Loss Mechanisms in Shear-Force Pump With Multiple Corotating Disks

Abstract

In a shear-force pump with multiple corotating disks, the pressure gain is obtained by utilizing the shear force produced on the surfaces of the rotating disks. Thus, it is expected to have advantages as a microfluid device compared to a conventional bladed compressor or pump, which suffers greatly from viscous loss. However, in previous studies, a shear-force pump could not achieve high efficiency in experiments, even though very good efficiencies were predicted in numerical and analytical studies on the flow field between corotating disks. Therefore, the objective of the present work was to investigate the internal flow dynamics and clarify the loss mechanisms in a complete shear-force pump device consisting of both rotor and stationary components. In order to achieve this goal, a numerical simulation using an independent rotor analysis was first performed on the internal flow field between two corotating disks to evaluate the isentropic efficiency and pressure coefficient that could be achieved. Then, an experimental test rig for a shear-force pump was designed and built, and an experiment was carried out to determine the performance of a complete pump device with the same corotating disk design as the independent rotor analysis. In addition, a numerical simulation was executed for the flow field of a pump system consisting of both rotor and stationary components based on the present test rig to investigate the flow field and loss factors of this device. The results of this independent rotor analysis showed that the corotating disks can achieve a fairly high efficiency at a low flow coefficient with a high dynamic pressure, and the flow direction is extremely close to the tangential direction at the disk outlet, which caused difficulties in the design of the diffuser and scroll. In the experimental test, the high total pressure loss in the parallel diffuser and scroll parts was observed. This was found to be the result of the significant friction loss caused by the long flow path due to strong recirculation in the diffuser and scroll volute, which was found in the simulation results for the internal flow in the whole pump system. In addition, a reverse flow appeared in the rotor part at a low flow coefficient, which significantly deteriorated the rotor performance. These conclusions provided some clues for improving the performance of a shear-force pump device in future work.