Pool Fire Burning Facilitated by Subcooled Nucleate Boiling Heat and Mass Transfer Processes

Pi, Xiaoyue

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Pool Fire Burning Facilitated by Subcooled Nucleate Boiling Heat and Mass Transfer Processes

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In-situ burning of oil spills has been one of the most effective methods to clean up oil leaks in offshore areas. However, it is highly challenging to efficiently burn a thin layer of oil floating on the water surface. A novel technique for oil spill burning developed at WPI in 2014, named Flame RefluxerTM, is further analyzed in this thesis to obtain controlling parameters. Unlike the conventional heat transfer from the flame to the fuel surface, the Flame RefluxerTM creates an additional thermal loop to collect heat and transfer it to the liquid fuel. As a result, the in-situ burning rate improves notably. Furthermore, subcooled nucleate boiling phenomena on the surface of the immersed object significantly improve both boiling and burning rates. The nucleate boiling is analyzed in depth in this thesis. Several existing works have reported the positive impact of the immersed object. However, the mechanisms and interactions remain unclear, and further investigations are desired. This dissertation performs three phases of experiments, followed by a comprehensive numerical model development. The first-stage experiments are performed in a subcooled dodecane pool, where an electrically heated wire-shaped nichrome object is immersed. Various bubble phenomena are characterized to analyze the boiling process. The inclination of the object, φ, is varied as the variable, where φ = 0° (horizontal), 22°, 33°, 44°, 49.5°, 74° and 90° (vertical). The second-stage experiments are performed by immersing a composite-shaped aluminum object in a burning liquid ethanol pool with refilling. The heated object, bulk liquid, and fire interactions are analyzed and coupled to various bubble phenomena observed with different immersion depths. The initial immersion depth, l, is varied as the variable, where l = 0 mm, 2.5 mm, 4.5 mm, and 7.0 mm. Further analyses state the inconsistency in mass loss rate as a function of depth from the processed data and bubble visualization perspectives. The third-stage experiments are performed by immersing a composite-shaped copper object in a burning liquid ethanol pool with refilling. The difference between the second and third stage experiments is the inclusion of regularly spaced holes added to the immersed object serving as active nucleate boiling sites. Three cases are analyzed: “no holes”, “small holes” (D = 1.09 mm), and “big holes” (D = 2.06 mm) cases. In all experiments (Stages 1, 2, and 3), unique photography techniques are employed to capture various bubble phenomena allowing qualitative and quantitative analysis. Using the Finite Difference Method (FDM) and an explicit time marching scheme, a numerical model is developed to discretize the governing equations and boundary conditions on the C programming platform. The convergence is verified by checking the residue at interfaces and the energy imbalance for the domain. The simulation results are validated by comparing the results with the experimental data from the literature. After the model is verified and validated, two parametric studies are conducted to explore the influence of the object configurations on the pool fire for potential optimal designs. Ultimately, this thesis provides a framework to seek and examine potential designs while using the Flame RefluxerTM technique, with a long-term goal of providing solutions to clean up oil spills at sea effectively.

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