Nanofluids are a potential alternative to significantly improving the performance of heat transfer applications. In this work, a numerical analysis to examine the eff ect of dispersing copper (Cu), copper oxide (CuO), and aluminum (Al2O3 ) nano-particles in pure water on the performance of a flat plate solar collector (FPSC) and a numerical model was proposed. The influence of the nanofluid type on the thermal efficiency was critically investigated and discussed. The eff ect of the mass flow rate on the performance was also analyzed and discussed. Based on correlations of the thermophysical properties of nanofluids, a sensitivity analysis was used to analyze the impact of the nanoparticles on the base fluid. The results indicate that the performance of the FPSC with Cu/water nanofluid was better than that of FPSCs using CuO/water or Al2O3 /water nanofluids. When the mass flow rate of the nanofluids was 8.0 L/min, the efficiency of the FPSC was much greater than those at the flow rates of 5.0 L/min and 2.0 L/min. Mean enhancements in thermal efficiency of 4.44％, 4.27％, and 4.21％ were observed when 2.0 L/min was applied using Cu/water, CuO/water, and Al2O3 /water nanofluids, respectively. Improvements in thermal efficiency of 2.76％, 2.53％, and 2.47％ occurred when 8.0 L/min was applied.