In automotive sector, in order to reduce the space occupied by engineradiators,the use of micro air channels with different cross-sections hasbeen intensified.In these channels both;the hydrodynamic entry-lengthandthe thermal entry-lengtharesmall enoughcompared to the total length of the channel.The flow in the channel occurs in laminar regime and it is plausible to assume itto behydro-dynamically and thermally fully developed flow.In radiators, despite that several air channels with differentcross-sectionssuch as; tetragon, triangle, hexagon, sinusoid, parabolaetc. are used, the channels with nosharp corners have advantages from manufacturing point of view and heat transfer point of view. In this study, the convective heat transfer in parabolic, elliptic, sinusoidal and triangular cross-sectioned air channels has been investigated under the condition of constant heat flux.By using appropriate transformations,thesolution domains ofthemomentum and energy equations, which are irregular for numerical solution,weretransformed to regulardomainslike rectangle or square. By conducting case studies for different aspect ratios of air channels, Nusselt number,and the relations between Darcy friction factor and Reynolds number (Poiseuille number) have been determined.The accuracy of theNusselt number and Poiseuille number wereconfirmed by comparing with the literature values given for other channels similar to parabolic channels.