INFLUENCE OF CU-WATER AND CNT-WATER NANOFLUID ON NATURAL CONVECTION HEAT TRANSFER IN A TRIANGULAR SOLAR COLLECTOR

A numerical study on natural convection heat transfer in a right triangular solar collector filled with CNT-water and Cu-water nanofluids has been conducted. The inclined wall and the bottom wall of the cavity are maintained at a relatively lower temperature (T-c), and higher temperature (T-h), respectively, whereas the vertical wall, is kept adiabatic. The governing non-dimensional partial differential equations are solved by using the Galerkin weighted residual finite element method. The Rayleigh number (Ra) and the solid volume-fraction of nanoparticles (phi) are varied in the range of 10(3) <= Ra <= 10(6), and 0 <= phi <= 0.1, respectively, to carry out the parametric simulations within the laminar region. Corresponding thermal and flow fields are presented via isotherms and streamlines. Variations of average Nusselt number as a function of Rayleigh number have been examined for different solid volume-fraction of nanoparticles. It has been found that the natural convection heat transfer becomes stronger with the increment of solid volume fraction and Rayleigh number, but the strength of circulation reduces with increasing nanoparticles' concentration at low Ra. Conduction mode dominates for lower Ra up to a certain limit of 10(4). It is also observed that when the solid volume fraction is increased from 0 to 0.1 for a particular Rayleigh number, the average Nusselt number is increased to a great extent, but surprisingly, the rate of increment is more pronounced at lower Ra. Moreover, it is seen that Cu-water nanofluid offers slightly better performance compared to CNT-water but the difference is very little, especially at lower Ra.