Effect of various multiple strip inserts and nanofluids on the thermal–hydraulic performances of parabolic trough collectors

The thermal performance of the parabolic trough collectors can be improved by the use of swirl generator inserts added to the solar receiver. These inserts help improve the energy capture from the internal receiver walls and reduce the external wall thermal losses. If nanoparticles are added to the heat transfer fluid of the solar receiver tube, then this also increases the output working fluid temperature thereby reducing the outer wall's temperature. The main objective of the current study is to assess the effect of various straight strip shapes with and without nanofluids. Four different strip arrangements were considered; large conical-shape strips, small conical-shape strips, rectangular-shape strips and elliptical-shape strips. All of these configurations were then also tested in 6% of SiO₂ nanoparticles mixed in Therminol® VP-1 (TO) forming the nanofluid. Results showed that the straight large conical strips lead to the maximum enhancement in the Nusselt number (up to 57.49% for the pure base fluid and up to 62.53% for the nanofluid). The thermal efficiency improvement for this optimal configuration with nanofluid was found to be 15.41% with a thermal loss reduction of around 26%. A similar trend was found for the thermal exergy efficiency which showed an improvement of 15.32% for this optimal configuration with the use of nanofluid.