Physics of the air

Abstract

An experimental investigation of dust explosions was conducted in a 1.23 I cylindrical pressure vessel known as the Hartmann bomb. A series of explosion runs were carried out using lycopodium as the test dust. The following parameters were varied: ignition delay time; dispersing air pressure; and nominal dust concentration. A companion set of experiments, in which velocity measurements were made during the dust injection process (without ignition), was conducted in a plexiglass version of the Hartmann combustion chamber. These measurements were made using a laser Doppler velocimeter (LDV). The cold-flow velocity measurements indicated that the decay of turbulence in the Hartmann bomb is very rapid and is essentially complete within 200 ms after introduction of the dispersing air. This time frame coincides with the results from the explosion tests, in which the maximum rate of pressure rise displayed a rapid drop in value as the ignition delay time was increased from 40 to 180 ms. The dust constant, Kst, was correlated with turbulence intensity expressed as an rms velocity. The correlation obtained was dependent on the nominal dust concentration and the dispersing air pressure. We have demonstrated a methodology whereby initial turbulence may be correlated with the maximum rate of pressure rise during a confined dust explosion. This approach should yield useful results if applied to larger test vessels.