Study On Internal Flow For A Circulating Axial-flow Pump

Circulating axial-flow pump is a non-guide vane pump, which plays a significant role in promoting the circulation of liquid material and improving the heat transfer coefficient of material evaporation process. It is also widely used in Chinese chemical and oil industries. As a core device of the chemical production process, circulating axial-flow pump is usually long-term running and its power consumption is quite large. Due to energy shortage and environmental pollution, it is necessary to improve the operational efficiency of the circulating pump. As the main element of the circulating pump, the design quality of impeller will directly affect the pump operation efficiency. Therefore, designing efficient axial-flow impeller is the best way to improve the efficiency of the circulation pump.Due to the impeller is the important component of axial-flow pump, the guide cone is installed on the top of impeller which make the fluid of impeller inlet steady. So guide cone is designed and its passage is researched in order to obtaine internal flow characteristics. Meanwhile, the change of impeller tip clearance and the selection of impeller circulation would directly affect the internal flow of the impeller. In this paper, the self-designed model axial-flow pump impellers with three different circulations are adopted as the study object. By using theoretical analysis, numerical simulations and experimental research methods to study efficient impeller guide-cone type, circulation distributions and selections of the tip clearance.The major works and achievements are as following.1. The impeller hydraulic efficiency of Witozinsky cone is higher than Bicubic curve cone and Fifth degree polynomial curve cone.2. The numerical simulation results show that the rotating of impeller has great effects on the uniformity of axial velocity distribution, but the effect of head loss and velocity average drift angle is small. The rotating of impeller also has a little influence on radial-velocity distribution. With cone export section near to the impeller, the influence of the impeller rotating is increasing.3. Different lengths of guide cone flow field are compared. It is found that appropriate increase of guide water cone length can improve the hydraulic efficiency of the impeller. The roundness of the water cone head can effectively eliminate the adverse pressure gradient caused by the sharp head. With the increase of the water cone round length, the hydraulic loss is reduced and the impeller hydraulic efficiency is increased. it is suggested that the optimal length of the guide cone is 0.5~0.7 times as impeller diameter. After tentative exploration, the optimal round length of guide cone is 0.125~0.142 times as length of guide cone.4. Combined with the analysis of flow mechanism in axial-flow pump impeller, the nature of variable circulation design is discussed. The impeller is designed by three types of impeller outlet circulation distribution and the validity of design is verified by pump performance tests.5. Based on the three dimensional incompressible Navier-Stokes equation and SST k-ω turbulent model, the flow field of axial-flow pump with different tip clearances is simulated by employing CFD method. Based numerical simulations, this paper qualitatively analyze the effect of the tip clearance and the variation of circulating distribution on impeller efficiency, outlet circulation distribution, blade load and tip leakage vortex. It is preliminary estimate the relationship between circulation distribution and tip clearance.6. Based on numerical method, it is found the pressure pulsation characteristics in impeller and tip clearance under different axial-flow pump tip clearances. By comparing with the pressure pulsation, it is found that increasing the tip clearance would aggravate disturbance of pressure fluctuation in the front of blade tip clearance and reduce high frequency pressure pulsation at tip clearance trailing edge. However, pressure pulsation of central tip clearance is less affected by the size of the tip clearance.7. Based on the test result, it calculated the impeller outlet rotational energy loss that was caused by the lack of rear diffuser. By the calculated energy, it also forecasted the hydraulic performance of the pump without diffuser.