Abstract

Thermal radiation is an important fundamental process in flame spread, transferring heat from the flame ahead of the pyrolysis front. This work introduces a tractable contour formulation to model transient radiation from the flame to the heated zone in horizontal-concurrent flame spread over 0.5 and 1 mm thick black cast polymethyl methacrylate (PMMA) sheets in a bench-scale flow duct under steady inlet airflow. The transient radiant heat flux distribution to the heated zone is estimated with a side-facing radiometer and view factors between the flame and both the side-facing radiometer and a point at a variable location in the heated zone. View factors are calculated using information about the flame geometry extracted from image analysis using a contour integral technique with an idealized geometry of the flame. The methodology produced similar results, with some discrepancies due to the assumptions involved in this work, when comparing the second radiometer measurement to the heat flux calculated with the view factor between the second radiometer and the flame. The tractable contour formulation with the side radiative heat flux measurement enables the determination of the two-dimensional spatial distribution of radiative heat flux within the heated zone of PMMA during the horizontal-concurrent flame spread process. © 2025 The Authors