Design and Experimental Investigation of Thermosiphoning Heat Transfer through Nanofluids in Compound Parabolic Collectors

Abstract

The limited availability of fossil fuels, as well as its negative ecological repercussions, has prompted humanity to seek other renewable technologies. One of the obvious options is solar energy, especially for energy deficient and solar rich countries like Pakistan. Flat plate, evacuated tube, and parabolic trough collectors are among the primary solar thermal collectors being employed. However, energy saving can be further enhanced by applying the thermosiphoning concept. Therefore, in the current study, an experimental analysis of a thermosiphoning-based heat transfer mechanism with two different nanofluids (Fe₂O₃ and Al₂O₃) in a compound parabolic trough collector (CPC) is presented. Initially, a numerical analysis is performed through ANSYS to determine fluid flow under free convection at a certain temperature gradient. Afterwards, a laboratory-scale thermosiphoning experimental setup is developed under controlled conditions. Finally, the same phenomena is applied in CPC and analysis is performed under real climate conditions of Taxila, Pakistan. The highest numerical flow rate attained with Fe₂O₃ was 9.3 mL/s, according to the research. In outdoor setup, 10.78 mL/s was the highest flow rate achieved. With some variation, theoretical and analytical results were confirmed with prior studies. As a result, using nanofluids and thermosiphon to lower a pump's mechanical strain can considerably improve the efficiency of the solar thermal system.