1960 Loaded Hole The interaction of AN-based bulk explosives with hot ground were modelled, in this case the selfheating coal seam, through conductive heat transfer. It involved testing two distinct products, being a traditional pumped emulsion blend behaving as a solid, and ANFO, defined as porous media. The unstemmed section just above the bulk was air, open to the atmosphere, defined by the same physics as in the open blasthole scenario in the previous section. Mesh The mesh refers to the size and refinement of 3D elements which create nodes throughout the model, it is at each node where calculations occur based on the conditions at neighbouring nodes. It is thought that a finer mesh produces more physically real results. However, too fine of a mesh can induce convergence issues and significantly increase computation time, so a balance must be struck between result validity and runtime feasibility (Cadiou S, 2020). For the blasthole model, a ‘finer’ tetrahedral mesh was employed at the wall boundary between the ground, coal seam and air, as well as inside the blasthole itself, where heat transfer and fluid flow interactions are most significant. The mesh grows outward to a normal size by the edge of the ground boundary, as heat transfer interactions become insignificant, except for the top of the blasthole at the open boundary. A vertical cross-section of the mesh used across all models is shown in Figure 119 (a) and (b), a wireframe shows the mesh at boundaries rather than throughout the 3D model. (a) (b) Figure 119: (a)Full and (b) zoomed vertical cross-sections views of the mesh at each boundary. Boundary layers are a needed component of models with a solid-fluid interface, as well as those with abrupt changes in material, temperature or heat generation, which is present at the wall of the cylindrical blasthole for all three scenarios. A horizontal cross-section from the centre of the coal seam illustrates the use of boundary layers in Figure 120 (a) and (b).
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