Key words: Natural convection, nanoparticles, Nusselt number, Rayleigh number.

Abstract: This work deals with a numerical study on natural convection problem in a rectangular cavity, two-dimensional, differentially heated: the left vertical wall is heated to a constant temperature TH, while the right vertical wall is kept at a cold temperature TC such as (TH ? TC) filled with nanoparticles at different concentrations φ. The fluid is considered incompressible, Newtonian and obeys the Boussinesq approximation. The influence of nanofluid, on the structure of the flow and heat transfer in the cavity was examined for a Rayleigh number Ra varies between 103 ≤ Ra ≤ 106 and concentration of nanoparticles ranging from 0% ≤ φ ≤ 4% in order to examine the best average heat transfer rate through the cavity. The results show, in particular, that the increase of the volume fraction of the nanoparticles (φ) increases the average heat transfer rate.