Analysis of energy management via entropy generation approach during natural convection in porous rhombic enclosures

Analysis of ‘entropy generation’ is an important strategy to optimize the natural convection process in order to achieve efficient heat transfer within the system. Rhombic enclosures of various inclination angles ( φ = 30 ° , 45° and 75°) filled with porous media and bounded by adiabatic top wall, cold side walls, isothermally (case 1) and non-isothermally (case 2) heated bottom wall have been considered for the analysis of thermal processing of various fluids ( Pr =0.015, 0.7, 7.2 and 1000) in the range of Darcy number ( Da =10 −5 – 10 −3 ). At Da =10 −5 , the total entropy generation, S total , is found to be significantly high for φ = 30 ° and low for φ = 75 ° and is dominated by heat transfer irreversibility ( S θ ) for all Pr in case 1 whereas the distributions of S total for φ = 45 ° , 75° and 90° closely follow the distributions of φ = 30 ° for all Pr in case 2. Cup mixing temperature ( Θ cup ) is higher for φ = 75 ° and 90° whereas overall heat transfer rate, Nu ¯ , is higher for φ = 30 ° compared to other φ s in both heating cases except at high Pr ( 0.7 − 1000 ) fluids at Da =10 −5 . On increase of Da to 10 − 3 , fluid friction irreversibility, S ψ also increases for all φ s irrespective of Pr in both cases. Increase in S total with Da is small for lower φ ( φ = 30 ° ) due to insignificant S ψ of S total and large for higher φ ( φ = 75 ° ) due to significant S ψ of S total at Da ≥ 10 − 4 irrespective of Pr in both cases. Also, Θ cup slightly decreases at Da ≥ 10 − 4 and further, that reaches a constant value at higher Da as well as S total in both cases irrespective of φ for all Pr except Pr =0.015. Maximum Nu ¯ occurs for φ = 30 ° cavities at Da =10 −3 for all Pr in case 1 due to less available energy loss corresponding to less S ψ . Current work attempts to analyze energy efficient thermal convection strategies within porous rhombic enclosures based on entropy generation minimization vs enhanced thermal mixing or heat transfer rates for various fluids in porous media.