Resolving the initial spray structure of fire sprinklers with a volume-of-fluid modeling

Abstract

The initial spray formation process of commercial fire sprinklers was investigated with a Large-eddy simulation and a Volume-of-Fluid model. The water-supply flow rate was set to 80 L/min corresponding to the minimum required flow rate in South Korea. From the study of grid dependency, a mesh size of 62.5 μm was adopted. Using this size of the mesh, unstable wave growth on the surface of the liquid sheet was captured, which corresponds to 1/16 the size of a sprinkler droplet that was derived in a previous study to be 1 mm. Sprinkler spray consisted of horizontal sheets generated by tines and vertical sheets generated by slots. Ligaments were produced by vortices on the air-water interface and droplets were generated by both longitudinal and lateral stretching. The flow rate of the tine section was larger than that of the slot section due to the large section angle. The water at the tine section was delivered to neighboring slot sections as flowing downstream. A formula for the sheet thickness was calibrated with measured mass outflow, which showed a more accurate value than the original formula driven by the mass conservation for the plate.