Energy, exergy and environmental analysis of concentrated parabolic trough collector using alumina-water nanofluid and twisted tape insert

Abstract

Concentrating parabolic trough collector (CPTC) is used to convert energy of solar radiation into useful heat energy utilized in different thermal applications. The present article discusses the use of nanofluids and inserts in CPTC to improve its performance parameters such as collector efficiency, exergy efficiency, Nusselt number, friction factor, and performance augmentation factor (PAF). Al2O3-water nanofluid with different volume concentrations of 0.25%, 0.5%, 0.75%, and 1% was used as working fluid. The effect of simple twisted-tape insert (STI) and overlapped twisted-tape insert (OTI) were studied with the nanofluid to evaluate performance of CPTC. Nanofluid, with highest volume fraction (φ = 1%), demonstrated maximum enhancement as 5.3%, 17.4%, 70%, 230%, and 140% in collector efficiency, exergy efficiency, Nusselt number, friction factor, and PAF as compared to water as working fluid flowing through plain absorber tube. Employing STI and OTI with nanofluid (φ = 1%) represented maximum enhancement of 14.5% and 15.9% in collector efficiency, 19.9% and 20.8% in exergy efficiency, 282% and 367% in Nusselt number, 1800% and 1900% in friction factor, and 231% and 475% in PAF as compared to water flowing through bare absorber tube at a minimum flow rate. OTI with nanofluid (φ = 1%) demonstrated maximum CO2 reduction of 1.61 tons/year and maximum enviro-economical gain of 23.41 $/year.