Comparative Study on Upward Flame Spread Over Single and Twin Polyethylene-Insulated Copper Core Wires at Different Inclination Angles

In this paper, a series of comparative experiments were performed to study the upward flame spread over single and adjacent twin polyethylene-insulated copper wires from horizontal (0°) to vertical (90°). The flame morphology and flame spreading rate of single and twin wires were compared at different inclination angles, which show a larger flame size, but a lower overall flame spread rate over twin wires. As the inclination angle increases, the flame characteristic length, and flame spread rate increase with the inclination angle for both wire arrangements. The flame spreads steadily to the end of the sample without molten dripping or sliding for single-wire conditions. However, molten dripping or sliding behaviors were found during flame spreading for twin-wire conditions, and the averaged dripping or sliding frequency increases with the inclination angle. Correspondingly, the periodical variation of flame characteristic length, flame height, and flame spread rate for twin-wire conditions have been investigated in detail compared with single-wire conditions. Finally, a simplified heat transfer analysis is carried out to quantitatively study the flame spread rate for both wire arrangements, and the effects of molten dripping/sliding and overlapped area on the heat transfer and flame spread rate are qualitatively discussed.