Nonhomogeneous distributions of particle concentration and axial fluid velocity for
negatively buoyant suspensions flowing in horizontal tubes. Column A corresponds to pure
fluid and B, C, and D to solids fractions* f*_{s}=0.09,
0.23, 0.39, respectively while the rows are at increasing flow rates from the bottom. Each
data set is a pair of false color images of the spatial varation of the fluid
concentration *f*_{f} (upper image of
pair, scaled from black for no fluid to white for pure fluid) and the velocity in the
plane normal to the flow direction (lower image of pair, scaled from cyan, representing
zero velocity to white, representing the peak fluid velocity measured to the particular
experiment). The pure oil flow data in the left column show: *f*_{f
} as homogeneous pure fluid with this colored annuli from edge resolution and
filtering effects and <v> as concentric rings due to the parabolic velocity
distribution. Going across each row notice that with increasing solids fraction (left to
right) the flow becomes stratified with a region of clear fluid flowing above a highly
concentrated bed. Note dilation and viscous resuspension of the concentrated solids bed as
flow rate is increased (bottom to top).