This article presents a numerical visualization of heat transport for forced convective heat transfer by a two-dimensional heat function formulation through a direct absorption solar collector (DASC) filled with water-copper nanofluid. The penalty finite element method is used to solve nonlinear partial differential equations, and the numerical results are presented for variations in the radiative heat flux, Prandtl number, particle diameter, and solid volume fraction of the nanoparticle. The rate of heat transfer, thermal efficiency, mean entropy generation, and Bejan number are strongly dependent on certain parameters. It is observed that the radiative heat flux variation decreases the mean heat transfer, but increases the collector efficiency and entropy generation for nanofluids more than that for pure water. According to the results obtained from this study, under similar operating conditions, DASC is found to have higher efficiency than a flat-plate solar collector (FPSC). Generally, a DASC performs better than a flat-plate collector; however, much better designed flat-plate collectors might be able to match or outperform the efficiency of a nanofluid-based DASC under certain conditions.

The problem of steady, laminar, and incompressible mixed convection flow in a horizontal lid-driven cavity is studied. In this investigation, two vertical walls of the cavity are perfectly insulated and the wavy bottom wall is considered at an identical temperature higher than the top lid. The enclosure is assumed to be filled with a Bousinessq fluid. The study includes computations for different physical parameters, such as cavity aspect ratio (AR) from 0.5 to 2, amplitude of undulating wall (A) from 0 to 0.075, and number of undulations (λ) from 0 to 3. The pressure-velocity form of Navier-Stokes and energy equations are used to represent the mass, momentum, and energy conservations of the fluid medium in the cavity. The governing equations and boundary conditions are converted to dimensionless form and solved numerically by the penalty finite element method with discretization by triangular mesh elements. Flow and heat transfer characteristics are presented in terms of streamlines, isotherms, average Nusselt number (Nu), and maximum temperature (θ _max ) of the fluid. Results show that the wavy lid-driven cavity can be considered an effective heat transfer mechanism at larger wavy surface amplitude, as well as the number of waves and cavity aspect ratio.