4. Convection heat transfer

The focus here is on flows generated by a thermal gradient within a fluid-saturated porous matrix, in the presence of gravity or any other external force field. The temperature gradient induces variations in fluid density which, under the action of external forces, lead to fluid movement in the pore space. This mode of heat transfer, known as thermal convection, results from thermal conduction at the contact between the fluid and the solid pores, and from energy transport by the fluid particles moving in the pore space.

Natural convection. As with pure fluids, there are several different types of convection in porous media:

• natural convection in a single-component fluid in the presence of the gravitational field