Chapter 14 - Free and mixed convection from cylinders and spheres in porous media

Abstract

Cylindrical and spherical geometries arise in power plant stream lines, industrial and agricultural water distribution lines, buried electrical cables, oil and gas distribution lines, storage of nuclear waste, and solar collectors. This chapter reviews the state-of-the-art of the steady free and mixed convection flow from cylinders (horizontal and vertical) and spheres placed in an infinite fluid-saturated porous medium. Several investigations that have considered the problem of immersed cylinders assumed the surrounding medium to be purely conductive. However, the assumption that a pure conduction model can be used to calculate the heat losses from an immersed cylinder (or pipe) may not be valid for high permeability saturated soil. If the surrounding medium is permeable to fluid motion, the temperature difference between the cylinder (or pipe) and the medium gives rise to a free convection flow. As a result, the total heat transfer from the cylinder (or pipe) consists of both conduction as well as convection. Generally, the contribution of free convection to the heat loss from immersed cylinders is as large, and in some cases larger than, the contribution of conduction.