Vapor condensation on nanoparticles in the mixer of a particle size magnifier Sergey P. Fisenko a , Wei-Ning Wang b , Manabu Shimada b , Kikuo Okuyama b, * a A.V.Luikov Heat and Mass Transfer Institute of National Academy of Sciences, Minsk, Belarus b Department of Chemical Engineering, Graduate School of Engineering, Hiroshima University, Higashi Hiroshima 739-8527, Japan Received 23 January 2006; received in revised form 16 October 2006 Available online 28 December 2006 Abstract The vapor condensation on nanoparticles in a supersaturated gaseous mixture is considered. Supersaturation was created by mixing two flows with different temperatures in a cylindrical mixer at atmospheric pressure. The conditions for mixing were chosen such that the homogeneous nucleation of vapor did not mask the growth of heterogeneous droplets with nanoparticles inside. A mathematical model of the growth of heterogeneous droplets was developed at one-dimensional description of the mixer. Five parameters that affect the per- formance of the particles size magnifier were identified: temperature of the saturator and the flow with nanoparticles, the number density and initial radius of the nanoparticles, and ratio of flow rates. The results of the simulation are compared with our experimental data. Ó 2006 Elsevier Ltd. All rights reserved. Keywords: Supersaturation; Kelvin’s effect; Heterogeneous droplet; Depletion; Mixing of flows; Droplets growth 0. Introduction The development of nanotechnology has led to an important problem of capturing nanoparticles from a gas flow. Different variants of the laminar flow diffusion cham- ber can be used for this purpose [1–3], but there is a sim- pler, cheaper and faster devise in the form of a particle size magnifier (PSM) [4–6]. To create a supersaturated medium, the hydrodynamic mixing of flows at different temperatures is used at this devise. The flow, which has rel- atively low temperature, keeps nanoparticles. This paper describes some simulations for ethylene gly- col as the vapor, and nitrogen as the carrier gas because numerous experimental data have been reported for this vapor [5], some of these findings have been repeated during our previous research on the subject. It is important to cre- ate a not very high supersaturation in the mixer of the PSM so that the homogeneous nucleation of ethylene glycol does not contribute. The physical properties of ethylene glycol are taken from reference [7]. The term counting efficiency, introduced in [5], is the ratio of the number density of het- erogeneous droplets, measured by an optical counter to the number density, measured by another device, using a differ- ent physical principle [5]. The aim of this paper is to provide further insights into PSM performance using simulation methods. The paper is organized as follows: Section 1 gives models for describing PSM parameters after mixing. A mathematical model for the growth of heterogeneous droplets with nanoparticles inside is considered in Section 2. A one-dimensional model was developed for the parameters of the gaseous mixture. The results of the simulation and comparisons with our experimental data are presented in Section 3. Our results and comparison with experimental data are summarized in the final section. 1. Parameters of mixing in PSM A schematic diagram of the PSM mixer is presented in Fig. 1; details of the design can be found elsewhere [4–6]. The length of the mixer is about 2 cm with much smaller 0017-9310/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.ijheatmasstransfer.2006.10.046 * Corresponding author. Tel.: +81 82 424 7716; fax: +81 82 424 7850. E-mail address: okuyama@hiroshima-u.ac.jp (K. Okuyama). www.elsevier.com/locate/ijhmt International Journal of Heat and Mass Transfer 50 (2007) 2333–2338