  Individual constituent balance equations are often used to derive expressions
for species-specific segregation velocities in flows of dense granular
mixtures. We propose a semiempirical expression for the interspecies momentum
exchange in density-bidisperse granular flows as an extension of ideas from
kinetic theory and compare it to a previous viscous drag approach that is
analogous to particles settling in a fluid. The proposed model expands the
range of the granular kinetic theory from short-duration binary collisions to
the multiple enduring contacts characteristic of dense shear flows and
incorporates the effects of particle friction, concentration ratio, and local
flow conditions. The segregation velocities derived from the momentum balance
equation using both interspecies drag models match the downward and upward
segregation velocities of heavy and light particles obtained from DEM
simulations through the flowing layer depth for different density ratios and
constituent concentrations in confined shear flows. Predictions of the kinetic
theory inspired approach are additionally compared to results from free surface
heap flow simulations, and, again, a close match is observed.
