Abstract
We study the effects of thermal radiation and porous drag forces on the natural convection heat and mass transfer of a viscous, incompressible, gray, absorbingemmitting fluid flowing past an impulsively started moving vertical plate adjacent to a non-Darcian porous regime. The governing boundary-layer equations are formulated in an (X∗, Y∗, t∗) coordinate system with appropriate boundary conditions. The Rosseland diffusion approximation is employed to analyze the radiative heat flux and is appropriate for non-scattering media. The model is non-dimensionalized and solved with the network simulation model. We study the influence of Prandtl number, radiation-conduction parameter, thermal Grashof number, species Grashof number, Schmidt number, Darcy number and Forchheimer number on the dimensionless velocity, temperature and species function distributions. Additionally we compute the variation of the local skin friction, Nusselt number and Sherwood number for selected thermophysical parameters. Increasing Darcy number is seen to accelerate the flow; the converse is apparent for an increase in Forchheimer number. Thermal radiation is seen to reduce both velocity and temperature in the boundary layer. The interactive effects of second order porous drag and thermal radiation are also considered. The model finds applications in solar energy collection systems, porous combustors, transport in fires in porous media (forest fires) and also the design of high temperature chemical process systems.
Highlights
Many high temperature processes in industrial design and combustion and fire science involve thermal radiation heat transfer in combination with conduction, convection and mass transfer
Hossain et al [7] studied the effects of thermal radiation heat transfer on combined forced and free convection boundary layer flow past a horizontal cylinder
We study the laminar unsteady viscous free convection heat and species transfer of an incompressible, absorbing, emitting and non-scattering, gray, Newtonian fluid past an impulsively started vertical semi-infinite surface adjacent to an isotropic, non-Darcian, porous medium
Summary
Many high temperature processes in industrial design and combustion and fire science involve thermal radiation heat transfer in combination with conduction, convection and mass transfer. Raptis and Singh [27] studied numerically the natural convection boundary layer flow past an impulsively started vertical plate in a Darcian porous medium. Thusfar the transient laminar heat and mass transfer past an impulsively-started surface embedded in a non-Darcian porous medium with thermal radiation present has to the authors’ knowledge not been considered. The transformed problem is shown to be dictated by eight thermophysical parameters, viz dimensionless time, thermal Grashof number, species Grashof number, Darcy number, Reynolds number, Forchheimer number, Prandtl number and Schmidt number The influence of these parameters on the velocity profiles, temperature function, mass transfer function, local shear stress, local Nusselt number and local Sherwood number are presented and discussed at length
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