Flame spread over inclined electrical wires with AC electric fields
KAUST DepartmentClean Combustion Research Center
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AbstractFlame spread over polyethylene-insulated electrical wires was studied experimentally with applied alternating current (AC) by varying the inclination angle (θ), applied voltage (VAC), and frequency (fAC). For the baseline case with no electric field applied, the flame spread rate and the flame width of downwardly spreading flames (DSFs) decreased from the horizontal case for −20° ≤ θ < 0° and maintained near constant values for −90° ≤ θ < −20°, while the flame spread rate increased appreciably as the inclination angle of upwardly spreading flames (USFs) increased. When an AC electric field was applied, the behavior of flame spread rate in DSFs (USFs) could be classified into two (three) sub-regimes characterized by various functional dependences on VAC, fAC, and θ. In nearly all cases of DSFs, a globular molten polyethylene formed ahead of the spreading flame edge, occasionally dripping onto the ground. In these cases, an effective flame spread rate was defined to represent the burning rate by measuring the mass loss due to dripping. This effective spread rate was independent of AC frequency, while it decreased linearly with voltage and was independent of the inclination angle. In DSFs, when excessively high voltage and frequency were applied, the dripping led to flame extinction during propagation and the extinction frequency correlated well with applied voltage. In USFs, when high voltage and frequency were applied, multiple globular molten PEs formed at several locations, leading to ejections of multiple small flame segments from the main flame, thereby reducing the flame spread rate, which could be attributed to the electrospray phenomenon.
CitationLim SJ, Park SH, Park J, Fujita O, Keel SI, et al. (2017) Flame spread over inclined electrical wires with AC electric fields. Combustion and Flame 185: 82–92. Available: http://dx.doi.org/10.1016/j.combustflame.2017.07.010.
SponsorsThis research was supported by the SGER (C-D-2016-1210) Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science, and Technology (2016-2017). S.H. Chung was supported by King Abdullah University of Science and Technology, and O. Fujita was supported by JAXA as a candidate experiment for the third stage use of JEM/ISS titled “Evaluation of gravity impact on combustion phenomenon of solid material towards higher fire safety” (called as “FLARE”).
JournalCombustion and Flame