The study of internal heat and variable gravity field on the onset of convection in a sparsely packed porous medium

The qualitative influence of internal heat and variable gravity field on the onset of convection in a sparsely packed porous layer with horizontal fluid-saturated are investigated. Linear stability analysis is performed using the normal mode tech-nique. The dimensionless governing equations with four cases of gravity field variation: (1) F(z) = -z, (2) F(z) = -z(2), (3) F(z) = -z(3), and (4) F(z) = -(e(z) - 1) are solved using bvp4c in MATLAB R2020a and the corresponding eigenvalue problem is calculated for three types of boundaries, namely free-free, rigid-free, and rigid-rigid, respectively. The effect of an internal heat parameter (Q), Darcy number (Da), and gravity variation parameter (delta) for the stability of the system is investigated graphically. The critical value of the Rayleigh number and corresponding wavenumber are calculated for other fixed parameters. It is observed that internal heat parameters enhance the onset of convection, whereas the gravity vari-ation parameter delays the same. It is also observed that the system becomes more stable for the exponential variable gravity function and less stable for the cubic variable gravity function.