Research On Aerosol Filtration With Microfluidic Inertial Impactor

When a severe accident occurred in the nuclear plant,radioactive fission products are released from the fuel elements and carried into the containment,which can cause the overpressure of containment.The containment is the last barrier to prevent radioactive aerosols from entering the atmosphere,and the internal pressure must be kept within normal limits.Once the pressure exceeds the limit,the emitted aerosols will cause serious damage to the atmospheric environment.Therefore,it is important to find an effective way to filter the aerosol before it is released.At present,most of the aerosol filters used in nuclear power plants use filter media directly or indirectly.These filter media need to be replaced periodically,but it is difficult and challenge to replace them under the highly radioactive condition.Furthermore,in order to obtain a high filtration efficiency,the size of pores in those filters are small,which gives rise to high manufacturing costs and large flow resistance in the process of aerosol deposition and influence the relief of containment pressure when a nuclear accident occurs.In order to find an aerosol filtration technology that can meet the requirements of nuclear power plants in terms of overall performance,a microfluidic inertial impact aerosol filter is designed based on the principle of inertial impactor.Through theoretical analysis,modeling calculation and experimental verification,the aerosol flow characteristics inside the microfluidic inertial impactor are studied,and the impactor’s filtration performance is studied in conjunction with the impactor’s structural dimensions and operating parameters.The internal relationship between the change rule of different parameters and the filtration efficiency is mastered,which provides a reference for the design of high-demand aerosol filters for nuclear power plants.The main research contents of the paper are as follows:(1)A single-channel flat nozzle inertial impactor was designed.Through reasonable simplification,a two-dimensional model of the inertial impactor was established,and the flow field of aerosol particles in the impactor was simulated using ANSYS Fluent software.In addition,four factors that can be controlled in the design stage were selected for optimization research.Utilize the principle of orthogonal experiment to establish multiple sets of experimental schemes and conduct corresponding numerical simulations.Through the analysis of variance and range analysis of the test results,determine the degree of impact and the best level of various factors.(2)Without changing the basic structure of microfluidic inertial impactor,an inertial impactor with a circular inlet was designed.By establishing a three-dimensional calculation model of the impactor,the effects of inlet diameter,tube length,turning angle,air velocity and particle size on the filtration performance of the impactor are analyzed.Taking the filtration efficiency and pressure drop of the microfluidic inertial impactor as response indicators,the response surface method was used to study the influence degree of different structural parameters and operating parameters on the filtration performance and the interaction between various parameters.At the same time,a prediction model for predicting the performance of the impactor is also obtained.(3)A multi-channel inertial impactor with different structures was designed and manufactured,and an experimental platform was built to test the filtration performance of the inertial impactor,with which the operation mechanism,flow characteristics and filtration performance of the microfluidic inertial impactor were studied.The results show that the filtration performance of the microfluidic inertial impactor for aerosols is closely related to the structural and operational parameters of the impactor,and filtration efficiency and pressure drop are in conflict with each other,that is to say,improving the filtration efficiency of the impactor will increase its flow resistance.To obtain an impactor that meets the requirements,it is necessary to comprehensively consider the filtration efficiency and pressure drop to optimize the structure and operating parameters of the impactor.(4)A multi-channel inertial impactor model was established,and the flow field was numerically studied with Fluent.In this paper,the change process of flow field is analyzed in detail,and the simulation results are compared with the experimental data.The result shows that the simulation results of RNG κ-ε and κ-ε models are in good agreement with the experimental data.These two models can be used to simulate the filtration performance of multi-channel inertial impactors.The proceeding of the project referred in this paper provide an important reference for the theoretical research and structural optimization of inertial impactors,and have a certain guiding significance for the design and manufacture of inertial impact aerosol filters in the Filtered Containment Venting System(FCVS)in the future.