Although heterogeneous condensation on fine particles is one of the most promising precondition technologies for particles abatement which has been proved by many works, little direct data were reported on the process of particles enlargement by vapor condensation. A direct measurement of enlarged particle size distribution in a lab scale growth tube by water vapor condensation is presented. Four parameters that affect the performance of the particle enlargement at high particle number by heterogeneous condensation were identified: supersaturation, particle size, residence time and particle wettability. The results show that particle enlargement exponentially increases with the increase of supersaturation. The particle size has a negative impact on particle growth ratio. The residence time is in favor of the particle enlargement which depends on the supersaturation level. Additionally, the residence time extension would weaken the vapor depletion on particle enlargement caused by particle number increase. Particle wettability may lead to different processes of particle enlargement. This work deeply revealed the process of vapor condensation on particles at high concentration by direct measurement. (C) 2016 Elsevier B.V. All rights reserved.