Natural convection heat transfer of SiO 2 /water nanofluid inside a inclined enclosure in the presence of electric field was studied experimentally. The test cell is a rectangular enclosure whose dimensions width × length × height (mm) is 60 × 60 × 135, respectively. It was made of two vertical copper plates as hot and cold walls and the other sides were made of acrylic. . The Rayleigh number was varied in the range of 9.5 × 10 6 -1.5 × 10 8 . The effects of different concentration of nanofluids, the presence of electric field and variable tilt angle on natural heat transfer coefficient and Nusselt number were examined. The results indicate that using nanofluid for concentrations less than 0.01% increases the natural convection heat transfer coefficient Compared with water. The maximum increase of heat transfer coefficient was observed at 0.01% concentration of nanofluid and about 5%. Adding nanoparticles with volume fraction more than 0.1% to the base fluid deteriorate the natural convection heat transfer. The tilt angle of the enclosure can be a control parameter for heat transfer. It was varied from 0? ( horizontal cavity heated from below ) to 120?. The Nusselt number of base fluid and nanofluids decrease with increasing inclination angle of cavity for all Rayleigh numbers. So that the maximum and minimum natural convection heat transfer coefficients of base fluid and nanofluid were occurred respectively at 0? and 120?. It is found that increasing the concentration of nanofluids decreases the effect of inclination angle of enclosure and changing tilt angle of cavity has no effect on natural convection heat transfer of high concentration nanofluid. The effect of nanofluid concentration on Nusselt number decreased with increasing tilt angle of cavity. Maximum value of natural convection heat transfer occur at 0.01% of nanofluid inside the horizontal cavity heated from below (?=0?). Also it is found that the electric field has no effect on natural convection heat transfer coefficient. Keywords : natural convection heat transfer, nanofluid, inclined enclosure
