On the effect of initial pressure on the minimum explosive concentration of dust in air

Standard explosion tests were performed in the 20 l sphere to measure the minimum explosion concentration (MEC) of nicotinic acid in air at different initial pressures. CFD simulations were also run in order to gain insight into the experimental results particularly in terms of effects of initial pressure on turbulent flow field, and dust dispersion and feeding efficiency. According to the literature results, it has been found that MEC increases with increasing initial pressure. This trend has been attributed to the decrease of the burning velocity with pressure. It has been shown, via CFD simulations, that the actual dust concentration in the whole vessel and at the center of the vessel, where ignition is provided, is much lower than the nominal dust concentration. Thus, the MEC values measured in the sphere on the basis of the nominal dust concentration are misleading. We computed a scale factor to correct the "nominal" MEC, MECNominal, to the "actual" MEC, MECActual. In particular, we may suggest that, when measuring the MEC in the standard 20 l apparatus, MECActual may be obtained by multiplying MECNominal by the ratio, ?, between the dust concentration in the center of the vessel (@ t = 60 ms) and the nominal dust concentration: MECActual = ? MECNominal. MECActual is much less sensitive to variations in initial pressure than MECNominal.