Impact of Immersed Conductive Objects and Relative Influence of Immersion Depth on Quasi-Steady Burning Behavior of Dodecane Fuel Slick on Turbulent Waters

Kottalgi, Mahesh

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Impact of Immersed Conductive Objects and Relative Influence of Immersion Depth on Quasi-Steady Burning Behavior of Dodecane Fuel Slick on Turbulent Waters

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With the increase in industrialization, activities in the modern world predominantly have revolved around the usage of liquid/ fossil fuels for transportation and energy requirements directly or indirectly. A large percentage of these fossil fuel needs are accommodated by offshore drilling. These drilling methods and subsequent oil transport used for offshore oil rigs increase the risk of accidental release of fuel into water bodies. Oil contamination can create a hazard to life and property. In-situ burning (ISB) is one of the spill response techniques in practice, where the spill area is subjected to a controlled ignition and burned till extinguishment [4-8]. Although ISB is an effective countermeasure to burn fuel spills, understanding the burning behavior of fuel under wavy water conditions is necessary to increase the effectiveness of the overall burn. To understand the heat transfer mechanism for a fuel layer burning in ocean conditions, an experimental platform is used to simulate wavy water surfaces. Furthermore, the study investigates the influence of turbulent water and the immersed conductive object on the steady burning behavior of a fuel layer floating on a turbulent water surface. To systematically investigate the effect of turbulence, an experimental platform simulating free surface turbulence is created using a submerged axisymmetric jet pointing upwards, the result is an isotropic regime in the horizontal plane with the free bulk flow for experimenting. The corresponding turbulence created lies in the range of 0 cm/s to 4.2 cm/s. For Phase-I of the study, a 5 mm fuel slick is used to study turbulence as a parameter for the experiments. Results show a change in turbulent boundary conditions causes an increase in heat extraction from the bottom of the fuel layer, thereby reducing the mass burning rate by 45 % at a turbulent intensity of u' = 4.2 cm/s, along with a decline in overall flame height compared to no turbulence case. A model developed to predict the heat transfer coefficient at the fuel-water interface shows the heat transfer coefficient value (h) dominates as a result of internal mixing with the increase in turbulence. For Chapter 3, based on the studies in Chapter 2, an intermediate turbulence intensity equal to 1.7 cm/s comparable to water turbulence in a calm ocean is chosen for the experiments. To improve the burning under the turbulent water sublayer condition, a 10 mm diameter copper conductive object is immersed at different depths in the fuel. The copper rod collects the flame’s heat and transmits it into the fuel layer via conduction, thereby increasing the burning rate by more than 1.4 times. A heat transfer model shows that the case with a small rod immersion depth (~10 mm) in a 40 mm fuel layer is best at improving burning because the heat losses from the object to the water sublayer are the lowest. The model also shows that the heat from the flame transmitted by the rod is primarily distributed in a region close to the surface of the fuel, where nucleate boiling around the rod surface dominates. As more of the rod is immersed in the fuel layer, the heat dissipation to the turbulent water increases nearly five times, thereby reducing the nucleation sites around the rod surface and the burning rate. The implications of burning fuel slicks during in-situ burning in turbulent water conditions are espoused.

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