Rotating drums are used in many industrial applications, such as mixing, granulation, milling, or coating of granular particles. When a mixture with different sizes or densities of particles is filled in the drum, it is known that radial and/or axial segregation takes place. Thus many researchers have studied both experimentally and numerically about particle motion in the rotating drum. It is, however, difficult to visualize or measure the particle motion inside of the rotating drum.

Several non-invasive techniques have been developed for the measurement of the dense granular flows. X-ray tomography has been applied to a fluidized bed, a hopper flow and so on. An electrical capacitance tomography has been used to measure the flow in a horizontal and a vertical pneumatic conveying system. PEPT (Positron Emission Particle Tracking) has been employed to measure the particle motion in a rotating drum, a gas fluidized bed or a vibrofluidized granular bed. MRI (Magnetic Resonance Imaging) is also one of the non-invasive measurement techniques. MRI has been applied to granular flows such as a rotating drum, a vibrofluidized granular bed, a blender and so on.

In the present study MRI is used to analyze the size segregation of binary mixtures in steadily rotated horizontal drums. Especially the axial segregation in tapered drums is evaluated quantitatively by the MRI measurement in this paper.

MRI successfully visualized the radial segregation which took place in the tapered drum as well as in the straight drum. The radial segregation was observed at any axial position. In addition to the radial segregation, the axial segregation was also observed in the tapered drum. The axial segregation was quantified by the MRI measurement. The axial segregation exhibited the qualitatively different trend depending on the size of the granular mixture.