Fire Safety Science Digital Archive

Experiments have been conducted to study the effect of flow velocity and grid generated turbulence intensity on the surface regression rate of thick PMMA sheets burning in a forced air flow. All the tests are carried out in a laboratory-scale combustion tunnel with flow velocities ranging from 1 4 s to 4 m/s and turbulence intensities from 1% to 20%. It is found that for all turbulence intensities, the regression rate decreases with the distance from the fuel sheet upstream edge, and increases with the flow velocity, in agreement with boundary layer analyses of the process. It is also found that flow turbulence has a strong influence on the surface regression rate due primarily to an enhancement of the heat transfer from the flame to the fuel that is caused by turbulence generated flame fluctuations. It is shown that the experimental data can be correlated in terms of a non-dimensional mass burning rate, m” Lx/ (? (Tf - Tp )) that is approximately linearly proportional to the turbulent flow parameter ((u’/u)? Rex0.8)0.5. The good correlation of the data in terms of these parameters indicate the potential predictive capabilities of theoretical models of the process that incorporate the flow turbulence through an eddy viscosity, and thermal and mass diffusivities. Explicit expressions for the laminar and turbulent mass burning rates in terms of the solid fuel and flow properties are reported.