The evolution of particle size distribution (PSD) of fine polydisperse particles at high number concentrations (>10(5) cm(-3)) was simulated through a combined model employing direct quadrature method of moments (DQMOM) with heat and mass transfer equations. The PSD was assumed to retain log-normal distribution during the heterogeneous condensation process. The model was first verified by exact solution and experimental data prior to investigating the influence of initial conditions on final PSD under an octadecane-nitrogen atmosphere. Low particle number concentrations and high vapor concentrations were beneficial to shift the PSD to larger particles having a narrower distribution. Additionally, vapor depletion has more influence on the final PSD than the heat release parameter for a number concentration of 10(6) cm(-3). This study may assist the design process of a gas-solid separating cyclone, to eliminate dust from high-temperature volatiles by pyrolysis of solid fuels. (C) 2017 Chinese Society of Particuology and Institute of Process Engineering, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.