基于Monte Carlo方法的PM2.5在声场中的动态过程及高效凝并研究

PM2.5 (Fine particles)suspended in the atmosphere do great harm to environment and human health. Because of their fine sizes, it is difficult for the present dust removal devices to capture them from the gas stream economically and effectively.Therefore PM2.5 emission control has become a tough problem to solve around globe. Acoustic field can be used to promote relative motion, collision and finally agglomeration of PM2.5, leading the fine particles to shift to larger ones. The larger particles after agglomeration can then be removed by the tranditional dust removal devices.Acousic agglomeration is a significant technical route to control the emission of PM2.5. However, because the dynamic process of PM2.5 subjected to an acoustic field is not yet fully understood, and because the effective agglomeration method is not yet developed, the acoustic agglomeration of PM2.5 is still in the range of fundamental research. This has been a big obstacle to development of practical PM2.5 removal technology. Numerical simulation is an effective way to explore the underlying mechanisms and dynamic disciplines in studing the micro-scale systems and complex processes. This project is to establish the PM2.5 dynamic model in the acoustic field, to investigate the motion of PM2.5 and the interaction mechanisms between the particles, to visually simulate the dynamic process of PM2.5 under the effect of acoustic field based on Monte Carlo Method, and to seek out the method for promoting effective acoustic agglomeration of PM2.5. The research results can offer theoretical basis and methodological guidance for development of efficient PM2.5 removal technology with low cost.

悬浮在空气中的PM2.5对环境和人体健康危害严重。由于PM2.5粒径微小，现有除尘装置难以经济、高效地将其清除，使得PM2.5的排放控制成为世界难题。利用外加声场对PM2.5产生作用，促使其发生相对运动、碰撞接触，进而凝并为粒径较大的颗粒，以便于常规除尘器将其清除，是控制PM2.5排放的重要技术途径。然而，由于PM2.5在声场中的动态过程尚未被充分认识，PM2.5的高效凝并方法仍未形成,使得声凝并仍处于基础性和探索性研究阶段，严重阻碍着PM2.5排放控制技术的发展。数值模拟是揭示微尺度体系和复杂过程的内在机理和动态规律的有效途径。本项目将构建PM2.5在声场中的动力学模型，探索PM2.5在声场中的运动特性和相互作用机理；基于Monte Carlo方法可视化模拟PM2.5在声场中凝并的动态过程；寻求促进PM2.5高效凝并的方法，以期为PM2.5的低成本、高效脱除提供理论基础和方法指导。

本项目针对PM2.5 在声场中的动态过程及高效凝并方法开展研究，通过理论分析和数值模拟方法，结合文献中的实验结果，研究了PM2.5在声场中的运动、相互作用和凝并的动态过程，揭示了PM2.5的声凝并机理，获得了声场中PM2.5高效凝并的方法。以单颗粒为研究对象，根据声波引发PM2.5运动的关键要点，建立综合考虑非稳定力、漂移力的更精准的颗粒动力学模型，获得了颗粒的夹带和漂移特性，以及颗粒运动特性的关键控制因素，为揭示颗粒运动机理提供了理论依据。解析颗粒的存在对声场的影响，建立了声场中PM2.5颗粒对的相互作用模型，数值模拟了声场中PM2.5颗粒对运动直至碰撞的过程，获得了颗粒粒径、颗粒间距、声场强度、声场频率对碰撞时间的影响规律，揭示了实验难以获得的超细颗粒相互作用动态过程。基于求解颗粒碰撞的直接模拟Monte Carlo方法，从颗粒动力学方程出发，建立PM2.5声凝并模型，模拟了PM2.5的声凝并过程和效果，验证了数值模拟的有效性。利用基于Monte Carlo方法的PM2.5声凝并数值模拟平台，开展PM2.5声凝并过程和外加颗粒、蒸汽相变对PM2.5声凝并过程影响的数值实验，提出了“外加颗粒+声场”、“蒸汽相变+声场”联合作用促进PM2.5凝并增长的合理优化方案，为发展PM2.5 的低成本、高效脱除技术提供理论基础和方法指导。