A numerical study has been carried out to investigate the natural convection and entropy generation for different nanofluids within an inclined half-annulus heated from above. The conservation equations in cylindrical coordinates are solved using an in-house FORTRAN code based on the finite volume method coupled with multigrid acceleration. Water-based nanofluid containing various types of nanoparticles (Au, Ag, Cu and CuO) are used to examine the fluid flow and potential heat transfer enhancement in the annulus. The effective thermal conductivity and viscosity of nanofluids are calculated using the Maxwell-Garnetts (MG) and Brinkman models, respectively. The results demonstrate clearly that the average entropy generation due to heat transfer () is strengthened by increasing Phi and Ra. Furthermore, for small inclination angles gamma = 0 degrees and 45 (