Natural convection enhancement in an eccentric horizontal cylindrical annulus using hybrid nanofluids

The problem of natural convection in an eccentric annulus between two horizontal cylinders filled with Cu-Al2O3/water hybrid nanofluids is investigated numerically in this paper. The inner cylinder wall is heated at a uniform temperature whereas the outer wall is kept isothermally cooled. The basic equations that govern the problem are formulated in the bipolar coordinates and written in terms of the vorticity-stream function equations using the dimensionless form for the bidimensional, laminar, and incompressible flow under steady-state conditions. The dimensionless equations are discretized using the finite-volume method and solved by a FORTRAN program. A numerical parametric study is performed for an annulus filled with regular water, Al2O3/water nanofluid, and Cu-Al2O3/water hybrid nanofluid for various volume fractions of nanoparticles and hybrid nanoparticles (0 phi 0.12) and Rayleigh numbers (10(3)Ra10(6)). It is found that employing a Cu-Al2O3/water hybrid nanofluid provides a better thermal and dynamic performance compared with the similar Al2O3/water nanofluid.