A computational approach to simultaneous two-dimensional heat and mass transfer in a heat generating porous media

The use of activated carbon in the recovery of evaporative fuel emissions has become commonplace with the advent of stricter requirements imposed upon the automobile industry by the Environmental Protection Agency and the California Air Resources Board. The adsorption of the hydrocarbon based fuel vapors on the activated carbon is an exothermic process that is a function of temperature and mass concentration of fuel vapors. To further understand the interaction of the fuel vapors and the activated carbon, an investigation was undertaken to analyze the complex relationship of the coupled heat and mass transfer in this heat generating porous media. The investigation includes the analysis of linear and non-linear flow in several different porous media resulting in a recommended approach to determine the permeability and Forchheimer coefficient for non-linear flows. The heat transfer is analyzed with a uniform flow model using the classic approaches to porous media analysis: single and dual energy equations. The importance of axial conduction is determined for this model as well as the appropriateness of the single and dual energy equations to the specifics of the given porous media as well as generalizations to different porous media. The geometric nature of the given problem allows for the application of an iterative boundary condition to balance the heat flux across the separation wall that adds a unique nature to the problem. An experimentally determined adsorption isotherm for hydrocarbon based fuels onto wood-based activated carbon is utilized to model the source term in the heat transfer equations. This source term is closely coupled with the mass adsorption term in the mass species equation. The presented heat and mass transfer equations are coupled partial differential equations that are numerically solved utilizing a fully implicit second order correct finite difference scheme.