Metastability, disorder and jamming are the typical characteristics of amorphous systems, while the related structure changes remain unclear. Sphere packing is often used as a structure model for amorphous and crystalline states. In this article, sphere packing systems with packing densities ranging from 0.50 to 0.74 were simulated by using Discrete Element Method (DEM), and the obtained packing structures were assessed to investigate the densification process and jamming properties. An order parameter that can effectively distinguish the order and disorder of packing structures was proposed based on the distribution characteristics of jamming angles. Then the evolution of jamming characteristics during the transition from Random Loose Packing (RLP) to Random Close Packing (RCP) and the jamming-jamming relations of different packing structures were demonstrated. On this basis, a correlation between order-jamming-metastable states from the microscopic structural perspective was established, which is of valuable theoretical and practical implications for the characterization and synthesis of crystalline and amorphous materials.

The packing of multi-sized wet spheres is highly intricate, shaped by the interplay of interparticle forces induced by the presence of liquid. This study presents a comprehensive and quantitative analysis of the microscopic particle arrangement within a multi-sized wet sphere packing. To achieve this, a multi-sized wet sphere packing is obtained experimentally and is then characterized by various analytical techniques, in terms of coordination number (CN), pair correlation function (PCF), topological and metric properties of the Voronoi-Delaunay tessellation. Through CN and PCF analysis, distinctive packing features such as agglomerates and particle chains are identified and characterized. Furthermore, the application of the Voronoi and Delaunay tessellation techniques uncovers the existence of heterogeneous clusters of particles in contact and non-contact states. These tessellation methods also shed light on the distorted pore structure that emerges within the packing. The insights gained from this study may serve to enhance the assessment and development of innovative simulation methods where capillary and liquid-related forces acting on wet particles with a size distribution are considered.

In packed beds, bed structure significantly influences heat transfer between particles and fluids. A pore-network model (PNM) incorporating conduction, convection, and radiation is developed to investigate heat transfer in packed beds at the particle-pore scale. The model reveals how structural variations, such as bed porosity and pore geometry, influence heat transfer mechanisms. Validation against experimental data from demonstrates strong agreement in temperature evolution and heat transfer coefficients, confirming the model's accuracy. Bed-scale simulations reveal that bed porosity, gas velocity, and temperature collectively determine the dominant heat transfer mode. Convective heat transfer prevails at higher gas velocities, accounting for over 80 %, particularly in loosely packed beds. Conduction is more significant in denser beds and at lower velocities, contributing up to 40 %. Radiative heat transfer becomes substantial, accounting for up to 30 % only at elevated temperatures (e.g., 1000 °C), surpassing conduction in loosely packed configurations. At the pore scale, denser beds exhibit more uniform pore geometries that enhance local convective transfer through pores with near-regular shapes, such as smaller pores approximately half the particle size, typically observed in cells with porosities below 0.4. Conversely, increased heterogeneity in high-porosity beds promotes advective transport through larger pore throats. This model offers convenience in exploring and quantifying how bed porosity and local structural heterogeneity governs heat transport in granular systems and offers a flexible modelling framework for exploring structure–property relationships under diverse thermal and flow conditions.

Powder bed fusion additive manufacturing has been applied to the fabrication of functionally graded materials. A new design that allows the material composition to change along the direction perpendicular to the powder spreading has been reported in the literature. Based on this design, this work examines the quality of the graded spread powder layer with two powders, which have a large difference of density. The results reveal that during the spreading of graded powders, the volume of particles on the heavy powder side is deposited less than that on the light powder side, indicating that heavy particles diffuse to the light powder side. This diffusion is affected by the spreading speed, but not much by the layer gap. Large spreading speed causes more significant deviation. The results also show that particle size affects diffusion, indicating that decreasing the particle size of the heavy powder may be a solution to reduce diffusion. [Figure not available: see fulltext.]