Experimental study with analytical validation of energy parameters in parabolic trough collector with twisted tape insert

Thermo-hydraulic performance evaluation of parabolic trough collector is important while introducing heat transfer augmentation techniques to it. In the present outdoor experimental study, the role of twisted tape is justified in laminar flow-based parabolic trough collector. For the Re range of 544-1742 and solar beam radiation of 400-750 W/m², the use of twisted tape (twist ratios: 5.2, 4.1, and 2.7) resulted in maximum instantaneous efficiency of 22.3%, 29.5%, and 40%, respectively, against 19.1% with plain receiver. The effect of pressure drop rise on system performance due to twisted tape is found to be insignificant as effective thermo-hydraulic efficiency recorded are 21.8%, 29.3%, and 39.7%, respectively, with maximum uncertainty involved of 1.01%. In view of the importance of system performance evaluation over a wide range of operating parameters and limitation of outdoor experiments, an analytical model has been developed which followed the similar trend. The model takes into account various operating conditions, viz. laminar, twisted tape-based laminar and turbulent flow condition as well as air-in-annulus and evacuated receiver cases. Using the model (laminar region) in both plain and twisted tape cases, the maximum percentage deviation in the prediction of exit fluid temperature (in °C) and effective thermo-hydraulic efficiency are 1.6 and 13.3, respectively. Further, for a turbulent case, the maximum percentage deviation in exit temperature (in °C) noticed is 2.9. Hence, the developed analytical model is having a good agreement with the experimental outcomes.