© Author(s) 2010. This work is distributed under the Creative Commons Attribution 3.0 License. Atmospheric Measurement Techniques

Abstract. In this work, we modelled activation and growth of silver particles in the water-operated TSI model 3785 wa-ter condensation particle counter (WCPC). Our objective was to investigate theoretically how various effects influence the counting efficiency of this CPC. Coupled fluid and particle dynamic processes were modelled with the computational fluid dynamics (CFD) code FLUENT in combination with the Fine Particle Model (FPM) to obtain profiles of tempera-ture, vapour concentration, nucleation rate, and particle size. We found that the counting efficiency of the TSI 3785 for small particles might be affected by the presence of larger particles. Moreover, homogeneous nucleation processes can significantly influence counting efficiency.