目的：核用高效过滤器最难过滤颗粒的直径在0.1-0.3μm范围，效率检测要求仪器可以测量的数量浓度范围大于5个数量级。目前，钠焰法是核用高效过滤器的效率检测的基准方法，但计数法是发展趋势。本论文重点解决气溶胶的关键技术，首先确定一种计数效率检测方法：蒸发冷凝法产生亚微米级准单分散气溶胶，使用乙醇做冷凝工质的CPC测量数量浓度；然后提高钠焰法的检测精度；最后保证气溶胶到达被测过滤器时速度场和浓度场分布均匀。最终获得一套共用钠焰法和计数法的效率检测系统。方法：针对关键技术环节，首先通过分析控制方程，建立了数学物理模型，然后使用一些实验测量手段分析气溶胶参数和气流速度，SMPS测量仪用于测量气溶胶的粒度分布，CPC用于测量气溶胶的数量浓度，静电计用于测量气溶胶的总荷电量，钠焰光度计测量燃烧NaCl产生的光电流强度，热球风速仪用于测量气流速度等。通过实验结果和模拟结果比较，获得合适的数理模型和技术参数。结果：（1）在气溶胶发生技术环节，建立了“移动分区+离散法”模型，来描述DEHS蒸气均相成核、颗粒异相成核和凝结生长过程，实验证明是准确的，当异相成核完全抑制均相成核时，可以获得稳定的亚微米级准单分散气溶胶，并且确定了运行参数；（2）在气溶胶测量技术环节，使用乙醇作为冷凝工质，通过实验和数值模拟，验证了颗粒在CPC中的长大时无均相成核现象存在，证明了使用微毒的乙醇工质可以完全取代低毒的正丁醇工质，用于CPC测量；同时开发了新的钠焰光电测量仪；（3）在气溶胶输送技术环节，验证了气相使用k-ε模型、颗粒相使用FPM模型来三维描述气溶胶颗粒在效率检测管道中的运动规律是准确和快速的。结论：本论文获得了几项气溶胶关键技术：（1）蒸发冷凝法产生亚微米级准分散气溶胶过程的数理模型和技术参数；（2）乙醇工质用于CPC，可以测量0.1μm以上的气溶胶数量浓度；（3）描述管道内气粒两相流动的数理模型。通过上述关键技术研究，获得了一套钠焰法和计数法共用的效率检测系统。
Objective: The most penetrating particle size of nuclear-grade HPEA filter is of 0.1-0.3μm, and the apparatus used for testing filtration efficiency can measure more than 5 orders of magnitude range of number concentration. Currently Sodium Flame method is the primary method used for testing the filtration efficiency of nuclear-grade HEPA filter, but the counting method is the development trend. This paper focuses on how to resolve the key techniques in the aerosol field. Firstly, a counting method is developed that the submicron quasi-monodisperse aerosol is generated by evaporation-condensation method and the number concentration is measured by CPC with ethanol as the working fuild. Secondly, this study is also to increase the precision of flame photometer. Finally, it will ensure that the velocity and concentration of aerosol are uniformly distributed while it arrives at the challenged HEPA filter. As a result, one testing system is built that is not only suitable for the Sodium Flame method, but also for the counting method.Method: As for key techniques, firstly, one suitable mathematical and physical model is figured out through analyzing the control equations. Secondly, the aerosol’s parameters and flowrate are analyzed with experimental instruments, eg, the size distribution, the total number concentration, the total charges and the total light intensity of NaCl are measured by SMPS, CPC, AE and flame photometer, respectively. Finally, through comparision between the simulating result and the experimental result, the comparably proper mathematical and physical models and running parameters are obtained. Result: (1)It is proofed correct in this study that the moving grid sectional method and discrete method are designed to simulate the process of DEHS vapor homogeneous nucleation, particle heterogeneous nucleation and condensational growth in the laminar tube in the aerosol generating process, and the stable submicron quasi-monodisperse aerosol is obtained accordingly when the heterogeneous nucleation process suppresses that of the homogeneous nucleation, what’s more, the useful running parameters are determined. (2)At the measurement stage, with ethanol as the working fluid and comparing the experimental data with the simulation data, it is demonstrated that the homogeneous nucleation phenomenon doesn’t occur in the condensational laminar tube of CPC, and also further clarified that the micro toxicity ethanol can substitute low toxicity n-butanol for CPC without configuration modification is needed; In the mean time, one new higher precision sodium flame photoelectric measuring instrument is developed. (3)In the aerosol transport stage process, it is presented that with the air phase of k-εmodel and particle phase of FPM model, the 3D numerical simulation is of higher precision along with faster calculation speed for the study on the aerosol delivery in testing system. Conclusion: This paper has obtained a few key aerosol techniques: (1)one mathematical and physical model and a few running parameters are developed for generating submicron quasi-monodisperse aerosol by evaporation-condensation method. (2)The number concentration with the aersol size of above 0.1μm can be monitored by CPC with ethanol as working fluid. (3)one model is summarized for simulating aerosol transport in testing system is developed. As a summary, in this paper, one system used to test the filtration efficiency of nuclear-grade HEPA filter is developed, which not only can be applied for the improved Sodium Flame method, but also for the proposed counting method.
