Experimental investigation on a solar parabolic trough receiver tube enhanced by toroidal rings

The experimental investigation with the incorporation of toroidal rings in an absorber tube of a lab-scale solar parabolic trough collector is carried out in the present study. Five different cases of the absorber tube including the reference smooth absorber tube and the absorber incorporated with 2, 4, 6 and 8 mm thick toroidal rings are investigated. The influence of performance parameters like thermal efficiency, heat loss, thermal enhancement index and so on with different absorber tube configurations are evaluated, compared and illustrated to determine the best case. The outcomes indicate that the absorber tube with 6 and 8 mm thick toroidal rings are the best cases, with the 8 mm case exhibiting a higher exergy efficiency in the range of 38.57%-24.64%. The thermal efficiency for the best absorber cases is found to be 69.43% and 70.34% with the pressure drop being 1.67 and 0.93 kPa, respectively. Also, the cost of heat gain produced with the efficient absorber case is seen to be (sic) 3.43/kWh (US$ 0.045/kWh and euro 0.040/kWh), which is nearly 15.51% lower than the reference case. Hence, the incorporation of toroidal rings could be effectively utilized in a large-scale solar thermal system for improved thermal performance.