Galerkin fem simulation of natural convection in an annular porous medium-based solar collector system

Motivated by simulating emerging hybrid designs in annular solar direct absorber collectors, a theoretical and numerical study of natural convection in an annular hybrid porous medium solar collector is presented. An aspect ratio of 2 is considered where the annular geometry is twice the depth relative to the diameter. The non-dimensional conservation equations for Newtonian absorber fluid are solved in an axisymmetric coordinate system (R, Z) using the COMSOL finite element platform, which uses a Galerkin ormulation. An optimized mesh is designed following a mesh independence test. Extensive visualization of the streamline, isotherm, and pressure contours is included over a range of Rayleigh (103 ≤ Ra ≤ 106) and Darcy number (0.0001 ≤ Da ≤ 0.1), e.g., (inverse permeability). Additionally, Nusselt number distributions at the inner cylindrical wall of the annulus are presented. Furthermore, cutthrough semi-annular contour plots are displayed. Validation with previous studies for the geometrically mapped case of axisymmetric flow is also included. The simulations establish a good foundation for future extensions to consider radiative heat transfer and other working fluids, including nanofluids and non-Newtonian fluids.