  We present and derive a novel double-continuum transport model based on
pore-scale characteristics. Our approach relies on building a simplified unit
cell made up of immobile and mobile continua. We employ a numerically resolved
pore-scale velocity distribution to characterize the volume of each continuum
and to define the velocity profile in the mobile continuum. Using the
simplified unit cell, we derive a closed form model, which includes two
effective parameters that need to be estimated: a characteristic length scale
and a ratio of waiting times RD that lumps the effect of stagnant regions and
escape process. To calibrate and validate our model, we rely on a set of
pore-scale numerical simulation performed on a 2D disordered segregated
periodic porous medium considering different initial solute distributions.
Using a Global Sensitivity Analysis, we explore the impact of the two effective
parameters on solute concentration profiles and thereby define a sensitivity
analysis driven criterion for model calibration. The latter is compared to a
classical calibration approach. Our results show that, depending on the initial
condition, the mass exchange process between mobile and immobile continua
impact on solute profile shape significantly. By introducing parameter RD we
obtain a flexible transport model capable of interpreting both symmetric and
highly skewed solute concentration profiles. We show that the effectiveness of
the calibration of the two parameters closely depends on the content of
information of calibration dataset and the selected objective function whose
definition can be supported by of the implementation of model sensitivity
analysis. By relying on a sensitivity analysis driven calibration, we are able
to provide a good interpretation of the concentration profile evolution
independent of the given initial condition relying on a unique set of effective
parameter values.
