On the transient flow in the 20-liter explosion sphere

The turbulence level in the 20-l explosion sphere, equipped with the Perforated Dispersion Ring, was measured by means of laser Doppler anemometry. The spatial homogeneity of the turbulence was investigated by performing velocity measurements at various locations in the transient flow field. Directional isotropy was investigated by measuring two independent components of the instantaneous velocity. The transient turbulence level could be correlated by a decay law of the form

in which the exponent, n, assumes a constant value of 1.49±0.02 in the period between 60 and 200 ms after the start of the injection process. In this time interval the turbulence was also observed to be homogeneous and practically isotropic. The results of this investigation imply that the turbulence level in the 20-l explosion sphere at the prescribed ignition delay time of ms is not equal to the turbulence level in the 1 m³-vessel. Hence, these results call into question the widely held belief that the cube-root-law may be used to predict the severity of industrial dust explosions on the basis of dust explosion severities measured in laboratory test vessels.