Experimental performance enhancement of a flat plate solar collector using straight and twisted flow inserts

The thermal performance of a flat plate solar collector (FPSC) is limited minimum due to higher heat loss of the collector and poor heat exchange with the heat transfer fluid. The current study investigates the effect of single-slit twisted tape (TT), double-slit TT, and double-slit straight tape passive-insert devices on enhancing the heat transfer of the FPSC at a constant water flow of 0.025 kg/s. Double-slit inserts have a higher heat transfer area and reduced hydraulic diameter than conventional single-slit TT inserts. The double-slit TT insert creates more fluid mixing and turbulence in the flow than a single-slit TT. The convective heat transfer coefficient for double-slit TT, single-slit TT, and the double-slit straight insert is 47.7%, 26.9%, and 8.7% higher than FPSC with the plain absorber. Double-slit TT inserts are observed with improved energy and exergy efficiency by 23.9% and 46.2% compared to conventional collectors without a flow insert. The average energy efficiency of FPSC without inserts is 48.2%, whereas the double-slit TT is 66.5%. The pressure drop is higher for the collector with inserts than for the collector without inserts, which leads to a little more pump power. Thus, passive inserts help to augment heat transfer in the FPSC.