On the transient flow in the 20-liter explosion sphere

The turbulence level in the 20-1 explosion sphere, equipped with the Perfor ated Dispersion Ring, was measured by means of laser Doppler anemometry. Th e spatial homogeneity of the turbulence was investigated by performing velo city measurements at various locations in the transient flow field. Directi onal isotropy was investigated by measuring two independent components of t he instantaneous velocity. The transient turbulence level could be correlat ed by a decay law of the form nu'(rms)/nu'(rms)degrees=(t/t(0))(n), in which the exponent, n, assumes a constant value of 1.49 +/-0.02 in the p eriod between 60 and 200 ms after the start of the injection process. In th is time interval the turbulence was also observed to be homogeneous and pra ctically isotropic. The results of this investigation imply that the turbul ence level in the 20-1 explosion sphere at the prescribed ignition delay ti me of ms is not equal to the turbulence level in the I m(3)-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 th e basis of dust explosion severities measured in laboratory test vessels. ( C) 2001 Elsevier Science Ltd. All rights reserved.