The effects of coolants on the flow and heat transfer characteristics in a non-rotating and rotating two-pass rectangular channel with 45-deg angled rib turbulators are numerically investigated using the CFD software ANSYS-CFX. The three-dimensional Reynolds-Averaged Navier-Stokes (BANS) solution with SST turbulence model is applied in this paper. Four kinds of coolants, such as air, steam, mist/air and mist/steam, are used to analyze the effects of coolant types on the heat transfer performance in the channel at six different Reynolds number flow conditions. The channel averaged Nusselt number for air-only are numerically studied and the results are in good agreement with the experimental data. The internal flow pattern and heat transfer characteristics in the channel with air-only are conducted at two kinds of temperature difference. The results indicate that the 39 K temperature difference provides a slightly better heat transfer performance than that of the 60 K temperature difference. In addition, the obtained results show that the mist/steam gives the best heat transfer enhancement and thermal performance in the channel. The detailed flow pattern and Nusselt number distribution for four coolants are also illustrated and discussed. (C) 2015 Elsevier Ltd. All rights reserved.