Mixed convection in straight and curved channels is investigated:when buoyant forces are perpendicular to the bulk flow direction. Grashof numbers are based on temperature difference range from 0 to 50 x 10(6), and Reynolds numbers are based on channel width range from 343 to 2057 which gives laminar and transitional forced flow. Four difference regimes of behavior are apparent : pure natural convection, mixed convection with strong buoyancy, mixed convection with weak buoyancy and pure forced convection. Differences in behavior between these different regimes are discussed, along with curvature influences, the effects of buoyancy on forced flow behavior, and Nusselt number correlations for the two mixed convection regimes.