Flame Spread and Dripping Behaviors in Horizontal and Vertical Wires

摘要

Dripping of polymer insulations in wire fire has a potential risk of igniting nearby objects and expanding the size of the fire, but has not been well studied so far. In this work, dripping behaviors during the flame spread over horizontal and vertical polyethylene (PE) insulated wires were investigated. Wires of 8- and 9-mm diameter with and stainless steel core were tested. The temperature profile of core and insulation were also measured during the flame spread. Experimental results showed that a high-conductance copper core acted as a heat source downstream to increase the flame spread. However, in the upstream burning region, the copper core acted as a heat sink, cooling and reducing the mobility of melting insulation. Therefore, the copper core facilitates burning and reduce dripping. Moreover, in the vertical downward flame spread, the insulation drips flowed downward to preheat the wire, and this dripping heating dominated over the heating by the core. Therefore, higher dripping fraction for wires with lower thermal conductance resulted in a faster flame spread. This is the first time that the simultaneous dual effect of the heat source and heat sink for wire core was observed, and the influence of dripping on the flame spread over the wire was discovered.