Numerical and Experimental Study on the Jet Behavior of Ultrafine Dry Powder Based on a Supersonic Nozzle.

To improve the dry powder jet extinguishing efficiency, the velocity change and spatial distribution of ultrafine dry powder particles under the action of high Mach number compressible air are studied by using the SST turbulence model and the gas-solid two-phase coupled model. The effects of nozzle pressure ratio, particle diameter, and mass flow on parameters such as Mach number and radial diffusion width are analyzed,and the influence of injection pressure and jet performance is verified by ultrafine dry powder jet experiment. The results show that the increase in the particle size will weaken particle flowability; the Saffman lift force has a significant effect on the particles when the nozzle expansion angle is large, and a particle-free zone is produced near the center axis; increasing the nozzle pressure ratio or reducing the dry powder mass flow rate will help improve the particle velocity in the core jet area outside the nozzle, and the accuracy of this law is proved by experiments. These findings are expected to provide valuable insights for the design of fire extinguishing nozzle structures.