Experimental investigation of CuO nanofluid-based Direct Absorption Solar Collector for residential applications

Solar water heating systems are the most economical and large scale application of solar energy in residential buildings. In order to enhance the efficiency of these systems, Direct Absorption Solar Collector (DASC) which used nanofluids with appropriate optical and heat transfer properties as absorbing medium, has been recently proposed. In this study, a prototype of this new type of collector was built with applicability for domestic solar water heater. Different volume fractions of copper oxide nanoparticles in water and ethylene glycol mixture (70%:30% in volume) as the base fluid were prepared and their thermo-physical and optical properties were presented. The procedure of EN 12975-2 standard was used for testing the thermal performance of the collector. The tests were performed in different flowrates from 54 to 90 l/h (0.015–0.025 kg/s) and two different internal surfaces (black and reflective) of bottom wall. The efficiency of the collector with black internal surface is about 11.4% more than that of with reflective internal surface using the base fluid at 90 l/h flowrate. The collector efficiency is increased by increasing nanofluid volume fraction and flowrates. The nanofluids improved the collector efficiency by 9–17% than the base fluid. Based on the results, the performance of this new kind of collector as the main part of solar water heater appears promising, leading to considerably higher efficiencies.