Abstract
Flat-plate solar collectors are one of the cleanest and most efficient heating systems available. Studies on the presence of covalently functionalized graphene (Gr) suspended in distilled water as operating fluids inside an indoor flat-plate solar collector (FPSC) were experimentally and theoretically performed. These examinations were conducted under different testing conditions namely 0.025 wt.%, 0.05 wt.%, 0.075 wt.%, and 0.1 wt.%, 0.5, 1, and 1.5 kg/min, 30, 40, and 50 °C, and 500, 750, and 1000 W/m2. Various techniques were used to characterize the functionalized nanofluids’ stability and morphological properties namely UV/Vis spectrophotometry, EDX analysis with a Scanning Electron Microscope (SEM), zeta potential, and nanoparticle size. The results showed that the collected heat improved as the percentage of GrNPs and the fluid mass flow rates increased, although it decreased as the reduced temperature coefficient increased, whereas the maximum increase in collector efficiency at higher concentration was 13% and 12.5% compared with distilled water at 0.025 kg/s. Finally, a new correlation was developed for the base fluid and nanofluids’ thermal efficiency as a function of dropped temperature parameter and weight concentration with 2.758% and 4.232% maximum deviations.
Highlights
Flat-plate solar collectors (FPSCs) are the most basic and studied systems for solarpowered hot water technologies in domestic water
Many advancements and continuous improvements have been undertaken to reduce the size of FPSCs and increase their performance
The maximum absorption peak indicated at ~264 nm is possibly due to the π→π* transition of C=C bonding for the graphene [35,36]. Following this peak and within the spectrum of wavelengths revealed in Figure 5, a reduction in absorbance was noticed in all tests at a minimum peak of ~974 nm [37]
Summary
Flat-plate solar collectors (FPSCs) are the most basic and studied systems for solarpowered hot water technologies in domestic water. The usage of FPSC is widespread for low-and medium-heat applications. A black surface absorber, riser, and header pipes with coolant, a glazing cover, coolant, and thermal insulation are the essential components of flat plate collectors. The investigations of Hottel and Woertz in 1942 [1] and Hottel and Whiller in 1958 [2], were among the first studies on FPSC. In 1955, Tabor [3] used selected black surfaces to enhance the heat collected performance. His optical absorption studies showed an optical concentration capability to generate high-pressure steam.
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