Modeling emulsification after an oil spill in the sea Hao Xie a , Poojitha D. Yapa a, ⁎ , Kisaburo Nakata b a Department of Civil and Environmental Engineering, Clarkson University, Potsdam, NY 13699, USA b School of Marine Science, Tokai University, Shimizu, Shizuoka, Japan Received 23 September 2005; received in revised form 13 February 2007; accepted 13 February 2007 Available online 20 February 2007 Abstract A conceptual model for simulating oil emulsification after a spill in the ocean is presented. This paper contains the complete model formulation and scenario simulations. The model formulation is based on the most up-to-date research information available in the literature. The model uses minimum turbulence energy as a criterion to determine whether emulsification occurs. Once the emulsification happens, the model simulates water uptake and viscosity changes during emulsification. The model classifies emulsion into three categories: stable, meso-stable, and unstable emulsions based on a concept “stability index”. The model estimates the stability of the emulsion and simulates the process of de-emulsification when the emulsion is meso-stable or unstable. The model also considers the effects of evaporation on the formation of emulsification. Scenario simulations show how different types of emulsions are formed under different conditions. They also show how the emulsion stability changes with oil weathering. © 2007 Elsevier B.V. All rights reserved. Keywords: Emulsions; Emulsification; Oil-in-water content; Oil pollution; Oil spills; Tar balls 1. Introduction To meet worldwide demand, oil exploration, produc- tion, and transportation either remain steady or are increasing. As long as oil is used, the risk of an oil spill exists. An oil spill can occur from a transportation ship accident, broken pipeline, collapse of a storage tank, or an underwater well head blowout. Realizing the threat of oil spills, computer models have been developed to simulate the fate and transport of oil after a spill (e.g. Huang and Monastero, 1982; Yapa, 1994; Yapa and Zheng, 1995; ASCE, 1996; Reed et al., 1999). Although oil spill models have improved signifi- cantly over the last 20 years, their capability for model- ing of chemical processes is weak. Oil spilled in water undergoes a variety of physical–chemical processes, such as spreading, vertical mixing, evaporation, disso- lution, emulsification, photo-oxidation, oil–sediment interaction, sedimentation, and biodegradation. Fig.1 is a schematic diagram showing these processes. During oil emulsification, oil takes up water to form the emulsion. As one of the important chemical pro- cesses, oil emulsification plays a significant role after a spill. Formation of emulsions changes the properties and characteristics of oil drastically. According to Fingas (1994), stable emulsions contain between 50 and 80% water thus expanding the volume of spilled material from two to five times the original volume. The density of the resulting emulsion can reach 1.03 g/ml compared to a starting density as low as 0.80 g/ml. Most signif- icantly, the viscosity typically increases by a few orders of magnitude. Available online at www.sciencedirect.com Journal of Marine Systems 68 (2007) 489 – 506 www.elsevier.com/locate/jmarsys ⁎ Corresponding author. Tel.: +1 315 268 7980; fax: +1 315 268 7985. E-mail address: [email protected] (P.D. Yapa). 0924-7963/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jmarsys.2007.02.016