Effect of copper core diameter on heat transfer and horizontal flame spread behaviors over electrical wire

The laboratory polyethylene wire with different core diameters of 3 mm, 5 mm, 6 mm, 7 mm, 8 mm, 10 mm and 12 mm was used to study the flame spread characteristics. The flame spread could be divided into initial oscillation stage, stable oscillation stage and burn-out stage. With the increase of the copper core diameter, the flame width and flame area increased firstly and then decreased. For wires with intermediate copper core diameters of 6 mm, 7 mm, 8 mm and 10 mm, the relationship between flame area and core diameter was established as A similar to d(c), the total mass loss rate k with the copper core diameter d(c) followed as k(similar to)d(c), and the combustion mass loss rate and dripping mass loss rate gradually equaled to each other at stable oscillation stage. By analyzing the temperature field during the process of flame spread, the temperature gradient was almost same for diameters from 3 mm to 10 mm, which demonstrated the radiation heat would be influenced by flame height. Combined with the increased flame spread, the dominant conduction heat transfer mechanism was built. When the diameter was 12 mm, the smaller conduction heat transfer, which illustrated the core material Cu played an cool effect on flame, thus the dominant heat transfer of Cu was changed from a heat source to a heat sink.