Upward flame spread on vertical walls.

摘要

Free burning turbulent upward flame spread on a vertical wall was studied both experimentally and theoretically. Experiments were performed (heat feedback from flames to unburnt material above pyrolysis height) in vertical wall fire situation with a transient upward flame spread for various practical materials including cardboard, clear and black polymethylmethacrylate, polyurethane, masonite, textile, particle board, and wood. An experimental apparatus was designed to measure the local mass loss rate in upward spreading vertical fire situation and the measured local mass loss rate was used as an input to a mathematical model for prediction of upward flame spread.;The model was developed to accept certain measurable "fire properties" obtained from small scale experiments in order to predict the upward propagation of fire on a vertical wall made of practical, combustible material with a finite thickness. The surface temperature as well as the inside temperature of the two-dimensional vertical slab, initially at the ambient temperature, were obtained by solving a transient two-dimensional heat conduction equation with transient boundary conditions. The total heat flux distribution obtained from the experimental study as a generalized function of pyrolysis height, flame height, and the distance from the leading edge, was supplied to the upward flame spread model as a boundary condition. The local mass loss rate was used to calculate the flame height at a given time. The set of equations including results from experiments was solved using the finite difference method with a nonuniform grid pattern because of the steep temperature gradients close to the surface.;The forward heat flux results provided valuable information about the flame spread process and the mass loss rate results proved the importance of transient burning. Predictions for the flame height and the pyrolysis height compared reasonably well with the experimental data.