Study Of The Air-blast Atomization For Coaxial Four-channel Nozzle

Nozzle is one of the key technologies of coal-water-slurry gasification.The research on atomization can provide guidance for the industrial application of nozzle.In this paper,the process of air-blast atomization for coaxial nozzle is studied by using the high-speed camera and laser particle size analyzer,etc.A ligament-mediated distribution model for coaxial twofluid air-blast atomization is developed,and the effects on the atomization process of coaxial four-channel nozzle is analyzed in terms of media flow rate,media mass ratio,media distribution ratio and other factors.The details are as follows:1.The finite stochastic breakup model of air-blast atomization process is optimized by combining the K-H and R-T interfacial instability theories with the ligament-mediated breakup mechanism and critical breakup conditions.A ligament-mediated distribution model for coaxial two-fluid air-blast atomization is developed.At low air velocities,the droplet size distribution index N of R-R model does not change with the size of the atomized droplet;at high air velocities,N tends to increase slowly and then rapidly as the atomized droplet size decreases.The total number of droplets num produced by the rupture of a single filament decreases with the increase of gas velocity and eventually tends to a constant value of 2.The experimental results of six coaxial nozzles shows that the ligament-mediated distribution model can predict the nonlinear relationship between the droplet diameters and particle size distribution at different velocities well.2.The atomization characteristics of the "gas-wrapping-liquid" coaxial four-channel nozzle were investigated,with a "liquid-gas-liquid-gas" arrangement from the center towards the wall.The atomization droplet size decreases slowly and then rapidly as the liquid volume distribution ratio between channel 1 and channel 3 decreases.The gas distribution ratio αbetween channel 2 and channel 4 has a non-monotonic effect on the atomization effect.When a is less than 0.6.the droplet size increases with increasing α,and when α is greater than 0.6,the droplet size decreases with increasing α.The sequence of the influences on atomization from high to low of a single channel is channel 4,channel 1,channel 2 and channel 3.Based on the interaction mechanism of two-channel atomized droplets,an empirical formula for estimating the droplet size of the "gas-wrapping-liquid" coaxial four-channel nozzle was proposed.3.The atomization characteristics of the "liquid-wrapping-gas" coaxial four-channel nozzle were investigated,with a "gas-liquid-gas-liquid" arrangement from the center towards the wall.The atomization droplet size decreases as the distribution ratio of the liquid volume between channel 2 and channel 4 increases,and increases as the width of the outermost ring gap increases.The sequence of the influences on atomization from high to low of a single channel is channel 3,channel 4,channel 2 and channel 1.For industrial-scale coal-water slurry coaxial four-channel nozzle,the critical liquid velocity condition of channel 4 filled with liquid is 1.0 m/s,with the increase in channel four liquid velocity,the more uniformly distributed atomization in space.The four-channel nozzle of industrial pulverized coal can be used to treat the waste liquid,and the critical liquid velocity condition of filling liquid is 0.35 m/s,the atomization angle increases with the increase of gas velocity and increases first and then decreases with the increase of liquid velocity.Based on the interaction mechanism of twochannel atomized droplets,an empirical for predicting the droplet size of the "liquid-wrappinggas" coaxial four-channel nozzle was proposed.