In this paper, the potential for improved thermal performance of a high concentration ratio parabolic trough solar energy system working with high thermal conductivity single-walled carbon nanotubes (SWCNTs) and Therminol®VP-1 nanofluid is numerically investigated. In the numerical analysis, the practical heat flux profiles expected for parabolic trough receivers were obtained using Monte-Carlo ray tracing and coupled with a computational fluid dynamics tool using user defined functions to investigate the thermal performance of the parabolic trough solar energy system. A parabolic trough system with a concentration ratio of 113 was considered in this study and heat transfer fluid inlet temperatures between 400 K and 650 K were used. The volume fraction of SWCNTs in the base fluid was in the range 0% to 2.5% and the flow rates used were in the range 0.82 to 69.41 m3/h. Results show improvements in the convective heat transfer performance and receiver thermal efficiency as well as a considerable reduction of the receiver thermal losses with increasing volume fractions. The heat transfer performance increases up to 64% while the thermal efficiency increases by about 4.4%. Higher increments are observed at low flow rates and inlet temperatures. The receiver thermodynamic performance also increases significantly with the use of nanofluids. Entropy generation rates reduce by about 30% for the range of parameters considered.
Analysis of heat transfer performance of the absorber tube with convergent-divergent structure for parabolic trough collector
