Comparative study on upward flame spread interactions and heat transfer over two parallel wires with various spacing distances in open space and vertical channel

Most previous work focused on the flame spread interactions and heat transfer over two parallel wires in open space, but few studies considered the vertical channel effects. Experiments were carried out to investigate the influence of vertical channel on the flame spread interactions and heat transfer over two parallel wires. Two types of polyethylene-insulated copper wires were used with spacing distance ranging from 0 mm to 52 mm. Whether for open space or vertical channel, four typical regimes of upward flame interactions are observed as a function of spacing distance, but the range of these regimes is affected by the vertical channel. For open space and vertical channel, the flame width, flame length and flame spread rate rise first and then drop, but these parameters for vertical channel are larger than that for open space due to the enhanced induced flow and the heat transfer. A heat transfer model is established for upward flame spread over two parallel wires taking the effects of spacing distance and vertical channel, in which the radiation from flame is considered, as well as the difference between the solid-phase and gas-phase heating lengths. The flame heat feedback is the dominant mechanism for upward flame spread over two parallel wires, and it for vertical channel is larger than that for open space.