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Review

Thermo-Hydraulic Performance of Solar Air Collectors with Artificially Roughened Absorbers: A Comparative Review of Semi-Empirical Models

Faculdade de Engenharias e Tecnologias, Universidade Lusíada Norte, 4760-108 Vila Nova de Famalicão, Portugal
Energies 2020, 13(14), 3536; https://doi.org/10.3390/en13143536
Received: 18 June 2020 / Revised: 2 July 2020 / Accepted: 4 July 2020 / Published: 9 July 2020
(This article belongs to the Special Issue Optimization of Solar Thermal Systems for Buildings)
Due to the poor thermal characteristics of the air, the absorber roughness of solar air collectors is commonly artificially increased in order to enhance the heat transfer to the air stream. However, this is also accompanied by an undesirable increase in the pumping power due to increased friction losses. As a result, several authors have experimentally investigated several ways of maximizing the heat transfer while minimizing the friction losses of different absorbers, resulting in the development of semi-empirical functions relating the Nusselt number (a measure of heat transfer) and the friction factor (a measure of friction losses) to the Reynolds number and the roughness parameters considered for each absorber. The present paper reviews, considering the publications from the last ten years, these semi-empirical functions. Moreover, the optimum roughness parameters and operating conditions of the absorbers were estimated by finding the maximum values of two performance parameters (the thermo-hydraulic efficiency and effectiveness), calculated using the semi-empirical functions, in order to classify the absorbers in terms of their energy characteristics. This approach proves to be a rather effective way of optimizing the roughness characteristics of solar air collector absorbers. It is also concluded that, considering the range of absorbers analyzed here, generally, multiple V-shaped ribs with gaps provide the most effective roughness geometry. View Full-Text
Keywords: solar air heating; absorber; artificial roughness; optimization solar air heating; absorber; artificial roughness; optimization
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MDPI and ACS Style

Araújo, A. Thermo-Hydraulic Performance of Solar Air Collectors with Artificially Roughened Absorbers: A Comparative Review of Semi-Empirical Models. Energies 2020, 13, 3536. https://doi.org/10.3390/en13143536

AMA Style

Araújo A. Thermo-Hydraulic Performance of Solar Air Collectors with Artificially Roughened Absorbers: A Comparative Review of Semi-Empirical Models. Energies. 2020; 13(14):3536. https://doi.org/10.3390/en13143536

Chicago/Turabian Style

Araújo, António. 2020. "Thermo-Hydraulic Performance of Solar Air Collectors with Artificially Roughened Absorbers: A Comparative Review of Semi-Empirical Models" Energies 13, no. 14: 3536. https://doi.org/10.3390/en13143536

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