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

Abstract

<jats:p>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.</jats:p>

Applications of Metaheuristic Algorithms in Solar Air Heater Optimization: A Review of Recent Trends and Future Prospects

“…The collector's thermohydraulic performance was popularized by Webb and Eckert [80]. Thus, the thermohydraulic performance of a coarse SAH is expressed as follows [79][80][81][82][83][84][85]:…”

“…This article presented heat exchange and friction parameters of distinctly roughened geometries in artificially roughened SAHs. By 2020, a new study by Araújo [82] considered recent publications of the last ten years, using semiempirical investigations. The study generally concluded that the multiple Vshaped ribbed gap absorbers provided the most optimal roughened configuration.…”

Exergy Optimization of a Solar Collector in Flat Plate Shape Equipped with Elliptical Pipes Filled with Turbulent Nanofluid Flow: A Study for Thermal Management

“…Said et al [19] carried out an energetic and exergetic assessment of an FPSC filled with an aqueous aluminum oxide NF. In recent years, new studies have been conducted in similar fields [20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35]. Although the usage of NFs for the increased efficiency of FPSCs has been assessed, there is no study investigating the impacts of using elliptical tubes and aqueous, multiwalled carbon nanotube (MWCNT) NF-based heat sink solar collectors on the efficiency of exergy of solar collectors.…”