Separating convective and radiative heat fluxes in horizontal flame spread over PMMA

This study proposes a methodology to separate the radiative and convective heat flux components from the flame to the fuel surface during horizontal-concurrent flame spread. Experiments are conducted in a bench-scale flow duct under steady forced flow conditions, using 1 mm thick black-cast polymethyl methacrylate (PMMA) sheets as the fuel. Two sensors (a radiometer and a total heat flux gauge) are used to quantify radiative and total heat transfer during the flame spread process. The radiometer (sensor 1) captured a portion of the flame's radiative emission, and a view factor between the flame and the sensor is calculated to estimate the total emitted radiative heat flux. The total heat flux gauge (sensor 2), located near the downstream edge of the sample holder, measured the total heat flux. A second view factor is used to estimate and subtract the radiative component and isolate the convective contribution in the total heat flux. The convective heat transfer to the heated zone is estimated by adjusting the convective heat flux to the sensor to account for the difference in surface temperature. The total heat flux to the heated zone is considered as the sum of radiative and convective contributions, where radiation is spatially resolved along the fuel sample centerline, while convection is represented as a mean value integrated over the centerline of the heated zone. Dimensional analysis shows that the heat flux data falls onto a single curve across all tested conditions. The average flame spread rate was measured in the experiments measurements and estimated using the calculated heat fluxes, and the results from the two methods show strong agreement. Novelty and significance statement This study introduces a novel experimental approach to separate radiative and convective heat transfer during horizontal concurrent flame spread. By combining direct measurements with a detailed radiation analysis, the work provides spatially resolves incident radiation heat flux to the sample alongside an average convective heat flux. The measured heat fluxes are used to predict the flame spread rate, finding good agreement with the model. Incorporating the convective component strengthens the physical basis of flame spread modeling, enabling more accurate descriptions of flame growth and material response. The approach can be adapted to other scenarios allowing for the relative contributions of convection and radiation to be determined.