Ignition phase transition of a polymer: Convective exposure

Abstract

SUMMARYThe ignition of a semi-infinite solid polymer under convective exposure is investigated. A quasi-steady approximation is used for the gas phase and the transient effect is accounted for in the solid phase only. Both surface and gas phase chemical reactions are included simultaneously. The ignition mechanism is studied in terms of the concurrent heat transfer, mass transfer and chemical processes at the surface as well as in the gas phase. The gas phase governing equations are integrated independently from the solid phase energy equation using the Adams-Moulton subroutine. Corrections to the iterative procedure are carried out by establishing a set of perturbation equations and using the Newton-Raphson and least-squares methods. The results indicate that ignition occurs in the heterogeneous mode within a narrow range of low flow velocities and high temperatures. An ignition phase transition point exists, and within a wide range of high flow velocities, ignition switches to the homogeneous mode.

Convective ignition of polymers: New apparatus and application to a thermoplastic polymer

“…These experiments help in the understanding of ignition. A topic which is not yet well studied is ignition under convective heating, which is gaining evidence as a primary mode of heating in wildfires [2,3] and is, next to radiation, a major mechanism in fire spread in buildings [4] Previous studies on convective ignition of polymers were primarily conducted in the 1980's with little contemporary work to be found [5,6,7,8,9,10,11,12,13,14,15]. The primary focus of those studies was the study of measuring the chemistry of thermal degradation of polymers, but these methods have now been superseded by the use of thermogravimetric analysis [16].…”

“…They found that the ignition behaviour switches from pyrolysis-controlled at low flow velocities to gas phase reactioncontrolled at higher air flows. Later, Durbetaki [9] numerically studied the ignition of a semi-infinite solid polymer under convective exposure. This model agreed with the experimental observation of the change in ignition mode.…”