Direct Absorption Solar Collector: An Experimental Investigation of Al2O3-H2O Nanofluid over the Flat Plate at Different Tilt Angles, and Mass-Flow Rates

Abstract

The escalating demand for solar thermal energy, coupled with the current inefficiencies in existing systems, underscores the critical need for innovative advancements in thermal storage solar collectors. The efficiency of solar collectors relies not solely on design effectiveness but also on the thermophysical properties, such as heat capacity and thermal conductivity, inherent in the working fluid. This study investigates a novel solar collector with a gross area of 0.36 m2, operating on the principle of direct absorption. Experimental investigations were done at various tilt angles (15°, 20°, and 30°) with respect to the horizontal, considering different flow rates and nanofluid settlement within the base fluids. The use of Al2O3 nanoparticles into the base fluid as water, exhibits significant positive effects on the thermophysical properties of the nanofluids, with a volume concentration of 0.003%. The efficiency of the solar collector was calculated across three mass flow rates (0.5, 1, and 1.33 L/min) at each tilt angle. Notably, the study reveals that the efficiency peaks at a 15° tilt due to an optimal flow configuration for maximum energy harvest across all three mass flow rates. Increasing the mass flow rate yields efficiency increments for all tilt angles (15°, 20°, and 30°), with 1 L/min emerging as the optimal mass-flow rate in most cases. This research not only addresses the immediate need for improved solar thermal technologies but also aligns with global sustainability goals, contributing to the IEA Net Zero Emissions initiative and supporting UN Sustainable Development Goals 7, 9, and 11. The paper also includes a critical literature review on the use of nanofluids in solar thermal collectors to improve thermo-physical properties and enhance solar efficiency. Additionally, the key findings regarding the influence and tilt angle on solar efficiency are discussed.