Impact of pore structure and morphology on flow and transport characteristics in randomly repacked grains with different angularities

The flow and transport behaviors in porous media are closely linked to the structure and morphology of the pore space. A fundamental objective of most studies of porous media is to link the pore structure to the hydraulic functions, such as the permeability, capillary pressure and diffusivity, which are necessary for engineering applications. In this paper, an attempt is made to build a direct link between the hydraulic functions and the morphological measures of diverse porous media. Porous columns with different structures and morphologies are generated by randomly packing grains with different shapes and sizes. The pore structure of the repacked porous media is visualized through X-ray computed tomography and quantified by a series of parameters, including the set of Minkowski functionals, diverse characteristic pore sizes, geometric tortuosity and fractal dimension. The intrinsic permeability, molecular diffusivity and apparent thermal conductivity of the repacked porous media are simulated numerically. The Minkowski functionals have the capacity to characterize the microscale complex pore domain of the porous media in a macroscale way. A good linear relationship is shown among the effective pore size, nominal opening dimension and critical pore neck size obtained from the morphological analysis regardless of the shapes and sizes of the grains. The three different pores may serve as the characteristic pore correlation to the intrinsic permeability. The Kozeny-Carman equation can be used to mimic the intrinsic permeability and to serve as a quality-control tool for porous media with different grain angularities. A topologically based model can generally provide a single relationship for porous media randomly repacked with grains of different angularities. The molecular diffusivity of angular grains is found to be larger than that of round ones. The molecular diffusivity is linearly related to the porosity and fractal dimension. Porous media repacked with round grains tend to attain denser packing, a higher number of contacts per unit volume and higher thermal conductivity than media packed with angular particles. The apparent thermal conductivity has a negative linear correlation to the porosity and fractal dimension of porous media with different grain morphologies.