184. IGNITION AND FLAME SPREAD OF ELECTRICAL WIRES

Department: Mechanical & Aerospace Engineering
Research Institute Affiliation: Center for Energy Research (CER)
Faculty Advisor(s): Forman A. Williams

Primary Student
Name: Xinyan Huang
Email: x9huang@ucsd.edu
Phone: 858-534-6505
Grad Year: 2012

Abstract
Ignition and flame spread of thin electrical wires are investigated in order to gain a better understanding of the initiation and development of electrical-wire fires. An ignition-to-spread model is developed to systematically explain ignition and the following transition to spread. This ignition model predicts that for a higher-conductance wire it is more difficult to achieve ignition and the weak flame may extinguish during the transition phase because of a large conductive heat loss along the wire core. In addition, a simplified flame-spread model is developed in an effort to identify the most important effects on the spread rate of the wire thermal conductivity and diameter, the thickness of the insulation, and the oxygen concentration. An experimental study was performed using several sample wires with different core metals, diameters and coating thicknesses of polyethylene under various ambient conditions. Experiments show that additional heating times after flash are required in order to fully pass the transition and achieve a spreading flame, agreeing with model predictions. Also, flames spread faster for wires of a smaller diameter and a large thermal conductivity. As the oxygen concentration increases, the flame becomes brighter, and the spread rate monotonically increases. At the same time, the flame shape and dripping of the molten polymer change appreciably. The experimental results agree qualitatively with the model predictions. This study may be useful for upgrading the design and standards of future fire-safe wires.

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