Effects of heat-light source on the thermal efficiency of flat plate solar collector when nanofluid is used as service fluid

The current experimental study aimed to investigate the effects of different nanofluids and heat-light sources on the thermal energy absorption of a laboratory-scale flat plate solar collector (FPSC). Water-based nanofluids containing Al2O3, SiO2, and TiO2 nanoparticles at a concentration of 0.2% were utilized as the service fluid in this study. The thermal behavior of the nanofluids in the FPSC was studied in two stages: heat absorption and heat retention periods. Both the heat absorption and retention periods were conducted for a duration of either 120 or 240 min. Distilled water acted as operating fluid circulating inside the insulated tank and the collector tubing system. Tungsten heat, halogen pencil, infra-red, and mercury vapor lamps were considered as heat-light sources. Among different heat-light sources considered, the collector utilizing a tungsten heat lamp demonstrated the highest thermal efficiency. For this lamp, the efficiencies for 120 min heat absorption were 67.37% for Al2O3, 66.21% for SiO2, 64.64% for TiO2 nanofluids, and 48.78% for base fluid. For the same lamp, during the 240 min heat absorption, these values were 44.72% for Al2O3, 43.42 for SiO2, 42.26% for TiO2 nanofluids, and 37.17% for base fluid. Aside from these, results showed that the thermal efficiency of FPSC with insulation and without insulation was 23% and 20% for 0.2% TiO2 nanofluid, respectively, when halogen pencil lamp was used. Finally, results of considering distilled water or distilled water containing 0.2%, 0.5%, and 1% SDS as service fluid indicated that the highest amount of heat transfer was related to the distilled water. Indeed, heat transfer decreased with increasing SDS content.