1959 Scenarios Three scenarios were investigated: 1) an open hole, to understand the impact of ambient air convection on temperature measurements essential to deciding if a hole is safe to load. 2) a hole loaded with ANFO to understand the impact a porous explosive will have on heat dissipation and the temperature over time. 3) a hole loaded with a pumped emulsion blend/ANFO blend to understand the impact of a solid explosive will have on the heat dissipation and temperature over time Figure 118 illustrates the scenarios and heat transfer regimes applied. Figure 118: Cross section illustration of the 3D model showing the heat transfer regimes of the three scenarios modelled, open air, traditional pumped emulsion explosive and ANFO. Air filled hole: Non-isothermal Flow and the Boussinesq Approximation With the absence of forced air flow in mining blastholes, the assumption was made that fluid flow and heat transfer was governed by natural, rather than forced, convection – arising due to temperature differences in the heated coal seam, ground and air. In COMSOL, this coupling was managed by the ‘Nonisothermal Flow’ module, as temperature was constantly changing in the transient system. This fluid behaviour is governed by a simplified form of the Navier-Stokes relation. As the air was near ambient temperature, there was a moderate temperature difference at the seam (70oC – 20oC), the hole was not enclosed, and to keep a feasible simulation time, the Boussinesq approximation was applied. This simplified the Navier-Stokes equation for incompressible flow, making the driving force buoyancy induced, arising from slight density differences (Carasi, 2016). Turbulent flow using a k-ε model was chosen as it provided good convergence at low velocities (COMSOL, 2018).
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