Characterization of flame spread over PMMA using a temperature reconstruction method

The contribution of heat transfer mechanisms for different configurations of opposed flow flame spread on cast PMMA is presented. Three opposed flow flame spread scenarios are considered, each in a quiescent atmosphere: downward spread on a vertical surface, buoyant horizontal spread (i.e. a pool fire-type spread), and lateral spread along a vertical surface. Video analysis and temperature measurements were used to determine flame spread rates; average flame spread rates were found to be 2.67, 2.54, and 3.54 mm/min for downward, horizontal, and lateral spread, respectively. These differences result from the varying magnitudes of the heat transfer mechanisms (e.g. gas-phase heat transfer and conduction through the solid) due to the changes in the flame characteristics. Past studies have investigated these regimes of flame spread, but have not directly compared experiments from the configurations used here to identify the relative importance of each heat transfer mechanism. Using temperature measurements, the thermal gradient, and hence conductive heat fluxes through the solid, were quantified. This allowed the different rates of heat transfer to be compared across each configuration. Downward and horizontal flame spread displayed similar flame spread rates and similar heat transfer contributions for both the gas phase and solid phase. However, lateral flame spread displayed characteristically higher rates of gas-phase heat transfer compared to downward and horizontal.