Concentration measurements in dense isothermal gas clouds with different starting conditions

Experimental results are presented for instantaneous finite-volume dense-gas releases in a channel of 20 m length. The gases used were argon and argon-air mixtures with density ratios relative to air varying from 1.15 to 1.35. The aspect ratio (height to length) of the initial volume was varied from 0.42 to 1.68 with gas volumes from 1.89 to 3.78 m3. Measurements with 50 fast-response gas sensors (aspirated hot-wires) gave concentration signals with good resolution in time and space. The data obtained allow the air entrainment rates (both local and global) to be determined and give detailed information on the influence of the initial aspect ratio. Comparisons with theoretical solutions from the shallow-layer approximation (code SHALADIS) and with a dynamic integral model (adapted from Van Ulden, 1986, J. Haz. Mat. 16, 411–425) are also included. In view of the limitations of the models, the agreement was good for both.