Wall-fire radiant emission—Part 2: Radiation and heat transfer from porous-metal wall burner flames

Abstract

Radiant emission and heat transfer from methane, ethane, ethylene and propylene fires burning on a vertical porous-metal surface have been measured. The water-cooled burner provides up to ten 380-mm wide and 132-mm high porous-metal panels topped by a 660-mm-high solid-metal heat-transfer plate. A scanning radiometer was used to obtain the vertical distribution of the outward-directed radiance No emitted normal to the burner surface. Results from six-panel fires, with fuel mass flux maintained constant over the active burner height, are reported. For any fixed fuel mass flux, the radiance No was found to increase linearly with height, z, after an initial jump at the flame base. At fixed z, linear relationships between reciprocal radiance No−1 and reciprocal mass flux m˙″-1 were obtained. For methane and ethane these relationships held over the entire range of mass flux, while, for ethylene and propylene, an abrupt transition separating two regimes occurred at critical mass fluxes. The ordinate intercept N∞, representing an asymptotic radiance, and the slope s of the linear relationship, are functions of height z. N∞ and s−1 increase with fuel sooting tendency at fixed z. Heat fluxes to the porous-metal panels decreased with increasing mass flux near the flame base, but were nearly independent of mass flux near the top portion of the porous-metal burner. These heat fluxes increased with fuel sooting tendency except for a reversed trend between methane and ethane. At sufficiently high mass flux, a jump of heat flux occurred at the junction between the porous-metal burner and the solid-metal heat-transfer plate, and the heat flux increased further with height in this over-fire region. In this zone, the data were separated into a lower overlapping set for alkane fuels, methane and ethane, and a higher overlapping set for the alkenes, ethylene and propylene.