An aerated hopper with pulsated aeration was designed to study the effect of square‐wave pulsated airflow on the discharge characteristics of cohesive and non‐cohesive powders. Experiments were carried out with pulsation frequencies between 0 (continuous) and 50 Hz. Two flow patterns were observed at different aeration rates and pulsation frequencies: intermittent and smooth. For non‐cohesive powders, pulsated aeration has a worsening effect on discharge flow. For cohesive powders, results revealed that pulsated aeration can reduce the minimum aeration necessary to allow continuous discharge. And the maximum discharge rate that can be attained applying pulsated aeration is higher than that of continuous aeration and it is significantly more uniform. The aggregates size of the powder was estimated and used to understand the stabilizing mechanism of pulsated aeration on the aggregative discharge. The model value of the minimum aeration rate and the discharge rate were obtained and compared with the experimental values.
Realizing the stable high-flux flow of cohesive granular materials is a complicated subject. We experimentally studied the dynamic characteristics of cohesive granular materials discharged from hopper under modulated pulsed airflow. Results show that pulsed airflow with a smaller duty cycle can effectively trigger the stable flow of jammed cohesive granular materials. Furthermore, under proper working conditions, the hopper flow will change from the classic arch breaking mode to a free flowing mode like liquid.The flow rate of the powder in the free flowing mode will decrease as powder bed height decreases, which overturns the consistent recognition. The oscillating shear provided by the pulsed airflow eliminates the Janssen effect and achieves a liquid-like stress transmission, which supports the above findings. Through energy analysis, we gave the scaling relationship between the pressure gradient and the pulse parameters to cover the experimental data and revealed the internal mechanism.
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