外加液滴条件下固体细颗粒声凝并特性

Acoustic agglomeration characteristics of fine solid particles under effect of additional droplets

外加声场激励下固体细颗粒的声凝并在燃烧污染物超低排放中具有应用潜力,添加大粒径液滴有望提高细颗粒声凝并效果.本文从颗粒运动、碰撞、凝并与反弹的动力学过程出发,基于直接模拟蒙特卡罗方法,建立气相中液滴与固体颗粒共存的气-液-固三相体系的声凝并模型,对外加液滴条件下固体细颗粒声凝并的过程和效果开展数值模拟.将模拟结果与实验相对比,验证模型可靠性.在此基础上,探究外加液滴条件下细颗粒声凝并动力学行为,考察外加液滴直径和数目浓度对细颗粒声凝并效果的影响规律.结果表明,外加液滴条件下,固体细颗粒迅速与大粒径液滴凝并,形成液-固混合相颗粒,细颗粒凝并效率显著提升.外加液滴直径和数目浓度是影响细颗粒声凝并的重要因素,随着直径的增大或数目浓度的提高,细颗粒凝并效率增大,而增幅趋于减小.研究结果可为复杂颗粒系统凝并模型的建立提供理论基础,并可为燃烧源细颗粒超低排放提供方法指导.

Agglomeration of fine solid particles under the excitation of external acoustic field has potential applications in the field of ultra-low emission of combustion pollutants.It is expected that the performance of particle agglomeration can be improved by adding large sized liquid droplets.According to the dynamic process of acoustic agglomeration,including the particle motion,collision,agglomeration and rebound,a model of acoustic agglomeration for gas-liquid-solid three phase system with coexistence of liquid droplets and solid particles in gas phase is developed by using the direct simulation Monte Carlo(DSMC)method.Using this model,numerical simulations are performed to investigate the process and performance of acoustic agglomeration of fine solid particles under the effect of additional droplets.The numerical results are compared with experimental data,and the proposed model is validated.On this basis,the dynamic behaviors of acoustic agglomeration of fine particles in the case with additional droplets are explored.Furthermore,the influences of the diameter and number concentration of additional droplets on the performance of acoustic agglomeration of fine particles are examined.The results show that rapid agglomeration among the solid fine particles and additional droplets can be achieved by adding droplets into the acoustic field,yielding large sized liquid-solid mixed-phase particles.In this process,the agglomeration efficiency of fine particles increases significantly.It is also found that the diameter and number concentration of additional droplets are important factors that affect the acoustic agglomeration of fine particles.The agglomeration efficiency of fine particles rises,while the magnitude of increase tends to decrease with the droplet diameter and number concentration increasing.The research results can provide both theoretical basis for modeling the agglomeration process of complex particle systems and method guidance for achieving the ultra-low emission of fine particles from combustion sources.