  Starting from the Boltzmann-Enskog kinetic equations, the charge transport
equation for bidisperse granular flows with contact electrification is derived
with separate mean velocities, total kinetic energies, charges and charge
variances for each solid phase. To close locally-averaged transport equations,
a Maxwellian distribution is presumed for both particle velocity and charge.
The hydrodynamic equations for bidisperse solid mixtures are first revisited
and the resulting model consisting of the transport equations of mass,
momentum, total kinetic energy, which is the sum of the granular temperature
and the trace of fluctuating kinetic tensor, and charge is then presented. The
charge transfer between phases and the charge build-up within a phase are
modelled with local charge and effective work function differences between
phases and the local electric field. The revisited hydrodynamic equations and
the derived charge transport equation with constitutive relations are assessed
through hard-sphere simulations of three-dimensional spatially homogeneous,
quasi-onedimensional spatially inhomogeneous bidisperse granular gases and a
three-dimensional segregating bidisperse granular flow with conducting walls.
