Heat Transfer from Flame Impingement Normal to a Plane Surface: Importance of radiation, convection, and thermochemical heat release in impinging flames

Impinging flame jets have been widely studied because of their importance in a range of applications such as materials processing and fire safety. The purpose here was to determine the importance of radiation, convection, and thermochemical heat release (TCHR) under a range of conditions. Natural gas was premixed with oxidants ranging from air to pure oxygen in a round burner that produced uniform exit conditions. Flames impinged perpendicular to a water-cooled flat disk segmented into 6 concentric calorimeteric sections to measure radial heat flux distribution. Many parameters were varied such as firing rate, burner-to-disk spacing, oxidant composition and disk surface treatment. Untreated, polished, blackened, alumina-coated and platinum-coated disk surfaces made of stainless steel, copper or brass were tested. High (blackened) vs. low (polished) emissivity surfaces showed nonluminous gaseous radiation was less than 10% of the total heat flux. Noncatalytic (alumina) vs. catalytic (platimum) surfaces showed that TCHR was only important for high O2 oxidants. The radial location of the highest heat flux depended on oxidant composition.