IRANIAN JOURNAL OF SCIENCE AND TECHNOLOGY-TRANSACTIONS OF MECHANICAL ENGINEERING

Natural convection in a trapezoidal cavity having different conductive obstacles which are portions of a full circular object and filled with different shaped nanoparticles (spherical, blade and cylindrical) was numerically investigated. The side walls of the trapezoidal cavity are kept at constant hot and cold temperatures, while the top and bottom walls are assumed to be adiabatic. The governing equations are solved with finite element method. The effects of the Rayleigh number (between 10(4) and 10(6)), inclination angle of the side walls (between 0 degrees and 20 degrees), thermal conductivity ratio (between 0.01 and 100), solid volume fraction of the nanoparticles (between 0 and 0.04) and nanoparticle shape (spherical, blade and cylindrical) on the fluid flow and heat transfer characteristics were studied in detail. It was observed that the shape of the obstacle is very effective to change the heat transfer characteristic for lower values of Rayleigh number. Thermal conductivity ratio influences the heat transfer characteristics slightly. Averaged Nusselt number increases linearly with nanoparticle volume fraction and the slope of the curves is highest for the cylindrical nanoparticle and it is not affected by the obstacle types. Averaged Nusselt number enhancements are in the range of 13 and 16% when cylindrical nanoparticles are used instead of spherical ones with different obstacle shapes for thermal conductivity ratio of 0.01 and 100