Experimental Investigation On Performance Characteristics And Stabilities Of A Double-suction Centrifugal Pump In Sand Water

The Yellow River is the second longest river in China. It’s well known for large quantity of silt content. Double-suction centrifugal pumps are widely used in irrigation pumping stations which are located along the Yellow River because of their obvious characters of a large flow rate and high pump lift. At present, the double-suction centrifugal pumps used in the Yellow River are designed by the circumstance of clean water, which means the research on the effects of sediment on the pump characteristic is not deep enough. As the government continues to improve the requirement of energy conservation and emissions reduction, it is particularly important to solve the problem of high-efficiency and stable operation of the centrifugal pump. Basing on the method of experimental investigation, this paper researched on the performance characteristics and the stabilities of a double-suction centrifugal pump in sand water. The main work was as following:The impacts of sediment concentration and sediment particle size on the performance characteristics of the double-suction centrifugal pump were investigated, the mechanism that sediment impacted on performance characteristics of a double-suction centrifugal pump was revealed. The research indicated that the double-suction centrifugal pump lift decreased with the increase of sediment concentration and sediment particle size. It was because when sediment particles and water leaving the impeller outlet, both of their relative velocity and relative flow angle were different. This diversity leaded to the decrease of circumferential component of velocity. Shaft power decreased with the increase of sediment concentration and sediment particle size, it was due to the resistance loss reduced with the effect of the turbulence prevention by sediment particles. On this basis, the double-suction centrifugal pump lift forecast model which applied for sand water of the Yellow River was established.The pressure fluctuation of the double-suction centrifugal pump in different operating conditions was investigated and the mechanism was revealed. It was showed that mainly impacted by cavitation, stall vortexs and the tongue of suction chamber, the rotating frequency and its three times frequency dominated in the suction chamber. Blade passing frequency and its harmonic frequency dominated in the volute chamber, which attributed to the rotor-stator interaction between the impeller and the volute, the casing tongue. The pressure fluctuation could be greatly decreased with the rotating speed reduced from the rated speed, but it increased after the rotating speed achieving a specific value. With the rotating speed reduced, the dominant frequency changed. Harmonic of the rotating frequency became the dominant frequency in several rotating speeds.The impacts of sediment concentration and sediment particle size on the static pressure and pressure fluctuation of the double-suction centrifugal pump were investigated. The research indicated that the static pressure of suction chamber increased with the increase of sediment concentration and the static pressure firstly increased and then decreased with the increase of sediment particle size at design condition. With the increase of the sediment concentration, static pressure increased in condition of small particle size, firstly decreased and then increased in condition of medium particle size and decreased in condition of large particle size in the volute chamber. The change of static pressure was related to the density, velocity, sediment concentration and uneven distribution of sediment of the sand water. The rules that sediment impacted on the pressure fluctuation of a double-suction centrifugal pump were nonlinear in general. At design condition, the pressure fluctuation in both of suction chamber and volute chamber firstly increased and then decreased with the increase of sediment concentration. With increase of sediment particle size, the amplitude of pressure fluctuation firstly increased and then decreased in suction chamber, and decreased in volute chamber.The research of vibration characteristics indicated that at design condition without the sediment, the maximum vibration intensity appeard at the axial direction of the pump bearing house, it was attributed to the unbalance of rotor system. The vibration intensity of the radial vertical direction was affected by the unbalance of rotor system and the pressure fluctuation.The minimum vibration intensity appeared at the radial horizontal direction was mainly impacted by the pressure fluctuation. Once deviating from the design condition, the vibration intensity at all direction of the bearing increased. At the design condition with sediment, when the sediment particle size was small, vibration intensity at radial horizontal direction was mainly impacted by the pressure fluctuation, while the vibration intensity was affected by the influence of pressure fluctuation and uneven distribution of the sediment in the impeller in the state of medium particle size and large particle size. The vibration intensity became the largest at the radial horizontal direction in the state of large particle size. The axial vibration intensity increased with the small sediment particle size because of the hydraulic load imbalance caused by the increasing density of sand water. The vibration intensity increased in the state of medium particle size and large particle size which was mainly due to the uneven distribution of the sediment in impeller. The largest axial vibration intensity was appeared in the state of medium particle size.The research in this paper could provide theoretical basis for design and operation of the double-suction centrifugal pumps in pumping stations located along the Yellow River, and could be used widely.