In this study; a theoretical work is performed on heat and fluid flow in a solar-air heater collector partially filled with porous medium. The most of the efforts are paid to understand the characteristics of heat and fluid flow in a duct filled with the porous media. Various porous-clear media configurations are investigated. The buoyancy effects are neglected. The air flow in the channel is assumed to be incompressible, laminar, and hydrodynamically fully developed. For the porous regions, Darcy and Darcy-Brinkman models are used to obtain the velocity profile. In all chapters, dimensionless forms of the governing equations for the heat and the fluid flow are used. In the chapters with asymmetric cases, three different Nusselt numbers are defined; two individual Nusselt numbers for the upper and the lower wall, and an overall Nusselt number. The study is mainly focused on heat transfer enhancement by using porous media and only for a few cases pressure-drop analyses are performed. It is concluded that the use of a porous medium affects the heat transfer significantly, and the rate of effect is influenced by the thickness and location of porous media. Finally, a twodimensional study including thermally entrance region for an air-solar collector with partially filled porous medium is performed. It is observed that the outlet and mean temperature along the channel are significantly affected by upper wall energy loss, and thickness and conductivity of the porous medium.