Efficient design of an artificially roughened solar air heater with semicylindrical side walls: CFD and exergy analysis

Nidhul, Kottayat and Yadav, Ajay Kumar and Anish, S and Arunachala, U C (2020) Efficient design of an artificially roughened solar air heater with semicylindrical side walls: CFD and exergy analysis. Solar Energy, 207. pp. 289-304. ISSN 0038-092X

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Abstract

Solar air heater (SAH) with semi-cylindrical sidewalls and W-baffles is analyzed for energy and exergy efficiency in the turbulent flow regime. Computational fluid dynamics (CFD) analysis is carried out for a fixed baffle inclination (β) and varying the relative baffle height (Rh = e/D) and relative baffle pitch (Rp = P/D) in the range 0.046–0.115 and 0.46–1.15, respectively. For Reynolds number (5000 < Re < 17,500), the numerical methodology is substantiated using experimental and theoretical correlations obtained from the literature. Smaller vortices near the sharp corners are removed by rounding the sharp edges, allowing the flow of fluid from inside and horizontal walls of the duct towards the semi-cylindrical sidewalls. This increases the overall turbulent kinetic energy. A peak augmentation of 3.24 and 4.03 times is obtained for Nusselt number (Nu) and friction factor (f), respectively, in contrast to conventional SAH. With a maximum enhancement of 127% in the effectiveness parameter relative to smooth SAH, this novel SAH design is evidently energy efficient. Based on CFD results, new correlations are developed in terms of Rh and Rp, which predicts the values with an absolute deviation of 4% and 7.4%, respectively. With lower exergy destruction, maximum enhancement in thermal and exergetic efficiency is obtained as 40.7% and 95.4%, respectively, for the proposed SAH relative to conventional SAH. Upon comparison with ribbed rectangular duct SAH configurations, the present design with semi-cylindrical side walls outperforms at all flow Re.

Item Type: Article
Uncontrolled Keywords: Artificial roughness Semi-cylindrical sidewalls Secondary flow Thermo-hydraulic performance Exergetic efficiency, exergy destruction
Subjects: Engineering > MIT Manipal > Mechanical and Manufacturing
Depositing User: MIT Library
Date Deposited: 06 Oct 2020 10:40
Last Modified: 06 Oct 2020 10:40
URI: http://eprints.manipal.edu/id/eprint/155814

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