Thermal and Hydraulic Performance Comparison of Carbon Based and Metal Based Nano fluids in Flat Plate Solar Collector: A CFD Analysis

Abstract

The constant rise in global temperature and the need to reduce fossil fuel consumption has made renewable energy sources desirable, especially solar energy systems. Flat plate solar collector (FPSC) is one of the most established solar energy technologies for lower to medium heat applications. FPSC has a wide range of implications because of their beneficiary of simple structure and low maintenance although the low thermal efficiency of the conventional system hinders their further development. The utilization of nanofluid as the heat transfer fluid in FPSC has been a popular trend for the last decades and significant improvements in the performance using this technique have been observed. Due to their better thermo-physical properties, carbon-based nanofluid possesses greater prospects compared to metal-based nanofluid. However, this subject matter has not been explored further yet. This study develops a CFD model to assess the performance of a metal-based based nanofluid (Al2O3/water) and two carbon-based nanofluids (SWCNT/water and MWCNT/water) at volume concentrations up to 1% in a simple FPSC. Based on thermal-hydraulic properties, a detailed comparison among these three nanofluids is made. The observation was, that, with the elevation of Reynolds number (Re) and volume concentrations the outlet temperature decreases and among the nanofluids Al2O3/water showed the lowest reduction. The types of nanofluids do not influence the friction factor. It was noticed that the friction factor decreases with the increase of Re while higher volume concentration necessitates greater pumping power. SWCNT/water nanofluid showed the best results in terms of heat transfer coefficient and Nusselt number followed by Al2O3/water and MWCNT/water. For enhancing both the Re and volume concentration the heat transfer coefficient is boosted. But for the Nu, the values rose with the higher Re while it deteriorated with the increasing volume concentration. The highest Stanton number was achieved for greater volume concentration and smaller Re. In the case of the thermal-hydraulic performance parameter (THPP) the values increased with higher volume concentrations although the Re had a negligible impact on it. The analysis indicates the SWCNT/water is the best performing nanofluid but requires a higher pumping power. This study concludes that carbon-based nanofluid outperforms metal-based nanofluid at both inlet temperatures of 303K and 313K. These findings from the study will be beneficial in future design of efficient solar thermal applications.