Abstract View
Optimizing the Activation Efficiency of Sub-3 nm Particles in a Laminar Flow Condensation Particle Counter by Model Simulation
WEIXING HAO, Mark R. Stolzenburg, Michel Attoui, Jiaoshi Zhang, Yang Wang, Missouri University of Science and Technology
Abstract Number: 108
Working Group: Instrumentation and Methods
Abstract
The measurement of airborne particles with sizes below 3 nm is critical, as it helps the understanding of atmospheric nucleation and elucidates important particle synthesis mechanisms in the gas phase. Condensation particle counters (CPC) have been widely used to measure the concentration of aerosols. However, it is challenging for the CPC to measure particles below 3 nm due to the insufficient activation of these particles via vapor condensation. Methods have been proposed to increase the saturation ratio of the condensing vapor to promote the detection efficiency of sub-3 nm particles in the CPC. Different working fluids also make a considerable impact on particle detection. Given the various types of parameters and the wide range of values these parameters can take, modeling studies are needed in searching for the optimal operating conditions of a CPC.
In this work, we simulated the sub-3 nm particle activation and growth in a laminar flow CPC using COMSOL Multiphysics, which has advantages of simulating complex flow conditions and interfacing with post-processing software such as MATLAB. Our simulation incorporates the influence of temperature-dependent fluid properties on particle activation and the impact of latent heat and non-continuum effects on droplet growth. The results were compared against the analytical Graetz model [1], and demonstrated excellent agreement (within 0.7%) between these two simulation methods. Our COMSOL simulations show that glycerine, diethylene glycol, ethylene glycol, 2-aminoethanol, and dimethyl phthalate are the best five working fluids achieving the smallest particle size activated among 45 commonly used solvents. We also discussed the effect of CPC operating conditions, such as the condenser geometry and flow conditions, on particle activation for optimizing the performance of the CPC in detecting sub-3 nm particles.
[1] Stolzenburg, M. R., & McMurry, P. H. (1991). Aerosol Sci. Technol., 14(1), 48-65.