凝结核粒子计数器的流场数值模拟及流量配比优化

Flow field simulation and flow ratio optimization of condensation particle counter

为推进凝结核粒子计数器(CPC)的研发并提升其检测性能,系统开展了CPC粒子生长器内的流场数值模拟和流量配比优化研究。对粒子生长器的基本结构和分析模型进行设计建立,通过Fluent软件模拟研究了粒子生长器内流场的参数分布情况,以及流量配比对饱和度等参数变化和CPC理论计数效率的影响。模拟结果表明,鞘流结构能够约束气溶胶颗粒保持在流场轴心处饱和度高的位置流动,且流量比越高,气溶胶颗粒的扩散范围越小;在一定范围内提升流量比可以增大蒸汽质量分数以及饱和度的值,降低临界直径。在最优化流量参数下,所设计粒子生长器颗粒扩散范围仅4 mm,流场内最高饱和度值可达7以上。基于数值模拟数据,自主研发了CPC测量系统,并开展了计数效率校准实验,结果表明在7~200 nm粒径范围内13个点位的校准相对误差均低于9%,符合校准规范。因此,基于数值模拟的CPC内粒子生长器结构设计及操作参数优化对CPC的研发具有指导意义。

To promote the development of condensation particle counter(CPC)and improve its detection performance,the research of flow field simulation and flow ratio optimization in CPC particle grower are carried out systematically.The basic structure and analytical model of the particle grower are designed and established.The parameter distribution in the flow field of the particle grower is investigated by Fluent software simulation.Meanwhile,the effect of the flow ratio on the variation of saturation and the theoretical counting efficiency of CPC is considered.Simulation results show that the sheath structure can restrict the aerosol particles to flow at the position with high saturation in the central axis of the flow field.The higher the flow ratio is,the smaller the diffusion range of aerosol particles is.In a reasonable range,the increasement of the flow ratio can increase the vapor mass fraction and saturation,and the critical diameter is reduced.Under the setting of optimized flow parameters,the particle diffusion range of self-designed particle grower is only 4 mm,and the maximum value of saturation can exceed 7.The self-designed CPC measurement system is designed according to the numerical simulation information,and the calibration experiment of its counting efficiency is carried out.The calibration results show that the relative errors of 13 points within the particle size range of 7~200 nm are all lower than 9%,which fit the calibration specifications well.Thus,the design of CPC structure and optimization of operational parameters based on the numerical simulation is instructive for CPC development.