Thermal performance analysis of flat-plate solar collector by using carbon and metal based nanofluids / Naveed Akram

Naveed , Akram (2021) Thermal performance analysis of flat-plate solar collector by using carbon and metal based nanofluids / Naveed Akram. PhD thesis, Universiti Malaya.

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Abstract

Thermal performance analysis of flat-plate solar collector by using carbon and metal based nanofluids were carried out in this study. Different nanomaterials such as, graphene nanoplatelets (GNPs) with SSAs of 750 m2/g, iron nanoparticles (Fe3O4) (< 9 nm), zinc oxide (ZnO) (< 50 nm), and silicon dioxide (SiO2) (10-20 nm) based aqueous nanofluids were synthesized at the weight concentrations range of 0.025% to 0.2%. Thermodynamic properties and colloidal stability of the nanofluids were thoroughly investigated. The overall performance of FPSC was analyzed using commercial ANSYS fluent 16.2 and was validated experimentally. Experiments were performed following ASHRAE indoor standard; where the inlet temperatures range of 30 - 50 ᵒC; flow rates of 0.8, 1.2 and 1.6 kg/min; and heat flux intensities of 597, 775 and 988 W/m2 were maintained. In this investigation the nanofluids were synthesized by probe sonication method. The maximum colloidal stability of nanofluid was obtained at 60 min ultrasonication time for the graphene nanoplatelets. Non-covalent functionalization with surfactants enhanced stability but created unnecessary foam. The undesired phenomena were avoided by covalent functionalization of the suspensions such as, clove-treated GNPs (CGNPs) and polyethylene glycol-treated Fe3O4. Successful functionalization was later confirmed through different characterization methods. Present investigation results revealed that the success of suspension stability was dependent on nanomaterial and weight concentrations, in the present case it was observed the suspension weight concentration of 0.9543 for PEG- Fe3O4, at 0.1wt.% nanofluid concentration. Thermophysical properties of the synthesized nanofluids were enhanced. The temperature was directly proportional to the thermal conductivity and indirectly proportional to the viscosity, density, and specific heat of the nanofluids. The noticeable increase in thermal conductivity was up to 25.68% at 0.1wt.% CGNPs. The measured thermal conductivity of CGNPs showed good agreement with the model of Lu-Li. The maximum increment in viscosity of nanofluid was 24.05% for SiO2, followed by 22.4% and 12% for PEG- Fe3O4 and CGNPs. The measured viscosity is well-matched with the Batchelor and Einstein model with a maximum deviation of 6.1%. The deviation in measured density is up to 0.08% higher and well-matched with Pak & Cho equation, while the specific heat deviation reduced up to 1.54% and showed good agreement with Xuan & Roetzel equation. The efficiency of FPSC is directly proportional to the heat flux intensity and flow rate and inversely proportional to the inlet fluid temperature. As the concentration of nanoparticles increased, the experimental values of AP and TW were decreased about 8.07% and 8.23%, respectively, in comparison with the water data, while efficiency was increased up to 18.2% at 0.1 wt.% CGNPs. Experimental results of efficiency, AP, and TW for water were well matched with the ANSYS Fluent results with the highest differences of 3.22%, 2.21%, and 2.48%, respectively. On the other hand, for CGNPs nanofluid, the maximum differences were 8.20%, 2.70%, and 1.88% respectively. The performance index was higher than one for all the nanofluids and increased up to 1.142 for 0.1wt.% CGNPs nanofluid. All the nanofluids have higher positive effectiveness effects than the negative pressure drops effects. Consequently, the investigated nanofluids can be used to enhance the thermal efficiency of FPSCs and at 0.1wt.% the CGNPs nanofluid provided the highest performance which could be considered superior to others.

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