Numerical Simulation Of Gas Jet In Supersonic Nozzle With Dry Powder Extinguishing Agent

Electrical failure and careless use of fire account for the absolute proportion of fire causes on the basis of the statistics of fire accident data in recent years,so the task of disaster prevention and mitigation is still severe.Professional,convenient and efficient fire extinguishing device design technology is of great significance for quickly controlling fire,avoiding casualties as much as possible,and effectively reducing losses.The application of supersonic aerodynamic technology in dry powder fire extinguishing device can improve the fire extinguishing performance.Therefore,the numerical simulation of gas-solid two-phase jet in convergent divergent nozzle can provide theoretical support for the application of supersonic dry powder fire extinguishing technology.In this paper,Lagrange method,gas-solid two-phase coupling model and shear stress transport are used to simulate the gas-solid two-phase jet in convergent divergent nozzle driven by supersonic air.The effects of Saffman force,particle diameter,particle loading ratio,semi divergent angle,nozzle inlet pressure and different powder injection positions on gas parameters,particle velocity and particle aggregation were analyzed.The main conclusions are as follows:(1)Because the gas transverse velocity gradient in the divergent section of the nozzle changes after adding particles,the particles will move from the nozzle axis to the wall under the action of Saffman force,which has a great influence on the gas-solid two-phase velocity and particle aggregation.Therefore,it is necessary to consider the Saffman force in the particle force model.(2)The velocity of gas passing through the convergent divergent nozzle will increase,and the particles will accelerate in the tube under the action of high-speed gas.At the same time,the existence of particles will reduce the velocity of gas.Thus,the continuous energy and momentum exchange between gas and solid in the flow field leads to the coupling between the two phases is very important,and this effect increases with the increase of particle loading ratio.(3)When the diameter of ultrafine dry powder is about 15 ? m,the fluctuation of gas flow field parameters is small,and the particle velocity and aggregation degree outside the tube are high.(4)The results show that increasing the semi expansion angle will enhance the expansion effect of gas in the nozzle,but too large semi expansion angle will lead to shock wave in the pipe,too small semi expansion angle will lead to insufficient expansion of gas in the pipe.Under the same inlet pressure,when the supersonic gas-solid two-phase flow is in a better expansion state(that is,the ideal semi expansion angle),the velocity and aggregation degree of particles outside the pipe are higher.(5)Under different inlet pressure,the nozzle will present three different working states,namely over expansion,full expansion and under expansion.The velocity of particles outside the tube is higher in the state of full expansion,and the gas low temperature region outside the tube is larger in the state of full expansion and under expansion.(6)When the particles are injected into the nozzle under non premixed condition,the aggregation degree of particles will become higher,which has a good effect on some special occasions,and the powder feeding position is better in the contraction section.