Thermal and economic analysis of a liquid flat plate solar collector system using green carbon nanofluids / Harish Kumar Loganathan

Harish Kumar , Loganathan (2022) Thermal and economic analysis of a liquid flat plate solar collector system using green carbon nanofluids / Harish Kumar Loganathan. PhD thesis, Universiti Malaya.

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Abstract

The present investigation deals with the effects of using cost-effective, eco-friendly, non-corrosive, covalent functionalized carbon-based nanofluids to evaluate the energetic, exergetic, and economic performance of a Liquid flat-plate solar collector (LFPSC) forced circulation system. Two types of green nanostructures namely, functionalized carbon nanostructures and hybrid carbon nanostructures were synthesized using the facile, eco-friendly, free radical technique. Different natural extracts such as gallic acid, parsley leaves, hibiscus leaves, and neem leaves are utilized in the preparation of green carbon nanofluids. The green nanofluids prepared are gallic acid graphene nanoplatelets (GGNPs), parsley graphene nanoplatelets (PGNPs), parsley multi-walled carbon nanotubes (PMWCNTs), GGNPs decorated with silver nanoparticles (GGNP-Ag), PGNPs decorated with copper oxide nanoparticles (PGNP-CuO), and PMWCNTs decorated with silver nanoparticles (PMWCNTS-Ag). The functionalization and decoration of carbon structures were confirmed using characterization techniques namely FESEM, EDX, TEM, XRD, FTIR, TGA. Green carbon nanofluids with base fluid distilled water were prepared with different weight concentrations of 0.025 %,0.05 % & 0.1 %. The green nanofluids prepared showed long-term colloidal stability compared to conventional nanofluids. Thermo-physical properties investigated showed increased thermal conductivity, viscosity, and density, while a decrease in specific heat capacity. For varying concentrations, fluid flow rates of 0.8,1.2, and 1.5 L/min, heat flux intensities of 600, 800, and 1000 W/m2, and inlet temperature ranging from 303 to 323 K were considered for the conduction of experiments. Improvement in energy and exergy efficiency was achieved using green carbon nanofluids than base fluid. Thermal efficiency surges with increment in flow rate and heat flux intensities, meanwhile it decreases for increment in inlet temperature. Maximum augmentation in thermal efficiency of about 30.2 % was achieved for PMWCNT nanofluid followed by 28.4 % for PMWCNT-Ag, 24.31 % for PGNP, 24 % for GGNP, 23.56 % for PGNP-CuO, and 22.24 % for GGNP-Ag at 0.1 wt. % and 1.5 L/min, respectively than the base fluid. Analysis of exergetic performance revealed that exergy efficiency reduces with a rise in mass flow rate meanwhile enhanced with an increase in nanofluid concentration. Exergy efficiency was maximum for 0.1% PMWCNT concentration and flow rate of 0.8 L/min. The maximum increase in friction factor values is approximately 11.61 % for 0.1 % PGNP-CuO nanofluids, followed by 10.9 %, 9.2 %,8 %,7.78 %,6.97 %, respectively for 0.1 % GGNP-Ag, PMWCNT-Ag, GGNP, PGNP and PMWCNT nanofluids than distilled water. Relative pumping power slightly increases with the increment of green carbon nanofluid concentration but is quite close to that of the base fluid. Performance index greater than one is obtained with higher values achieved at an increase in the weight concentration of green nanoparticles in the aqueous medium. Economic analysis showcased a maximum reduction of 28.89 % in the size of the collector area using 0.1 % PMWCNT nanofluid instead of distilled water. The average payback period for LFPSC using green carbon nanofluids was 6.40 % lesser than that of using distilled water. The enhanced properties of green carbon nanoparticles make them a favorable candidate in enhancing the performance of different thermal systems.

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