Convective Vapor Diffusion within an Unsymetrically Heated Saturated Porous Bed of Solids Open to the Atmosphere
A.A. Mohamad and G.A. Karim
Many situations are encountered in practice where a wet porous bed exposed to the atmosphere may become heated unsymmetrically due to an externally imposed heat source. A typical example of such a situation that is relevant to the safety and fire control in fuel installations is the case of the soil adjacent to a liquid fuel storage area when it becomes saturated with fuel due to a leakage. In the event of the presence of a heat source, fuel vapor flows outwardly due to natural convection to produce in the atmosphere adjacent to the outer surface of the bed, flammable regions of varying concentration and thickness. These can propagate, feed and augment a fire. Also, in landfill sites mainly due to bacterial action, the waste material produces methane gas, which is flammable.
The paper describes the modeling of the heat and vapor diffusion and convection transport processes within an unsymmetrically heated porous bed saturated with a fuel vapor. The rate of outflow of species is calculated together with the rates of heat and mass transfer. Also, flow structure, temperature and species distributions are illustrated. One of the main finding is that the flow may be driven to the cavity from far distance if the strength of the heat source is high and/or the permeability of the porous medium is high. Also, for high solutal to thermal buoyancy forces the flow may recirculates in the cavity. On the basis of such results, guidelines for reducing the fire hazards from fuel wetted soils may be made.