Abstract
Several artificial roughness (ribs) configurations have been used in flat plate solar air heaters (SAH) in recent years to improve their overall performance. In the present work, energy and exergy analyses of rectangular ribs in a triangular duct SAH for varying relative rib heights (e/D = 0.02–0.04), relative rib pitches (P/e = 5–15), and rib aspect ratios (e/w = 0.5–4) are evaluated and compared with smooth SAH. The analysis reveals that the entropy generated due to heat transfer is lower for the ribbed triangular duct compared to the smooth duct. It is also observed that the width of the rib plays a crucial role in minimizing heat losses to the environment. A maximum reduction of 43% and 62% in exergy losses to the environment and exergy losses due to heat transfer to the fluid is achieved, respectively, with a rib aspect ratio (e/w) of 4 compared to the smooth plate. It is found that in contrast to the smooth plate, ribs beneath the absorber plate effectively improves thermal and exergetic efficiency. Maximum enhancement of 36% and 17% is obtained in exergetic efficiency (ηex) and thermal efficiency (ηth), respectively, for e/w = 4, P/e = 10 and e/D = 0.04. Results also show the superiority of the ribbed triangular duct over the ribbed rectangular duct for an application requiring compact SAH with a higher flowrate.
Issue Section:
Research Papers
Keywords:
solar air heater,
triangular duct,
artificial roughness,
rectangular rib,
thermal efficiency,
entropy generation,
exergetic efficiency,
energy efficiency,
energy systems,
extended surfaces/fins,
forced convection,
heat exchangers,
heat transfer enhancement
Topics:
Ducts,
Entropy,
Exergy,
Heat transfer,
Solar energy,
Thermal efficiency,
Flat plates,
Surface roughness,
Fluids
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