Numerical simulations of velocity and temperature fields to study the performance of a single phase microchannel cooling system with spiraling radial inflow for high heat flux applications are presented. Skin friction coefficient and Nusselt number are calculated for different microchannel heights and flow inlet angles. As the fluid moves radially inward, entraining boundary layers develop due to a rotation induced crossflow. Entrainment effects are found to enhance convective heat transfer considerably due to motion of fluid towards the heat exchange surface. The strength of this effect depends on the structure of hydrodynamic boundary layers, which is characterized by the Reynolds number and the flow inlet angle. In this work it is found that boundary layers may merge and the entrainment effect is lost when reducing the microchannel height, therefore the total heat flux may not always increase with a decrease of the flow passage area, as opposed to conventional microchannels. The swirl flow microchannel heat sink showed promising cooling characteristics for applications such as thermal management of electronics or concentrated photovoltaics.