Effects of ambient wind speed and side-confinement on the flame spread behavior of wire combustion
In actuality,wire-confined combustion occurs frequently.Its fire threat is more likely to spread due to ambient wind speed.In this work,the flame spread behavior and characteristics of two types of polyethylene wires(the diameter of the copper core is 6 and 8 mm,respectively,and the thickness of the polyethylene insulation layer is 3 and 2 mm,respectively)under side-confined conditions(the side-confined distance is 10～40 mm)and horizontal wind speed(v=0.2,0.5,and 0.8 m/s)are studied experimentally.The experimental results reveal that as the wind speed increases,the flame height gradually decreases,and the flame width grow first increases and then decreases.The side-confinement promotes wire burning,but as wind speed increases,this effect eventually weakens.When the horizontal wind speed is low,the heat transfer of the gas phase improves while the heat transmission of the solid phase is reduced.As wind speed increased,the heat transfer mode altered,and heat transfer between the gas and solid phases weakened.This is mostly due to the tilt effect of the flame,which increases thermal radiation and convection in the preheating zone.At the same time,because wind speed lowers the temperature of the gypsum board,the gypsum board's thermal radiation and convection are lowered as well.Furthermore,the horizontal wind alters the"heat source"and"cooling"effects of the copper core.The copper core's"cooling"effect grows as wind speed and diameter increase.
wire fireside-confinementwind speedflame spread rateheat transfer
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