An experimental study on the heat transport in porous media convection

We investigate the heat transport in porous media convection (PMC) over a wide Rayleigh–Darcy number range of 26.8 less than or slanted equals upper R a less than or slanted equals 2.62 times 10 Superscript 5 26.8 ⩽ R a ⩽ 2.62 × 10 5 26.8 Ra 2.62× 10⁵ , and a Darcy number range of 6.18 times 10 Superscript negative 7 Baseline less than or slanted equals upper D a less than or slanted equals 1.21 times 10 Superscript negative 5 6.18 × 10 − 7 ⩽ D a ⩽ 1.21 × 10 − 5 6.18× 10⁻⁷ Da 1.21× 10⁻⁵ . In the experiments, we employ 3D-printed lattice structures as the solid porous matrix and water as the working fluid. Quantitative analyses of the porous medium Nusselt number italic Nu Subscript m Nu m Nuₘ and local temperature statistics reveal that the present system undergoes a transition through five distinct regimes: (I) conduction, (II) convection, (III) oscillation, (IV) transition, (V) classical Rayleigh–Bénard convection. This transitional process bridges the gap between Rayleigh–Darcy-like behaviour and Rayleigh–Bénard-like behaviour in PMC. By varying the permeability of the matrix, we further examine the role of the Darcy number italic Da Da Da , which turns out to have a profound impact on the transitional processes across different regimes. Flow field measurements reveal that the flow structures within regime IV and regime V evolve from several horizontally stacked convection rolls to a single-roll structure, and the pore-scale Reynolds numbers both exceed unity in these two regimes. Finally, we report the corresponding phase diagram in the italic Ra Ra Ra – italic Da Da Da space.