This study investigates numerically, in terms of Computational Fluid Dynamics (CFD), a Parabolic Trough Collector (PTC) system with nanofluid as the Heat Transfer Fluid (HTF). All the heat transfer mechanisms were taken into account to simulate the SEGS LS2-module PTC. The validation process showed very good agreement between the numerical results and the available test results from four typical testing conditions, with the use of Syltherm 800 liquid oil. Specifically, the maximum relative error observed for outlet temperature was 03% and 7.3% for the collector efficiency. In order to address the nanofluid modeling problem the two-phase approach was preferred (against single-phase) and validated against experimental and numerical results for a circular tube under constant wall temperature. Overall, a total of 20 different simulation cases were performed for the LS2 module, for a range of nanoparticle (Al2O3) concentrations (0%-4%), thus making it possible for a parametric evaluation on the LS2 efficiency. In addition, the temperature and velocity fields of the Syltherm 800/Al2O3 nanofluid were associated with the enhanced heat transfer occurring at higher nanoparticle concentrations. A boost up to 10% on the collector efficiency was reported for Al2O3 concentration of 4%, which is in accordance with relevant studies. (C) 2016 Elsevier Ltd. All rights reserved.