cfd investigation of gravitational sedimentation effect on heat transfer of a nano-ferrofluid

in the present attempt, flow behavior and thermal convection of one type of nanofluids in a disc geometry was investigated using computational fluid dynamics (cfd). influence of gravity induced sedimentation also has been studied. the commercial software, fluent 6.2, has been employed to solve the governing equations. a user defined function was added to apply a uniform external magnetic field. obtained results showed that the critical value for rayleigh number is near 1708, so simulations are in good agreement with the theoretical value for critical rayleigh number. in addition, it was found that gravity causes separation of phases and sedimentation of nanoparticles, besides, increase in natural convection due to presence of gravity, leads to heat transfer enhancement. in addition, results indicate that, thermal forces are able to disrupt agglomerates when ratio of thermal energy to dipole-dipole contact energy becomes more than unity.