The microchannel heat sinks play a very important role in the functioning of the microelectronic components. In this paper, the focus is on the convective heat transfer performance of the microchannels with different diameters and configurations. The heat transfer performance is a function of surface area available for the heat transfer and the heat transfer coefficient of the heat carrying medium. It is highly desirable to understand the fluid flow and the heat transfer characteristics of a buoyancy-induced micro pump and micro heat exchanger in microfluidic and thermal systems. In this study, we experimentally investigate the fully developed natural convection in an open-ended vertical cylindrical microchannel with asymmetric wall temperature distributions. The experiments were conducted in both horizontal and vertical orientations. Results reveal that in most of the natural convection situations, the volume flow rate at the micro scale is higher than that at the macro scale. It is, therefore, concluded that the temperature jump condition induced by the effects of rarefaction and fluid-wall interaction plays an important role in slip-flow natural convection and heat transfer rates are higher than vertical configurations the evaluated experimental results are compared with available literature and graphically noted.