Int. J. Appl. Comput. Math DOI 10.1007/s40819-017-0400-y ORIGINAL PAPER MHD Natural Convection Flow of CuO/Water Nanofluid in a Differentially Heated Hexagonal Enclosure with a Tilted Square Block Mohammad Mokaddes Ali 1 · Md. Abdul Alim 2 · Rowsanara Akhter 3 · Syed Sabbir Ahmed 4 © Springer (India) Private Ltd. 2017 Abstract A numerical investigation has been performed to analyze the effect of mag- netohydrodynamic natural convection flow in a differentially heated hexagonal enclosure having a tilted square block filled with CuO/water nanofluid. The horizontal walls of the cavity and tilted walls of the obstacle are uniformly heated of temperature T h while the inclined walls are kept at constant temperature T c . The governing conservation equations of the physical problem have been solved using finite element method based on Galerkin weighted residual technique and obtained numerical results are presented graphically in terms of streamlines, isotherms, average Nusselt numbers, mid height horizontal and vertical velocities, average temperature and average velocity of nanofluid for a range of Rayleigh number (10 3 ≤ Ra ≤ 10 6 ), Hartmann number (0 ≤ Ha ≤ 70) and solid volume fraction (0.1% ≤ φ ≤ 5%) to show the flow structures and temperature characteristics. It is found that the flow fields and temperature distributions are influenced significantly for the effect of pertinent parameters. In addition, overall heat transfer rate enhanced due to higher val- ues of Ra and φ along with lower value of Ha. Comparisons of the present results with the B Mohammad Mokaddes Ali mmali309@gmail.com Md. Abdul Alim maalim@math.buet.ac.bd Rowsanara Akhter rakhter309@gmail.com Syed Sabbir Ahmed fahim@juniv.edu 1 Department of Mathematics, Mawlana Bhashani Science and Technology University, Tangail 1902, Bangladesh 2 Department of Mathematics, Bangladesh University of Engineering and Technology, Dhaka 1000, Bangladesh 3 Department of Mathematics, International University of Scholars, Dhaka, Bangladesh 4 Department of Mathematics, Jahangirnagar University, Saver, Dhaka 1342, Bangladesh 123