Xin Li

This study focuses on a suction unit in which an electric ducted fan (EDF) drives flow through a gap flow resistance, referred to as the electric ducted fan–disk suction unit (EDFD). First, comparative experiments on suction force demonstrate that the suction capability of the EDFD significantly outperforms that of a standalone EDF. Subsequently, smoke flow visualization experiments reveal an intriguing anomalous phenomenon: varying the gap height induces flow reversal within the EDFD, manifesting as distinct positive and negative flow states. Because it is challenging to directly measure this flow rate without disturbing the internal flow field of the EDFD, an indirect measurement approach based on the momentum theorem is formulated. Furthermore, given that the EDF blades simultaneously act as both an “axial flow pump” and a “centrifugal pump,” we postulate that the EDFD essentially constitutes a system characterized by a “dual-pump reverse series driving a gap flow resistance.” Alterations in the gap height shift the flow characteristic curve of the “centrifugal pump–gap flow resistance” subsystem. This shifted curve intersects the flow characteristic curve of the axial flow pump at either the positive or negative flow regions, thereby elucidating the underlying mechanism of the EDFD flow reversal. Finally, the EDFD is implemented on a wall-climbing robot, demonstrating exceptional suction performance and obstacle-negotiation capability.

This study investigates a counterintuitive and intriguing phenomenon: the realization of noncontact suction of workpieces using an inhalation-type suction disk (thereafter, inhalation disk). Through experimental observations, we first identified the existence of a stable levitation zone in which the inhalation disk and the workpiece form a stable negative feedback system. Theoretical formulations were then derived to calculate the pressure distribution and suction force generated by the gap flow. The results reveal that the suction flow rate Q and the gap distance h between the disk and the workpiece jointly determine the variation in suction force F. Subsequently, a series-driven system consisting of a “pump + flow resistance” configuration was proposed to obtain the system's characteristic Q-h curve. The influence of the Q–h relationship on inertial, entrance loss, and viscous force components was further analyzed, elucidating the underlying mechanism responsible for the convex profile of the F–h curve. Finally, in comparison to Bernoulli suction disks developed by numerous researchers and commercial companies, the inhalation disk exhibits significantly superior suction force and force power ratio, outperforming the exhalation disk.

The characteristic curve of viscous flow resistance (i.e., the relationship between flow rate and pressure drop, commonly referred to as the Δp-Q curve) depends on several inherent variables, such as structural dimensions, fluid viscosity, density, and temperature. In most cases, altering the characteristic curve of viscous flow resistance requires changing these inherent variables. In previous studies [X. Shen and X. Li, “Variable viscous flow resistance based on rotational inertia,” Phys. Fluids 35, 073612 (2023); X. Shen, J. Xu, X. Yu, and X. Li, “A design based on centrifugal inertia of rotational oil film for reducing pressure at shaft hole,” Proc. Inst. Mech. Eng. Part C-J. Eng. Mech. Eng. Sci. 238, 1295 (2024)], we proposed a novel design approach for variable flow resistance, which modifies the Δp-Q curve by incorporating fluid inertia. The new variable flow resistance utilizes two coaxial disks that are relatively close to each other to construct a slit channel, using air as the fluid medium. When the air passes through the slit channel, it is constrained by the wall to generate viscous resistance. At the same time, the rotation of the lower disk drives the air in the slit flow field to rotate, thereby generating rotational inertia. Consequently, both viscous pressure drop and rotational inertial pressure drop act on the air in the slit. By adjusting the rotation speed, the Δp-Q characteristic curve can be translated. Previous studies were based on the rotation of a single disk. Based on this, we propose the concept of double-layer rotating disks, aiming at enabling the air in the disks to rotate more fully. This approach significantly shifts the Δp-Q curve and improves the linearity of the curve. Based on the similarity principle and von Kármán's hypothesis, a theoretical pressure distribution model for the slit flow field of double-layer rotating disks is derived. The variation of the velocity field in the slit flow path caused by the rotating double-layer rotating disks was investigated. Furthermore, the influences of flow rate and disk rotation speed on the components of the pressure drop are analyzed. Experimental measurements of the Δp-Q curves for the double-layer rotating disks slit flow field at various rotation speeds are conducted to validate the theoretical model. Finally, the theoretical Δp-Q drop characteristic curve is revised to reduce errors. As the rotation speed increases, the Δp-Q curve shifts significantly to the right and demonstrates excellent linearity, with the slope remaining nearly constant. Therefore, this approach can expand the measurement range of flow sensors when applied to flow sensing devices.

Water vortex unit (WVU) is a non-contact negative pressure generation device that uses water as the working fluid. It operates by injecting fluid into a cylindrical chamber through a nozzle, generating negative pressure and suction force through rotational flow. However, high-velocity swirling flow is confined near the cylinder wall, resulting in a pressure distribution characterized by a steep drop near the periphery and a relatively flat profile in the central region. This phenomenon limits further enhancement of suction force. This study redesigned the hydraulic circuit, allowing water that would have leaked to circulate within the hydraulic system. This modification resulted in a WVU with a steeper F–Q curve. Nevertheless, due to a reduction in the maximum flow rate, the maximum suction force only increased by 12%. The paper further proposes a new WVU structure that introduces a suction chamber. By drawing water through tangential suction holes on the suction chamber, the maximum flow rate of the WVU is increased, leading to an additional 83% increase in the maximum suction force. Finally, the role of the critical structural parameter, the suction chamber diameter, was analyzed. The results indicate that both excessively small and large suction chamber diameters can have adverse effects on the WVU.

Rough vacuum is widely used in various fields such as industry, health care, and scientific research. Typically, rough vacuum pumps are mainly displacement pumps and kinetic pumps (also known as momentum transfer pumps). Due to their different working principles, the former generally suffers from severe issues like vibration and wear. Recently developed screw-type positive displacement pumps address these problems by utilizing high-precision meshing components. In contrast, kinetic pumps are less effective at achieving high vacuum levels. This paper introduces the design concept of a hybrid vacuum pump that combines both positive displacement and kinetic mechanisms. The hybrid vacuum pump generates pressure differences and fluid flow by driving high-speed rotating liquid, while variable volume is induced by changes in the liquid level, resulting in reduced pressure leading to gas suction. A theoretical model for the maximum suction pressure of the hybrid pump is developed in this paper, and the Δp–q characteristic curve of the hybrid pump is experimentally measured. The influence of low-pressure boiling phenomenon on the performance of the pump is also thoroughly examined.

A rotating gap structure is a type of viscous flow resistance using two disks where the rotation of one disk drives the fluid within the gap, generating rotational inertia. This inertia, combined with viscous friction, determines the flow resistance characteristic curve (pressure drop vs flow rate, or Δp-Q curve). By adjusting the disk's rotational speed, the rotational inertia and the Δp-Q curve can be modified. This paper examines how the radial flow direction (positive and negative) affects the circumferential velocity, radial velocity, and the Δp-Q curve of the rotating gap structure through theoretical modeling and experiments. Results show that radial flow direction and rate influence the symmetric distribution of radial velocity and the linear distribution of circumferential velocity, altering the main components of the Δp-Q curve: the viscous flow resistance curve (Δpvis-Q) and the rotational inertia flow resistance curve (Δprot-Q). The study found that the slope of the Δpvis-Q curve is smaller for positive flow than for negative flow due to differences in radial velocity distribution. Additionally, the circumferential velocity is weakened in positive flow and enhanced in negative flow, resulting in a smaller slope of the Δprot-Q curve for positive flow. These factors cause the Δp-Q curve to deviate from linearity, with greater deviation at higher rotational speeds. Finally, experimental verification was conducted, and the measured Δp-Q curve closely matched the theoretical calculations.

A water vortex unit is a non-contact adsorption unit that utilizes water as a flowing medium. Negative pressure is generated on the adsorbed surface through the high-velocity rotation of the fluid, resulting in suction force. In comparison to the air vortex unit, the water vortex unit exhibits a substantial increase in suction force and has the capability to deliver greater power. However, the presence of the central bubble in the water vortex unit weakens the suction force. To address the impact of the central bubble, a suction hole was introduced on the vortex unit to remove them. Experimental results indicate that solely removing the central bubble has almost no effect on the radial pressure gradients in the gap flow path and chamber center of the water vortex unit. However, in the cylindrical neighborhood, the radial pressure gradient increases, leading to a certain degree of improvement in suction force. Further increasing the suction flow rate induces inward radial flow within the vortex chamber. This flow field further enhances the suction force. To analyze the reasons for this pressure distribution, we indirectly obtained the radial velocity distribution by examining the relationship between the pressure gradient and tangential velocity. The results of the tangential velocity distribution indicate that the radially inward suction flow significantly increases the rotational velocity of the fluid in the chamber center, enhancing the centrifugal inertial effect. This further reduces the negative pressure, resulting in a significant improvement in the suction of the vortex unit.