Numerical Simulation of Free Convection in a Porous Annulus of Rhombic Cross Section

Numerical solutions are presented for laminar natural convection heat transfer in a fluid saturated porous enclosure between two isothermal concentric cylinders of rhombic cross sections. Simulations are conducted for four values of Raleigh number (Ra = 104, 105, 106, and 107), three values of Darcy number (Da = 10-1, 10-3, and 10-5), and four values of enclosure gap (Eg = 0.875, 0.75, 0.5, and 0.25). The porosity and Prandtl number are assigned the values of 0.6 and 0.7, respectively. The results are reported in terms of streamlines, isotherms, and average Nusselt number values. The Bow strength and convection heat transfer increase with an increase in Ra, Da, and/or Eg. At low Eg values, the flow in the enclosure is weak and convection heat transfer is low even though the total heat transfer is higher than at higher Eg values due to an increase in conduction heat transfer. Furthermore, predictions indicate the presence of a critical Ra number below which conduction is the dominant heat transfer mode. Convection starts affecting the total heat transfer at Ra values higher than the critical one. The critical Ra decreases with increasing Da, and increases with de creasing Eg.