Analysis of entropy generation during natural convection in porous right-angled triangular cavities with various thermal boundary conditions

Abstract

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, Sθ,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, Sψ,max is observed near middle portions of the side walls for all cases and the location of Sψ,max mainly depends on the presence of high velocity gradients. The total entropy generation, Stotal, is found to be an increasing function of Da. It is observed that decrease in Beav with Da for both φs is due to increase in fluid friction irreversibility. Analysis of the variation of Beav with Da for various fluids indicates that, higher Beav values are observed for Pr=0.025 due to low frictional irreversibility. It is observed that Θcup 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 φ=15° cavities compared to φ=45° cavities at Da=10−3 in both isothermal and linear heating cases for all Pr due to larger thermal gradients at φ=15°. Overall, triangular cavities with φ=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 Θcup) and less total entropy generation (Stotal) for all heating strategies (cases 1–4) especially at Da=10−4.