Pressure modeling of fires controlled by radiation

Abstract

Pressure modeling involves the reduction of all length scales as the minus 2/3 power of ambient air pressure in order to preserve gas phase dynamics and solid phase thermal response during a fire. This concept has been critically tested until now only for convection dominated fires. The burning rate and radiant output of large-scale PMMA wall and pool fires dominated by radiative heat transfer are compared with model results in the present study. At ambient pressures from 5 to 35 atmospheres, measurements with PMMA walls from 10 to 41 cm high clearly show that modeling of fuel mass flux variations and overall burning rate of full-scale PMMA walls up to 360 cm high is highly successful. It is found that while radiative fluxes from the fire to the environment are often not modeled for such large wall fires, the net radiative feedback from flames to the fuel surface is approximately modeled. The computed magnitude of surface reradiation and the computed variation of flame radiation with pressure explain the detailed behavior of the model burning rate relative to that at full-scale. The degree of success observed here in modeling burning rates of PMMA pool fires up to 122 cm across at 1 atm is shown to be entirely consistent with the wall fire results. While the detailed behavior of the model pool and wall fires may not precisely simulate full-scale effects, the accuracy of overall predictions based on model results is still impressive.