Numerical investigation of heterogeneous nucleation of water vapour on PM₁₀ for particulate abatement

Abstract

A heterogeneous nucleation model with inclusions of the line tension effect, the particle roughness effect, and the surface diffusion mechanism was presented. Effects of the particle roughness and the wetting agent on the heterogeneous nucleation behaviour were examined. The scaled nucleation barrier was analyzed and subsequently implications of the nucleation behaviour in the particulate abatement by vapour condensation were discussed. It was found that the effect of particle roughness on the nucleation behaviour was greatly affected by the line tension. There existed an optimal concentration of wetting agent at which the lowest nucleation barrier and critical saturation ratio could be obtained. The surface diffusion mechanism played an overwhelmingly important role in governing the embryo growth for hydrophilic particles with a diameter D p > 0.1 mm and an embryo size smaller than the critical size, otherwise the contribution of direct vapour deposition mechanism could be significant. Based on the scaled nucleation barrier, three distinct nucleation regimes, i.e. athermal heterogeneous nucleation, thermal heterogeneous-dominant nucleation, and homogeneous-dominant nucleation, have been identified. When the contact angle was large, the wetting agent might need to be added to reduce the contact angle so as to reach the athermal heterogeneous and thermal heterogeneousdominant nucleation regimes, thus achieving efficient particulate abatement at low cost. The prediction results matched reasonably with the experimental data.

Bacteria as Cloud Condensation Nuclei (CCN) in the Atmosphere

“…The simulations were performed at surface altitude (θ = 55 • ) and they reveal the strong influence of particle size and ambient temperature on bacteria activation. Increasing the particle size results in easier particle activation due to the increased surface area [18,30]. In the atmosphere, bacteria can be attached to other airborne particles or can be found as agglomerates of different bacterial cells, and consequently the mean aerodynamic diameter was observed in sizes between 2 and 4 µm, whereas single bacteria have diameters closer to 1 µm [1].…”

Modeling of particle interaction dynamics in standing wave acoustic field

“…Thus, increased research attention is being focused toward development of preconditioning technologies to enlarge PM 2.5 particles. Preconditioning technologies presently under development include acoustic agglomeration (Fan, Yang, and Kim 2013;Fan et al 2017;Hoffmann 2000;Sheng and Shen 2007;Shang et al 2018), electrical agglomeration (Chang et al 2017), magnetic agglomeration (Huang et al 2015;Zhao et al 2007), and heterogeneous condensation (Fan et al 2009a(Fan et al , 2009b(Fan et al , 2019a(Fan et al , 2019bSmith, Shaviv, and Svensmark 2016). Among these, acoustic agglomeration has attracted the greatest interest from researchers owing to its simple installation and ease of adaptation.…”

Molecular dynamics study on the surface tension of succinic acid-water nano-aerosol droplets

“…光学特性、相态和粒径等影响其环境气候和健康效应。同时，气溶胶吸湿生长机理研究 也可为蒸汽相变凝并脱除细颗粒技术的改进和相关设备的研制提供基础科学依据 [3,4] 。 当前，气溶胶吸湿特性(即稳态时粒径和环境中水蒸气过饱和度的关系)主要采用经典 Köhler 理论进行描述，该理论将颗粒表面饱和蒸气压用拉乌尔效应和开尔文效应描述， 表面张力为开尔文项的核心参数 [5] 。 对于液体表面张力测量的常规方法包括气泡压力法、吊环法和悬滴法等。近年来， 出现了针对液滴表面张力测量的振荡液滴法和原子力显微镜法，前者通过对比液滴阻尼 振荡频率的实验和理论结果获取表面张力 [6] ；后者通过基底上液滴表面探针保持力的结 果获取表面张力 [7] ， 然而， 这些方法对纳米尺度气溶胶液滴表面张力的测量均难以奏效。 在液体表面张力的理论研究方面， Dutcher 等 [8] 提出了一个半经验模型用于预测电解质溶 液及其混合物的表面张力，其中电解质溶液的摩尔浓度从近似 0 到 1。该模型被集成到 描述气溶胶相平衡研究领域广泛使用的 E-AIM 模型 (Extended Aerosol Inorganics Model) [9] 中。 随着计算机技术的发展，分子模拟方法在气液界面结构和特性的定量描述中得到应 用。Chapela 等 [10] 用蒙特卡洛方法和分子动力学方法研究了纯 L-J 分子组成的水平气液 界面的张力，对比了两种方法得出的表面张力等热力学参量，验证了分子动力学模拟用 于求解表面张力的可行性。Blokhuis 等 [11] 对 Chapela 等 [10] 表面张力计算方法进行改进， 通过增加尾部修正项，获得了与宏观表面张力值更为接近的模拟结果。Chen 等 [12] 利用 3 分子动力学方法模拟了由不同水分子模型(TIP3P, SPC, SPC/E, TIP4P, TIP5P)构成的水 平液面在温度为 275-350 K 条件下的表面张力，发现 SPC/E 模型得到的结果与实验值吻 合最好。 Wang 等 [13] 基于分子动力学方法定量描述了 NaCl 溶液由极稀到高度过饱和时的 表面张力。Sun 等 [14] 研究了包含不同种类卤化钠(NaF，NaCl，NaBr，NaI)纳米液滴 的表面张力。Liu 等 [15] 研究了由不同种类离子和水分子构成团簇的表面张力及其对离子 诱导成核自由能的影响。 表面活性成分是大气气溶胶颗粒中一类常见且具有特殊性质的成分，其来源包括化 石燃料燃烧、植物排放和大气中的气-粒反应等 [16] 。由于表面活性成分同时包含疏水基 和亲水基，其趋向于分布于液滴表面，同时影响表面张力和体相内组分活度。近期，课 题组基于分子动力学方法研究了包含常见表面活性成分气溶胶吸湿生长后的结构和界 面微观特性 [17] 。本文在课题组前期研究的基础上，对含表面活性物质(丁二酸，SA) 气溶胶颗粒吸湿形成稳定液滴后的表面张力进行模拟计算，重点探究温度、粒径和丁二 酸浓度对表面张力的影响机制。 模拟过程中使用 Nosé -Hoover 热浴控制模拟体系的温度 [18,19] 。本文的分子模拟工作基于 LAMMPS (Large-scale Atomic/Molecular Massively Parallel Simulator) 开源程序 [20] 开展。 在模拟体系中， 丁二酸采用 OPLSAA 力场参数 [21] ， 水分子选用 SPC/E 水分子模型， 该水分子模型已被成功应用于包含无机盐或有机物液滴中水分的蒸发和凝结过程研究 [22,23] 。为了减少边界条件对模拟体系的影响，三个方向均采用周期性边界条件。体系中…”