Natural convective heat transfer of Ag-water nanofluid flow inside enclosure with center heater and bottom heat source

•The natural convective nanofluid flow is solved for convergent solution.•Finite volume method is applied to natural convection inside square enclosure.•Significance of diverse length of center heater on fluid flow is explored.•Effect of Rayleigh number and influence of Ag-water nanofluid flow on heat transfer is analyzed.•The results permit us to forecast characteristic features of isothermal heater inside enclosure.