Numerical predictions of three-dimensional flow and heat transfer are presented for rotating two-pass smooth channels with three aspect ratios (AR = 1:1; 1:2; 1:4). Detailed predictions of mean Velocity, mean temperature and Nusselt number for two Reynolds numbers (Re = 10,000 and 100,000) were carried out. A total of fifteen calculations have been performed with various combinations of rotation number, Reynolds number, and coolant-to-wall density ratio. The rotation number and inlet coolant-to-wall density ratio varied from 0.0 to 0.28 and from 0.13 to 0.40, respectively. The focus of this study is to investigate the effect of the channel aspect ratio, the Reynolds number, and the coolant-to-wall density ratio on the nature of the flow and heat transfer. A multi-block Reynolds-averaged Navier-Stokes (RANS) method was employed in conjunction with a near-wall second-moment turbulence closure. In the present method, the convective transport equations for momentum, energy, and turbulence quantities are solved in curvilinear, body-fitted coordinates using the finite-analytic method. © 2004 Elsevier Ltd. All rights reserved.