Properties, heat transfer, energy efficiency and environmental emissions analysis of flat plate solar collector using nanodiamond nanofluids

The collector efficiency, heat transfer, energy, and environmental emissions of water -based nanodiamond (ND) nanofluids circulate in flat plate solar collector (FPSC) has been analyzed experimentally. The analysis was performed at 0.2%, 0.4%, 0.6%, 0.8% and 1.0% particle concentrations, the stability and thermo-physical properties were also analyzed. The thermal conductivity and viscosity enhancements are 22.86% and 79.16% at particle loading of 1.0% against water data at 60 °C. The water and 1.0 vol% of ND/water nanofluids in collector shows efficiencies of 53% and 74%, respectively, which leads to 39.62% enhancement. The collector area was decreased to 28.66% with the use of 1.0 vol% of nanofluid against water data. The collector weight is decreased to 35.81 kg, at 1.0% particle loading, whereas the collector with water weighed 50 kg. The embodied energy of 1.0 vol% of nanofluid is decreased to 1039.51 MJ, whereas, the collector with water its embodied energy is 1451.4 MJ. The CO₂ emissions were noticed as 249.98 kg by using 1.0 vol% of nanofluid in FPSC. Additionally, the Nusselt number and heat transfer is augmented to 32.31% and 52.33% at 1.0% vol% with a friction factor penalty of 1.26-times at a Reynolds number of 12,766 against water data. The obtained data is validated with literature and the general form of regression equations was developed in order to evaluate the Nusselt number and friction factor.