Natural Convection and Conduction in Massive Wall Solar Collectors With Honeycomb and Without Vents

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Abstract
Steady heat transfer by natural convection and conduction is numerically studied in passive solar collector systems consisting of a massive wall with honeycomb structure and without vents. The boundary conditions are constant heat flux on the wall and fins, isothermal on the vertical bounding sides, and adiabatic on the horizontal sides. The governing parameters are the Rayleigh number (106 ≤ Ra ≤ 5 × 109), the aspect ratio of the enclosures (0.4 ≤ A = H′/L′ ≤ 1.4), the dimensionless lengths of the fins (0 ≤ B = l′/Ll′ ≤ 1), the aspect ratio of the microcavities (0.05 ≤ C = h′/L′ ≤ 1), the wall thickness (0.008 ≤ w = w′/L′ ≤ 0.033). The fin thickness (e = e′/H′ = 0.06) and the Prandtl number (Pr = 0.72) were constant, and the conductivity ratio was variable (10−4 ≤ kr ≤ 5 × 106). Local and average Nusselt numbers along the long sides are calculated as a function of various parameters. Streamlines and isotherms are produced. Effects of various parameters on the heat transfer are examined and heat transfer correlations are derived.

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