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Effective thermal conductivity is an important property of granular materials in engineering applications and industrial processes, including the blending and mixing of powders, sintering of ceramics and refractory metals, and electrochemical interactions in fuel cells and Li-ion batteries. The thermo-mechanical properties of granular materials with macroscopic particle sizes (above 1 mm) have been investigated experimentally and theoretically, but knowledge remains limited for materials consisting of micro/nanosized grains. In this work we study the effective thermal conductivity of micro/nanopowders under varying conditions of mechanical stress and gas pressure via the discrete thermal resistance method. In this proposed method, a unit cell of contact structure is regarded as one thermal resistor. Thermal transport between two contacting particles and through the gas phase (including conduction in the gas phase and heat transfer of solid-gas interfaces) are the main mechanisms. Due to the small size of particles, the gas phase is limited to a small volume and a simplified gas heat transfer model is applied considering the Knudsen number. During loading, changes in the gas volume and the contact area between particles are simulated by the finite element method. The thermal resistance of one contact unit is calculated through the combination of the heat transfer mechanisms. A simplified relationship between effective thermal conductivity and loading pressure can be obtained by integrating the contact units of the compacted powders.

Geothermal energy piles have emerged as a cost effective and efficient solution for heating and cooling buildings through renewable energy. Although significant research effort has been dedicated to investigating the performance of these systems, the effect of ground mineralogy has received little attention. This study examines the likely performance of energy piles in dense sand with varying mineralogy. A 3D thermal discrete element model is used to determine the dry thermal conductivity of quartz, feldspar and mica rich sand. This is then used in a 2D finite element analysis to estimate the dissipation/extraction capacity of the soil surrounding a typical energy pile. A 35% increase in quartz content is predicted to result in 51% improvement in the thermal performance of a pile.

This paper aims to provide a coupled finite element method (FEM) and smoothed particle hydrodynamics (SPH) approach capable of reproducing the blast response in rock. In the proposed approach, SPH is used to simulate large deformation and fracture of rock at the near detonation zone, while the FEM is adopted to capture the far field response of the rock. The explosive is modelled explicitly using SPH. The numerical simulations are carried out using LS-DYNA. The interaction of the SPH particles and FEM elements was modelled by the node to surface contact, and for the interactions between explosive and rock SPH parts node to node penalty based contact was used. In the present study, the Johnson and Holmquist constitutive model is used for rock. Jones–Wilkins–Lee model is used for TNT explosive. It is found that the preliminary numerical simulation reproduces some of the well-known phenomena observed experimentally by other researchers. The numerical results indicate that the coupled SPH-FEM approach used in this work can be applied to simulate effectively both compressive and tensile damage of rock subjected to blast loading.