Modeling study is conducted to reveal the heat transfer and flow features of the thermal plasma reactor with a counter-flow gas injection and used for nano-particle synthesis. The modeling results show that a variety of parameters, such as the temperature and flow rate of the carrier gas, the operation conditions of the plasma torch, the distance between the plasma torch exit and the carrier-gas injector exit, the swirling of the plasma jet or the carrier gas, etc., can all affect appreciably the temperature and flow fields and the locations of the stagnation layers formed in the plasma reactor. An appropriate combination of the operation parameters of the reactor is thus required in order to obtain a suitable stagnation layer for the synthesis of nano-scale particles. (C) 2008 Elsevier Ltd. All rights reserved.