Flow behavior and hopper design for black soybean powders by particle size

• The consolidation method successfully analyzed the flow properties of powders obtained from whole black soybeans.
• The black soybean powder with particle size below 0.43 mm showed low flow index (3.28) and the flow function was in the cohesive flow region.
• At the small particle size (740.06 μm), the high sensitivity circularity was observed and the high HSC affected the internal friction angle.
• The smallest particle size (d90 = 740.06 μm) required the largest hopper angle (32.40°) and opening size (1.14 m).

In this study, the flow properties of black soybean powders having different particle sizes (d90 = 1448.66, 1484.14, 1458.18, 1385.73, 1246.89, 740.06 μm) were measured, and the flow characteristics were applied to a hopper design. For a given black soybean powder, reducing the particle size tends to reduce flowability. At the smallest particle size (d90 = 740.06 μm), the flow function was located in the cohesive region and the ratio of change in the bulk density increased from 4.72% to 19.13% as the particle size decreased from d90 = 1448.66 μm to 740.06 μm. The results of the internal friction angle at different particle sizes were not exactly consistent with the results of the flow function, which could be a result of the different particle shapes in addition to the different sizes. Image processing of particles with different particle sizes revealed a difference of HSC (high sensitivity circularity), and particles with more circular shapes showed a lower internal friction angle. The black soybean powders with the smallest particle size showed poor flowability and required larger values of the hopper angle and a larger minimum size of the hopper opening.