Department of Mechanical and Electrical Engineering, Beijing University of Chemical Technology Beijing 100029, China
How the fitting clearance between the screw and the sleeve of a labyrinth screw pump (LSP) affects the pump performance and what law it follows are still unsolved problems for LSP design. So the fluid quasi-steady flow in the pump with different clearances is approximately modeled by the shear-stress transport k-ω model (SST k-ω model) in multiple reference frame (MRF) of CFD. The pump characteristics experiments are also carried out. In analyzing the simulated results, the fluid velocity in the pump is simplified as a linear superposition of a Couette flow dragged by the rotor screw and a pressure flow driven by the differential pressure of LSP. The CFD simulated results reveal that the clearance has scarcely effect on the drag flow. The mean axial pressure flow velocity in the clearance is the maximum and it increases with an increase of clearance. The leakage mainly occurs between the lands of screw and sleeve, and its rate can be simply estimated by leakage formulation for a narrow slot. With an increase in clearance, the pump maximum capacity changes little but the head and efficiency obviously decrease at the same flow rate. The changing tendency of simulated performances of the pump is in good agreement with the experimental results. At last, a set of modified relations between the pump performances and the relative diametrical clearance has been given, which can be applied to conveniently convert the LSP performance when the clearance changes.