Entropy generation due to natural convection in right-angled triangular enclosures filled with porous media with top angles 15° and 45° for various thermal boundary conditions (cases 1-4) has been studied numerically using Galerkin finite element method. Simulations are carried out for Pr = 0.025 and 1000 in the range of Darcy numbers 10 -5-10 -3. Note that, S θ,max is observed at vertex of the cavity for cases 1 and 3, near corner between left wall and bottom wall for case 2 and near lower portion of the right wall for case 4. It is found that, S ψ,max is observed near middle portions of the side walls for all cases and the location of S ψ,max mainly depends on the presence of high velocity gradients. The total entropy generation, S total, is found to be an increasing function of Da. It is observed that decrease in Be av with Da for both s is due to increase in fluid friction irreversibility. Analysis of the variation of Be av with Da for various fluids indicates that, higher Be av values are observed for Pr = 0.025 due to low frictional irreversibility. It is observed that Θ cup decreases with Da for all Pr due to decrease in thermal mixing. It is found that, the maximum heat transfer rate ( Nul or Nur) occurs for = 15° cavities compared to = 45° cavities at Da = 10 -3 in both isothermal and linear heating cases for all Pr due to larger thermal gradients at = 15°. Overall, triangular cavities with = 15° may be the optimal top angle for right angled triangular enclosure for thermal processing of all types of fluids (Pr = 0.025 and 1000) due to its high heat transfer rate ( Nul or Nur), high thermal mixing (high Θ cup) and less total entropy generation (S total) for all heating strategies (cases 1-4) especially at Da = 10 -4. © 2012 Elsevier Ltd. All rights reserved.