Mapping the Performance of a Small Mixing-type Condensation Particle Counter

Abstract. The performance of a small mixing-type condensation particle counter (sMCPC) was numerically evaluated. The modeling calculated the fields of turbulent flow and temperature, and species transport in the particle channel of sMCPC, and the growth of particles included the effects of Kelvin, non-continuum and latent heat. Upon the validated, the model was applied to investigate the effects of temperature difference (ΔT=T_s−T_c, where T_c and T_s are the temperature setting for working fluid saturation and sampled aerosol cooling, respectively), total flow rate (Q_g), and vapor fraction (f) on the working-fluid-governed supersaturation and particle activation in the sMCPC. It is found that the supersaturation ratio is increased, and the critical activation diameter (D_p,50) is lowered by increasing ΔT; the excessive increase of Q_g reduces the supersaturation ratio and shifts the ratio peak towards the downstream of carrier flow; both the supersaturation ratio and the D_p,50-slope are increased by increasing f. Under specific thermal and flow conditions, minimum activation diameters obtained in the cases with working fluids of ethylene glycol (EG), diethylene glycol (DEG), and dimethyl phthalate (DMP) is less than that in the case with n-butanol (B). Because of the particle growth after the activation, final sizes of particles exiting the particle growth tube are in micrometers in the case with n-butanol (B), and ~700 nm in case with EG; in contrast, final particle sizes in cases with DEG and DMP generally remain below the detection limit of typical optical particle counters (OPCs), i.e., ~0.3 μm.