Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: May 10, 2009
Publication Date: June 9, 2009
Citation: Hoffmann, W.C., Nedwed, T., Coolbaugh, T., Huber, C.A., Fritz, B.K. 2009. Wind-tunnel tests and modeling indicate that aerial dispersant delivery operations are highly accurate. In: Jones, N., editor. Proceedings of the Thirty-second AMOP Technical Seminar on Environmental Contamination and Response. Ottawa, Ontario, Canada: Environment Canada. p. 365-382. Interpretive Summary: Oil dispersants are used to break up oil spills and help mitigate the environmental impact of an oil spill. These dispersants are generally applied from aircraft; therefore, the airborne application equipment and operation of this equipment plays a vital role in the successful use of oil dispersants. Spray studies were conducted in a high speed wind tunnel to select the spray nozzles and operating pressure that produce large droplets, which will increase the accuracy and efficacy of the aerial spray application. Results from this study allow users of oil dispersants to select spray nozzles that will result in efficient and effective spray applications.
Technical Abstract: The United States Department of Agriculture’s high-speed wind tunnel facility in College Station, Texas, USA was used to determine droplet size distributions generated by dispersant delivery nozzles at wind speeds comparable to those used in aerial dispersant application. A laser particle size analyzer (LaVision SprayMaster) was used to quantify droplet distributions for fully developed dispersant sprays delivered from nozzles configured to simulate the delivery systems used by Marine Spill Response Corporation’s King Air BE90 and C-130 planes. Wind speeds used in the tests were in the range of speeds used by both planes to deliver dispersant. Wind-tunnel tests were performed using water, Corexit 9500, 9527, and a new dispersant gel being developed by ExxonMobil. The measured drop-size distributions were then used in an agriculture spray model to predict the delivery efficiency and swath width of dispersant delivered at flight speeds and altitudes typically used for dispersant application. The results of the wind-tunnel tests indicated larger volume median diameter (VMD) droplets sizes at wind speeds of 190-225 km/h (120 – 140 mph) than reported previously in full-scale field tests. Corexit 9500 had VMDs comparable to Corexit 9527, while the new dispersant gel had VMDs roughly 1000 - 1500 microns larger. Agriculture spray model predictions that used droplet-size distributions measured in the wind tunnel indicated that an aircraft flying at 240 km/h (150 mph) and at 23 m (75 ft) would be expected to deliver roughly 90% of the dispersant exiting the nozzles within the anticipated swath width on the ground. The wind-tunnel testing and the modeling provide additional evidence that current practices for aerial application of dispersants results in very efficient applications.