Experimental study on cylindrical and flat plate solar collectors’ thermal efficiency comparison

Abstract

This research examines the energy absorption efficiency of a cylindrical solar collector (CSC), and two flat plate solar collectors (FPSC). One of the FPSCs has larger plate area but same volume with other collectors to study effects of the surface area exposed to solar radiation. The solar collectors’ service fluid was TiO2 with 0.25% and 1% mass concentrations. The service fluid was static inside the solar collectors while pure water flowed as the operating fluid through the tubing system located inside the collectors and storage tank. Thermal efficiency tests were conducted in 120 and 240 min heat absorption, and 180 and 240 min heat retention durations. By increasing the concentration of nanofluid, the heat absorption efficiency of the collectors rose. Plus, the FPSC with a smaller area exposed to radiation had the highest heat absorption efficiency. The solar collector depth plays an important role. Furthermore, the 120-min absorption experiment yielded a higher efficiency than that of 240-min absorption. When using nanofluids with a mass concentration of 0.25%, thermal efficiency of 49.61%, 58.00%, and 34.23% were obtained. Finally, for nanofluid with a mass concentration of 1%, thermal efficiencies of 54.86%, 63.67%, and 39.89% were recorded for three collectors.