Local thermal non-equilibrium effects on the onset of convection in an internally heated layered porous medium with vertical throughflow

•Interactions between the effects of internal heating, throughflow, LTNE and heterogeneity are studied.•Upward throughflow is stabilizing while downward throughflow is destabilizing.•An increase in permeability in the upper region is strongly destabilizing.•An increase in the fluid thermal conductivity in the upper region is strongly stabilizing.•Increases in the solid conductivity and the interface heat transfer parameter are moderately stabilizing.

We investigated how local thermal non-equilibrium and vertical throughflow affect the stability of an internally heated fluid-saturated porous layer. In order to investigate the effects of heterogeneity, we considered a system composed of two horizontal porous layers with different properties. This allowed us to investigate the effects of vertical variation of various parameters. Due to a large number of parameters, our primary goal was to investigate which parameters have a significant effect on the stability of the system. We have found that heterogeneity of permeability and fluid thermal conductivity have a major effect, heterogeneity of interphase heat transfer coefficient and porosity have a lesser effect, while heterogeneity of solid thermal conductivity is relatively unimportant. At the same time we investigated the variation of both upward and downward throughflow, and variation of heat source strength between the layers and between the fluid and solid phases. Downward throughflow is destabilizing, while upward throughflow is stabilizing. The stability is strongly affected by the solid-to-fluid heat source strength ratio.