Numerical Study of Natural Convection of Al2O3-Water Nanofluid with Variable Properties in a Cavity

Heat transfer enhancement of Al2O3-water nanofluid with variable properties in a square cavity is investigated by solving the boundary layer equation and the Boussinesq-approximation form of the boundary layer equation. The governing equations are solved using the finite volume method and the SIMPLER algorithm. Temperature difference between the hot and cold walls of the cavity is considered to be 50°C, and the results are presented for Rayleigh numbers from 103 to105 and volume fraction of the nanoparticles from 0.0 to 0.09. The results show that the average Nusselt number and the maximum absolute value of the stream function for the case with variable density are greater than the corresponding value for the constant density case. Moreover, for the variable density case, the maximum heat transfer enhancement for the nanofluid occurs at Ra=103. However for φ=0.09, the average Nusselt number of the nanofluid for Ra=104 and 105 are lower than that of the base fluid. For φ=0.01, the maximum relative enhancement of the Nusselt number for Ra=103, Ra=104, and 105 are %26, %24 and %23, respectively.