A mathematical model is presented for the transient free convection flow of a viscous, incompressible, Newtonian fluid in a parallel-plate channel configuration containing an isotropic, homogenous, non-Darcian porous material with asymmetric cooling/heating of the plates. The governing unsteady partial differential equations are formulated in an (X,Y) coordinate system and obtained from the Navier-Stokes model. Using a set of transformations, these equations with appropriate boundary conditions are rendered into a set of second-order, nonlinear (momentum), and linear (energy) partial differential equations in terms of single independent spatial variable y and dimensionless time τ The unsteady coupled flow problem is solved using the network simulation method and the PSPICE algorithm database. The model finds applications in nuclear thermo-convection, cooling of electronic components, thermal power plant, ocean thermal energy conversion, etc.