Limiting Oxygen Concentration Trend of ETFE-Insulated Wires under  Microgravity

MIZUTANI Ken, MIYAMOTO Kyosuke, HASHIMOTO Nozomu, KONNO Yusuke, FUJITA Osamu

doi:10.15011/jasma.35.1.350104

This study investigated the flammability of the fire-resistant material ethylene-tetrafluoroethylene (ETFE) as insulation for copper wires under different flow velocity and gravity conditions. The limiting oxygen concentration (LOC) of flame spreading horizontally over the sample was investigated at external opposed flow velocities ranging from 0 to 200 mm/s under normal gravity (1g0) and microgravity (μg0). The LOC under μg0 showed a U-shape, which has been reported in previous studies. A minimum LOC of approximately 26% was found at external flow velocities ranging 50–100 mm/s. An expanded heat balance model and radiation number for wire combustion (𝑅𝑟𝑎𝑑,𝑤𝑖𝑟𝑒) were proposed considering the heat conduction through the copper core, which is a notable feature of wire combustion. The U-shaped LOC curve was qualitatively explained in the low flow velocity region by this model and in the high flow velocity region by the Damköhler number. We also compared the LOC trend of ETFE with that of polyethylene (PE)-insulated wires reported in a previous study and demonstrated that the drop of LOC in ETFE was much larger than that of PE when the gravitational condition was changed from 1g0 to μg0 (∆LOC). This large difference was explained by two factors. First, the rate of change of flame temperature with an increasing oxygen concentration is small at high oxygen concentrations. Second, the increase in heat input through the copper core owing to gravity change was larger for ETFE than for PE because of the difference in the rate of change in flame length along the copper core.

Limiting Oxygen Concentration Trend of ETFE-Insulated Wires under Microgravity

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