Fire cooling performance by water sprays using medium and small-scale model experiments with scaling relaxation

Abstract

The fire cooling performance by water sprays is investigated in medium and small-scale fire cooling experiments. The scaling relationships considered are the fire diameter, spray height, heat release rate, spray angle, flow rate, working pressure, and droplet diameter. Full-cone-type spray nozzles of different sizes are used in both scale experiments. Although spray conditions (spray angle, flow rate, pressure, and droplet diameter) satisfying the scaling relationships are used, when the geometrical scaling of the nozzles is not sufficient, the water spray mass flux distributions generated by the nozzles do not fulfill the scaling relationship. To resolve this problem, we propose a new scaling relaxation for scaling the fire cooling effect of water sprays even under incomplete scaling conditions in the water spray mass flux distributions. In the scaling relaxation, we propose an effective plane in which the group of water droplets collides with the fire plume, and assume that only the water droplets passing through the effective plane contribute to fire cooling. Based on the experimental data, we show that scaling with sufficient accuracy is possible by normalizing with the spray flow rate directly contributing to the fire cooling. The scaling accuracy tends to decrease with the increasing spray angle.