  Continuum fluid dynamic models based on the Navier-Stokes equations have
previously been used to simulate granular media undergoing fluid-like shearing.
These models, however, typically fail to predict the flow behaviour in confined
environments as non-equilibrium particle effects dominate near walls. We adapt
an extended hydrodynamic model for granular flows, which uses a
density-gradient dependent ``volume diffusion'' term to correct the viscous
stress tensor and heat flux, to simulate the shearing of a granular gas between
two rough walls, and with corresponding boundary conditions. We use our volume
diffusion model to predict channel flows for a range of mean volume fraction
$\bar{\phi}=0.01$--$0.4$, and inter-particle coefficients of restitution
$e=0.8$ and $0.9$, and compare with Discrete Element Method (DEM) simulations
and classical Navier-Stokes equations. Our model is capable of predicting
non-uniform pressure, volume fraction and granular temperature, which become
more significant for cases with mean volume fraction $\bar{\phi}\sim0.1$, in
which we typically observe non-uniform peak density variations, and large
volume fraction gradients.
