral local linearization method (SLLM), exhibiting both high accuracy and computational efficiency. Visualizations reveal how the pressure gradient/electric field, the electric double layer (EDL) width, and slip length affect velocity. The ratio of pressure gradient to electric field exhibits a nonlinear modulating effect on the velocity. The EDL is a nanoscale charge layer at solid–liquid interfaces. A thinner EDL thickness diminishes the slip flow phenomenon. The shear-thinning characteristics of the Powell–Eyring fluid are particularly pronounced in the central region under high pressure gradients and in the boundary layer region when wall slip is present. These findings establish a theoretical base for the development of microfluidic devices and the improvement of pharmaceutical carrier strategies. Full article