The Role of Thermal Conductivity on Opposed Flow Flame Spread

Abstract

Quantifying the magnitude of solid-phase and gas-phase heat transfer for opposed flow flame spread has been the subject of research, and debate, for decades. Many studies neglect the contribution of longitudinal conduction through thermally thick solids for opposed flow flame spread. This study demonstrates the role of thermal conductivity with the addition of unidirectional conductive elements (copper, steel, and carbon fiber) in 12-mm-thick polymethylmethacrylate (PMMA) substrates. A layer of conductive elements was placed either or 3 or 6 mm from the surface of the solid. The addition of conductive elements in the direction of flame spread was found to increase the rate of both downward and lateral flame spread. The addition of copper elements in particular was found to increase the downward flame spread rate by nearly 60%. The subsequent increase in flame spread rate for each sample orientation (lateral and downward) was contextualized using the ratio of gas-phase and solid-phase heat transfer, as determined in previous studies. Additionally, the flame spread rate was correlated to the effective thermal conductivity in the longitudinal direction and the spread rate was found to follow an approximately linear relationship with effective thermal conductivity.