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Numerical Simulation of Nano-scale to Micro-scale Particle Growth in Condensation Particle Counter

Srinivasan, Ganesh
http://rave.ohiolink.edu/etdc/view?acc_num=ucin1204577130

Abstract Details

2008, MS, University of Cincinnati, Engineering : Mechanical Engineering.
Condensation particle counters are used to measure the concentration of nano-scale particulates in air or gas. A small amount of air/gas is introduced in the particle counter and is mixed with a supersaturated mixture of vapor and a non-condensable gas. Due to the supersaturated conditions, vapor condensation occurs on the particle surface. The process is continued until the particle size increases to several micrometers whereby the particles can be detected by optical techniques. The understanding of the phase change phenomena and concomitant heat/mass transport, and their accurate predictions are necessary to design a condensation particle counter. The initial particle radius is much less than the mean free path of air and vapor molecules but becomes greater than the mean free path as it grows to micro-scale. In this thesis an analytical/numerical method is developed to model the heat/mass transport process from free molecular flow (particle size << mean free path) to continuum regime (particle size >> mean free path). The governing equations for vapor and non-condensate number density and temperature are obtained by taking four moments of the Boltzmann equation with an assumed two-sided molecular velocity distribution for vapor and non-condensable gas molecules. The resulting eight Maxwell's moment equations are solved numerically using a fourth-order Runge-Kutta method and the Newton-Raphson method. The developed method is used to simulate growth of nano-scale particles by vapor condensation in a condensate particle counter. The governing equations are solved to determine the temperature and density distribution for vapor and non-condensable gas, rate of vapor condensation, and transient particle/droplet temperature and size. The method is validated by comparing simulation results for the two limiting cases of free molecular regime and continuum conditions with results available in the literature. Effects of vapor supersaturation, ambient temperature, and particle size are investigated. It was found that the particle growth rate is nearly linear with time in the free molecular regime and becomes non-linear in the continuum regime. Increases in vapor supersaturation as well as ambient temperature were found to increase the particle growth rate. For supersaturation ratios between 1.2 and 1.4, the time required for particles with initial radius between 30 to 250 nanometers to grow to 1 micron size was less than 20 milliseconds.
Milind Jog, Dr (Committee Chair)
Prem Khosla, Dr (Committee Member)
Son Sang Young, Dr (Committee Member)
92 p.
Mechanical Engineering
condensation particulate counters; condensation; droplet growth

Recommended Citations

Citations

  • Srinivasan, G. (2008). Numerical Simulation of Nano-scale to Micro-scale Particle Growth in Condensation Particle Counter [Master's thesis, University of Cincinnati]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1204577130

    APA Style (7th edition)

  • Srinivasan, Ganesh. Numerical Simulation of Nano-scale to Micro-scale Particle Growth in Condensation Particle Counter. 2008. University of Cincinnati, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ucin1204577130.

    MLA Style (8th edition)

  • Srinivasan, Ganesh. "Numerical Simulation of Nano-scale to Micro-scale Particle Growth in Condensation Particle Counter." Master's thesis, University of Cincinnati, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1204577130

    Chicago Manual of Style (17th edition)

ucin1204577130
647
© 2008, all rights reserved.
This open access ETD is published by University of Cincinnati and OhioLINK.