The hydrothermal analysis of a C-shaped heat exchanger during the natural convection phenomenon is carried out. The heat exchanger is filled with Al2O3-EG/W (60,40 vol%) nanofluid. The thermo-physical properties of nanofluid, thermal conductivity and dynamic viscosity, are analyzed experimentally using modern measuring devices of KD2 Pro Thermal Analyzer Brookfield LVDV-III Rheometer. The fluid flow and heat transfer of natural convection are simulated using Double-MRT lattice Boltzmann method. The numerical simulations and experimental data are coupled using developed correlations which are based on temperature and nanoparticles concentration. Impacts of different effective parameters like Rayleigh number in range of 10(3) to 10(6), nanoparticle concentrations of 0, 02, 0.4, 0.6, 0.8 and 1 vol% and four different arrangements of internal active pipes on the streamlines, isotherm patterns, local/average heat transfer rate, local/average entropy generation and heatlines are presented graphically and statistically. (C) 2018 Elsevier B.V. All rights reserved.