Study On The Condensation Particle Growth Tube Under Laminar Flow And The Evolution Of Particle Extinction Coefficient Under Dynamic Process

Laminar Condensation Particle Counter(LCPC)is a detection instrument for airborne sub-micron and nano-scale particles.LCPC applies the principle of heterogeneous nucleation to force the particle to be as a nucleus for condensation process,and its size will grow up in a controllable supersaturated vapor condition,until the particle can be counted by optical detection.The particle growth tube under laminar flow is the key component for LCPC,and the interaction between structure and internal parameters is studied in this thesis.The content includes the following four parts:(1)The thesis starts with the phenomenon of heterogeneous nucleation in supersaturated vapor,and describes the growth process of the particle as condensation nucleus.The characteristics of different kinds of vapor are compared,and the difference in performance and practical applications is pointed out when using different type for vapor.(2)The thesis analyzes and studies the theory of aerosol particles extinction effect which is utilized in traditional optical particle detection.A new method combining the Taylor expansion method of moment and the Mie scattering approximate method is proposed,to calculate the evolution of the overall extinction for high particle concentration aerosol,which is the foundation of correction for the particle loss in detection process.(3)Water is selected as the vapor medium in this thesis,the structure and the size of the particle growth tube is designed,and the peripheral devices are selected,to build an experimental platform which can realize an airflow sampling and a water circulation process.(4)Through the experiment,the key parameters of the internal fluid field can be obtained,which can be used in fluid simulation,to reveal the distribution of important physical parameters such as vapor supersaturation and temperature.Through this result,the performance of particle growth tube is analyzed and evaluated,to show the lower limit of the particle activate size.Through the above work,the conclusion is the basis for future improvement and optimization,and then we hope to develop a more accurate and efficient particle growth tube.