平面射流场中纳米颗粒的成核与凝并

Nucleation and coagulation of nanoparticles in a planar jet

采用大涡模拟和直接积分矩方法,数值模拟了在Reynolds数为8300的平面射流中,水蒸气(相对湿度φ=70%)和硫酸蒸气(质量分数为5×10-6)二元体系中纳米颗粒的成核与凝并,详细分析了颗粒数密度、体积密度和平均粒径的分布.计算结果表明.射流场混合动量厚度的增长和实验结果一致;射流场的拟序结构导致了涡核中心处硫酸蒸气浓度的明显减小,而纳米颗粒数密度则明显增加;拟序结构的出现导致颗粒碰撞概率增大,提高了颗粒凝并效率;在颗粒数密度较大的涡核中心,颗粒成核作用增强,从而加速了颗粒的凝并.

The nucleation and coagulation of nanoparticles in the binary system of water vapor （ relative humidity 70% ） and sulfuric acid vapor （5 × 10-6） were detailedly studied by performing numerical simulation in a planar jet （Re = 8300）. The large eddy simulation was utilized to calculate the flow field,and the particle field is obtained by using the direct quadrature method of moment to solve the particle general dynamic equation. The distributions of particle number concentration,volume concentration and average diameter were discussed. The result shows that the growth of the calculated momentum thickness is consistent with the previous experimental data. The interface of the jet will roll up and generate the coherent vortices which will lead to an obvious decrease of the specie concentration of sulfuric acid vapor and increase of number concentration of nanoparticles in the vortex core. The appearance of the coherent vortices increases the possibility of particle collision and enhances the particle coagulation. The nanoparticle nucleation is enhanced in the vortex core where high particle number concentration will accelerate the particle coagulation.