Thermal-hydraulic performance and entropy generation analysis of a parabolic trough receiver with conical strip inserts

This paper presents a numerical study on the thermal-hydraulic and thermodynamic performance of a parabolic trough receiver with conical strip inserts. The effects of geometric parameters including central angle, hollow diameter, and pitch ratio on the performances are determined. The mass flow rate is found to vary in the range of 0.57-11.40 kg/s, with the corresponding Reynolds number ranging from 5000 to 791,000, which depends on the fluid inlet temperature. In the present study, four fluid inlet temperatures (400, 500, 600 and 650 K) are applied, and it is found that the heat transfer is effectively enhanced by the conical strip inserts, with the Nusselt number being enhanced 45-203%. Consequently, the temperature of the absorber tube and the heat loss are apparently reduced and the maximum reduction in heat loss is 82.1%. However, considerable increase in pressure loss penalty is also caused by the inserts, with the friction factor being 6.17-17.44 times that of the smooth parabolic trough receiver. Thus, the overall thermal-hydraulic performance (performance evaluation criteria) is ranged in 0.70-1.33, and the thermal efficiency is enhanced by 0.02-5.04%. In addition, Entropy and exergy analysis is carried out and it is found that for every given value of geometric parameters and fluid inlet temperature, there is a Reynolds number or mass flow rate below which the entropy generation rate is lower than that of the smooth parabolic trough receiver. The maximum reduction in entropy generation rate achieved in this study is 74.2% and the maximum enhancement in the exergetic efficiency is approximately 5.7%.