Analysis of the Influence of Nozzle Structure of Dry Powder Fire Extinguishing System on Supersonic Jet Characteristics

The nozzle, as a critical jet component in dry powder fire extinguishing systems, significantly affects jet characteristics through its geometric configuration. To explore the influence of structural parameters on ultrafine dry powder gas-solid two-phase jet characteristics, a bidirectional coupled numerical model based on the SST k-omega turbulence model and the Discrete Phase Model is employed. This study examines how variations in the semi-expansion angle (alpha) and semi-contraction angle (beta) of the nozzle affect compressible gas flow behavior and particle distribution trajectories through a combination of simulations and experiments. The results indicate that when alpha = 2 degrees, the gas jet is in an under-expanded state, leading to increased particle dispersion due to the stripping effect of the surrounding high-speed airflow. Within the range of x = 0-180 mm, the dry powder exhibits a diffusion trend. When alpha = 4.5 degrees, the gas jet core region is the longest, providing optimal particle acceleration. Under constant inlet pressure, reducing alpha enhances particle collimation. The reduction of alpha alters the gas jet state, with alpha = 2 degrees showing better powder diffusion compared to alpha = 6 degrees. However, an excessively small alpha is detrimental to increasing the range of dry powder. With consistent structural parameters, the diffusion and range of dry powder remain the same across different beta values, and variations in beta have a relatively minor impact on supersonic jet characteristics. These findings offer theoretical guidance for optimizing and improving nozzles in ultrafine dry powder fire extinguishing systems.