Analysis of natural convection via entropy generation approach in porous rhombic enclosures for various thermal aspect ratios

Abstract

Analysis of ‘entropy generation’ is an important strategy to build, optimize and operate the heat exchange systems within their maximum operating efficiency. Porous rhombic cavities with various inclination angles, φ and various thermal aspect ratios, A, have been considered for the numerical investigation of thermal processing of various fluids (Prandtl number, Pr=0.015 and 1000) in the range of Darcy number (Da=10−3–10) due to its extensive energy related applications. The effect of A and φ for various governing parameters during convection are discussed in detail via heat transfer irreversibility (Sθ) and fluid friction irreversibility, Sψ. At lower A, the entropy generation in the cavity is dominated by both Sθ and Sψ for all φs irrespective of Da and Pr. As A increases, Sθ as well as Sψ decreases for all φs which in turn decreases Stotal with A irrespective of Da and Pr. The total entropy generation (Stotal) is found to be lower for φ=30° and higher for φ=75° for all Pr and Da. Analysis of variations of Beav with A for higher Da (Da=10) indicates that, entropy generation is highly fluid friction dominant irrespective of φ and A. Lesser entropy generation (Stotal) with larger heat transfer rate (Nub¯) and reasonable heat transfer rate (Nub¯) occurs for Pr=0.015 and Pr=1000, respectively at φ=30° cavities with all A irrespective of Da. Current work attempts to analyze energy efficient thermal convection strategies and role of thermal aspect ratio within porous rhombic enclosures based on entropy generation minimization vs heat transfer rates for various fluids.