Modeling of thermal mass transfer in porous media with applications to the organic phase transition in landfills

In order to describe the thermomechanical behavior of landfills, a constitutive model based on the macromechanical Theory of Porous Media (TPM) for a saturated thermoelastic porous body has been developed. The body under investigation consists of an organic and inorganic solid phase and a gas phase. All interaction relations between the constituents such as mass transfers, interaction forces and energy supplies are taken into consideration. Based on a consistent thermomechanical treatment the governing equations are obtained as a set of equations which consists of the balance equations of momentum and mass for each individual constituent, the balance equation of energy for the mixture and the physical constrained conditions. In this set of macroscopic equations, several parameters are contained. They are interrelated by constitutive relationships in order to complete the system of equations. This procedure renders the set of equations solvable. Thus, we obtain a mathematical concept to describe the motion of the solid phase, the pressure of the gas phase, the temperature of the mixture and the biodegradation of organic material into a gas mixture of methane and carbon dioxide produced by bacterial decomposition during stable methane fermentation (biogas).