Xiepeng Sun

A Mathematical Model on Interaction of Smoke Layer with Sprinkler Spray

Abstract A mathematical model was developed for predicting the downward descending behavior of the buoyant smoke layer under sprinkler spray. The behavior of the smoke layer was determined by considering the interaction between the drag force of the sprinkler spray and the buoyancy force of the hot smoke layer itself in the spray region. The smoke layer may be pulled down with its thickness increased at the center of the spray region due to the cooling and drag effects of the sprinkler spray, thus to form a downward “smoke logging” plume. In the mathematical model developed in this paper, the critical condition under which the smoke layer lost its stability, as a serious concern, was predicted. Additionally, the length of the downward plume, which was rarely investigated before, was also further calculated. Full-scale experiments were carried out to validate the model. Results showed that the predictions, including the critical condition and the length of the plume, by the mathematical model agreed well with that observed and measured in the experiments. The length of the downward plume was shown to increase with the sprinkler operating pressure by an approximately linear correlation.

A Mathematical Model for Cooling Effect of Sprinkler on Smoke Layer

A mathematical model for predicting sprinkler cooling effect on smoke layer was developed. Results of calculation showed that the temperature difference between droplets and smoke layer and the thickness of smoke layer are major factors of the cooling effect. The cooling effect might lose its efficiency when the sprinkler pressure became relatively high. Experiments were carried out to validate the model and compared with Morgan model. The experimental results show that temperatures predicted by the current model agree well with the experimental results when temperature difference is high. However Morgan model is more suitable for low temperature difference.Copyright