The enhancement to the flow and heat transfer in a semi-circular protrusion fitted with fins. Understanding these kinds of pin fins which are used widely in industry are believed give a rich contribution to elucidation of the phenomena in normal and compact heat exchangers used in different application. It was, therefore, chosen to investigate the heat transfer and pressure drops characteristics in a channel containing semi-circular fins at both low and high Reynolds numbers. the present report deals with the numerical investigation of various aspects of single-phase convective heat transfer enhancement in a two dimensional semi-circular protrusion on fin surface at a constant heat flux (CHF) condition. By applying the conjugate heat transfer boundary conditions, numerical simulations close to the realistic working conditions were performed. Pressure, temperature and velocity profile were drawn for different inlet velocities for a protrusion arrangement, considering the flow to be laminar and turbulence. The working fluid considered here is air. Numerical study was done using Fluent software, for the same Reynolds number and under same boundary conditions by applying single protrusion of semi-circular shape on a longitudinal fin of inner tube and the results revealed that the same Nusselt number 20, results at Reynolds number of 300 with single protrusion using air as cooling fluid. The present numerical result at Reynolds number 300 is validated with the results of Kubacki S. for the same conditions and constraints. Further numerical study has been done for the optimization of gap between the two protrusions for the maximum heat transfer and results reveal that at a gap of 4L the heat transfer is maximum and both protrusions dissipates equivalent amount of heat. The present work is undertaken to evaluate the performance of the vortex generator used to enhance the heat transfer rate in a heat exchanger. These vortex generators are mounted on the circular fins which are used as inserts between the plates. For detailed investigation a circular protrusion which produces vortex are considered. This work deals with the formulation of the present problem.