Fire Safety Science Digital Archive

A theoretical model was developed to predict the flammable liquid vaporization rate from a heated pool subjected to impingement of a vertical air jet. The model divides the air flow field into two regions: one is the bulk air jet turning region and the other is the thin boundary layer formed on the liquid surface. The model is based on the premise that the thickness of the boundary layer in which vapor diffusion takes place above a liquid pool is mainly controlled by the impinging air jet. The model predicts that the liquid vaporization rate increases with the pool temperature and increases linearly with the impinging velocity, as opposed to the square-root dependence in the case of air flow parallel to the pool surface. The model was validated with vaporization rate data of high flash-point liquids. It is shown in this paper that the vapor blowing effect on boundary layer thickness greatly diminishes as the impinging air velocity increases from quiescence to 3.3 m/s for the high flash-point liquid pools analyzed in this study. The analysis also indicated that the boundary layer thickness on a small curbed pool could be greater than that predicted for an infinite pool. The resulting thicker fuel vapor diffusion layer tends to lead to lower vaporization rates than those expected from an infinite liquid pool under the same air impingement condition.