Parabolic trough collectors (PTCs) can provide a wide range of applications from domestic hot water production to energy demands of the industry. Heat transfer improvement of PTCs can reduce the system size and the cost. The use of corrugated tubes as a heat transfer improvement method is essential in industrial applications. Therefore, this study aim is to investigate the impacts of the pitch to diameter ratio and the roughness height to diameter ratio of corrugated tubes on the thermal efficiency and exergy efficiency of PTC. To this end, nine different helically corrugated tubes were analyzed experimentally under the ASHRAE standard 93 (2010). The Reynolds number changes in the range of 5000-10000. The results indicated that the reduction in the pitch ratio and the increase in the rib-height ratio result in increasing the thermal and exergy efficiencies of the PTC. The maximum efficiency of 65.8% can be achieved for the PTC with an absorber tube (P/D-H =0.12 and e/D-H = 0.06). The friction factor increases by about 35.5%-84.8%. Based on the experimental results, due to the high thermal potentials, it is recommended to use a helically corrugated tube in PTC for thermal applications. (C) 2020 Elsevier Ltd. All rights reserved.