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Turbulent Flame Spread on Vertical Corner Walls.


pdf icon Turbulent Flame Spread on Vertical Corner Walls. (337 K)
Qian, C.

NIST GCR 95-669; 161 p. April 1995.

Sponsor:

National Institute of Standards and Technology, Gaithersburg, MD

Available from:

National Technical Information Service
Order number: PB96-114764

Keywords:

flame spread; turbulent flames; walls; corners; fire research; experiments; fire science; fire spread; heat transfer; polymethyl methacrylate; fire growth; flow visualization

Abstract:

Fire science is a rapidly growing research area. The motivation of fire research is to reduce fire loss and the cost of fire protection. Fire research is devoted to better understanding and prediction of fires. Flame spread is one of the most important phenomena in fire study because the spread rate is the measure of fire growth. In reality, flames are nearly all turbulent due to the large scale of building fires. Turbulent flame spread along vertical corner walls has the fastest spread rate among building fires. Because of the complex geometrical configuration and strong unsteady properties, the conventional instrumentations encounter great limitations. Therefore, there is relatively little data directly bearing on corner fire spreads. In this study, attention is given to the corner fire spread mechanism and the flame spread behavior. Infrared (IR) radiometry and image analysis techniques have been developed in this study to measure flame spread rate on large areas with high resolution and frequency. In addition to the flame spread measurement, the fire-induced flow was studied by flow visualization, and the total incident heat flux to the wall surface from the flame was measured by Gardon-type heat flux meters. Based on these experimental studies, a thermal model for corner fire spread has been successfully developed. The burning wall temperature measurement through flames using an IR imaging technique has been studied both theoretically and experimentally. For most materials, the constant emissivity 1.0 can be used to determine the pyrolysis front temperature due to soot deposition on the surface. The flame effect consists of band emissions mostly from excited CO2 and H2O and a continuous emission from soot particles. The effects of the band emissions can be eliminated by a bandpass filter (10.6 + 0.5 mm), and the soot particle effects can be neglected (epsilon < 0.03) for wall fires due to the small optical depth. Two-dimensional flame spread rate and the area of pyrolysis zone can be obtained by the IR imaging technique.