Spheroidal Particles Research Articles

Graph-Property Relationships for Complex Chiral Nanodendrimers.

Organic, polymeric, and inorganic nanomaterials with radially diverging dendritic segments are known for their optical, physical, chemical, and biological properties inaccessible for traditional spheroidal particles. However, a methodology to quantitatively link their complex architecture to measurable properties is difficult due to the characteristically large degree of disorder, which is essential for observed property sets. Here, we address this conceptual problem using dendrimer-shaped gold particles with distinct stochastic branching and intense chiroptical activity using graph theory (GT). Unlike typical molecular or nanostructured dendrites, gold nanodendrimers are two-dimensional, with branches radially spreading within one plane. They are also chiral, with mirror asymmetry propagating through multiple scales. We demonstrate that their complex architecture is quantitatively described by image-informed GT models accounting for both regular and disordered structural components of the nanodendrimers. Furthermore, descriptors integrating topological and geometrical characteristics of particle graphs provide physics-based analytical relations to the nontrivial dependence of optical asymmetry g-factor on the particle structure. The simplicity of the GT models capable of capturing the complexity of the particle organization and related light-matter interactions enables the rapid design of scalable nanostructures with multiple functions.

Sum-Frequency Generation in the Surface Layer of a Dielectric Spheroidal Particle: Analytical Solution

Sum-Frequency Generation in the Surface Layer of a Dielectric Spheroidal Particle: Analytical Solution

Drag, lift, and torque on a near-wall oblate spheroid in linear shear flow

This study performs particle resolved simulations (PRSs) to investigate the behavior of linear shear flow over a near-wall oblate spheroidal particle. Simulations are conducted for particles with aspect ratios (λ) of 1.5, 2, and 4, covering Reynolds numbers (Re) ranging from 1 to 200 and particle inclination angles (θ) from 0° to 180°. The resulting drag, lift, and torque coefficients exhibit unique patterns of variation with respect to θ, showing significant differences compared to particles in unbounded uniform flow. These variations are elucidated by examining the flow field surrounding the particle, alongside the distribution of pressure and skin-friction coefficients on its surface. Based on these findings, correlations for the drag, lift, and torque coefficients are proposed, demonstrating strong agreement with the PRS results across different aspect ratios and Reynolds numbers, thereby providing accurate predictive models for near-wall oblate spheroidal particles in linear shear flow.

A mid-20th century stratigraphical Anthropocene is recognisable in the birth-area of the industrial revolution

The formalisation of the Anthropocene as a subdivision of the Geological Time Scale has been under debate. Its stratigraphic boundary has been proposed as a precise Global boundary Stratotype Section and Point (GSSP) in the mid-20th century, but it is part of an episode of human-induced changes to the Earth System that have unfolded over millennia. Here we attempt to identify stratigraphical patterns of the Anthropocene from a previously well studied lake sedimentary archive from the English Midlands, located in one of the most heavily human-modified landscapes in the UK, and the birthplace of the Industrial Revolution. Our analysis is predicated on the sedimentary succession of Groby Pool, a small lake situated to the immediate northwest of Leicester. We have found that whilst proxy signals for biotic change are indicative of significant landscape and consequent ecological changes prior to the 20th century, the signal from radiogenic fallout and rapid increase in spheroidal carbonaceous particles indicative of fossil-fuel combustion yield a clear mid and later 20th century stratigraphical signature that corresponds with the Great Acceleration of the post-WWII period. We therefore demonstrate clear stratigraphical signatures in the oldest Industrial Revolution landscape on Earth that are consistent with a mid-20th century start point for the Anthropocene.

Land use, hydroclimate and damming influence organic carbon sedimentation in a flood pulse wetland, Malaysia

ABSTRACTWater bodies located in floodplains and tropical forests are known to be important carbon stores, but many are subjected to intensive pressures from damming, land use and climate changes. Sedimentary records preserve long‐term archives for understanding how such changes affect the quantity and quality of carbon stores. We analysed sediment cores from seven sites across a flood‐pulse multi‐basin wetland, Tasik Chini in Peninsular Malaysia (for percentage LOI550, sediment density and spheroidal carbonaceous particles), and conducted more analyses on three 210Pb‐dated cores (X‐ray fluorescence of elements, grain size analysis, carbon isotopes, C/N ratios, carotenoid pigments) to gain an understanding of the drivers of organic carbon accumulation rates (OCARs) since 1860 ce. The median OCAR of 85 g m−2 a−1 for the basin since 1945 ce was higher than in other floodplain and temperate lakes and in line with other tropical forest lakes. However, we found evidence for different mechanisms of OC deposition across the basin. In ‘autochthonous mode’, the site with minimal local land disturbance had lowest OCARs and OC was derived mainly from autochthonous production, which rose slightly around 1940 ce when regional land disturbance increased nutrient influx to the basin. The site with the most long‐term and intensive land disturbance through forest removal (1940s) and then conversion to rubber and oil palm farming (1980s) functioned mainly in ‘allochthonous mode’; that is, increases in OCARs after 1940 ce were driven by deposition of soil‐derived OC. The highest OCARs were in the basin that was converted to oil palm after the 1980s and had increased iron mining activity in the 2000s; because this site was located distal from the flood pulse and became increasingly hydrologically disconnected after a low rainfall period in the 1970s, the lake responded strongly in ‘autochthonous mode’, through encroachment of fringing swamp, the spread of benthic algae and macrophytes, and efficient sediment retention. Weir installation in 1995 ce raised water levels and increased lentic conditions, promoting autochthonous OC production and sedimentation across all basins. The long‐term fate of this more recently deposited OC remains uncertain because it is more labile. Overall Tasik Chini has responded strongly to land use changes since at least the 1940s, earlier than anticipated in this region of Southeast Asia, and the sedimentary proxies indicate large changes in the ecosystem function and capacity for C storage over the past ca. 80 years. Most of these shifts have increased OC accumulation by strengthening autochthonous production or allochthonous OC fluxes, but the implications for other aspects of the C cycle, including catchment soil C loss and greenhouse gas production, need to be accounted for when evaluating the overall impacts of land and hydrological disruption.

Testing assumptions of spheroidal carbonaceous particle (SCP) quantification at very low concentrations: Implications for dating geologic archives

Spheroidal carbonaceous particles (SCPs) are preserved in geologic archives such as lake sediments, ice cores, or peatlands, and can provide chronology for cores. SCPs are only produced during the combustion of coal and fuel oil, so they are a reliable global marker of the onset of industrialization and can be used to track deposition from these sources. While the usage of SCPs as chronostratigraphic indicators in recent sediments is common, the enumerative method of quantifying their sedimentary concentrations has remained virtually unchanged, and assumes that one subsample is representative of the entire sediment sample. We test this assumption and explore its implications for the SCP chronological method of dating recent sediments by analyzing multiple subsamples to characterize the precision and accuracy of SCP concentration measurements. Notably, we do not use the conventional SCP quantification method and focus on samples with lower concentrations and larger SCPs than are typically quantified in the literature. However, we base our conclusions and inferences on insights gained from analyses of the effects of subsampling on SCP numerosity (counts), which are translatable insights to all sizes and methods of SCPs quantification which rely on particle counts. We quantified SCPs in sets of 30 subsamples for 14 riverine sites (n = 420). SCP concentrations varied (0 SCPs/gDM – 2141±825 SCPs/gDM), but reflect the typical ranges of SCP concentrations quantified in modern sediments in other environmental settings. For each site, we used a bootstrapping method to approximate the theoretical mean of SCPs at 1–30 subsample sizes, then compared the theoretical mean and relative standard deviation. We found that enumerating 10 subsamples per sample better represents the theoretical mean of SCPs than the enumeration of 1 subsample, especially for lower SCP concentration samples. The greatest chance for falsely reporting the absence of SCPs was when <10 SCPs/gDM were measured in fewer than 10 subsamples, indicating that more replicates could provide greater confidence in SCP-based dating of geologic archives. If aiming to delineate the stratigraphic onset of SCP presence for dating purposes, we recommend enumerating a minimum of 10 subsamples for samples with low SCP concentrations to ensure the reliability of these measurements. We acknowledge that enumerating multiple subsamples is time and resource intensive, but provide some strategies (e.g., limiting subsampling) for minimizing additional cost and argue that the advantages afforded for dating reliability outweigh the costs in paleoenvironmental research.

Boosted the thermal conductivity of liquid metal via bridging diamond particles with graphite

The liquid metal (LM) composite is regarded as having potential and wide-ranging applications in electronic thermal management. Enhancing the thermal conductivity of LM is a crucial matter. Herein, a novel LM composite of eutectic gallium-indium (EGaIn)/diamond/graphite was developed. A highest thermal conductivity of 133 ± 3 W m−1 K−1 was achieved, 411 % higher than that of the matrix. The bonding mechanism reveals that the interfacial adsorption energy (ΔE) of graphite and EGaIn can be effectively decreased by the functional groups of graphite (by −108 % for –OH and −125 % for −CO) and the oxide of EGaIn (by −64 %). Furthermore, the ΔE of diamond and EGaIn can be significantly reduced through the oxidation of EGaIn (by −83 %) and the H-terminal of diamond (by −187 %). The thermal conductance mechanism suggests that a 3 vol% graphite content in the EGaIn/40 vol% diamond/graphite composite can form an excellent thermal conductance bridge among diamond particles. However, the thermal conductivity of the composite significantly decreased when too much graphite was added due to the tendency of the graphite to coat the diamond particles. There was no significant change in the melting point of EGaIn after being mixed with diamond and graphite. The EGaIn/diamond/graphite composite also demonstrated excellent thermal management performance in LED lamps and CPU heat dissipation as a thermal interface material, particularly in high-power electronic devices. This work presents the potential to enhance the thermal conductivity of LM-based composite by bridging spheroidal particles with a flaky material.

Advanced nano-composite coatings of ZrB₂/ZrC/SiC on carbon fibers via eco-friendly precursor synthesis

This study presents a comprehensive investigation into the synthesis and characterization of ZrB2/ZrC/SiC composite coatings on carbon fiber substrates via a solution-based process followed by high-temperature pyrolysis. The precursor solution was prepared using Gum Ghatti (GG), zirconyl chloride, tetraethyl orthosilicate, and boric acid. Optimization of precursor concentration and molar ratios was performed to achieve suitable viscosity and composition. The pyrolysis process was conducted in an argon atmosphere, resulting in the formation of well-defined ZrB2, ZrC, and SiC phases. XRD analysis confirmed the phase composition, while SEM imaging revealed spheroidal particle aggregates with a uniform distribution of composite phases. TG-DTA analysis reveals the thermal decomposition behavior, highlighting distinct stages of mass loss and phase transformations. Coated carbon fibers exhibited enhanced oxidation resistance, as evidenced by TGA analysis. SEM analysis confirmed the uniform distribution and adhesion of the composite matrix on the carbon fiber substrate. This study demonstrates the successful synthesis of ZrB2/ZrC/SiC composite coatings with promising thermal properties for advanced applications.

Developments in Localized Surface Plasmon Resonance

AbstractLocalized surface plasmon resonance (LSPR) is a nanoscale phenomenon associated with noble metal nanostructures that has long been studied and has gained considerable interest in recent years. These resonances produce sharp spectral absorption and scattering peaks, along with strong electromagnetic near-field enhancements. Over the past decade, advancements in the fabrication of noble metal nanostructures have propelled significant developments in various scientific and technological aspects of LSPR. One notable application is the detection of molecular interactions near the nanoparticle surface, observable through shifts in the LSPR spectral peak. This document provides an overview of this sensing strategy. Given the broad and expanding scope of this topic, it is impossible to cover every aspect comprehensively in this review. However, we aim to outline major research efforts within the field and review a diverse array of relevant literature. We will provide a detailed summary of the physical principles underlying LSPR sensing and address some existing inconsistencies in the nomenclature used. Our discussion will primarily focus on LSPR sensors that employ metal nanoparticles, rather than on those utilizing extended, fabricated structures. We will concentrate on sensors where LSPR acts as the primary mode of signal transduction, excluding hybrid strategies like those combining LSPR with fluorescence. Additionally, our examination of biological LSPR sensors will largely pertain to label-free detection methods, rather than those that use metal nanoparticles as labels or as means to enhance the efficacy of a label. In the subsequent section of this review, we delve into the analytical theory underpinning LSPR, exploring its physical origins and its dependency on the material properties of noble metals and the surrounding refractive index. We will discuss the behavior of both spherical and spheroidal particles and elaborate on how the LSPR response varies with particle aspect ratio. Further, we detail the fundamentals of nanoparticle-based LSPR sensing. This includes an exploration of single-particle and ensemble measurements and a comparative analysis of scattering, absorption, and extinction phenomena. The discussion will extend to how these principles are applied in practical sensing scenarios, highlighting the key experimental approaches and measurement techniques.

Pairwise interaction of in-line spheroids settling in a linearly stratified fluid

AbstractThis study investigates the transport of particles in density-stratified fluids, a prevalent natural phenomenon. In the ocean, particles and marine snow descend through fluids with significant density variations due to salinity and temperature gradients. Such heterogeneity in the background fluid affects the settling or rising rates of particles, often leading to accumulation at transitional density layers. Previous research has primarily focused on spherical particles, examining their isolated motion, pairwise interactions, and collective transport in stratified fluids. This work, however, extends the investigation to the interaction between two spheroidal particles settling in-line in a linearly stratified fluid. This study employs an immersed-boundary technique to perform particle-resolved numerical simulations in a three-dimensional Cartesian domain. The results showcase the effects of varying the stratification strength through the Froude number, the particles’ aspect ratios, and the initial separation distance between the particles on the interaction dynamics between the settling spheroids.

Evaluating microplastic particles as vectors of exposure for plastic additive chemicals using a food web model

Microplastic particles (MPs) represent potential hazards for humans and wildlife, including as vectors for chemical exposure (e.g. plastic additives and pollutants sorbed from the surrounding environment). The leaching of chemicals from MPs has been identified as a potential exposure pathway but the relative magnitude of this pathway under environmentally relevant conditions remains unclear. Here, we describe a modification of the ACC-HUMANSTEADY bioaccumulation model to include dietary exposure to MPs containing either accumulated chemicals from the surrounding environment or embedded plastic additive chemicals (PACs). Chemical transfer to humans and wildlife is described using two-film resistance concepts assuming spheroidal particles of different sizes. The relative contribution of MPs and environmental media to the estimated daily chemical intake in humans was assessed in various exposure scenarios, for a range of hypothetical chemicals with varying octanol-water and air-water partition coefficients (KOW and KAW, respectively; i.e. 0 < log KOW <8 and − 5 < log KAW < 3). Results imply that MPs could act as sources of exposure to chemical additives when the ingestion rate of 1 μm MPs is ≥ 10 mg d− 1, and the concentration of hydrophobic plastic additive is ≥ 5% wt wt− 1. The contribution made by MPs as vectors of exposure decreased with increasing particle size and decreasing ingestion rates of MPs. Human health risks were evaluated for four specific PACs to illustrate the application of the model for risk assessment. Risks were negligible when the ingestion rate of MPs was < 100 μg d− 1. Uncertainties are high regarding the characterization and quantification of ingestion of MPs by humans and wildlife, including particle sizes and polymer composition, as well as on the presence of PACs in MPs. These data gaps need to be addressed if the issue of MPs as vectors of chemical exposure is to be fully understood. The work illustrates that mechanistic models, which account for all major exposure pathways, can be used to identify the importance of different exposure pathways, help prioritize research needs and support decision making.

Dynamics of an oblate spheroidal particle in a square duct filled with viscoelastic fluids

Herein, we used the fictitious domain method to numerically investigate the lateral migration and rotation of an oblate spheroidal particle in a square duct filled with Oldroyd-B fluids. We adopted Reynolds numbers ranging from 25 to 100 and Weissenberg numbers from 0.01 to 0.50. At low to moderate Weissenberg numbers (Wi ≤ 0.50), viscous forces remain dominant in particle motion. Additionally, we considered the effects of initial lateral position, orientation, and blocking ratio on particle dynamics. The results indicate that for flow in square channels with finite fluid inertia, as Wi increases, the elastic effects gradually strengthen, causing the equilibrium position of the particles to shift from near the centerline of the channel toward the diagonal. Notably, under significant fluid elasticity conditions, additional equilibrium positions emerge in the corners of the channel. When released with their x0–y0 plane (containing the two longest axes of the oblate spheroid) parallel to the x–y plane (duct cross section) of the flow field, particles exhibited three distinct motion modes: tumbling, rolling, and kayaking. Tumbling was influenced by fluid inertia and corner attraction, which exhibited transitions to rolling or kayaking. The study also emphasized that the initial orientation of the particles impacted their sustained tumbling under low inertial flows. In addition, the blockage ratio (the ratio of the equivalent diameter of the particle to the duct height) mainly affected the equilibrium positions, and particles with a blockage ratio β ≤ 0.125 were readily attracted to the corners.

Developing a self-calibrating system for volume measurement of spheroidal particles using two acoustically levitated droplets.

Acoustically levitated droplets in the nanoliter to microliter range are studied in various fields. The volume measurements of these are conventionally done using image analysis. A precision-produced calibration sphere is often used to calibrate the recording equipment, which is time-consuming and expensive. This paper describes a self-calibrating method to measure the volumes of acoustically levitated droplets as a versatile and low-cost alternative. The distance between two levitated droplets in a horizontally oriented acoustic trap is processed via real-time or recorded frame data using image analysis. To assist in setting the cavity length for the acoustic trap, a simulation of the acoustic field is utilized based on the temperature in the trap, thereby also predicting the distance between the central nodes used to determine the scale factor. The volumes of the spheroidal-shaped levitated droplets can then be calculated from the pixel data. We use a modified version of the well-known TinyLev, and our method has been tested with two types of transducer packing. Its accuracy for volume measurements has been verified in comparison with the standard calibration sphere technique. Self-calibration of the system is demonstrated by changing the camera zoom during data collection, with negligible effects on measured volume. This is something that could not be achieved with conventional static methods.

Orientation of inertialess spheroidal particles in turbulent channel flow with spanwise rotation

The orientation dynamics of inertialess prolate and oblate spheroidal particles in a directly simulated spanwise-rotating turbulent channel flow has been investigated by means of an Eulerian–Lagrangian point-particle approach. The channel rotation and the particle shape were parameterized using a rotation number Ro and the aspect ratio λ, respectively. Eleven particle shapes 0.05 ≤ λ ≤ 20 and four rotation rates 0 ≤ Ro ≤ 10 have been examined. The spheroidal particles retained their almost isotropic orientation in the core region of the channel, despite the significant mean shear rate set up by the Coriolis force. Irrespective of channel rotation rate Ro, rod-like spheroids tend to align in the streamwise direction, while disk-like particles are oriented in the wall-normal direction. These trends were accentuated with increasing departure from sphericity λ = 1. The changeover from the isotropic orientation mode in the centre to the highly anisotropic near-wall orientation mode commenced further away from the suction-side wall with increasing Ro, whereas the particle orientations on the pressure side of the rotating channel remained essentially unaffected by Ro. We observed that the alignments of the fluid rotation vector with the Lagrangian stretching direction were similarly unaffected by the imposed system rotation, except that the de-alignment set in deeper into the core at high Ro. This contrasts with the well-known substantial impact of system rotation on the velocity and vorticity fields. Similarly, slender rods and flatter disks were aligned with the Lagrangian stretching and compression directions, respectively, for all Ro considered, except in the vicinity of the walls. The typical near-wall de-alignment extended considerably further away from the suction-side wall at high Ro. We conjecture that this phenomenon reflects a change in the relative importance of mean shear and small-scale turbulence caused by the Coriolis force. Preferential particle alignment with Lagrangian stretching and compression directions are known from isotropic and anisotropic turbulence in inertial reference systems. The present results demonstrate the validity of this principle also in a non-inertial system.

Photocatalytic degradation of phenol and polycyclic aromatic hydrocarbons in water by novel acid soluble collagen-polyvinylpyrrolidone polymer embedded in Nitrogen-TiO2

The photocatalytic degradation of phenol, naphthalene, fluoranthene, phenanthrene, pyrene, benz[a]anthracene, and anthracene was investigated using a novel nitrogen-doped TiO2/acid-soluble collagen-polyvinyl pyrrolidone nanocomposite (N-TiO2/ASC-PVP). Characterization through X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) revealed that the nanocomposite consists of spheroidal particles smaller than those of undoped TiO2. X-ray photoelectron spectroscopy (XPS) confirmed the incorporation of nitrogen within the TiO2 lattice, appearing as both substitutional nitrogen (OTiN) and interstitial nitrogen (TiON). The degradation process followed apparent first-order kinetics, with the N-TiO2/ASC-PVP calcined at 200°C and 400°C demonstrating high photocatalytic degradation efficiencies. The nanocomposite achieved a remarkable 98.6% degradation of the targeted compounds within 120 minutes at a concentration of 10 mg/L. The enhanced photocatalytic activity under visible light can be attributed to several factors: the smaller crystal size, increased surface hydroxyl groups, improved visible light absorption, and a reduced band gap energy. This N-TiO2/ASC-PVP photocatalyst shows significant potential for applications in materials science and nanotechnology, supporting advancements in environmental and energy-related fields.

Rotational Taylor dispersion in linear flows

The coupling between advection and diffusion in position space can often lead to enhanced mass transport compared with diffusion without flow. An important framework used to characterize the long-time diffusive transport in position space is the generalized Taylor dispersion theory. In contrast, the dynamics and transport in orientation space remains less developed. In this work we develop a rotational Taylor dispersion theory that characterizes the long-time orientational transport of a spheroidal particle in linear flows that is constrained to rotate in the velocity-gradient plane. Similar to Taylor dispersion in position space, the orientational distribution of axisymmetric particles in linear flows at long times satisfies an effective advection–diffusion equation in orientation space. Using this framework, we then calculate the long-time average angular velocity and dispersion coefficient for both simple shear and extensional flows. Analytic expressions for the transport coefficients are derived in several asymptotic limits including nearly spherical particles, weak flow and strong flow. Our analysis shows that at long times the effective rotational dispersion is enhanced in simple shear and suppressed in extensional flow. The asymptotic solutions agree with full numerical solutions of the derived macrotransport equations and results from Brownian dynamics simulations. Our results show that the interplay between flow-induced rotations and Brownian diffusion can fundamentally change the long-time transport dynamics.

The Role of Hydrocarbons in the Genesis of Mississippi-Valley-Type (MVT) Zn–Pb Deposits: Insights from In Situ Sulfur Isotopes of Sphalerite from the Southwestern Margin of the Yangtze Block, SW China

The coexistence of numerous Mississippi-Valley-type (MVT) Zn–Pb deposits and (paleo) oil/gas reservoirs in the world suggests a close genetic relationship between mineralization and hydrocarbon accumulation. Xuequ–Shandouya middle MVT Zn–Pb deposits are mainly hosted in the Lower Cambrian Maidiping Member siliceous dolostone on the southwestern margin of the Yangtze Block, accompanied by large amount of bitumen in the orebodies. Therefore, this type of Zn–Pb deposit is a natural laboratory for studying the relationship between the mineralization and the accumulation of paleo-oil/gas reservoirs. The deposit is characterized by spheroidal and concentric banded sphalerite. In situ sulfur isotope studies are carried out to determine the sulfur sources, sulfate reduction mechanisms, and role of hydrocarbons in the zinc–lead mineralization process. According to the mineral paragenesis and relative temporal relationship, two mineralization stages (1 and 2) are identified. An in situ sulfur isotope analysis of spheroidal and concentric banded sphalerite particles from Stage 2 shows that there are the two following types of sulfur isotopes in the sphalerite: one with relatively invariable δ34S values in the core (+8.31 to +9.30‰), and the other with a gradual increase from the core margin (core) to the rim (+0.39 to +16.18‰). These two types reflect that they may have formed in different times, with first type forming in the early period of Stage 2, while the second type was formed in the late period of Stage 2. The sulfur isotopic data suggest the sulfur source of evaporated sulfate minerals and multiple formation mechanisms for reduced sulfur (H2S). In the early period of Stage 2 mineralization, the sulfate reduction mechanism is mainly a mixture of bacterial sulfate reduction (BSR) and/or thermochemical sulfate reduction (TSR), while a very small amount may come from the thermal decomposition of organic compounds (DOCs). In the late period of Stage 2, TSR is dominant, and the gradual increase in the δ34S value may be related to Rayleigh fractionation. The oil/gasreservoir not only acts as a reducing agent to provide the required hydrogen sulfide for zinc–lead mineralization through TSR or BSR, but also provides reduced sulfur for mineralization through the thermal decomposition of organic compounds directly.

Experimental assessment of a multilayered packed-sphere La–Fe–Si active magnetic regenerator

This study investigates the performance of a multilayered packed-bed active magnetic regenerator (AMR) using spheroidal particles with first-order magnetocaloric properties. The hydraulic performance is assessed via the interstitial friction factor, showing significant underestimation by the Ergun Equation at high mass flow rates. Coefficient adjustments are made to accurately represent the AMR pressure drop, considering particle nonuniformity and structural components, such as layer mesh dividers. This facilitates the pressure drop modeling and provides a means to check the AMR integrity on a routine basis, without requiring AMR disassembly. The thermal performance, evaluated in terms of the regenerator effectiveness, shows a satisfactory cooling potential for practical applications but emphasizes the need for flow control to prevent effectiveness imbalance between hot and cold flows, crucial for optimal operation. The cooling capacity and maximum temperature span are also evaluated, demonstrating that higher mass flow rates yield higher cooling capacities with lower temperature spans, while lower rates achieve higher spans. Varying the blow fraction shows that regenerators at 50% blow fraction achieve 10% higher cooling capacities than at 37.5%. Increasing operational frequency improves cooling by increasing the number of cycles and reducing losses, resulting in a 15% capacity increase between 0.25 and 0.50 Hz. However, this trend may reverse at higher frequencies beyond the experimental limits. While this study improves the understanding of the hydraulic and thermal performance of packed-bed AMRs, its findings underscore the importance of flow balance and frequency in achieving optimal performance, thus providing insights for future system improvements.

Modelling aerodynamic forces and torques of spheroid particles in compressible flows

In the present study, we conduct numerical simulations of compressible flows around spheroid particles, for the purpose of refining empirical formulas for drag force, lift force, and pitching torque acting on them. Through an analysis of approximately a thousand numerical simulation cases spanning a wide range of Mach numbers, Reynolds numbers and particle aspect ratios, we first identify the crucial parameters that are strongly correlated with the forces and torques via Spearman correlation analysis, based on which the empirical formulas for the drag force, lift force and pitching torque coefficients are refined. The novel formulas developed for compressible flows exhibit consistency with their incompressible counterparts at low Mach number limits and, moreover, yield accurate predictions with average relative errors of less than 5%. This underscores their robustness and reliability in predicting aerodynamic loads on spheroidal particles under various flow conditions.

3D characteristic indicator analysis and comprehensive evaluation of manufactured sand particles used in high-performance concrete

Two-dimensional particle morphology indices face challenges in accurately depicting the characteristics of three-dimensional (3D) manufactured sand (MS), which does not effectively guide the selection of MS for high-performance concrete (HPC). This study aimed to obtain a quantified comprehensive evaluation of actual MS particle groups with specific gradations by thoroughly analysing 3D geometric characteristics. Two representative MS samples were selected for exploration, and river sand (RS) was used as the control. A random selection of sand particles was screened on six sieve levels ranging from 0.15 mm to 4.75 mm. Using X-ray computed tomography and associated image processing technologies, 3D models of these particles were generated, and MATLAB was used to extract their 3D morphology information. Subsequently, the change rules and validity of current 3D particle morphology indicators were examined, focusing on shape, angularity, and texture. Moreover, a comprehensive morphology index, Cm, was proposed by considering the effects of gradation and particle shape classification. The results showed that shape indices more accurately reflected particle characteristics, notably, a higher proportion of spheroid particles, a lower aspect ratio, and greater sphericity correlated with improved particle shape; contrary to traditional beliefs, the angularity index suggested that greater roundness did not necessarily equate to more rounded particles owing to the influence of the proportion of spheroid and cubic particles; meanwhile, texture indices showed minimal difference in the mean values of the 3D fractal dimension for the three types of sand. The proposed index Cm effectively differentiated the particle morphology states of the three sands, with higher Cm values indicating superior particle morphology. The smaller the difference between the Cm values of MS and RS, the better substitute of MS for RS.