Boundary and internal heat source effects on the onset of Darcy-Brinkman convection in a porous layer saturated by nanofluid

► The model for nanofluid contains effects of Brownian motion and thermophoresis. ► We have obtained the critical Rayleigh number using 6-term Galerkin method. ► Constant internal heating makes basic state to deviate from linear to nonlinear. ► The critical Rayleigh number decreases with as increase in internal heat source.