Research On The Particle Movements And Heat Transfer In The Atomization Sprays

Atomization spray plays a pivotal role in manufacture of high quality materials. The atomized liquid media are not limited to the traditional single-phase and low-viscosity fluid, but would extend to liquids with complex physical properties, such as viscous solutions, suspensions, non-Newtonian fluid and so on. Besides the atomized liquid, the spraying environments are also beyond the traditional conditions, involving magnetofluid, extremely high temperature, vacuum et al. The dissertation developed two numerical models to analysis the movements and heat-mass transfer for the viscous liquids and suspensions. One of the model accounts for the effervescent atomization spray and the other is aimed at the radio frequency suspension plasma spray. The main contents and achievements of the thesis are outlined as below:(1) A comprehensive three-dimensional model of droplet-gas flow was presented to study the evolution of spray in the effervescent atomization spray. For gas phase, the N-S equation with the k-εturbulence model was solved, considering two-way coupling interaction between droplets and gas phase. Dispersed droplet phase is modeled as Lagrangian entities, accounting for the physics of droplet generation from primary and secondary breakup, droplet collision and coalescence. The numerical results are compared with abundant experimental data and good achievements have been attained. Based upon this, the evolution of droplets mean diameter along axial distance, the mean size and statistical distribution of atomized droplets at cross sections, as well as the change of droplet velocity are calculated and analyzed to reveal their inner driving force. The influence of operating conditions and liquid physical properties are discussed. The factors that benefited for achieving good atomization effects are concluded.(2) Numerical calculations are performed for the atomization impinging spray. A proper nozzle-to-plate distance, with which the finer and uniform droplets near the plate can be obtained, is analyzed. By integral consideration of atomization and impingement, the ranges of operating conditions benefited for droplet deposition onto the plate are defined. The principles of adjusting the operating conditions to achieve a better result of droplet deposition onto the plate are provided(3) Based on the extensive computations, the influences of various operating conditions and liquid physical properties on atomization effects are quantified. The formula of droplet Sauter mean diameter is obtained with curve fitting technique. Another analytical model is used to predict droplet mean velocity in the downstream region of the spray. Combined the validated expressions of droplet mean diameter and velocity, the new formulae relating the Weber number and the K number to the operating parameters and liquid properties are deduced, which can be used to judge the deposition properties of droplet onto surface for various Newton liquid conveniently and effectively.(4) A comprehensive model was developed to investigate the suspension spraying for a radio frequency (RF) inductively coupled plasma torch. First, the electromagnetic field is calibrated and validated by the analytical solutions. Second, the plasma field is simulated by solving the governing equations coupled with the RF heating. Then, the suspension droplets are modeled in a Lagrangian manner, considering particles tracking and acceleration; suspension droplets collision, heating and evaporation of suspension droplets and the nano or agglomerate particles. the trajectory, velocity, temperature and size of the in-flight nano- or agglomerate particles are calculated. The effects of both operating conditions and intial inputs are investigated to find the critical factors. Finally the statistical distributions of multiple particles' size, velocity, temperature are also discussed for the cases with and without consideration of suspension droplets collision.This thesis developed a comperhensive numerical model for effervescent atomization spray, improved the former primary breakup model to apply to short wave breakup and combined the the primary breakup model with secondary breakup model to desicribe the whole atomization process. Then, the expressions of prediction the evolution of SMD along axial distance are established and the relationships between K, We and initial conditions are presented; the way to optimized the spray effects are proposed,. Besides, the thesis established a comprehensive model for the suspension spraying for a radio frequency torch. The movements and heat-mass transfer events of the suspension droplets are simulated to fill the gaps in this area.