The effects of packing structure on the effective thermal conductivity of granular media: A grain scale investigation

Abstract

Structural characteristics are considered to be the dominant factors in determining the effective properties of granular media, particularly in the scope of transport phenomena. Towards improved heat management, thermal transport in granular media requires an improved fundamental understanding. In this study, the effects of packing structure on heat transfer in granular media are evaluated at macro-and grain-scales. At the grain-scale, a gas-solid coupling heat transfer model is adapted into a discrete-element-method to simulate this transport phenomenon. The numerical framework is validated by experimental data obtained using a plane source technique, and the Smoluschowski effect of the gas phase is found to be captured by this extension. By considering packings of spherical SiO2 grains with an interstitial helium phase, vibration induced ordering in granular media is studied, using the simulation methods developed here, to investigate how disorder-to-order transitions of packing structure enhance effective thermal conductivity. Grain-scale thermal transport is shown to be influenced by the local neighbourhood configuration of individual grains. The formation of an ordered packing structure enhances both global and local thermal transport. This study provides a structure approach to explain transport phenomena, which can be applied in properties modification for granular media. discrete element method. Highlights 1. A numerical framework combining finite element analysis and discrete element simulation is established to study heat conduction in granular media.2. Finite element analysis is used to correct the conventional analytical solution and an empirical correlation is provided to implement the correction.3. The modified heat transfer model is incorporated into discrete element simulation.4. The effects of structural transitions on effective thermal conductivity is evaluated by grainscale structure index, and meso-scale mechanisms of the effect are identified.

Parameter analysis and wall effect of radiative heat transfer for CFD-DEM simulation in nuclear packed pebble bed

“…2 Cell model for the particle-particle thermal radiation. parameters are much greater than that of common conditions in packed beds (Rouhani et al, 2018;Dai et al, 2019). The results of effective thermal conductivity are shown in Fig.…”

Modeling and validation of heat transfer in packed bed with internal heat generation

“…Spherical lithium titanate pebbles of diameters 1, 3, 5, 7, and 10 mm were dumped along with steel balls of diameters same as that of lithium titanate pebbles in a column of 81.5 mm radius and 360 mm height. The Li 2 TiO 3 pebbles and steel balls were well‐mixed and the mixture of pebbles was simply poured into the column to achieve a random distribution, as structured packing is not studied the bed height and diameter is sufficient enough to estimate heat transfer properties of larger particles 39,40 . The physical properties of the pebbles are studied elsewhere by Mandal et al 41 The pebbles were supported by a mesh, which also acted as a distributing plate.…”

Effective thermal conductivity in granular media with devolatilization: the Lattice Boltzmann modelling

“…In result, it is argued in (Asinari et al 2007) that optimization of the fluid element paths would produce an increase in macroscopic performance. An example of modelling of fluid flow in granular media where various kinds of disorder is obtained for a given porosity is presented by Dai et al (2019); in their work, phenomena of invading fluid injection are modelled with special attention given to various deviation of local porosity. Heat transport in complex geometry was also analyzed by Wang and Pan (2008), focused on the REV domain; discussion is mainly concentrated on the comparison of computational results with theoretical predictions.…”