Effects of droplet size on intrusion of sub-surface oil spills
Author(s)Chan, Godine Kok Yan
Massachusetts Institute of Technology. Department of Civil and Environmental Engineering.
E. Eric Adams.
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This thesis explores the effects of droplet size on droplet intrusion in sub-surface oil spills. Laboratory experiments were performed where glass beads of various sizes, which serve to simulate oil droplets in deepsea oil spills, were released vertically in a quiescent salinity stratified ambient and descended as multi-phase plumes. The two-tank stratification method was used to create linear density profiles for all experiments. The resulting radial concentration distributions of the dispersed phases were obtained by collecting the settled particles from the bottom of the tank. The radial distributions recorded were found to resemble Gaussian distributions, based on visual observations and analyses of kurtosis, which is consistent with particles being vertically well mixed in the intrusion layer. A new typology was proposed to describe plume structures with UN= us/(BN)¹/⁴ </= 1.4. For UN </=1.4 particle detrain from the plem, but only those with smallest slip velocity (UN </+0.3) intrude. An analytical model assuming well-mixed particle distributions within the intrusion layer was also used to predict the spread of the particle distribution based on initial buoyancy flux B, stratification frequency N, the particle slip velocity us, and the non-dimensional slip velocity UN. Comparison between experimental results and the analytical model suggested that the model accurately predicts the spread of the particles for UN </=1.4. Experiments with beads of difference sizes also suggested that the interaction between two particle groups has minimal effects on their radial particle spread. This indicates that particles of difference sizes can be treated independently when analyzing their radial plume spread. Chemical dispersants produce small oil droplets and the current experiments provide references on the minimum diameter needed for efficient particle spread (Type la* plume). By knowing the following parameters for a scenario - 1) initial buoyancy flux B; 2) the ambient stratification profile N; and 3) the slip velocities of the droplets u, - suitable amounts of dispersant can be determined and applied to reduce the size of the particles exiting the spill, allowing them to intrude and spread for a larger distance in the ocean column. A hypothetical example with conditions taken from the 'Deep Spill' experiment and Deepwater Horizon oil spill was also presented for reference.
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, February 2013."February 2013." Cataloged from PDF version of thesis.Includes bibliographical references (p. 86-90).
DepartmentMassachusetts Institute of Technology. Department of Civil and Environmental Engineering.
Massachusetts Institute of Technology
Civil and Environmental Engineering.