Downward flame spread over PMMA spheres

Experiments were conducted to measure downward flame spread over PMMA spheres, and an underpinning theoretical basis was developed explain the relevant mechanisms governing spherical geometries. Flame a sphere classified into two distinct regimes, that being upper lower hemispheres. using cast spheres 40 50 mm in diameter. Samples ignited at top of progression front determined video analysis. The time resolved rate found increase nearly linearly while across hemisphere sample (at rates ranging from approximately 2.0–3.5 mm/min). on observed accelerate nonlinearly reaching instantaneous greater than 15 mm/min. be unsteady (i.e., continuously increasing) throughout each experiment. A Stokes flow solution adequately characterize opposed with respect induced buoyant flow. controlled by combination increasing velocity ambient increased heat transfer through interior solid. for diameter tested normalized presented as function relative angle inclination front, θ. Thus, regimes identified this work are largely independent size diameters used study. study provides unique condition observe transition dictated well-defined one which effects solid become increasingly significant.