Evacuated U-tube solar collector (EUSC) using Al2O3/Pure Water (PW) as working fluid was investigated numerically in this research paper. The collector efficiency of the EUSC was analyzed for different operating conditions. Al2O3 nanoparticles suspended in the pure water (PW) with different nanoparticle volume concentrations and shapes were used as collector fluid. Four different nanoparticle volume concentrations (1.0, 2.0, 3.0 and 4.0 vol%) and three different nanoparticle shapes (blade, brick and platelet) were used for formation of nanofluid. Calculations were also performed with three different mass flow rates (0.01, 0.015 and 0.025 kg/s). The effect of volume concentration and shape of nano -particle on the collector efficiency of a EUSC was analyzed in detail. The highest collector efficiency was obtained at 67.1% for 4.0 vol% Al2O3/PW nanofluid with bricks nanoparticle shape which is 19.1% higher than PW as the working fluid in the system. (C) 2020 Elsevier Ltd. All rights reserved.