The solar flat plate collector effectiveness enhancement was studied experimentally using Al2O3 /water nanofluids and with longitudinal strip inserts. The experiments were conducted in the Reynolds number range from 5000 to 13,500, longitudinal strip inserts of aspect ratios (AR) equal to 1, 1.5 and 3, volume concentrations of 0.1% and 03%. From the results, it is noticed that the Nusselt number enhancement for 0.3% volume concentration of nanofluid is 8.53% and 20.9% at Reynolds number of 5000 and 13,500, respectively compared with water data. The Nusselt number is further enhanced to 29.46% and 57.83%, as compared to water data, for 0.3% volume concentration of nanofluid with a longitudinal strip insert of aspect ratio (AR) equal to 1 at Reynolds number of 5000 and 13,500, respectively. The thermal effectiveness of plain collector is enhanced to 58% for 0.3% volume concentration of nanofluid at a Reynolds number of 13,500 and it is further enhanced to 84% for 0.3% volume concentration of nanofluid with longitudinal strip inserts of aspect ratio equal to 1 at a Reynolds number of 13,500. (C) 2018 Elsevier Ltd. All rights reserved.