Study On The Subsequent Development Of Droplet Collisions In Impinging Streams

By the collision of two or more strands of a multiphase fluid to make kinetic energy changes suddenly has became one of the widespread topics in chemical reaction and project transfer engineering. However, the motions and collisions of particles in impinging streams are complex and stochastic, so far, it still can not be described quantitatively. In this paper, the subsequent development of droplet collisions in gas-liquid two-phase impinging flow have been studied by experiment and numerical simulation to acquire the general rules.In order to research the subsequent development of polyethylene or secondary atomization caused by droplet collisions in impinging flow, the gas-liquid two-phase experiment platforms supported by high-speed digital camera systems which are used to record the collision process of droplets in the impinging streams have been designed and built. Then more experiments are conducted by varying the particles’ size, speed, viscosity and collision angle, after analyzing the result of the experiments, the general rules and key factors about the subsequent development of droplet collisions are drew. Experiment results are as follows:(1) Conditions that two droplets moving in opposite direction after the collision occurs stretching separation are: We≥6.29B-4,0.38<B<1; Conditions that two droplets moving in opposite direction after collision occurs reflexive separation are: We>18.67[2(1.08-B)5/2-1]-1,0<B<0.28.(2) Two droplets moving in opposite direction occur reflexive separation after collision when the sizes and velocities are small; With sizes and velocities increasing, burst will be occurred.(3) Two droplets moving in opposite direction occur collision, different collision results may be the same as the Weber number.(4) Two droplets moving in opposite direction occur collision, the larger the droplets’ viscosity is, the less easily the droplets to be broken.(5) Two droplets moving in opposite direction occur collision, the greater the droplets’ surface tension is, the more easily the droplets to be broken.(6) Two droplets moving in the same direction occur coalescence after collision; Two droplets moving at a certain angle occur stretching separation after oblique collision; Two droplets moving in opposite direction occur reflexive separation or burst after collision.(7) Two droplets moving in opposite direction occur collision with the same velocity, viscosity and collision angle, the smaller the Oh number is, the more easily the droplets to be broken.Theoretical model that correctly reflect the droplets collision and subsequent development is established to simulate the polyethylene or secondary atomization caused by droplet collisions in impinging flow, then the particle sizes distribution of droplets between two nozzles are theoretically studied, and the influence of size, velocity, viscosity and impact angle on droplets size distribution is analyzed. Simulation results show that:(1) The smaller the droplet size is, the greater the probability of collision coalescence is; The greater the viscosity is, the greater the probability of collision coalescence is.(2) Droplets occur coalescence when the velocities are small, with the velocities increase, the probability of secondary atomization is increasing.(3) Under the same conditions, when droplets occur oblique impact, the probability of secondary atomization is larger than direct impact.