A computational analysis has been performed in a horizontal channel with an open cavity filled with hybrid nanofluid of Al2O3 - Cu-water having an adiabatic square obstacle inside. The bottom wall of the cavity is taken as hot while all the rest walls of the channel and cavity are adiabatic except the left end of the channel which is taken as cold. Three different vertical locations of the obstacle are considered. The governing partial differentials equations are solved via Galerkin finite element method in space and the Crank-Nicolson in time. Newton method is utilized to cope with discretized nonlinear systems of equations and the Gaussian elimination method has been applied to solve the associated linear subproblems in each nonlinear iteration. The emerging parameters are Richardson number (0.01 <= Ri <= 20), nanoparticle volume fraction (0.0 <= phi <= 0.04), (1 <= Re <= 200) and Hartmann number (0 <= Ha <= 100). Calculations of the streamlines, isotherms, average Nusselt number and entropy generation will be the main focus of interest in this study. (C) 2017 Elsevier Ltd. All rights reserved.