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ICLASS 94<br>Proceedings of the Sixth International Conference on Liquid Atomization and Spray Systems

ISBN:
978-1-56700-019-1 (Print)
978-1-56700-445-5 (Online)

TRANSIENT BEHAVIOUR OF AEROSOL CLOUDS IN A CONFINED VOLUME: AN EXPERIMENTAL AND COMPUTATIONAL STUDY

J.R. Richer
Sheffield University, Sheffield, England

Jim Swithenbank
Department of Chemical and Process Engineering, University of Sheffield, Sheffield, United Kingdom

M. Wedd
Malvern Instruments Ltd, Malvern, England

Abstract

Combustible transient aerosol sprays may be formed when pipe or vessel failures on process plant lead to a leak of high pressure hydrocarbon fluids. The measurement of such transient aerosol clouds poses two diagnostic problems: the first is to measure very small droplets distributed over a large volume, the second is to dynamically measure the change in drop size and concentration over a short time period. In this study, transient homogeneous aerosols of water and kerosene were created inside a confined rig of 1.67m length, 1.5m width and lm height by various combinations of half-cone and full-cone Schlick spray nozzles. The aerosol decay was measured by the classical light scattering technique using the Malvern 2600 and Mastersizer-X particle sizers. A standard 300mm lens was used to measure the fine spray and a novel composite Fresnel lens was also employed to combat vignetting due to the large dimensions of the rig. Experimental results with water showed an initial D3.2 of between 15 and 32µm. The kerosene tests showed an initial D3.2 of about 5.6µm which fell very quickly to about 2.8µm, and the resulting aerosol took about 200 seconds longer to fully disperse than a water aerosol created under the same conditions. This difference in dropsize arose because kerosene and water have a surface tension of 0.026 Nm-l and 0.072 Nm-l respectively, hence kerosene is atomised much more easily than water. The results from the Mastersizer-X show the aerosol development and decay, and its new features allow many measurements to be made over a short time interval. The aerosol decay was also modelled using FLUENT to predict the effects of the purges on the droplet fall-out, and size distribution over time.