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.
|Number of pages||5|
|Publication status||Published - 2017|
|Event||47th International Conference on Environmental Systems - Charleston, United States|
Duration: 16 Jul 2017 → 20 Jul 2017
Conference number: 47
|Conference||47th International Conference on Environmental Systems|
|Period||16/07/2017 → 20/07/2017|