Modeling And Numerical Simulation Of Fine Particles Complex Coagulation Under The Effect Of Swirling Atomization

Fine particles from coal combustion and automobile exhaust emissions have become the main source of PM2.5 in the air,which seriously pollute atmospheric environment and endanger human health.The numerical particle size distributions of particles related to coal or heavy fuel oil combustion are mainly concentrated at submicron level.However,the conventional particle filtering devices are far less efficient in removing the fine particles,especially those in the range of 0.1 to 2?m.In fact,highly efficient removal with conventional particle filtering devices can be achieved if the particles are first enlarged by means of a coagulation technique.Turbulent coagulation,seed particles combined with acoustic coagulation and heterogeneous condensation are the research focus of fine particle removal.On the basis of a large number of literature researches,the mathematical models,of complex coagulation of fine particles under the effect of swirling atomization,were established.According to the established mathematical models,the coagulation of fine particles with size of 0.4~10.2?m was studied by FLUENT16.2 of CFD software.The coagulation of fine particles under the effect of those three coagulation techniques was respectively simulated by coupling population balance model(PBM)and Eulerian multiphase model,via introduction of the corresponding coagulation kernel function and the condensation growth rate function by UDF.The results show that the method of turbulent coagulation is uncomplicated and easy to combine with other coagulation techniques;while its coagulation efficiency is less than 2% under the assumed conditions,which is poor efficiency.The acoustic coagulation efficiency of fine particles can be further promoted by adding seed particles,which can be increased by 11.96% or more;while it is necessary to take high energy consumption to obtain higher coagulation efficiency.The number concentration percentage of fine particles with a particle size of less than or equal to 1?m can be decreased markedly by heterogeneous condensation,which can be reduced from the initial 32.77% to 1% or below.Combining the characteristics of three coagulation technologies above,a complex coagulation device under the effect of swirling atomization was designed.In order to study the coagulation of fine particles in the complex coagulation device,the stream field and particles moving trajectories were simulated using discrete particle model(DPM).The coagulation efficiency of fine particles was further simulated by the use of PBM.Results show that the swirling atomization has good swirling and mixing effects that benefit for the collision and coagulation of fine particles.The fine particles,existing simultaneously turbulence,seed particles combined with acoustic wave,heterogeneous condensation and the mutual coupling among them in the complex coagulation,can be further coagulated under the interaction of the three coagulation mechanisms above.Extending residence time is helpful to promote the coagulation of fine particles that can be coagulated within hundreds of milliseconds in the complex coagulation device.With increasing the amount of atomization vapor,the fine particles that smaller than the peak particle size can be further coagulated,and the total coagulation efficiency of fine particles is also promoted accordingly.The above research methods and conclusions provide a new way for the efficient removal of fine particles.