Effect of Flow Direction on the Extinction Limit for Flame Spread over Wire Insulation in Microgravity

Masashi Nagachi, Fumiya Mitsui, Jean-Marie Citerne, Hugo Dutilleul, Augustin Guibaud, Grunde Jomaas, Guillaume Legros, Nozomu Hashimoto, Osamu Fujita

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Abstract

Experiments to determine the Limiting Oxygen Concentration (LOC) of a flame spread over electric wire insulation were carried out in microgravity provided by parabolic flights. The difference between the LOC in opposed and concurrent flows was evidenced. Polyethylene insulated Copper (Cu) wires and polyethylene insulated Nickel-Chrome (NiCr) wires with inner core diameter of 0.50 mm and insulation thickness of 0.30 mm were examined with external flow velocities ranging from 50mm/s to 200mm/s. The results for the Copper wires show that with increasing external flow velocity, the LOC monotonically decreased for the concurrent flow conditions and the LOC first decreased and then increased (“U” trend) for the opposed flow conditions. Similar trends were found in the experiments with NiCr wires. Also, in terms of the minimum LOC value, the minimum LOC was comparable for both wire types in both flow conditions. However, for the concurrent flow, the minimum LOC was about 1-2% lower (in oxygen concentration) than for opposed flow for both wire types. A heat balance model for the electric wire with flame propagation was established to estimate the LOC under opposed and concurrent flow conditions in microgravity. In this model, it was suggested that the LOC can be estimated using the normalized radiative heat loss from the sample surface. Result of the calculation qualitatively matched the LOC profile extracted from the experiments.
Original languageEnglish
Publication date2017
Number of pages5
Publication statusPublished - 2017
Event47th International Conference on Environmental Systems - Charleston, United States
Duration: 16 Jul 201720 Jul 2017
Conference number: 47

Conference

Conference47th International Conference on Environmental Systems
Number47
Country/TerritoryUnited States
CityCharleston
Period16/07/201720/07/2017

Bibliographical note

ICES-2017-244

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