doi:10.3850/978-981-08-7724-8_14-04

ABSTRACT

A fire whirl may occur when a pool fire interacts with a swirling flow. In real fire accidents, fire whirls have appeared repeatedly several times and caused severe consequences. To prevent the damages caused by fire whirls, it is essential to gain a deep insight into the phenomena of fire whirls. However, these phenomena have not yet been sufficiently studied. In particular, it is not clear why the flame height could increase. In this study, the generation mechanism of fire whirls was examined in the laboratory-scale experiments. Small scale experiments were performed to investigate, in particular, the relationship between flame height and burning rate (fuel evaporation rate). The fire whirl generator consisted of two split cylinders that were used to obtain fundamental characteristics of axisymmetric fire whirls. In the experiments, the flame height of fire whirl was found to become higher compared with that without a swirling flow. The dependences of the flame height on the Reynolds number, Re, based on the evaporating fuel vapour velocity, and the Froude number, Ff, were examined for the conditions with and without swirling flow to investigate the mechanism. It was found that the dimensionless flame height (flame height divided by pool diameter) is proportional to Re regardless of the presence of swirling flow. There is no clear relation between the dimensionless flame height and Fr. As a result, it was found that a swirling flow and buoyancy effect had little direct impact on flame height; rather, the fuel evaporation rate could be a controlling parameter. The swirling flow changed the shape of flame base and increased the heat flux to the liquid fuel. It might enhance the fuel evaporation and thereby increase the flame height.

Keywords: Fire whirl, Flame height, Pool fire, Swirling flow.

© 2011 CPD Unit, University of Leeds