Energy and Exergy Analysis of a Flat-Plate Solar Air Heater Artificially Roughened and Coated with a Novel Solar Selective Coating

Tarek Kh Abdelkader,Eid S Gaballah,Shaowei Wang,Qizhou Fan,Yanlin Zhang

doi:10.3390/en13040997

Tarek Kh Abdelkader, Eid S Gaballah + Show 3 more

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https://doi.org/10.3390/en13040997

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Journal: Energies	Publication Date: Feb 23, 2020
Citations: 10	License type: CC BY 4.0

Affiliation: Huazhong Agricultural University, Fayoum University

Abstract

Enhancements in heat transfer, and consequently the thermohydraulic performance of solar air heaters (SAHs), are necessary to widen and optimize their use in many applications such as solar drying or heating buildings. In this investigation, two techniques were used. A novel solar selective coating combined with broken arc ribs roughness was employed with a SAH and the evaluation of the energetic and exergetic performance was applied under four airflow working conditions compared to a smooth absorber SAH coated with the same coating. The results revealed that the Nusselt number of roughened SAH with the new coating exhibited a notable improvement compared to a smooth absorber SAH and a roughened SAH without a coating. Furthermore, the thermal efficiency increased with the increase in the air flow rate and the maximum rise was 18.8% compared to a smooth SAH. The highest increase in exergy was 51.6% with minimum values of exergy destruction and improvement potentials. In brief, the roughened SAH with 4% CNTs/CuO-black paint under the airflow rate of 0.0244 m3/s (condition C) exhibited the best energetic and exergetic performance.

Highlights

Solar air collectors (SAHs) are the main component of solar energy utilization systems that absorb incoming solar radiation, transforming it into thermal energy and conveying the energy to the collector’s fluid [1]
The performance of a solar air heater with broken arc ribs coated with a new solar selective coating compared to a smooth SAH was evaluated
The SAHs were tested under clear sky conditions for several days in October and November (2018) since each airflow rate was conducted for three different days, and one sunny day was selected to represent each airflow rate

Summary

Introduction

Solar air collectors (SAHs) are the main component of solar energy utilization systems that absorb incoming solar radiation, transforming it into thermal energy and conveying the energy to the collector’s fluid [1]. As a result of the intrinsic drawback of SAHs, which is weak thermal efficiency, the use of expanded heat transfer elements like porous and corrugated surfaces as well as finned absorbers, is a necessary solution [5]. Other techniques have been proposed to improve the heat transfer coefficient such as different shaped baffles [6], chemical surface treatments [7], reorganizing the flow directions [8], and impinging air jets [9]. Solar selective coatings are recommended to be deposited on the surface of the SAH’s absorber for their ability to enhance the SAH’s performance [10].

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