Efficiency Improvement of Electrically Activated Rotation-Flow Suction Unit Based on Drag Torque and Suction Force Modeling

An electrically activated rotation-flow suction unit uses rotating airflow to generate negative pressure and suction force on a working surface. Because the centrifugal force generated by the rotating flow helps prevent vacuum leakage, the suction unit can operate efficiently on rough and uneven surfaces even when placed at a distance from the working surface. In this article, a theoretical model of the drag torque and suction force, considering roughness and unevenness of the working surface and the gap between the suction unit and the working surface, was developed and verified. Based on this model, two modifications to the suction unit were made to improve its efficiency. The first modification involved adding a disc at the top end of the blades. The disc could transform the flow between the fan and the upper shell wall into a plane Couette flow, thus reducing the drag torque on the upper shell wall by 65%. The other modification involved installing a soft skirt on the periphery of the suction unit. The skirt helped reduce the turbulent length scale in the gap between the suction unit and the working surface, thus decreasing the drag torque therein.