Mechanical behavior of rice seed particle discharge and arcing blockage probability in conical silo

The particle flow is often required during the unloading of rice seeds from a conical hopper. In this study, a discrete element model (DEM) was established for the "conical hopper-rice seeds" system. A systematic investigation was implemented to examine the translational and rotational mechanical behaviors of the rice seeds within the hopper feeding zone. Key parameters were then quantified during discharge, including the seed orientation, internal granular pressure, and blockage probability. Ultimately, the simulation was carried out to reveal the relationship between granular flow rate at the discharge gate and the probability of blockage occurrence. The results demonstrate that the static lateral pressure from the rice seeds increased with the increasing depth from the material surface within the hopper. Notably, a sharp rise in the lateral pressure was observed specifically within the transition zone between the feeding and the discharge area. Furthermore, the peak dynamic lateral pressure by the rice seed particles on the hopper wall was consistently exceeded the static lateral pressure at the same height in the initiation of unloading. There was an increasing trend with the greater depth from the material surface. The particle motion revealed that the translational velocity of the rice seed particles displayed a radial distribution symmetric about the hopper axis. Axially, there was a significant increase in the translational velocity, as the flow was shifted from the near-wall region towards the central flow channel. The rotational velocity of the rice seed particles reached its maximum at the discharge outlet, and then diminished progressively upwards. Within the mass flow zone, the rotational velocity near the wall was slightly lower than that observed in the central region. Axially, the rotational velocity also followed an exponential distribution relative to the discharge height, except for the immediate wall region. A relatively high rolling contribution rate for the rice seed particles was the discharge gate and the near-wall zones of the hopper. The relative tangential velocity from the particle rotation was constituted a significant proportion of the total motion in these critical areas. In particle orientation, the seeds in the upper feeding zone were predominantly adopted a near-horizontal alignment. There was the noticeable reorientation, as the particle mass descended to the critical height. Specifically, the particle orientation gradually shifted towards a near-vertical alignment within the middle section of the hopper. As such, the orientation vectors of the surrounding particles progressively pointed either towards or away from the hopper axis during discharge. Crucially, there was the significant relationship between flow rate and the probability of blockage at the hopper discharge gate. Therefore, an "upward convex" arch was selected to calculate the theoretical blockage probability under the identical silo discharge gate width and silo charging port width. While a "non-upward convex" arch was selected to simulate the blockage probability. The calculated values shared the significantly closer agreement with the simulation as the assumed failure mechanism. The silo charging port width was used to enlarge the flow rate. There was an inverse correlation with the blockage probability. Once the flow rate reached more than 31.78 g/s (corresponding to a silo charging port width less than 41 mm), the discrepancy between theoretical and simulated blockage probabilities diminished to less than 0.3%. The theoretical blockage probability was derived from a random walk model, in order to accurately predict the simulated values over the tested range. These findings can provide the theoretical guidance for the practical material handling and storage, particularly in the hopper structural parameters for the high operational efficiency and reliability, like the cone angle and outlet size. The insights can offer the valuable references to mitigate the flow obstruction during grain handling and processing in conical hopper.