Study On Atomization Process Of Double-flow Centrifugal Nozzle

Fire is a double-edged sword,which promotes the progress of human civilization.At the same time,the damage caused by fire is creepy.The water mist gradually replaces the application of halon fire extinguishing agent into the market due to its environmental protection,high efficiency and low price.The design and atomization mechanism are one of the key technologies of the water mist fire extinguishing system.The centrifugal nozzle is a simple structure,reliable operation and good atomization quality.Therefore,the numerical simulation and experimental research on the atomization process of the centrifugal nozzle are carried out.The three-dimensional physical model and the geometric model of gas and liquid entering the nozzle were established and centrifugal nozzle models were simplified accordingly.Fluent software's VOF two-phase flow model and Realizable k-? turbulence model were used to research on numerical calculation of single-phase flow inlet and two-phase flow inlet.The simulation focused on the internal flow field and the parameters of the outlet at the nozzle.The single-phase flow explored the effects of the length of the swirl chamber,the diameter of the swirl chamber,the diameter of the outlet and the viscosity of the water on the outlet parameters,air core diameter and flow coefficient.The center of the single-phase flow inlet swirl chamber is a stable cylindrical air core,the tangential velocity and radial velocity of the outlet gas phase region are almost zero,and the axial velocity is vertically upward.At the inlet of the double-flow medium,a funnel-shaped air core appears in the swirling chamber,the tangential velocity and the radial velocity are not zero,there is no air recirculation in the outlet,and the axial velocity values are positive.The transparent plexiglass nozzle was made and the high-speed camera system was used to observe the double-flow medium to visualize the internal and external flow fields of the centrifugal nozzle and the internal filling process during the nozzle startup.According to the experimental results,it can be concluded that when the double-flow medium enters the centrifugal nozzle,the upper part of the swirl chamber is a relatively uniform gas-liquid mixing zone and the lower part to the nozzle outlet is a cylindrical air core.The atomization cone angle at the outlet increases with the increase of pressure and tends to be stable during high pressure.The atomization cone angle decreases with the decrease of the outlet diameter.There is a shaking phenomenon inside the nozzle and the liquid film is unstable when the pressure is low.The shaking is reduced and the liquid film at the outlet is basically stable when the pressure is high.The higher the pressure,the shorter the liquid film breakage distance and the better the nozzle atomization effect.The atomization characteristics of the single-tube conveying double-flow medium centrifugal nozzle were observed by the Dual PDA system based on the fine water mist fire-extinguishing centrifugal nozzle.It was found that the nozzle flow rate increased with the increase in pressure.The average velocity of the main stream of the droplet is positively distributed and the center velocity of the nozzle is the highest on the same horizontal plane.The closer to the nozzle,the larger the average velocity of the main stream is and the higher the pressure,the higher the velocity on the central axis.Droplet diameter is distributed symmetrically about the nozzle center in the radial direction,the particle size of the nozzle center is the smallest and the particle size of the edge area is the largest on the same horizontal plane.The SMD increases with the increase of the axial distance and decreases with the pressure increases as a whole at the central axis.The closer to the nozzle,the better the atomization effect.The atomization process of the centrifugal nozzle is a complex variable damping process.The preliminary exploration of this paper,especially the numerical calculation and visualization experiment of the dual-flow medium,provides a reference for further theoretical analysis and application.